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ZMA tube bias below 50? (Read 62864 times)
Jeff1
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ZMA tube bias below 50?
04/21/18 at 00:26:40  
Has anyone experimented or is running their ZMA with the tubes biased lower than 50? What differences have you noticed?
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Archie
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Re: ZMA tube bias below 50?
Reply #1 - 04/21/18 at 00:59:19  
Honestly, I don't notice a difference with bias settings but in general, I think higher bias is supposed to give better sound.  That said, some tubes won't bias as high as others.  When I've run EL34s they top out below 50mA and I never had an issue with their sound.  Originally Steve specified 60mA for the KT66s but went down to 50mA for the manual.  The 60mA ran the transformers a little hot -- at least for me.  I run my 6P3Ss near the top of their range which is about 52mA on my ZMA.
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Jeff of Arabica
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Re: ZMA tube bias below 50?
Reply #2 - 04/21/18 at 08:37:49  
I've recently gone the other direction.  I am running my ZMA hot!  I have a set of Gold Lion KT88's and I am running them at 78mA.  Previously, I was running a set of TJ Full Music KT88's at about 74mA with great results.  

I am liking the KT88's in my ZMA and consequently, I have to run them hotter than other tube types by nature - they simply will not bias any lower.  So, if I want to run a lower bias, I have to swap out with other tubes such as KT66's, EL34's, etc., but they don't sound as good in my system as the KT88's I have.  

Out of curiosity, I've hit the transformers with my infrared thermometer on numerous occasions while the ZMA has been running pretty hard.  The range of temperature readings I get is between 130 and 140 degrees, which is well within normal operating temperatures for any quality transformer.  

With the hotter running KT88's in my system, I am getting better overall output, along with a greater dynamic range.  These tubes, along with my recent power supply mod, I am hearing greater detail, particularly improved at lower volumes.  The instrument separation is dumbfounding.  Ive had this amp for quite some time now and the width and depth of the soundstage, and placement of the musicians/singers is surreal.  The ZMA has always been my jam but running her at higher RPM's with KT88's and improving what I would consider the "throttle response" and "top speed" of this amp with the capacitor mod, I really have zero desire to do anything else to this amp or my system in general.  That "itch" to tweak/add/modify/ is gone for the very first time.  Will it last?  Probably not, but it sure is nice to simply sit back and take pleasure in the music flowing from my system.  
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Archie
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Re: ZMA tube bias below 50?
Reply #3 - 04/21/18 at 17:18:22  
Quote:
Out of curiosity, I've hit the transformers with my infrared thermometer on numerous occasions while the ZMA has been running pretty hard.  The range of temperature readings I get is between 130 and 140 degrees, which is well within normal operating temperatures for any quality transformer.


I've talked to Steve about high bias and he said he ran his high too but he was the builder and could repair his easily, if needed.  He didn't recommend I do the same.  Back in time, Raven and I were comparing notes on temperatures and we were getting about 120 F which is what Steve said was a safe operating temperature.  He said you ought to be able to put your hand on the transformers for a few seconds.  I'm sure this "tank" of an amp can take hotter but for those of use who are more conservative, I'd caution pushing things that much.
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Jeff of Arabica
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Re: ZMA tube bias below 50?
Reply #4 - 04/21/18 at 17:42:56  
120 is conservative. 130-140 is safe. The finger test is fine and all but depends on one’s pain tolerance. Even at 140 I can touch it for 6-8 seconds. Based on folks I have consulted on this very matter, I have no worries running them anywhere below 80mA.

Of course Steve is going to advise ultra conservative. These amps are under warranty and it is on his dime if  they happen to go out in 20 years instead of 30.  At the end, it’s your amp and you run it how you are comfortable. Based on what I have read and what I been told by a competent and experienced technician, there is no need to fret over biasing up to 80mA - on the ZMA that is.
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Archie
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Re: ZMA tube bias below 50?
Reply #5 - 04/21/18 at 18:29:45  
Jeff, I'm not suggesting that you run your amp any way other than you choose.  I just thought I'd share what Steve told me for the benefit of other ZMA owners.  If a "technician" told you what is "safe" for an amp he didn't design and build and you want to follow his advice, that's fine.  For me I'll stick with the "horse's mount" approach.

As I mentioned, Steve originally specified 60ma with the KT66 tubes (the picture might still be in the Manual) but changed it to 50mA soon after. Moreover, the KT88 isn't listed as an alternate tube.  Again, you can use whatever you want but I think it's a bit dangerous to suggest it's generally fine and "safe" on the Forum.
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Archie
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Re: ZMA tube bias below 50?
Reply #6 - 04/21/18 at 18:35:21  
I don't mean to beat this to death but this is from the ZMA Manual:

WARNING
This amplifier is designed to operate with a 50ma bias on each output tube.
Running higher bias currents for any length of time will overheat the power supply
transformers and could cause pre-mature failure. We recommend no more than
60ma per tube at any point. Running less is not an issue for the power supply but
doing so will reduce the power output of the tubes and change how they sound.
Some will use this technique as an esoteric voicing tool.


