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Opinions on Reissue 6CA7 and KT77 tubes

Tom Bombadil said:
Just noticed someone on that auction site has listed a pair of NOS Genalex KT77 for $1499 !!!! A rather astounding price. $2998 for a quad at that price.
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That's because they are all gone, they just sounded too good. I like to blame the guitar guys, but the HiFi guys used their share I'm sure. I've run a whole lot of different EL34s / 6CA7s in my modified Dynaco 70 and the real GEC 77s are by far the best, with 88s good too, esp. if you need a bit more power. The old second run EI 90s sound good too, but they push the amp a bit harder than I like.
 
Tom Bombadil said:
Thanks for all of the feedback. A lot of love for the new reissues, on the whole. This is consistent with what I've read in other forums and from tube dealers who tend to be straight shooters.

As to reliability, what I've heard was that it was more of a problem with the earlier production reissues, but that over the past 5 years, it has improved a lot. Two tube dealers told me that in recent years they have had few reports of tube failures and that feedback from customers has been very positive.
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Whichever tube you choose, get them from a dealer that does rigorous testing. Upscale Audio, Jim Mc Shane etc.

I think you may also be able to use the 6P3S-E's. They are cheap, tough and well regarded. They are a Russian 6L6 variant that can be biased as an EL34. Check with the amp manufacturer.
 
I was just researching the 6P3S-E yesterday. They look decent. Not sure it is worth it for the small savings from the EH 6CA7. Would probably have a bit less output from my amp. But it might be fun to pick up a quad on the cheap.
 
Tom Bombadil said:
I was just researching the 6P3S-E yesterday. They look decent. Not sure it is worth it for the small savings from the EH 6CA7. Would probably have a bit less output from my amp. But it might be fun to pick up a quad on the cheap.
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I'd start with the EH's. They are inexpensive, well regarded and may be just right in your amp. What works for you in your amp is all that matters. :thmbsp:
 
I'm still on the hunt to try to match up one of the pairs I've got now. As I wrote in my first post, I have a pair of EI 6CA7 thin base and a pair of Gold Lion (really GE) fat boy 6CA7s. All of them test as strong as new on my little emission tester (for what that is worth) They are both quite good, and the amp sounds pretty good running the EI's on one channel and the Gold Lions on the other. That's how it was when I purchased it.

The EI's are quite expensive nowadays. New ones are essentially gone, and when they come up for sale they are usually priced at around $400/pr. The USA big bottles commonly sell for $120-$150/pr used but testing strong.

So I could probably sell off my two pairs for $250-$300, buy new GL KT77s and still have perhaps $100 in hand. Or I could buy two quads of the EHs. But I do hate to sell off classic tubes. Thus my continuing to look around to find a match.
 
Tom,
I just retubed my Dyna ST-70 with JJ KT77s and so far (about 20 hours) they sound great. Better than my RFT German EL34s. I find myself inching the Bass down a bit because the Bass is stronger than before. They bias in well too, no drift once set to 100mA/pr.
My biggest concern with using EL34s is that the Screen Grid voltage in the ST-70, at 122Vin, runs about 430v. This is above the 425v MAX for G2. The KT77s are rated 800v plate, 800v Screen Grid so no problems there. I recommend them.
 
triode17 said:
My biggest concern with using EL34s is that the Screen Grid voltage in the ST-70, at 122Vin, runs about 430v. This is above the 425v MAX for G2.
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Not sure where you got that value for G2. The Mullard data sheet says 500v, and the JJ data sheet says 450v for max. G2. Even the Shuguang sheet says 500v for G2. I bet there are lots of EL34's in guitar amps that see more than that.

jeff
 
After all of the research, and good feedback from AK, it turns out that I'm not going to buy any new reissues, even though I think there are some very good ones out there. I started with two GE 6CA7 big bottles and found 6 more, enough for 2 quads. All test as new and look little used. Got pretty decent deals on them, paying $180, for an average of $30 per tube.
 
