Modern EL-34 for high voltage application.

[cluster]

Hello all,

I have a few high voltage, vintage amps that I need EL-34s for. 71 Marshall Plexi's and a couple early 70's HiWatts (both with ~525VDC on the plates). Can anyone recommend a solid, modern (good sounding) EL-34 that isn't going to crap out too soon? I won't be getting any NOS Mullards or anything like that. What's everyone using for these vintage high voltage amps?? Thanks so much.

Joseph

[copperheadroads]

JJ 6CA7's or JJ EL34L

[cluster]

thanks

[Enzo]

I was very happy with the RUby EL34BSTR Sturdy tube, sounded good.

meanwhile 525v is not high voltage. EL34s are made for higher voltages, and some amps like Music Man had 700-800v on the plates.

What kills EL34s is excess screen current and excess dissipation.

[Leo_Gnardo]

I've used all the tubes mentioned so far with a good rate of success. In those vintage amps, often the manufacturer left out screen grid resistors and control grid "stopper" resistors. You can enhance tube survival rate by installing those resistors. Marshall's standard value for "stoppers" is 5K6, half watt. Screen grids generally 1K ohm 5 watt wirewounds. In amps with B+ 500V and above it doesn't hurt to go 1K5 or 2K, up to 10W screen grids. Yes you'll lose a couple watts of power to the speakers, but it's a good trade as you'll gain reliability. The amps will still be loud enough to make your ears hurt.

[Zouto]

Since I had some troubles with Ruby EL34BSTRs and JJ EL34Ls , I've used Tung Sol EL34Bs in vintage Orange, Hiwatt and MusicMan Amps with best results in reliability and sound. It's absolutely important to check the bias for a slightly "colder" value and take care for ALL the topix LeoGnardo mentioned above.
Zouto

[big_teee]

I've had problems with JJs with higher voltage.
Not tried the JJ 6CA7's yet.
They are a little pricey, but I've had nothing but great luck with TAD tubes.
Tad does a great job of screening their valves!
T

[Chuck H]

What Leo said. And what Enzo said. Something I recently discovered is that EL34's seem especially prone (during clipping) to watts finding an easier path through the screen circuit than the plate circuit due to relative impedances. When that happens you over dissipate the screens. Ergo the 5W rating on screen grid resistors (that still blow on occasion). So WRT modern tubes it's a good idea to add the grid stoppers and 1k screen grid resistors. In my limited experience with different brand tubes I've only had consistent survival in higher voltage applications with the Ruby tubes. They sound good too, but tend to be a little microphonic. Sometimes too much so for combo amps, but never any problems in a head.

[Jazz P Bass]

And then you have the seriously high plate voltage on the Univox U1061 amps. (700 some volts at modern line voltage)

There, they throttle back the screen voltage.

[Chuck H]

And then you have the seriously high plate voltage on the Univox U1061 amps. (700 some volts at modern line voltage)

There, they throttle back the screen voltage.

Then there's the vintage specs for nearly all brands that states max at 800V plates and 800V screens! Try THAT with any modern el34.

[Leo_Gnardo]

Then there's the vintage specs for nearly all brands that states max at 800V plates and 800V screens! Try THAT with any modern el34.

Remember those Chinese EL34's from early 90's? The ones that were so lame they had a splint spot welded to the plate to keep it from warping at high temperature? The ones that sent Marshall scurrying to populate their mid-90's amps with reliable Sovtek 5881 wafer-base outputs? Surprise, I sometimes find those crappy EL34's in MusicMan amps, working just fine. 700+ volts on the plates, half that on the screens, delivering good power and no noises of doom. Apparently in high B+ amps, the secret to safe operation is low screen grid voltage, then you can get away with almost anything.

800V plate + 800V screen, yes stand well back. I doubt even the most robust EL34's in the good old days would really put up with that, and I'm not gonna try.

[Randall]

Take a look at ValveQueen.com. Laura burns them in, tests them and guarantees Rubys for six months at different B+ V's. Tell her what the amp is running for B+ and she will hook you up with a matched pair to suit that. I put them in a Marshall Jubilee that was eating tubes a year ago, and it's still good AFAIK.