This also addresses the original question of this thread regarding lower bias settings.
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Jeff of Arabica
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Re: ZMA tube bias below 50?
Reply #7 - 04/21/18 at 19:47:06  
Archie,
With all do respect, please don’t make assumptions about what I know, don’t know, or how I form my opinions.  Just to clarify, I didn’t form this opinion from one conversation from a random “technician” who knows nothing about this amp.  As a matter of fact, he had my ZMA on his bench when I did the recent power supply capacitors upgrade/modification.  

This has nothing to do with the design of the amplifier.  We are talking about the impact of heat on the power transformers with respect to its operating temperature.  I am not sure if you are aware, but Steve doesn’t manufacture these power transformers.  You may also not have known that Decware uses a Hammond 372FX power transformer.  If you care to look at the MANUFACTURER’S specification sheet for this transfomer, it advertises an operating temperature range of 0 C to 105 C (32F to 221F)!!  Again, this is an off-the-shelf part, built by Hammon Manufacturing, that Steve sources for the ZMA.  As I stated earlier, this transformer operating at 130F-140F is SAFE!  More than safe to be frank.  It is not even close to reaching its stated maximum operating temperature.  I know you did not know this when you posted about me making a “dangerous” comment in this forum, so I won’t be too offended.

And to further drive home the fact that I am not just shooting from the hip, I did do my due dilgence by contacting the designer of this amp, Steve.  Three months ago, I specifically asked steve about biasing the ZMA at 70+mA.  Here is what he told me via email:

Hi Jeff,

No worries, it's a conservative recommendation.  I run my own amp frequently with some tubes that will not bias any lower than 75 milliamps.

Steve

I am not here to be argumentative, so I will no longer comment on this issue as I feel I provided more than adequate facts/data to support my position.   Based on the tone of your prior post, I felt compelled to substantiate the information contained in my initial post in this thread.
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Jeff of Arabica
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Re: ZMA tube bias below 50?
Reply #8 - 04/21/18 at 20:54:49  


Quote:
Moreover, the KT88 isn't listed as an alternate tube.


I apologize, but I forgot to point out for anyone interested in using a KT88 with your ZMA, Page 11 of the current ZMA Manual lists the KT88 as an alternative to the KT66.  

For me, the KT88 have bested any other tube type and brand that I personally have rolled in my ZMA, in my system.  I will continue to enjoy this most amazing sound that flows through these very dynamic tubes.
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Archie
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Re: ZMA tube bias below 50?
Reply #9 - 04/21/18 at 21:54:49  
Jeff,

You just posted a LOT of great information.  I took the lack of KT88 as an alternative from the ZMA web page.  I didn't realize that it was now in the Manual.  Thanks for pointing that out.  Also, you end the argument by quoting Steve.  I always defer to him -- for obvious reasons.  What concerned me wasn't' necessarily that the transformers couldn't handle the heat but that the ZMA as a system might be impacted.  But if he says it's fine then good.  He had a slightly different take when I spoke to him about it but that also may have been a couple years ago.

Don't get hung up on my "tone" in my posts because, like text messaging, they really don't convey much in the way of that.  I'm sure that you are very knowledgeable and I wasn't trying to imply otherwise.
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Jeff1
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Re: ZMA tube bias below 50?
Reply #10 - 04/21/18 at 23:00:22  
JFC I don't think my question was a difficult one. I specifically asked if anyone was biasing tubes UNDER the 50 mark and their thoughts on that.
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Re: ZMA tube bias below 50?
Reply #11 - 04/22/18 at 00:04:09  

I feel obligated to apologize for the confusion on the ZMA biasing...  The Hammond 372FX is rated around 170mA. A pair of KT88 biased at 80 mA and the two input tubes adds another 10 or so. This combination will drive the temperatures to the higher side of cozy, but as Jeff points out is not actually damaging the transformer.  

My conservative recommendations in the manual are two fold:

A) a warm power transformer is confidence building. A hot power transformer is concerning unless you're a technician and even then if given the choice you would pick warm over hot.

B) the black 1/8 inch thick steel plate that the amplifier is built on absorbs and moves heat.  Since we're using beeswax capacitors we would rather keep the internal temperatures moderate so the wax doesn't melt out of the capacitor.  The original caps used in the ZMA were flat stacked copper where this was more of an issue.  Now those are no longer available having been replaced by round copper foil which is going to be less of an issue.

That said, there are many exotic KT88's out there. The PSVANE KT88-TII, the TJ FULL MUSIC KT88 DELUXE edition are two that I wanted to hear in the Zen TORII MONO's. It never went very well, as the ZTM's run the tubes at 100 volts higher than the ZMA, and since the concept of quality control and repeatability is alien to these companies, I blew up a lot of these tubes. This led to wondering how they would do in the ZMA knowing it was lower voltage.  

Had there been cool KT66's out there beyond N.O.S. Genolex and others, I would have just used those. One of my favorite tubes in the ZMA is N.O.S. 7027's. Good luck finding a new matched quad.

