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Anyone Tube Roll with the ZMA yet? (Read 99578 times)
NormD
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Re: Anyone Tube Roll with the ZMA yet?
Reply #550 - 11/09/18 at 03:10:19
 
I learn something new every day.  I'll pull the tubes and take a look one of these days.
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Archie
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Re: Anyone Tube Roll with the ZMA yet?
Reply #551 - 11/09/18 at 15:34:53
 
I looked at both my Tung Sol KT66s (2004)and 7581As (2012) and they look completely different inside.  Also the bias window for the 7581As is wide and goes into the 80s.  I don't remember the KT66s going that high but it's been years since I had them in.
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stone_of_tone
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Re: Anyone Tube Roll with the ZMA yet?
Reply #552 - 11/09/18 at 22:35:55
 
LR wrote:
"Sorry if I stepped on your d**k there and got you all bent out of shape"!

No need for sorry. I had that coming ~ touche'.

Very interesting info and appreciated.
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Lonely Raven
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Re: Anyone Tube Roll with the ZMA yet?
Reply #553 - 11/10/18 at 07:18:13
 

Archie, cool, that's what I was trying to investigate. I think there is a difference with the newer tubes, but photos online aren't helping to prove or disprove this.

Does your 7581A innards look like this pic, or does it have 3 holes instead of 2 squares?




I know for a fact the older 7581A looked just like the KT66. I'm betting that now they look more like the KT88

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stone_of_tone
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Re: Anyone Tube Roll with the ZMA yet?
Reply #554 - 11/10/18 at 14:42:12
 
The bias window is enjoyable Arch. Thank goodness, they sound nothing like KT66's or my KT88's. Interesting though, the innards might be KT88 stuffed in the smaller envelope. Cool, if so. .....all about the sound and they are special in the ZMA. IMO.

I look forward to hearing the 7581A's with my ZMA 25th. Also, Archie, was it you whom mentioned with your 25th, KT88's are running the power trannies cooler too? Subjectively, to hand touch. I don't believe you said you measured the temp. If bypass is bringing 88's more in congruence .....all for that!
J of A, have you noticed this? I would like to not be reticent about the KT88's and really enjoy them. However, if I never put KT88's in my ZMA again. I can be happy with the other three quads I roll and will find a fourth quad I bet.
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Archie
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Re: Anyone Tube Roll with the ZMA yet?
Reply #555 - 11/10/18 at 17:44:25
 
LR,

My Tung-Sol KT66s from Steve look just like yours.  The 7581As have 3 holes but the grey thing (whatever it's called) is a completely different shape.  I don't have any Tung-Sol KT88s to compare with but given the high bias, maybe you are right?  Although plate dissipation should be the same between the KT88 and 7581A.



Stone,

I think the 7581As with bias set to 68mA are running cooler compared to other tubes with bias set mid 50s and pre-mods.  All purely subjective but J of A measured a 5 degree temperature drop, I think he posted.

I hope you get your ZMA back before you have to pull the trigger on the Rachael.  It might make you change your mind.   Wink
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stone_of_tone
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Re: Anyone Tube Roll with the ZMA yet?
Reply #556 - 11/10/18 at 18:03:17
 
Hi Arch, Timeline on the Rach' bypassed would be next Sept/Oct for order. Right now the ZMA 25th'd and its enjoyment. ZBIT in February too, coming.
Plus, Steve's Power Conditioner 10 Amp.

Good news on the 7581A's running cooler. Should bode well when I get the 88's in. Yes, the high bias of the A's like a 88 could be 88 in there. The 88's like the 66's though, stay in a tight margin bias, as where the 7581A's have a beautiful swing Bias I love to utilize.
Even if the 88's don't run cooler trannies... still will use for 4 to 6 hour sessions. All day on my other quads of course.
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Lonely Raven
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Re: Anyone Tube Roll with the ZMA yet?
Reply #557 - 11/10/18 at 22:43:33
 

I'll be digging out my IR Thermometer as well. I have some of the new 7581A on the way, and I'm listening to NOS GE 7027 right now. I'm hoping I like the new tubes as much as you guys do. The GE seem to be throwing a very large image compared to the stock KT66.

Beatles White Album (Super Deluxe 2018 Mix) spinning now.

I got some unusual preamp tubes on the way - I'll share what they are if they work well in the ZMA.
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stone_of_tone
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Re: Anyone Tube Roll with the ZMA yet?
Reply #558 - 11/11/18 at 17:33:30
 
LR, look forward to reading.

