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electropt 24th June 2004 06:48 PM

Flashing EL34

I have a Class AB push-pull integrated amp with 4 EL34 on the output stage. One of them in some music passages flashes a lot! I came to the conclusion that it should be on its way out and already ordered a mached quad of SED EL34.

My question is this, is it normal to a tube die this way? I guess it was defective since day one, from the first time I used this set of tubes one of them flashed very faintly, but now... WOW! :eek:

I made a video of the flashing tube, its here.

Only one of the four glows like this, the other of the same channel only blinks slightly, I guess due to the current drawn of the other tube.

How about the SED EL34 (Svetlana old factory tubes now with the =C= logo), are they any good?

Thanks in advance.


kevin gilmore 24th June 2004 10:10 PM

Sure looks like a cathode to heater short of some kind...

Jax 27th June 2004 05:10 PM

It seems to me to be the screen grid that is flashing. It's not normal, there should never be an orange flashing during operation.

Why this happens is difficult to diagnose without a schematic but the most common cause for this flashing is a way too high voltage on the screens. I've seen it myself when I ran the screens at 430V in a pentode circuit.

By all means, try a new quad but if you see flashing, turn off and have the amp investigated.

benny 27th June 2004 05:13 PM

really, i have no idea... what voltages are you using???

you maybe have a too high a screen voltage and there is arcing or something ocouring... my guess is at the too high a voltage.


EDIT: oh well, that was a lot of using saying the same kind of thing as what jax just said...

Sch3mat1c 27th June 2004 11:03 PM

I have a 6V6GT that sorta does that. It glows brighter than most, probably a broken screen wire or something. Never seen it vary in the SE amp it was in though.

Also had a 6L6GC from Valve Art that smoked a screen wire or something, it was running within limits (right on max. voltage, but 6L6s have been treated worse so I'm not sweating that). Still works fine to this date, AFAIK...


karma 28th June 2004 01:16 AM

2 Attachment(s)
my amp did the same thing. cheaper to replace the quad
than to leave it like i did. 2 weeks ago my amp finally died. only would have cost me $60 for new tubes now its $200 for part's and tube's:(

you shoulds see it when it really short's:D

could this happen it could or maybe not see pic;)

>>Svetlana old factory tubes now with the =C= logo anygood?<<

i was looking at this type allso with the gold pins. not sure if there good. still need to pic them up

Sch3mat1c 28th June 2004 06:58 AM

Long as we're posting blue glow shots, here's some of the GOOD kind. ;)

- Revision 3 with Sylvania 6L6GC and JAN-CRC 6L6GA respectively. No wait... that must be the 6F6. :)


karma 28th June 2004 07:26 AM

2 Attachment(s)
nice here's one of mine not blue but not of the bad kind:D

Sch3mat1c 28th June 2004 09:28 AM

Purpley, looks more like gas to me.. ?


Duo 28th June 2004 09:32 AM

haha, that's definitely arcing.

I have a tube tester here on which if you press the incorrect button with 6AL5 in, you get a very nice bright arc like that, and the tube is fried.

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