The bias window on the ZMA was set for KT66 so when you put some KT88's in it, they will not bias lower than 70 or 80 mills.  This is as we've discussed not a serious problem for the average 4 hour listening session, but I wouldn't want to leave the amp on for days biased like that.

After spending almost a grand for carbon plate KT88's from TJ, and not wanting to risk irritating them in the TORII MONO's, I modified the bias window on my ZMA so that I could swing the bias on a KT88 down to 60 mills. This makes it hard to use KT66 now, because they won't bias high enough. So basically it's a bias mod the changes the amp from KT66 to KT88.

A few years back when I tried to create the TORII MK5, I scrapped it because the transformer temperature was 140 degrees and the chassis itself got hot enough to make the metal volume control knobs extra warm. There was nothing wrong with the amplifier from a reliability standpoint, but I could invasion the phone calls and the internet chatter about how hot it ran and decided not to do it.  If everyone was a bit more technical like Jeff, I probably would have proceeded.

So I apologize for the mixed messages.  If your run your amp at 80 mills, don't leave the amp on all day.

As for biasing the amp lower than 50mA, the power will drop slightly and the sound will be drier. This can be handy if the music is too fat.  You hear the change from 40mA to 50mA, but from 50 to 60 is much harder to detect.

Hope this helps!

Steve
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Archie
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Re: ZMA tube bias below 50?
Reply #12 - 04/22/18 at 01:01:03  
Quote:
JFC ...
  Huh

Does that mean what I think it does?  Come on, you ought to expect a certain amount of off topic in these threads.  I'm glad it went this way so we could get some clarification on bias vs temperature.
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Jeff of Arabica
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Re: ZMA tube bias below 50?
Reply #13 - 04/22/18 at 03:35:40  
Hey Archie,
All good amigo.  This is one of my favorite forums due to the wonderful people.  I love the fruitful, entertaining, and soothing conversation that occurs here on a dailly basis.  Certainly no hard feelings on my end.

Steve, thanks for chiming in with the very usefully insight and background information on this topic.  This is your company, your designs, your amps, so always a bliss to hear from the man himself.

Jeff1, I apologize if you were offended by my input on a higher bias.  The only reason I chimed in is because I have found lower bias settings uninspiring.  I have played the game across the spectrum and would never advocate lower than 50mA (with the exception of some EL34’s).  Going the other direction, as I stated above, has led to an exponentially greater enjoymnent of my Decware ZMA.  So, to be more direct, as it seems you want/need, DONT DO IT.  It sucks!

I honestly, cannot believe how good this amp is sounding, with my KT88’s, biased at 78mA.  I will repeat, I have no desire to deviate.  
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stone_of_tone
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Re: ZMA tube bias below 50?
Reply #14 - 04/22/18 at 15:15:40  
Off topic and then back to the topic is a Hallmark of this Forum. You won't find any of these moniker's here: 

Smiley

Spirited debate should be welcomed....as was this discussion (and I learned a half a dozen other things just now). I have had a few spirited posts, with a couple member's myself, in the 17 years I have been on this Forum.  ....and we come back to on TOPIC succinctly.

I make no apologies for NOT liking high sensitivity Speaker's (I run 91/92db @ 1 watt/1 meter).....AND wanting Steve's input about enhancing the ZMA power supply/speed....talk about off topic for this Thread?!

Now, back to Topic.... I agree with J of A....lower than 50...no good.


Thanks Archie, Steve and J of A.....as discussed here and in the ZMA tube rolling Thread....I need to get some KT88'S... .
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Archie
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Re: ZMA tube bias below 50?
Reply #15 - 04/22/18 at 18:19:53  
As for KT88s, any thoughts on lower priced quads?  I like trying new tubes but I'm CHEAP!   Grin
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Archie
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Re: ZMA tube bias below 50?
Reply #16 - 04/22/18 at 21:00:07  
I see Electro Harmonix quads of KT88s for about $120.  Does anybody have experience with these tubes or EH tubes in general?  They also have a 6550 which is supposed to be compatible but I don't know what the difference is.

This is cheap for a quad of KT88 tubes -- maybe too good to be true?  I don't want to throw away $120 on crappy tubes.
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stone_of_tone
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Re: ZMA tube bias below 50?
Reply #17 - 04/23/18 at 14:26:41  
I am not a fan of EH tubes.

I'm going to go for a quad of cryogenic TAD KT66's this summer and a cryo quad of Gold Lion KT88 in the fall.
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Archie
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Re: ZMA tube bias below 50?
Reply #18 - 04/23/18 at 16:51:07  
Stone, thanks. That's enough for me to avoid them.  Any thoughts on JJ tubes?  I'm going down the list of inexpensive KT88s on ebay.
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Re: ZMA tube bias below 50?
Reply #19 - 04/25/18 at 01:09:24  
I'm taking a slight risk and I bought a quad of "JJ Electronics" KT88s.  They are unmarked tubes that the seller claims are sold for use in new amps.  They have internals that sure look like the JJ tubes.  At less than $120 delivered they are a deal if as advertised.

