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KT88s and Rachael (Read 2412 times)
Palomino
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KT88s and Rachael
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?
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busterfree
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Re: KT88s and Rachael
Reply #1 - 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.
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hifitubes
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Re: KT88s and Rachael
Reply #2 - 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.
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Palomino
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Re: KT88s and Rachael
Reply #3 - 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.
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hifitubes
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Re: KT88s and Rachael
Reply #4 - 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
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Palomino
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Re: KT88s and Rachael
Reply #5 - 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.
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hifitubes
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Re: KT88s and Rachael
Reply #6 - 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.
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Palomino
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Re: KT88s and Rachael
Reply #7 - 01/14/14 at 12:45:38
 
I know someone on this forum as well that prefers th KT77s.
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beowulf
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Re: KT88s and Rachael
Reply #8 - 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?
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Palomino
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Re: KT88s and Rachael
Reply #9 - 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.
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Palomino
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Re: KT88s and Rachael
Reply #10 - 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.
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Fireblade
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Re: KT88s and Rachael
Reply #11 - 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
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Palomino
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Re: KT88s and Rachael
Reply #12 - 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.
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Palomino
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Re: KT88s and Rachael
Reply #13 - 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.
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Fireblade
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Re: KT88s and Rachael
Reply #14 - 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?
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