Stupid question: EL34 tubes.

[kmcarpenter]

Well, after getting the old heath running and running well I might add, I have a dumb question for those who are experienced at flogging EL34's

The situation is that I ran the amp wide open with the pre amp also wide open for a little while the other day, no red plates nothing. I did notice that the screen was glowing a little bit when the bass hits.

It stops glowing immediately when the volume is brought down off the stop, but I was just wondering if EL34 grids are supposed to glow when they are being run wide open.

[Matt.B.H.]

I would say no!! take it easy on them man. The possibilitys for runaway are all there!! when the screen is glowing it is a pretty good emitter of electrons and the rest is history, litterally. I blew up some of my rather nice 5B255 by abusing the screen rating. Be warned. All the best.

Cheers Matt.

[jfitz57]

Hi!

Were you running it into a dummy load or very ineficient speakers, or your neibors don't care?
The G2 of those tubes are at very close to the plate voltage (rating)so there is not much to suck electrons if they did start to glow. Still not a good idea to abuse them.

Jim

[kevinkr]

Originally Posted by kmcarpenter

Well, after getting the old heath running and running well I might add, I have a dumb question for those who are experienced at flogging EL34's

The situation is that I ran the amp wide open with the pre amp also wide open for a little while the other day, no red plates nothing. I did notice that the screen was glowing a little bit when the bass hits.

It stops glowing immediately when the volume is brought down off the stop, but I was just wondering if EL34 grids are supposed to glow when they are being run wide open.

Hopefully you had some sort of load on the output of that amplifier - never run a tube amp without a load unless you want to run the risk of frying your OPT.

[richwalters]

Originally Posted by kmcarpenter

I did notice that the screen was glowing a little bit when the bass hits.

It stops glowing immediately when the volume is brought down off the stop, but I was just wondering if EL34 grids are supposed to glow when they are being run wide open.

No...bright screens is sure way of putting the nail into their coffin. ALways use a load on the secondary.

r;-

[kmcarpenter]

They were hooked up to 4 ohm Polk Monitor 10's. The neighbors werent there.

THey are fairly inefficient.

[kmcarpenter]

They were hooked up to 4 ohm Polk Monitor 10's. The neighbors werent there.

THey are fairly inefficient.

[jjman]

I've read a few times that EL34 tubes have temperamental screens. Many recommend higher value screen resistors than say a 6L6 would use in the same application.

[Captn Dave]

Originally Posted by kmcarpenter

They were hooked up to 4 ohm Polk Monitor 10's. The neighbors werent there.

THey are fairly inefficient.

The Polk monitor 10s I have owned all had 6 ohm impedance. I can't imagine that this has anything to do with your problems, but there it is. You might want to try the 8 ohm taps too.

[danFrank]

Originally Posted by kmcarpenter

The situation is that I ran the amp wide open with the pre amp also wide open for a little while the other day, no red plates nothing. I did notice that the screen was glowing a little bit when the bass hits.

It stops glowing immediately when the volume is brought down off the stop, but I was just wondering if EL34 grids are supposed to glow when they are being run wide open.

EL34's are not made the way they used to make them when this amp came out (very late 50's, early 1960's).
EL34 screens are rated at 400 volts and you are running them at 500 volts, which makes them dissipate more power than they want to see. This is why you see it when cranked up or when playing heavy bass notes. The old Mullards could do this without problems but today's tubes don't do it very well.
What brand tubes do you have? I have some old Tesla (good EL34's but not as good as the old Mullards) EL34 tubes in a guitar amp that run at 500 volts and the screens glow also. They seem to take it but don't last that long.
You will know if your tubes go into run-away as something BAD will happen rather quickly, so your tubes might take the abuse (like mine) but they will not last as long as they should.
Daniel