Thanks Jeff for the bias information that prompted me to try the KT88s in my ZMA.   Smiley
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Re: ZMA tube bias below 50?
Reply #20 - 04/25/18 at 02:03:36  
While I haven’t rolled any of the JJ tubes, my gut feeling is you will like dynamics the KT88 in general brings to the ZMA.  

Steve intrigued me by the N.O.S. 7027 mention.  I just picked up a set of (10) closely matched RCA brand 7027’s to try.  Wasn’t in the market for 10 of these tubes, but if the results are good, Ill have a complete second set, for when they wear out.  I’m curious how these will bias.
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Re: ZMA tube bias below 50?
Reply #21 - 04/25/18 at 15:46:17  
It's hard to keep up with all the options!
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Re: ZMA tube bias below 50?
Reply #22 - 04/25/18 at 17:19:54  
Let us know what you think of those JJ's Arch and I look forward to your opinion Jeff on the 7027's. It is great to have all these options!

I'm going to stick with my plan, but instead, get the cryo Gold Lion KT88's in here soon/first and then the TAD cryo KT66's.

Since, I am not getting back in to low power Amp's...tube rolling input tubes with my stalwart Telefunken inverters with output tube rolling will certainly continue for me.

I've been enjoying my Mullard's ~ Tele's & 6P output tubes so much I have had no desire lately to put my Tung-Sol KT66's in. Need to get those KT88's soon though... .

I might get a couple more pair of input tubes on my radar from Upscale.

Lately, I am enjoying the adjustment of my ZDSD's input volume and output level.....manipulating Redbook CD's for the way better!




~ All NOS Platinum graded Tubes from Upscale Audio (except 6N23P's):

(Great Britain) Mullard 7308/E188CC ~  2 pair (both pair Cryogenic)
(Germany) Telefunken 6922/E88CC ~ 1 pair (painfully expensive/worth it)
(US/Great Britain) Ediswan CV2492/6922 ~ 2 pair (one pair Cryogenic)
(Hungary) Tungsram 6922/E88CC ~ 1 pair
(Hungary) Tungsram PCC88/7DJ8 ~ 1 pair

(Russia) 6N23P's ~ 2 pair/came with ZMA.  





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Decware ZDSD DAC / Recorder
***************************************************************
W/Steve's Output Transformer's/kicking to the Curb quite a few superb DAC'S
***************************************************************
(@ -20 Ref Level, 0.0 Input volume and @ 16/192)
~Adjustments made often to Input volume: -.5, -1.0, -1.5 & -2.0 max
~Adjustments made often to Ref Level: -20, -18, -16 & -14 max


WBT-0102Ag RCA Kimber Select KS1030 ~.75 meter


Decware Zen Mystery Amplifier
~BIASED at *56* mA~
NOS/Platinum/Mullard E188CC/7308's in my A12 an B12 Input positions Cryogenic~NOS/Platinum/Telefunken 6922/E88CC for Inverter Tubes~NOS RCA 0A3's & matched Quad/Tung-Sol KT66's or 6P3S-E's




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Acoustic Zen Adagio - Black Pearl (Modified)
.....enjoying from 8 ohm ZMA Taps


Caintuck Audio Eminence Alpha 15" OB BASS Unit
at 43Hz, with my Velodyne CHT 130 watt plate amp and 0 degree phase
Plate Amp....regen'd clean ~ plugged into P3
Auralex Subdude (a must)
(NOTE ~ Only needed when the recording calls for...Open Baffle Bass has been the best integration I have witnessed when needed and called on)







Acoustic Zen Adagio's x-over's Modified/Full Range with Mundorf MCap Supremes-single Cap to each Tweeter/4.5k cross
(Gutted: 3kHz/18dB/Octave, Linkwitz/Riley Crossovers....with all crappy parts = gone)


ZMA, updated with robust Western Electric Bias/Balance Meter's and new Resistor's ~ Feb/17

XLO Pro Power Cord to ZMA
Shunyata Research Zitron Alpha Digital Power Cord to ZDSD {Significant}
PS Audio P3 Power Plant / Pangea AC-9SE from wall to P3
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Re: ZMA tube bias below 50?
Reply #23 - 04/26/18 at 01:01:25  
Stone, like you I'm enjoying the 6Ps.  I'm very curious to see if I like the KT88s as much or more.  I'm hoping for a very different sound -- for variety.
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Re: ZMA tube bias below 50?
Reply #24 - 04/26/18 at 20:18:43  
Yes, for sure - variety, Archie.

I put my Tung' KT66's back in today. As much as I enjoy the presentation/way, of detail and very good dynamic's of the 6P's........... the KT66's open back up the SLAM Dynamic and love the fuller output settings of my DAC (ZDSD)!

KT88's, as J of A mentions in his reply #2 & #8.....I got to get the Gold Lion (cryo'd) KT88's in here.

Arch, let us know....cause' those JJ KT88's you have coming, I bet, are no slouches either.
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Re: ZMA tube bias below 50?
Reply #25 - 04/27/18 at 02:44:37  

Recommended affordable new production KT88 is the Tungsol which is Russian.