I'm suffering. My ZMA has been gone 8 days. I usually get a great Saturday morning and Sunday session in. Well, you guys suffered 3 to 4 weeks...so must I.
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Lon
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Re: Anyone Tube Roll with the ZMA yet?
Reply #559 - 11/11/18 at 18:03:01
 
I totally understand that feeling Larry, I've been through it before. Be strong! You'll get through!
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Jeff of Arabica
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Re: Anyone Tube Roll with the ZMA yet?
Reply #560 - 11/11/18 at 22:12:34
 
Hey Guys,
Sorry for the late reply..  been one of those weeks.

Yes, based on my random observations using my IR thermometer, I do believe my trannies are in the ballpark of 5 degrees F cooler after power supply mods.

Still have my Phillips ECG N.O.S. tubes in play and digging them tremendously. Even found a single for sale on Ebay to replace the one tube gone bad in one of the quads I purchased.  So, now I have a full backup set again.

LR, I cant speak to the GEs but this Phillips set of 7027As are my favorite tubes I have rolled thus far. I have not tried the 7581As though, to compare.  It seems there may be some similarities in SQ between the 7027As and 7581As based on Stones and Archies observations. The 1 and 6 pins of the 7581As and 7027As are unused, but unlike the 7581As, those pins on the 7027As are tied to the screen and control grids - therefore acting as heat sinks for improved heat dissipation.
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stone_of_tone
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Re: Anyone Tube Roll with the ZMA yet?
Reply #561 - 11/13/18 at 21:25:21
 
So true Lon, you've been thru it a few times.

J of A, cool! A little lower temp on my Cryo'd GL KT88's will be nice. +, the other quads.
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Lonely Raven
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Re: Anyone Tube Roll with the ZMA yet?
Reply #562 - 11/18/18 at 00:25:29
 

How about some old Brimar KT8C tubes for the ZMA?

I got 12, randomly grabbed 4 and put them in the Mystery amp, and they were within 5% of each other!



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Archie
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Re: Anyone Tube Roll with the ZMA yet?
Reply #563 - 11/18/18 at 20:01:56
 
LR, I saw your tube reply in the other thread but I figured this is a better place to continue.

Those Brimar KT8Cs are interesting. What class of tube do they correspond to, if that makes sense? There aren't many listed on ebay and they aren't cheap too!

Do you have a ZR2? With a ZR2, I'm wondering if the other tube bass might catch up with the KT8C or if the KT8C bass might go through the roof!  (or floor)
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will
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Re: Anyone Tube Roll with the ZMA yet?
Reply #564 - 11/18/18 at 23:10:07
 
Archie,

These tubes LR pictured look like variations on British KT66 and Brimar 807s, Brimar 807s looking like some Russian 807s. When you read up on them, this makes some sense. Here is one explanation of the KT8C http://www.r-type.org/exhib/aab0080.htm
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Archie
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Re: Anyone Tube Roll with the ZMA yet?
Reply #565 - 11/19/18 at 00:13:14
 
Cool, thanks.
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Lonely Raven
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Re: Anyone Tube Roll with the ZMA yet?
Reply #566 - 11/19/18 at 21:12:23
 
Yes, what Will posted.  These set is supposedly the very last of the KT8C done to Milspec for the British Navy. The note that the seller found in the box of them said they are direct replacement for the Ceramic versions and to bias like KT66. They are ruggedized with ceramic standoffs in the structure and (obviously) the classic curvy "coke bottle" shape vs the larger KT66 shape. Milspec typically requires smaller, ruggedized versions of our audiophile tubes that bias up lower and are pre-matched in batches so once the equipment is biased, the radio tech can just swap out tubes quickly and get back to work.

I'm typically really skeptical of tubes that are "milspec" unless they come in large batches and are re-matched. So I was very pleasantly surprised when I grabbed four from the 12 I picked up and they were so closely matched I hardly had to tweak the ZMA. Usually I'm balancing each pair (on the ZMA) for 2-3 minutes as they warm up and tweaking the overall bias. With these, they warmed right up, settled, and were all within a half-space of each other on the gauges. I sat there gawking for a minute waiting for something to change, then laughed and went to listening.

I don't have a ZROCK, I tend to be a purest and go as direct as possible, so I'm XLR out of my DirectStream directly into the ZMA XLR. The DAC is at 100% and I use the attenuation on the ZMA which is typically at 85% all the time, though with these tubes I lowered it a couple times during my listening session! LOL

I do have some Milspec CV124 which are the earlier versions of these tubes that are much more like the 807 tube. These KT8C sound similar, but BIGGER. I'm listening to the CV124 as I type this in fact.

Later this week I'll have different adapters in hand, and I'll be trying out some 6BG6GA, some of which are supposed to have the same guts as the 7581A that Jeff likes.

Speaking of, here is a tip for those of you looking to try out the Phillips ECG but can't find nor afford the 7581A - look closely as these.

https://www.ebay.com/itm/Lot-of-Eight-Heavy-Duty-JAN-6L6WGB-Tubes-By-Philips-USA...