Pio1980 said:
Afaik, G2 is the usual point where flash-over failure occurs.

Sent from my SM-N900V using Tapatalk
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Flash-over occurs more frequently in pentode-mode amps, than in ultralinear or triode-mode.

In a pentode-mode circuit, G2 is held at a high DC voltage, regardless of plate voltage. In this case, the plate can be quite a bit more negative than the screen- which can significantly increase the amount of current that the screen sees- causing excessive screen heating and then flash-over.

In a UL amp, the plate can still go negative compared to the screen- but to MUCH LESS of an extent. The screen will also drop in voltage, in sync to the plate, to a lesser degree- so it's harder to generate nearly as much relative potential between the two (which reduces screen current).

Triode mode is relatively easy on screens- they're ALWAYS the same potential as the plates. Not much screen current, and not much heating at all, even at high screen voltage. This is why tubes with low screen ratings, can oftentimes be run in triode mode, with plate voltage much higher than the nominal screen rating.

Regards,
Gordon.
 
Tom Bombadil said:
After all of the research, and good feedback from AK, it turns out that I'm not going to buy any new reissues, even though I think there are some very good ones out there. I started with two GE 6CA7 big bottles and found 6 more, enough for 2 quads. All test as new and look little used. Got pretty decent deals on them, paying $180, for an average of $30 per tube.
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For that price, I think I'd have done the same.


RE the flash-over thing. Dave Gillespie did a fair bit of research on that, and his solution was a simple resistor to reduce the amount of current available on the screen. I skipped this on my Pilot and the very first time I turned it up the damn tubes flashed over. I shut it off and installed the resistors. I have not seen so much as a flicker since then. 4 100 ohm resistors is mighty cheap insurance to keep that from happening. Mine is a UL amp too, so its not under the conditions you'd expect to be most prone to arc issues.
 
Tom Bombadil said:
After all of the research, and good feedback from AK, it turns out that I'm not going to buy any new reissues, even though I think there are some very good ones out there. I started with two GE 6CA7 big bottles and found 6 more, enough for 2 quads. All test as new and look little used. Got pretty decent deals on them, paying $180, for an average of $30 per tube.
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The four I have installed now matched exactly on emissions tests on two tube testers, and that number was the same as a new tube. On conductance, they measured 51, 51, 50, 50.

Popped them into my amp for a few hours of listening and they sound great.
 
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Have now tested and run all 8 of my 70s era 6CA7 made in the USA big bottle tubes. They have various names on them: GE, Sylvania, Gold Lion, and RCA. But all appear to be the same tubes. They all test as new on my Sencor emissions tester, and range from 49 to 51 on my Sylvania conductance tester. Tight matches. Thanks to AK'er BYOUNGMAN1 for providing a couple of these. He may be a source for more of these if one is interested.

They sound beautiful in my amp, a Korato KVA-20 made in Serbia amp using Audio Note output transformers, running in triode mode. Also sound surprisingly powerful given that the amp is rated to produce from 18 to 20 wpc, I'm using 90dB sensitivity Von Schweikert speakers in a 600 sf room. Have yet to hear any clipping. The bass is strong and well defined. The transformers stay very cool, feeling cool to the touch even after 4 hours of use.

I would like to run a set of those new Genalex Gold Lion KT-77s, just to compare the sound. But am unlikely to pop for $160-$180 for that experience. And while I was at it, it would be fun to compare the new big bottles, the EH 6CA7, vs the old fat boys. I would not be surprised if, in a weak moment, I might break down and pop the $80 to try that.

Using a mid-90s Dynaco (by Panor) PAS-4 preamp, running Amperex 7308 military grade tubes in the line stage. This is an underated preamp, IMHO. It got a very good review in the now-defunct "FI" magazine back in the 90s, and when it was using inexpensive 6DJ8's. It was designed by John Nunes, who went on to design some well regarded preamps at MFA. Being fed by a Parasound D/AC-2000HD, which is one of the best DACs I've ever heard.