Jeff,

I believe based on all the tubes I've heard in my lifetime that there is no faster 8 pin output tube than the 7027's and also the most neutral.  It's total hardcore.  In a push-pull amplifier there is absolutely nothing that has the leading edge attack and slam to back it up of a 7027.

Steve
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Re: ZMA tube bias below 50?
Reply #26 - 04/27/18 at 04:01:01  
Thanks Steve, on the KT88 new prod recommendation.

I'm in for the 7027 too. Jeff found some RCA NOS. Any recommendation for new production on these? JJ or Tung-Sol?
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Re: ZMA tube bias below 50?
Reply #27 - 04/27/18 at 07:09:42  
Quote:
Jeff,
I believe based on all the tubes I've heard in my lifetime that there is no faster 8 pin output tube than the 7027's and also the most neutral.  It's total hardcore.  In a push-pull amplifier there is absolutely nothing that has the leading edge attack and slam to back it up of a 7027.


Steve, this is a very interesting tube.  Its hardware design shares a lot of similarities to the 6L6’s but with a slightly different pin configuration and the ability to handle higher plate voltage and power dissipation.  It sounds like these differences in design provide a clear advantage over the 6L6’s. I am very excited to try them in my  system, especially after reading your comments on the attributes of this tube type in the ZMA.  

I found a matched quad, N.O.S. Philips ECG 7027A’s.  They are supposed to be superior to the RCA’s based on what I have read.  Pricey though at $362 a set but from what folks are saying, these are military grade and will last a LONG time.  I can easily dump more than that on a fancy set of boutique Chinese tubes that will last a year if I am lucky.  I think I am going to pull the trigger and grab these Philips as well.  

Out of curiousity, how do the 7027’s bias in the ZMA?  50’s, 60’s, or higher?
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Re: ZMA tube bias below 50?
Reply #28 - 04/27/18 at 19:40:39  
Nice to have the KT66 back in (in my System/Speakers/Kabling = no edge). However, the 6P's micro dynamic's are to be appreciated.

I am intrigued by the 7027. Maybe, its design provides an advantage over the 6L6. I'm going for a matched quad of the JJ's. Leading edge attack & slam?  ....Look forward to these puppies for under 100 duckets.

...With the leading edge transient attack of the 7027...and its smaller envelope like the 6P's....maybe I get my micro dynamics of the 6P's too? I should..... .    

I love my music and this hobby!

This very right now? Jammin' to the macro' of the KT66 Tung-Sol's ....yeah it's Friday......I cracked open ~ THE HOPCROMANCER - AMERICAN IPA!
http://www.badweatherbrewery.com/beer-series/

Cheers!

Of course with nothing less than these guys too:  NOS/Platinum/Mullard Cryogenic E188CC/7308's in my A12 an B12 Input positions~NOS/Platinum/Telefunken 6922/E88CC for Inverter Tubes~NOS RCA 0A3's.  8-)
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Re: ZMA tube bias below 50?
Reply #29 - 04/28/18 at 02:38:07  
Jeff,

If I remember they biased on the higher side of things.


I have never tried any of the new production, but I would expect coming from the G.E. and RCA NOS references, the new production would not be as good.  Of course that is true of all new production compared to NOS.

Steve
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Re: ZMA tube bias below 50?
Reply #30 - 04/28/18 at 18:07:17  
Quote:
...the new production would not be as good.  Of course that is true of all new production compared to NOS.


Why is that exactly?  Is it just an experience curve or something with the materials?  I see tubes that are supposed to be exact copies of the originals.
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ZLC
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ZR2 (25th A Mods)
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Re: ZMA tube bias below 50?
Reply #31 - 04/28/18 at 18:49:26  
Some NOS tubes are just phenomenal. . . but over the last decade I've come to really like some new production tubes. New production output tubes can be worked with to sound with the right complement around them. And I've come one eighty recently and prefer Steve's chosen Russian inputs to NOS tubes in my preamps and amps.
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Re: ZMA tube bias below 50?
Reply #32 - 04/28/18 at 18:54:34  
Steve's Russian tubes are also NOS, aren't they?
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ZLC
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Re: ZMA tube bias below 50?
Reply #33 - 04/28/18 at 19:05:14  
Yes, probably. Not sure to be honest how many of those are produced today. . . I've been buying 6N1P and 6N5P from other sources with no knowledge of manufacturer or date. They are a newer design of tube than many of the usual NOS types.

I was perhaps typing out of turn with generalizations about NOS and new production tubes; I realize that Steve's statement (and your query afterwards I suspect) was about that specific tube type, and I don't doubt that the NOS are considerably better. Reading up it seems that the JJ in particular is less truly like a 7027 than the originals.
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Re: ZMA tube bias below 50?
Reply #34 - 04/28/18 at 19:33:51  
I took Steve's comment to be generally across all tubes.  That's why it caught my eye.  But maybe he didn't mean it that way.

