EL34s, 520V plate...hm which tubes to use?

[strummer_83]

I was wondering what the tube to get is, I'm using a garnet session man, the plate voltage is 520V, and it is a Combo. I was wondering which new production EL43 can stand up well in these conditions.

[dano-rator]

I've had long life, good luck and equally good sound, with jjel34l's in my musicman hd65 head with ~700v on the plates. Occasionally I transfer the guts of the musicman to a 1x15 combo cab depending on the situation.
From trdpartsonline.com:

The JJ-EL34L's 1st grid can take a larger maximun voltage than a standard EL34. (-13.5 to -16 volts as compared to -10 to -13.5 volts)

Although, from thetubestore.com:

From our review of this EL34 tube: "The sound is well balanced with tight bass response and great mids. As with many of the Eastern European tubes, mechanical noise is an issue if used in high power combo style amps. In a stereo system or remote head, these should provide a good tonal balance and service life."

I've never had noise issues with them, but i guess the threat is there.
Dan

[Andy Le Blanc]

second on the JJ's. I'd be more worried about the screen voltage limitations.
You can also go with 6CA7. The larger bottle dissipates heat a bit better than
the narrower envelope of a EL34.

[jjman]

I've read many stories about EL34s being sensitive to screen voltage. The schematic doesn't show the voltages but I suspect it's pretty high. And the screen resistors are only 470ohm.

http://www.lynx.bc.ca/~jc/SessionManPwr.gif

[img3000]http://www.lynx.bc.ca/~jc/SessionManPwr.gif[/img]

[strummer_83]

The JJ's sound good, i've also heard incredible things about the tungsol el34s and the Mullard reissue. I've been searching for spec sheets on them with no luck. the screen limiting resistors have been changed on the amp from 470ohms to 1K5 at garnet's suggestion to better accommodate new production tubes. I need to take everything apart to get measurements on the voltages again I should have written the info down when i had it apart.

I have a schematic with some voltages
Point A 520V
Point B 520V
Point C 380V
Point D 300V
Point E 230V

[pinkmarkos]

i know that NOS/used mullards xf2, xf3, xf4 (not the reissues) can handle in excess of 5oo volts on the plate, and they have the benefit of sounding really good- smooth cleans and very nice breakup characteristics. They are very smooth at all frequencies. I haven't heard the JJ EL34's, but I do have a set of the Tesla EL34's (running at 415 plate volts), and the mullards smoke em. My $0.02

[collinsamps]

Gotta plug JJ as well. I just did a Kensington(my JTM) with their KT77 running just under 500vdc. I did a not so traditional screen resistor value of 2.5K which ended up sounding killer, but selected the value more so because the owner switches to KT66's now & then and the recent chinese versions will sometimes oscillate with a 1.5K.

[Alexo]

Every EL34 datasheet I've seen, from Mullard and Telefunken through JJ and Svetlana lists a max. plate voltage of 800, so technically, 520VDC should not be an issue. But that's datasheet world, not the real world...

[Andy Le Blanc]

its the screen grid that you have to pay attention to, itll have a limit of around
425v, you can push it 10-20% which puts it around 510v but the screen grid
dissipation figure is around 8w, so you need to mind the screen grid resistor
to limit current. something from 1k to 2.2k.

[strummer_83]

the screen limiting resistors have been changed to 1.5 K
Thanks for the help i'll give the JJs a go