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The Poor Man's KT88

ScooterMcTav

ScooterMcTav

I know less than I think
Just wanted to share a recent experience.

My Jolida JD302BRC can use a variety of power tubes including those usually compatible with EL34 (EL-34, KT77, 6CA7) and the higher powered KT88, 6550, etc. The amp just needs to be manually biased with a multimeter.

When I first got the amp, it came with two sets of EL-34 (JJ and EH), and a set of Tung Sol 6550. I found the 6550 to be harsh in the mids, and both sets of EL-34 to be pleasant, but without punch.

Based on feedback from AK members, and as a rock fan, it was suggested I try EH KT88. I was able to source an affordable slightly used quad, and yup, these were the tubes. Clean top end, solid vivid mids, and punchy, solid bass.

Unfortunately, my KT88 started to die last week, so in went the EL34 (ick) and off I went to order tubes.

I was certainly shocked when I saw the price of a new quad - close to $280 all-in delivered in Canada. Yikes! I used to feel like a big spender when I bought an AVR for that price.

Based again on feedback I could find on the web, thought I'd take a flyer on a set of EH 6CA7. Their cost was roughly 1/2 of the KT88, yet they were described as a punchier version of an EL34.

Well, the tubes arrives yesterday, and I finally had a chance to warm them up and bias them tonight. Hold sheep dip, what bass!

Were they KT88? No, but they certainly had more in common with them than the EL34. The bottom end and midrange warmth were excellent. Mids were clear without being brash or harsh. The top end was slightly more recessed than the KT-88, but not significantly so.

Will be giving them a much more thorough workout while working from home this coming week. But for now, initial impressions are that the EH 6CA7 is about 90%-95% of the EH KT88 for 50% of the price.

For someone who loves rock, and loves a fat bottom end, these are excellent budget tubes.
 
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That's pretty much what I think about them--sort of a cross between a KT88 and an EL34, with the positive attributes of both. And I like them with classical and classic jazz. Excellent piano reproduction in my amps.
 
I tried EL34's, KT77's and KT88's in my ST-70. Between them I preferred the KT77's. But recently I bought a quad of EH 6CA7's myself. They are now my favorite tube in this amp. In some amps they have been said to be overly bright. I hear none of that. The midrange sounds right and the top end is great. My system has no tone controls and the bottom end is the way I like it with these tubes.
 
Lavane said:
I tried EL34's, KT77's and KT88's in my ST-70. Between them I preferred the KT77's. But recently I bought a quad of EH 6CA7's myself. They are now my favorite tube in this amp. In some amps they have been said to be overly bright. I hear none of that. The midrange sounds right and the top end is great. My system has no tone controls and the bottom end is the way I like it with these tubes.
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I went the other way with the amp recently. I had a set of 6CA7's in there forever and changed over to a set of GL KT77's. The KT77's are definitely brighter in my amp but in a real pleasant way. I'm sure i'll pop the 6CA7's back in one day and enjoy them when I get bored of the way things sound now.
 
dannyr said:
I went the other way with the amp recently. I had a set of 6CA7's in there forever and changed over to a set of GL KT77's. The KT77's are definitely brighter in my amp but in a real pleasant way. I'm sure i'll pop the 6CA7's back in one day and enjoy them when I get bored of the way things sound now.
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I found the KT77's to be nicely balanced top to bottom in the amp I had them in. The biggest difference I heard between the two was the bottom end. The EH's ottom end sounded a little more forward, it not bloated.
 
Lavane said:
I found the KT77's to be nicely balanced top to bottom in the amp I had them in. The biggest difference I heard between the two was the bottom end. The EH's ottom end sounded a little more forward, it not bloated.
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Your assessment sounds pretty spot on. The EH's were my favorite for many many years. I have a real set of Mullard XF2's, RTF's, Winged C's etc. I play guitar and am a Marshall guy so I don't want to waste a set of tubes in a stereo unless they hold up. Anyway, sometimes I'll get into something for a bit just due to being different sounding and go back to the tried and true combo. BTW, I did super like the JJ KT77's back when they came out but they were so unreliable. They have a different sound than the Gold Lions.
 
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dannyr said:
Your assessment sounds pretty spot on. The EH's were my favorite for many many years. I have a real set of Mullard XF2's, RTF's, Winged C's etc. I play guitar and am a Marshall guy so I don't want to waste a set of tubes in a stereo unless they hold up. Anyway, sometimes I'll get into something for a bit just due to being different sounding and go back to the tried and true combo. BTW, I did super like the JJ KT77's back when they came out but they were so unreliable. They have a different sound than the Gold Lions.
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I lost a JJ KT77's. It shorted out. They liked them too.
 