The Russian military 6N5Ps that Steve uses (I think) and the Russian Military 6N1Ps I've been getting are all NOS.  They have a date code printed on them.  For example, they might read III/72, which I interpret as March 1972.
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ZLC
Technics 1200G TT w/ Ortofon Jubilee MC cart
ZMC1
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ZR2 (25th A Mods)
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ZMA (25th A mods)
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Re: ZMA tube bias below 50?
Reply #35 - 04/28/18 at 22:03:14  
All the 6N5Ps I have bought except one pair have no markings at all on them, so no sense of provenance (and those I purchased were ridiculously cheap). The pair I have from Steve are also unmarked I believe. One pair I've bought (which were more expensive by far than the others I bought, and don't at least yet quite sound as good) the vendor says were from '79 and have the type printed on them. I've ordered a set from Steve to put in the ZTPRE replacing the cheap ones from ebay.
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Re: ZMA tube bias below 50?
Reply #36 - 04/28/18 at 23:53:27  
I bought some of this seller's tubes.  In this listing you can see the dates in the picture.  I don't know if all Russian 6N5Ps are the same or not.  In my previous post I said the 6N5Ps were "military."  Now I'm not sure.  I know there is a big difference in price between the Russian 6N1P and the military version.

Quote:
https://www.ebay.com/itm/8x-6N5P-Russian-Audiophile-Tubes-double-triode-tubes-Sa...
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ZLC
Technics 1200G TT w/ Ortofon Jubilee MC cart
ZMC1
ZP3 (25th A Mods)
ZR2 (25th A Mods)
CSP3 (25th A mods)
ZMA (25th A mods)
Homemade Big Betsy Speakers (F15s)
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Re: ZMA tube bias below 50?
Reply #37 - 04/29/18 at 00:06:05  
Back to the KT88 thread ...

I received the unlabeled "JJ" tubes today.  I get a bias window from 56ma to 96+ma.  I'm not hearing a difference in sound with different bias but I decided to bias at 70ma.  After a couple hours on an already warmed up ZMA, I really didn't feel much increase in transformer heat.

I like how these tubes sound and without doing a closer A/B test than I can with tube change out, they sound similar to the 6Ps that I like so much.

Jeff, maybe you could help me figure out what to listen for since you have both the 6Ps and KT88s (better versions than mine, I'm sure).

While nice tubes, so far I'm not hearing a big change.  I'd have to put my KT66s back in to see if I now like them better than I did before.  I've made so many changes in my system that I need to circle back.
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ZLC
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ZP3 (25th A Mods)
ZR2 (25th A Mods)
CSP3 (25th A mods)
ZMA (25th A mods)
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Re: ZMA tube bias below 50?
Reply #38 - 04/29/18 at 01:16:46  
Cool about those 6N5Ps. Mine are not the same, no ink at all on them. They sound pretty darned good.
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Re: ZMA tube bias below 50?
Reply #39 - 04/29/18 at 16:18:14  
Archie,
I am surprised you are able to get the bias as low as 56.  That seems odd to me.  I have not been able to get any of my KT88’s below 70.  I also find it a bit suspicious that the sound differential is not there.  This tube type results in greater power output overall, and is really dynamic.  To make some generalizations about the KT88, without getting into specific makes/models, I would say that add “boost” to my system across the spectrum.  The 6P’s are wonderful sounding tubes, and I still feel their midrange purity is second to none.  But they don’t excite the ZMA like the KT88’s.  Bass, and treble extension with the KT88’s is in a league of their own.  It's not just slam either.  The highs sparkle and create a wonderful balance that compliments the mids and bass.  

When I get my 7027A’s, if you pay the shipping, I will send you my Gold Lion KT88’s to audition.  I feel like you really need to put a known, reputable KT88 in your ZMA to really know how this tube type performs.  

Stone, the offer extends to you as well my friend.  If you want to give them a listen before dropping the cash on the set, I would be happy to oblige.
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Re: ZMA tube bias below 50?
Reply #40 - 04/29/18 at 18:55:30  
Jeff, I might take you up on your offer.  These tubes I got have a huge bias window though.  It's always hard to know what's what with a single data point.

I don't hear much difference with tube swaps, in general, in my system.  It's likely just me and how I hear, or don't hear. I kind of get an overall sense of things with time but I can rarely narrow it down to one tube, wire or whatever.  Also, a couple days ago I swapped out my ZP3 and CSP3 rectifiers and put in NOS RCA Type 80s and I pulled all the 6N5Ps from my CSP3 and ZMA and put in Russian 6N1P-EVs.  I also moved my ZR2 to be in front of my recently Anniversary modified CSP3 and then put in the KT88S.  And, to top it off, I was using a different cart than usual.  So, nothing like changing everything to make it impossible to hear what's doing what.
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ZLC
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ZR2 (25th A Mods)
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ZMA (25th A mods)
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Re: ZMA tube bias below 50?
Reply #41 - 04/30/18 at 16:26:42  
I'm back using the 6P3S-Es.  They seem to work best for my system giving me a stunning midrange and a brighter top end.  I think my old hearing favors the midrange and I might miss some of the benefits a tube can give to the highs.
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ZLC
Technics 1200G TT w/ Ortofon Jubilee MC cart
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ZP3 (25th A Mods)
ZR2 (25th A Mods)
CSP3 (25th A mods)
ZMA (25th A mods)
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Re: ZMA tube bias below 50?
Reply #42 - 04/30/18 at 18:52:21  
Thanks Jeff, much appreciated offer. However, I just went ahead and ordered a cryo matched quad from Ron S (the Lion's). I so look forward to getting these guys in my ZMA! I bet they lay the KT66's to rest... .

