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EQUIPMENT FORUMS >> SE34I.5 >> KT88s and Rachael
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Message started by Palomino on 01/06/14 at 18:49:14

Title: KT88s and Rachael
Post by Palomino on 01/06/14 at 18:49:14

I got a pair of TAD (Tube Amp Doctor) Cryo'd KT88s with an amp I bought.  They are listed in the Rachael manual as an approved tube, but I read somewhere that Steve felt they might sound thin due to higher bias.

At first, I agreed with him, but I gave them some time and they now have a fuller sound and better controlled bass with more slam.  They are currently my preferred power tube in combination with RCA NOS 5U4G rectifier and Gold Lion 6922s.

Anybody else try KT88s?

Title: Re: KT88s and Rachael
Post by busterfree on 01/07/14 at 02:45:20

I also have some KT88s (Genalex) that I got with another amp. I have used them in my Rachael for a day or so just to make sure that they work as a potential back up. For now, I am sticking with EL34s just because I want to.

Title: Re: KT88s and Rachael
Post by hifitubes on 01/07/14 at 06:40:19

Interesting, I would like to try KT88 and see. I am picking up some Tesla EL34 now, and some Gold Lion re-issue KT88 might be a good choice!

BTW - what are your setups and do you have any hum? I have a straight amp and it is very quiet overall (no spurious noises etc), but I'm trouble shooting some power issues in the house and do have some low-level hum.

Title: Re: KT88s and Rachael
Post by Palomino on 01/07/14 at 13:50:57

Ron Sheldon at cryoset likes the genelex kt88. I believe he said they were the best he sold. No noticeable hum on my system from the listener position.  Only 89db speakers though.

Running a Rachael with VCaps which Btw, I did a side by side with my other Rachael non-vcapped and its a big improvement in openness and soundstage.  I'd like to do the same comparison with jupitors.

Title: Re: KT88s and Rachael
Post by hifitubes on 01/12/14 at 07:27:58

Palomino,

Where do the KT88 bias at on the meters?

I'm curious about this because I may run my Mini-Torri to my subwoofer and my monitors start to roll off high at about 80hz.

What are the mids/highs like compared to EL34? I'm not so concerned about about the bass...

thanks

Title: Re: KT88s and Rachael
Post by Palomino on 01/13/14 at 15:59:23

The meters are just a hair over 42.

I think the biggest difference is in the bass.  Much tighter and more powerful with the KT88s.  The mids/highs are smoother than the EL34s I have (two sets) .Perhaps a bit rolled off, but it works well with my full range drivers.

Title: Re: KT88s and Rachael
Post by hifitubes on 01/14/14 at 04:57:10

Someone posted on AC that they have a Decware Hazen mod amp and prefer the Genalex re-issue KT77. I think I'm going to pick up a pair. I just sold a matched pair that I had left in the USA. dumb.

Title: Re: KT88s and Rachael
Post by Palomino on 01/14/14 at 12:45:38

I know someone on this forum as well that prefers th KT77s.

Title: Re: KT88s and Rachael
Post by beowulf on 02/04/14 at 02:17:11

I have heard that the KT88s tubes can go up to 100 watts, etc. ...

Sorry if this is a dumb question, but by using the KT88's would it provide more wattage in the Rachel?

Title: Re: KT88s and Rachael
Post by Palomino on 02/04/14 at 11:52:00

I don't know the technical answer but as I mentioned above the bias meters read higher and they sound louder.  

I did a quick testa at time I checked the room with a meter and didn't see a difference.

I need to do a better test with a meter to verify.

Title: Re: KT88s and Rachael
Post by Palomino on 02/04/14 at 14:18:41

I ran a more controlled test.  The KT88s were in fact not as loud (around 2db lower) as my JJ EL34s and Tung Sol EL34Bs.

But, the KT88s sounded fuller.  More body.  They just seemed to fill the room more and were not as forward.  I used a 100hz test tone for all the tests so wasn't a different frequency impacting the results.  Not sure I understand this.

While keeping the input/output tubes the same (6922s/EL34Bs) I switched out rectifiers.  None impacted the volume.