But perhaps I should just enjoy my sonic nirvana and push tube rolling madness to the side for a while.
 
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Tom Bombadil said:
Have now tested and run all 8 of my 70s era 6CA7 made in the USA big bottle tubes. They have various names on them: GE, Sylvania, Gold Lion, and RCA. But all appear to be the same tubes. They all test as new on my Sencor emissions tester, and range from 49 to 51 on my Sylvania conductance tester. Tight matches. Thanks to AK'er BYOUNGMAN1 for providing a couple of these. He may be a source for more of these if one is interested.

They sound beautiful in my amp, a Korato KVA-20 made in Serbia amp using Audio Note output transformers, running in triode mode. Also sound surprisingly powerful given that the amp is rated to produce from 18 to 20 wpc, I'm using 90dB sensitivity Von Schweikert speakers in a 600 sf room. Have yet to hear any clipping. The bass is strong and well defined. The transformers stay very cool, feeling cool to the touch even after 4 hours of use.

I would like to run a set of those new Genalex Gold Lion KT-77s, just to compare the sound. But am unlikely to pop for $160-$180 for that experience. And while I was at it, it would be fun to compare the new big bottles, the EH 6CA7, vs the old fat boys. I would not be surprised if, in a weak moment, I might break down and pop the $80 to try that.

Using a mid-90s Dynaco (by Panor) PAS-4 preamp, running Amperex 7308 military grade tubes in the line stage. This is an underated preamp, IMHO. It got a very good review in the now-defunct "FI" magazine back in the 90s, and when it was using inexpensive 6DJ8's. It was designed by John Nunes, who went on to design some well regarded preamps at MFA. Being fed by a Parasound D/AC-2000HD, which is one of the best DACs I've ever heard.

But perhaps I should just enjoy my sonic nirvana and push tube rolling madness to the side for a while.
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I have new old stock fatty Sylvanias here and will, in time, grab some of the new Gold Lions and EHs for backup sets. Might be birthday/Christmas requests.

I'll also check in with BYOUNGMAN1 to see what he's holding for NOS at some point.
 
Still glancing around at tube prices. Noticed a price that "takes the cake." A person on that auction site is selling a dead Mullard EL34/6CA7. Yep, a totally dead tube. He has set his Buy It Now price at $80, but is graciously allowing bids to start at $30. Plus $6.65 for shipping.

Seriously? I wouldn't pay only the shipping fee for a dead tube. What would I do with it?
 
Tom Bombadil said:
Still glancing around at tube prices. Noticed a price that "takes the cake." A person on that auction site is selling a dead Mullard EL34/6CA7. Yep, a totally dead tube. He has set his Buy It Now price at $80, but is graciously allowing bids to start at $30. Plus $6.65 for shipping.

Seriously? I wouldn't pay only the shipping fee for a dead tube. What would I do with it?
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Jeesh, the things people try to sell. I've seen "display" tubes, but they are always very old balloon or other odd shaped, or historically important dead tubes. Now if he could prove it was the first one ever off the line or something.................
 
first off, I'd check with your amp's manufacturer and ask why they recommend beam-tetrodes over
real EL34's. electrically they measure the same, and physically un-remarkable to the unit. second,
I'd ask why 35ma biasing. el34s tend to use 40ma+ for great sound.

I sold off all my Blackburn mullard XFs. kept a variety of 6CA7s and EL34s using them on a SE amp.

you may wish to try the Russian equivalents, and also the Chinese EL34s (not the re-issues). depending
on your music choices and, of course, the biasing, these may provide some sound pleasure.

lastly, running them in triode mode is not the same (sound) as in pentode/ul/Williamson mode.
different tubes in triode mode has as many sounds as they do in non-triode mode.

also, if you are able to, add stoppers to anode/screen/cathodes.
 
I don't think it is very helpful to the OP to say that this tube or that tube sounds great. Describe what is great about it. Does it have better imaging, bass, mids, highs, does it sound more lifelike?
 
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