For me in Canada, the GL KT77 would have cost more than the EH KT88. Looking for a budget tube, this wouldn't have worked.

This being said, the JJ KT77 would have cost the exact same amount as the EH 6CA7. Problem is (as mentioned) the poor quality. I had a quad of JJ EL34 stored - pulled them out to reinstall then, and noticed the getter was loose in one of the tubes!?!

Glad I saw this before installing, but this is the only tube I've ever owned where this happened.
 
When you say you didn't like the 6550s, were you referring to the reissued 6550s made in Russia, or did you try vintage 6550s made by Tung-Sol in America?
 
It may be that the output transformers and other things are designed with the EL34, 6CA7 in mind. They also bias differently than the big beam power tubes. I love the EH 6CA7 in vintage Hiwatt amps. It really makes those amps sound right. The 34's are too soft and that 6CA7 is tighter and has a bit of 6L6 edge. Had them in my old ST-70.
 
JohnT123 said:
It may be that the output transformers and other things are designed with the EL34, 6CA7 in mind. They also bias differently than the big beam power tubes. I love the EH 6CA7 in vintage Hiwatt amps. It really makes those amps sound right. The 34's are too soft and that 6CA7 is tighter and has a bit of 6L6 edge. Had them in my old ST-70.
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The amp can handle both types of tubes - although nominally designed for EL34 and equivalent tubes (biased at 400mv), the EH KT88 were biased at 500mv, and sounded great. Only difference was a bit more hum from the transformer.

dannyr said:
I wonder how the EH version compare to the original Sylvania's.
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Apologies, but cannot give a comparison in this specific case, though my limited experience with vintage tubes suggests that the modern ones sacrifice some lower-mid warmth for more dynamics and detail.
 
And now some longer term use feedback.

Working from home today, and thought I'd spin some vinyl. For the first time on my tube rig I dropped on the RSD release of Fountains of Wayne "Welcome Interstate Managers".

Not sure if I believe in tube break-in, and possibly it is just a really nice pressing, but I'm continuing to dial up the volume with each passing song.

IMHO, these tubes get the midrange more "right" than the KT-88 did. Certainly more of of those delicate dynamics that make certain instruments sound more live.

Plus the tubes generate a nice full bottom end without being thumpy. With this recording, I'd swear my ported MA Silver-6 were replaced with a nice set of acoustic suspension speakers. Some of the most tuneful bass I've heard in some time.

Very happy with the purchase still, and certainly a more than satisfying low-cost alternative to the KT-88.
 
ScooterMcTav said:
And now some longer term use feedback.

Working from home today, and thought I'd spin some vinyl. For the first time on my tube rig I dropped on the RSD release of Fountains of Wayne "Welcome Interstate Managers".

Not sure if I believe in tube break-in, and possibly it is just a really nice pressing, but I'm continuing to dial up the volume with each passing song.

IMHO, these tubes get the midrange more "right" than the KT-88 did. Certainly more of of those delicate dynamics that make certain instruments sound more live.

Plus the tubes generate a nice full bottom end without being thumpy. With this recording, I'd swear my ported MA Silver-6 were replaced with a nice set of acoustic suspension speakers. Some of the most tuneful bass I've heard in some time.

Very happy with the purchase still, and certainly a more than satisfying low-cost alternative to the KT-88.
Click to expand...
I never gave much stock in tube burn in myself until I built a clone of a Dynaco ST-35. While I was using it after some hours had already been put on it I suddenly noticed the music getting wider and deeper sounding. It only took about 5 seconds or so, but very noticable. Everything just filled out nicely. I haven't noticed anything like that with the EH-6CA7's in my ST-70. Maybe I missed it while in another room? But they sounded great right out of the box to begin with.
 
To what? I've tried the Soviet version in an EL34 amp. It worked but I found it to be very tinny and unpleasant sounding. That particular amp tends to be hot on the top end anyway though, and any tube that tends to extend HF response is generally a bad fit in it.
 
Wow...the 'poor man's KT88' used to be the TT21...just had to rig for running with a top cap. I think I will stick with the horizontal outputs, aka Sweeps.
cheers,
Douglas
 
I'm running a single ended ChFi amp designed for EL34. The seller said KT77 can be used, but the Gold Lions I tried sounded dull/thin. Looking at the specs compared to EL34, is there anything amiss that would cause the KT77 to be incompatible?

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