So while I don't know what I'm doing really, I think I have shown that KT88s produce a different sound, but not a louder sound.  Also, I thought that at least one of my rectifiers made for louder sound.  My NOS RCA. 5u4g, TAD GZ34 and Ruby 5u4G all played the same volume.

Title: Re: KT88s and Rachael
Post by Fireblade on 02/04/14 at 22:17:05

I don't know much about the topic either, but it seems to me that narrowing your reference tone to only 100 Hz is not representative of the real frequency distribution typically exposed in normal music listening.

The result would be constricted to the 100 Hz realm only, thus not a reference you could extrapolate to the rest of the distribution spectrum. My $0.02

Title: Re: KT88s and Rachael
Post by Palomino on 02/04/14 at 22:38:49

Thanks.  I agree with your conclusion.  It was more or less a quick test.  KT88 seem to do bass better so I chose a middle of the road bass frequency.  I was actually surprised that it was not louder than my other tubes given my perception.

I could repeat the test with pink noise or maybe play an entire song and record the average SPL.  

Title: Re: KT88s and Rachael
Post by Palomino on 02/04/14 at 23:39:37

I found this description of the KT88 from the Tubestore interesting:

"In general, the KT88 tube has a magical mid-range similar to the smaller EL34 tube, but with low and high end extremes that reach much further."

And this from an audiogon post comparing EL34 and KT88:

On sound quality, the consensus seems to be that the '34 has more lushness or richness in the midrange than almost any other mid- to hi-power output tube while being a little soft at the frequency extremes. The '88 (and its very close cousin the 6550) is more balanced across the frequency band, exhibiting more-extended and -controlled bass and better-quality treble than the '34 while lacking the '34's (euphonic?) midrange richness. These differences probably can be swamped by the extremes of different brands of the 2; the above is average or typical.

Title: Re: KT88s and Rachael
Post by Fireblade on 02/05/14 at 00:36:06

There seems to be a price to pay for the traditional lushness in the EL34's midrange through rolled ends on the frequency range. Linearity is supposed to be more desirable but that midrange 'to die for' has become an addiction for many a listener.

Linearity means, in this case, no overemphasis in a particular frequency subgroup ... That is why the lower frequencies and higher ones seem fuller and heavier, but I bet the midrange is not to die for anymore ...   tradeoffs?

Title: Re: KT88s and Rachael
Post by Lon on 02/05/14 at 00:49:55

I'm not sure that is the case with ALL EL34s or all amps they may be plugged into. I've seen individuals online making broad sweeping generalizations like this by using a half a dozen tubes in one machine.

Title: Re: KT88s and Rachael
Post by Palomino on 02/05/14 at 01:18:29

Yes, I think there are tradeoffs.  I had thought I liked the EL34 better overall because of the Hazen mod, but perhaps it is also the over emphasized frequencies in the KT88.

I was also having more trouble taming the low end of my room with the KT88s, so while I still use them, I have gone back to the EL34 as my go to setup.  I don't listen to as much rock anymore, but if I do, I go to the KT88s.

Title: Re: KT88s and Rachael
Post by Fireblade on 02/06/14 at 01:29:10

I agree. I think the EL34 in general ought to be more friendly when it comes to room conditions, relative to KT88's, precisely because the lower and higher frequencies are more aggressive when bouncing around against the room walls and such.

From these frequency distribution tails, the lower ones are the most difficult to manage successfully. This hobby is really tough and exciting.

Title: Re: KT88s and Rachael
Post by 4krow on 02/15/14 at 03:12:10

I found a similar situation today with my present amp. It is probably an apples to oranges comparison, but in my case, it involved changing out an input tube in my amp. Overall, I liked the sound this amp, but I had heard better. THEN I changed out the 12AX7 GE tube to a PS Vane 12AX7-T, whatever that means. Anyway, it almost makes me reconsider selling this amp in the first place! I won't go into details, but just say that tube equipment is so versatile in this way compared to anything that I have ever owned previously. I guess that's my point. You can have identical numbers on the glass with different results from one to another. Magic/preference can be the product of a happy accident.

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