Could not agree more guys, the 6P's midrange is stellar and I absolutely love these tubes. The ZMA however, is about being able to run the KT88 (especially the Lion's/never to be confused with a Lion KT66-I've been told; these KT88's are special). Treble extension & sparkle up top.....overall big picture gestalt.

The 6P's & the KT88 Gold Lion's with my preferred input tubes might be all I ever need.

PS~and to be able to Bias & Balance them/dead nuts in my ZMA. Especially these guys...KT88.
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Re: ZMA tube bias below 50?
Reply #43 - 05/02/18 at 14:35:43  
My GL KT88's are out for delivery. I will heed Steve's input, about an 4, 5 hour Listening session with this quad. NOT, to be on all day.

Well, here's hoping I can bias (& balance) them closer to 70 than 80mA.
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Re: ZMA tube bias below 50?
Reply #44 - 05/02/18 at 16:06:52  
One thing I did in the beginning was to mount a super quiet computer fan on the wall behind my ZMA transformers.  I keep the fan sat a low setting and I think it keeps things several degrees cooler.  This might be a good precaution when using high biasing tubes.  Steve kind of rattled me when he mentioned melting the beeswax out of the caps!   Cry
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ZLC
Technics 1200G TT w/ Ortofon Jubilee MC cart
ZMC1
ZP3 (25th A Mods)
ZR2 (25th A Mods)
CSP3 (25th A mods)
ZMA (25th A mods)
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Re: ZMA tube bias below 50?
Reply #45 - 05/02/18 at 17:56:24  
My particular set form GL KT88’s from Ron will not go below 78ma.  I am curious to see how consistent - or not - they are across different sets with its minimum bias point.  

The last set I had in, the TJ Full Music KT88’s, biased slightly lower at about 75ma.  

Looking forward to your impressions Stone.
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Re: ZMA tube bias below 50?
Reply #46 - 05/02/18 at 22:04:16  
You bet Jeff.

I will get out an initial impression and bias setting...then let them burn in 5 hours at a time....long time till the 100 hour mark....then impressions.
....Impressions at 20, 40, 60, 80 then 100 will be appropriate.

I have to remark more on the 6P's...great midrange as we know. However, with the ZDSD, I'm able to tame their top end with -.5 Input volume and -18 Reference Level output (recording dependent).

Then, I can put in the KT66 Tung-Sol's .......use -20.....and right now -18 Ref Level.....BUT, RUN +1.5 Input Volume with MACEO PARKER - LIFE ON PLANET GROOVE.....when he rises up the scale on his Alto....it is to DIE FOR.....with the ZDSD/ZMA Combo!  The whole Disc locked in at these Settings.....for this Live Recording of mind blowing!

Can't say enough about the ZDSD settings.....for Input & Output Tubes. NO, other DAC can do this.  .....Steve, great design....  ;) ........

because without your Output Transformer's....this DAC would not shine!






Tung-Sol KT66 matched quad
Reflector 6P3S-E cryo matched quad

Pending: Gold Lion KT88 cryo matched quad


~ All NOS Platinum graded Tubes from Upscale Audio (except 6N23P's):

(Great Britain) Mullard 7308/E188CC ~  2 pair (both pair Cryogenic)
(Germany) Telefunken 6922/E88CC ~ 1 pair (painfully expensive/worth it)
(US/Great Britain) Ediswan CV2492/6922 ~ 2 pair (one pair Cryogenic)
(Hungary) Tungsram 6922/E88CC ~ 1 pair
(Hungary) Tungsram PCC88/7DJ8 ~ 1 pair

(Russia) 6N23P's ~ 2 pair/came with ZMA.  





Listening Room:



Room Treatments from Michael Green & my Home Brew


Sony as Transport (DVP-NS57P)
Illuminati D-60 Digital Coax IC ~.5 meter


Shunyata Research Zitron Alpha Digital Power Cord to ZDSD {Significant}


Decware ZDSD DAC / Recorder
***************************************************************
W/Steve's Output Transformer's/kicking to the Curb quite a few superb DAC'S
***************************************************************
(@ -20 Ref Level, 0.0 Input volume and @ 16/192)
~Adjustments made often to Input volume: -.5, -1.0, -1.5 & -2.0
~Adjustments made often to Ref Level: -20, -18, -16 & -14
~+.5, +1.0 or +1.5 Input Volume...W/-20 or -18 Ref Level


WBT-0102Ag RCA Kimber Select KS1030 ~.75 meter


Decware Zen Mystery Amplifier
~BIASED at *56* mA~
NOS/Platinum/Mullard E188CC/7308's in my A12 an B12 Input positions Cryogenic~NOS/Platinum/Telefunken 6922/E88CC for Inverter Tubes~NOS RCA 0A3's & matched Quad/Tung-Sol KT66's or 6P3S-E's




