RH84 Finished- Voltage question

[nyazzip]

no, 333vdc anode to ground, @ pin 7.
so is it kosher to measure with a DMM, from cathode pin to anode pin? i have never tried to do so...forgive me, i am a relative newbie/ignoramus.

[Alex Kitic]

no, 333vdc anode to ground, @ pin 7.
so is it kosher to measure with a DMM, from cathode pin to anode pin? i have never tried to do so...forgive me

In that case, it's probably 320V across the tube, i.e. from pin 7 to pin 3. That is high-ish, if you ask me... but probably OK for most NOS EL84? Which make do you normally use (in your guitar amps as well)?

Kosher or not, I do that "all the time"... no need to excuse yourself!!!

[nyazzip]

...i have a lot of old stock el84/6bq5 which i rotate around. i have quite a few contemporary ones as well, the usual JJ/china/Sovtek, but as long as the old ones work i am using them
i just threw this amp together, its SS rectified and has no choke! so this winter i'll probably do it right, and get a choke, better OPT, and make room for an ez81...at that time i'll see if i can dial voltages in closer
sounds fine now, very very quiet, with dc filaments

[Alex Kitic]

I just threw this amp together, its SS rectified and has no choke! so this winter i'll probably do it right, and get a choke, better OPT, and make room for an ez81...at that time i'll see if i can dial voltages in closer
sounds fine now, very very quiet, with dc filaments

While the EZ81 is better than SS, try to avoid it for some octal tube... I presume even Sovtek garden variety GZ34 is a better choice. Or make it choke input...

DC on the filaments is not necessary, it's just a waste of heat and parts count.

If you like it as it is, you will be amazed by the improvements a choke, tube rectifier, etc. will make to the sound!

[nyazzip]

well....Epiphone corporation revised the circuitry on their Valve Junior guitar amps to include DC filaments, and most reports indicate it was a major improvement. i pirated the rectifier and capacitor from a VJ board so the cost was free.

.....why avoid the ez81 "for some octal tube"?

[Alex Kitic]

well....Epiphone corporation revised the circuitry on their Valve Junior guitar amps to include DC filaments, and most reports indicate it was a major improvement.

It's not forbidden, you know, just a waste of energy - beside the fact that heating tubes with DC means activating a galvanizing process that will eventually destroy the heaters... if you ask me, the cathodes will loose their ability to emit electrons prior to that... but the part count (rectifier, caps, etc) cannot be omitted.

.....why avoid the ez81 "for some octal tube"?[/quote]

I do not like the sound of indirectly heated rectifiers, and the EZ tubes are less acceptable in my view than 5AR4/GZ34.

While a good Philips GZ34 may sound fine enough (much much better than ss diodes), you start to discover the world of rectifiers when you switch to direct heated (not necessarily octal...).