These are the Phillips ECG 7581A guts stuffed into a smaller "ruggedized" envelope and relabeled as 6L6WGB for military use. I was told by some old timers that they might not get the full 35watts of dissipation due to smaller envelope, but they are basically the same tube as the 7581A. The link posted above is a rare find someone should jump on!
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Lonely Raven
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Re: Anyone Tube Roll with the ZMA yet?
Reply #567 - 11/19/18 at 21:55:22
 

Is there a secret magic password trick to getting these NOS boxes open without tearing the damn flap?  I've been taking a butter knife and carefully prying the flaps open and still tearing the bastards. Grrr.

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Lonely Raven
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Re: Anyone Tube Roll with the ZMA yet?
Reply #568 - 11/22/18 at 19:38:05
 
The tubes burning currently are GE Blackplate 6BG6GA on 6L6 adapters.

This was like finding a nice smooth set of $250 GE Blackplates. Although this quad is poorly matched. I have 8 more to go through and might need to mix and match them for better balance. If the ZMA didn't have the bias balance and gauges, these would be difficult to use. But hey, GE blackplates for the cost of a nice dinner, cool!

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Lonely Raven
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Re: Anyone Tube Roll with the ZMA yet?
Reply #569 - 11/26/18 at 21:31:45
 

I realized I had posted this in another thread when asked about the tubes, but didn't post it here, so this is me quoting myself on this thread I've apparently killed.   Tongue


Quote:
This weekend I swapped through Tung-Sol KT66, Tung-Sol 7581A, GE (NOS) 7027, 63PS-E coin base, and a well matched quad of '73 KT8C.

I wasn't super thorough and my room still isn't properly treated since installing the new hard floors yet, but my two favorites are the 7581A and KT8C.

The 7581A I biased at 50ma, then 60ma, and topped off at 64ma like Jeff mentioned earlier in this thread. They seemed the most even across the board and nice harmonics. Reminds me of the KT66 but on steroids.

The KT8C had bass that put all the others to shame in a big way, but the treble was a little etched. They only have 3 hours on them so I hope they will calm down with a few more hours. They bias up really low, and started sounding good at 40ma and *appear* to sound louder than even the 7581A...but I think it's just a trick of the huge bass and extended treble.

I forgot which set of tubes it was, I'll be going through them again once I get diffusers in the room, but one set had amazing upper bass that was tight and detailed and made everything pop more, but didn't have the huge, deep, tight bass of the KT8C.

I still have other tubes to try out, but they are in storage, and I'm waiting on more adapters to show up. Eventually I'll post a separate thread with my thoughts on all these.

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stone_of_tone
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Re: Anyone Tube Roll with the ZMA yet?
Reply #570 - Yesterday at 17:35:30
 
NORM! Help! Grin

Talk me out of some Mazda's & Amperex by noon 12/20. Brent's shuttin' down till the 14th of the new year!
http://www.audiotubes.com/
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NormD
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Re: Anyone Tube Roll with the ZMA yet?
Reply #571 - Yesterday at 19:02:34
 
Stone:
Which tubes are you considering?  I may get some myself!!

If you think Im going to talk you out of getting tubes, you must be hallucinating. Heck, you started me down this rabbit hole! I still have the 7027s staring at me every night asking when they will get tried in my ZMA.

Have a great Holiday!
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stone_of_tone
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Re: Anyone Tube Roll with the ZMA yet?
Reply #572 - Today at 16:11:54
 
GrinNo doubt, I'm guilty, I did start you down this rabbit hole, didn't I?!

I'm going to hold off for now. I need to figure my budget after the new year. I have a couple Decware products on the build sheet, I need to factor in. However, I think I'm going to grab a matched pair of 6N5P's from Steve next month........... .

You too Norm, have a great Holiday!

If I did not buy/tweak with another thing.....I'm very happy with my Decware/Kimber Select/Acoustic Zen Adagio/System of bliss! The glass is more than half full.
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NormD
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Re: Anyone Tube Roll with the ZMA yet?
Reply #573 - Today at 16:15:15
 
Im still enjoying my 7851s but I have made some significant and noticeable upgrades in my sound lately. My first change was plugging my ZMA back into my P5 regenerator. The second was to replace my DHC-1 with a AC12 power cable as recommended by Lon; that upgrade was a shocker especially in the bass extension. The third was replacing the hard rubber hockey pucks back under my speakers. I moved them to reroute cables and decided to try without them - big mistake. My listening room is on the second floor of a 1890s farm house with wood floors. The construction was not as solid as todays. The hockey pucks seem to decouple the speakers from the floor resonance and my bass and clarity were restored. Cheap upgrade and I may try some under my ZMA and regenerator.
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