***************************************************
Kimber Select KS6063 Speaker Cable 8ft WBT-0681-Ag Spades
***************************************************
Kimber (new jacket) 8TC ~ to remind me~how good the KS6063 are


Acoustic Zen Adagio - Black Pearl (Modified)
.....enjoying from 8 ohm ZMA Taps


Caintuck Audio Eminence Alpha 15" OB BASS Unit
at 43Hz, with my Velodyne CHT 130 watt plate amp and 0 degree phase
Plate Amp....regen'd clean ~ plugged into P3
Auralex Subdude (a must)
(NOTE ~ Only needed when the recording calls for...Open Baffle Bass has been the best integration I have witnessed when needed and called on)







Acoustic Zen Adagio's x-over's Modified/Full Range with Mundorf MCap Supremes-single Cap to each Tweeter/4.5k cross
(Gutted: 3kHz/18dB/Octave, Linkwitz/Riley Crossovers....with all crappy parts = gone)


ZMA, updated with robust Western Electric Bias/Balance Meter's and new Resistor's ~ Feb/17

XLO Pro Power Cord to ZMA
Shunyata Research Zitron Alpha Digital Power Cord to ZDSD {Significant}
PS Audio P3 Power Plant / Pangea AC-9SE from wall to P3
(Transport and ZDSD, Regenerated/*120*~ Multiwave off...ZMA on High Current Output)
System configured on Floor ~ Townshend Audio CD Seismic Sink deployed & other Isolation devices.
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Room Treats-M.Green & mine
Sony TPort
Illuminati D60
Shunyata Z-Alpha DigPcord
Decware ZDSD DAC
Kimber Select KS1030
XLOProPcord
Decware ZMA/25th Mods
Kimber Select KS6063
Acoustic Zen Adagio/Modified
Kimber PK10 Palladian from wall
to PS Audio P3
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Jeff of Arabica
Seasoned Member
****




Posts: 974
Re: ZMA tube bias below 50?
Reply #47 - 05/02/18 at 22:23:32  
Couldn’t agree more on the ZDSD Stone.  It is really an amazing piece of hardware.  I think it is fantastic that your are exploiting its strengths through the Ref. Level and Input Volume settings.  So powerful!  And I know, from my experience with my ZDSD, how effective those two settings can be.  Fun stuff.  

I have heard a lot of DAC’s these last two years.  I am fortunate to be in O.C. where the LA Audio Show and T.H.E Show Newport reside.  I have heard systems on the cheap and those priced only for the priveileged.  For the price of Steve’s custom ZDSD, I have heard no better.  As a matter of fact, its sound quality supersedes its price.  It is a phenomenal piece of hardware.
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Jadis JA-30 MKII//ZMA//Zen Ultra//Waversa DAC3//ModWright Oppo UDP-205//EMM Labs DS-EQ1//DS Audio DS-003//FFYX T1803 TT//SonoruS Reel-to-Reel & tube playback preamp//Pipedreams Reference 21 Speakers
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stone_of_tone
Seasoned Member
****


Listen Often/Listen
Deep

Posts: 3217
Re: ZMA tube bias below 50?
Reply #48 - 05/02/18 at 22:29:39  
Its tailoring for Redbook is Special.

Guess what just arrived!!  My Gold Lion KT88's!  

RatsSSS!  I have to make dinner and take care of some other stuff. But, I'm a fortunate Camper!  I can get them in tomorrow morning for a run!

....till then................ .
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Room Treats-M.Green & mine
Sony TPort
Illuminati D60
Shunyata Z-Alpha DigPcord
Decware ZDSD DAC
Kimber Select KS1030
XLOProPcord
Decware ZMA/25th Mods
Kimber Select KS6063
Acoustic Zen Adagio/Modified
Kimber PK10 Palladian from wall
to PS Audio P3
  IP Logged
stone_of_tone
Seasoned Member
****


Listen Often/Listen
Deep

Posts: 3217
Re: ZMA tube bias below 50?
Reply #49 - 05/03/18 at 15:31:13  
What a beautifully constructed tube!  Nice weight/heft to them too.

Jeff, Arch, they biased dead on at 80 and after 40 mins, settled in to just under, at 78.....and hold perfect there....now at 80-85 mins of Listening.

I like what I'm hearing as advertised. Definitely more powerful subjective behavior! To early to say anything else; except I know the direction their going with some seasoning...and for the better!
.....I'm able to enjoy another hour/then look forward to firing them up over the weekend once again............. .

You know what the really great part is? We get to run them in an Class A to AB1 Zen Mystery Amplifier!!  NOT, in some boat anchor/negative feedback Amp.   Smiley
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Room Treats-M.Green & mine
Sony TPort
Illuminati D60
Shunyata Z-Alpha DigPcord
Decware ZDSD DAC
Kimber Select KS1030
XLOProPcord
Decware ZMA/25th Mods
Kimber Select KS6063
Acoustic Zen Adagio/Modified
Kimber PK10 Palladian from wall
to PS Audio P3
  IP Logged
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