GEC KT66, what one to look for?

Seanxk

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Wow those prices ( Reverb ) are crazy, do they actually sell for these prices!!
I like the fact he's a vintage amp guy but he doesn't have an amp to test them in lol, which kind of contradicts his '' Perfectly Matched '' Quad I feel, although to be fair every dealer you see has matched valves only by Ia readings on their AVO or Hickock machines lol.
 

playloud

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Wow those prices ( Reverb ) are crazy, do they actually sell for these prices!!
I like the fact he's a vintage amp guy but he doesn't have an amp to test them in lol, which kind of contradicts his '' Perfectly Matched '' Quad I feel, although to be fair every dealer you see has matched valves only by Ia readings on their AVO or Hickock machines lol.

Yeah absolutely! They test them at 250V, but we're interested in running them close to 600V. As @StingRay85 has noted in the past, good matching at 250V is not necessarily the same as good matching at intended voltages. I actually experimented with this when biasing the RI Gold Lions the other day, using a variac. They were drawing very different plate currents at 250V, but converged to a 5mA range at 490V.

All these red flags and caveats aside, I've seen threads from the Metro forum a few years where people bought the GECs for US$250/piece and considered that a 'deal'. Perhaps it's like the plexis, where the price seems to have actually softened a little since 2010ish (maybe a generational thing?) - certainly if you account for inflation - but Ebay sales suggest they're not going for much less now.
 

StingRay85

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People ask close to 400 for a quad of CP Mullard EL34. Just to be clear, current production Russian tubes with a Mullard label.


I think they will sit forever at these prices. Gotta admit I'm very glad to have stocked up on NOS ECC83 and EL34 before prices started exploding.
 

_Steve

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You only have to go to post 43 lol

oops.

would still be good to get some opinions though? they seem on the cheaper side (relatively speaking) and the design on the glass is different to others. i dont know anything about GEC tubes so wondering if they are the real deal?
 

playloud

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oops.

would still be good to get some opinions though? they seem on the cheaper side (relatively speaking) and the design on the glass is different to others. i dont know anything about GEC tubes so wondering if they are the real deal?

I would also like to know this!

I think they're just the later (final?) 70s design, but would be good to confirm before making any offers.

I reached out to the seller and he said he didn't want to guarantee them, as he couldn't be sure any potential seller's amp was properly serviced (good screen resistors etc.) However, he did offer to test them in his '68 100W (EL34 amp, but he would run impedance mismatch for test). That obviously has lower screens/plates voltage though - and I imagine the risk of failure increases non-linearly with voltage. He's open to offers apparently.

I've contacted a NOS dealer in the UK for an alternative. He's going to see if he can match a quad and get back to me.
 

Sigs

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I would also like to know this!

I think they're just the later (final?) 70s design, but would be good to confirm before making any offers.

I reached out to the seller and he said he didn't want to guarantee them, as he couldn't be sure any potential seller's amp was properly serviced (good screen resistors etc.) However, he did offer to test them in his '68 100W (EL34 amp, but he would run impedance mismatch for test). That obviously has lower screens/plates voltage though - and I imagine the risk of failure increases non-linearly with voltage. He's open to offers apparently.

I've contacted a NOS dealer in the UK for an alternative. He's going to see if he can match a quad and get back to me.
Who's the UK dealer ?
 

Matthews Guitars

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Johan's video below tells the tale. And read the highest comments below it.

The truth is that there's such a tiny difference in the sound of a vintage KT66 and the modern Chinese made replicas that in my mind it'd be silly NOT to get the modern replicas, and run them. If you want to spend a mortgage payment on a set of "vintage" tubes that may or may not even be authentic (I've heard rumors of counterfeits....) then that is of course your business, but would you feel great about your purchase decision if you were to put those vintage tubes in your amp and coudn't tell any difference between them and the replicas you just took out?

Johan is testing a new reissue tube against two USED originals that must have worn down to some degree, particularly with that much heat damage visible on the label. That wear reduces tube headroom and makes it reach distortion more quickly. So it is reasonable to expect the worn tubes to be a bit dirtier. Otherwise, I don't hear ANY difference.

I run KT66s in my '69 Plexi. They're the Shuguang made replicas, and I have two matched sets of them. Given my playing habits I probably won't wear out both sets before my life expectancy has been exceeded. So I think I'm good on those tubes.

In any event, buy the reissue tubes now whether you buy the vintage tubes or not. Then you can get to playing them and enjoy the tone right away while you wait for the right deal to come along for vintage tubes.



 

Browneyesound

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I guess I’m somewhat biased from my admittedly limited experience with modern kt66 tubes, but when I built my JTM45 clone, VA KT66’s came with some of the parts I procured. I did think they sounded very close to the GECs, but when I pushed the amp hard, I would sometimes get arcy-sparkeys in the tubes (screen grid alignment issues?). Perhaps it was just something wrong with this pair of tubes, but since I have 2 pairs of GEC’s, I haven’t tried any other new production versions.

As for EL34’s in a superlead, I have found the difference in tone much greater between new production and mullards than I did with the KT66’s in the JTM45.
 

Matthews Guitars

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The reissue tubes are known to have voltage limitations that keep them from being run in some amps. But in my Plexi with 472 volts on the plates, I can dime the amp with no problems at all.

I think that the issue rears its head above 500 volts. So if you've got 540 volts of plate, they're not the tubes to use unless the power supply gets turned down.

The easy way to deal with that is a variac. I run my 120V line voltage down to 90 volts which is a 25 percent drop. If I had 540 volts of plate at 120 volts then that would drop to a very safe 405 volts on the plate at 90 volts on the variac.

And a Superlead really does sound good, maybe even actually better, at reduced line voltage.
 

Pete Farrington

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there's such a tiny difference in the sound of a vintage KT66 and the modern Chinese made replicas

Johan is testing a new reissue tube against two USED originals
Just to note that the "Gold Lion" modern production valve in the video was probably made in Mike Matthews' Saratov factory in Russia, rather than China.
 

Matthews Guitars

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Maybe so. I have no personal hands on experience with the Gold Lions. I had to check and yes, apparently they're made in Russia, but haven't seen a spec sheet on them. If that spec sheet exists, are they rated for more than 500 volt operation?
 

Browneyesound

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Fwiw, my JTM45 has “normal” voltages (I don’t remember exactly of the top of my head what they are), the PT was from a Marshall reissue JTM45.
 

Sigs

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I would also like to know this!

I think they're just the later (final?) 70s design, but would be good to confirm before making any offers.

I reached out to the seller and he said he didn't want to guarantee them, as he couldn't be sure any potential seller's amp was properly serviced (good screen resistors etc.) However, he did offer to test them in his '68 100W (EL34 amp, but he would run impedance mismatch for test). That obviously has lower screens/plates voltage though - and I imagine the risk of failure increases non-linearly with voltage. He's open to offers apparently.

I've contacted a NOS dealer in the UK for an alternative. He's going to see if he can match a quad and get back to me.
Who's the UK dealer ?
 

Pete Farrington

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... haven't seen a spec sheet on them. If that spec sheet exists, are they rated for more than 500 volt operation?
There seem to be at least 2 publications in that regard.
One is a crudely amended version of the GEC original (which had a 500V voltage limit anyway) https://www.thetubestore.com/lib/thetubestore/genalex-kt66.pdf
Another doesn't mention any anode or screen grid voltage limiting values https://docs.google.com/gview?url=h...og/tubes-specs/KT66 Genalex.pdf&embedded=true
 

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