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.
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.
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.
Cheers Matt.
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
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
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.
No...bright screens is sure way of putting the nail into their coffin. ALways use a load on the secondary.
r;-
They were hooked up to 4 ohm Polk Monitor 10's. The neighbors werent there.
THey are fairly inefficient.
THey are fairly inefficient.
They were hooked up to 4 ohm Polk Monitor 10's. The neighbors werent there.
THey are fairly inefficient.
THey are fairly inefficient.
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.
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.
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
I'd agree with that. I have a difficult time getting EL34 to behave, particularly if they are current production. A proper beam power tube should have aligned screen grids, and the screens have much better manners.
For modern production EL34 you should be running 1K Ohm resistors in series with the screen connections. Remember these have a "grid stop" function as well as a screen grid dissipation reduction function so the place for the resistors is with the resistor body hard up against the screen grid pin on the socket.
The "grid stop" function is VERY important when using Ultralinear connected outputs. I had a parallel push pull EL34 Amp which ran 150 Ohm Screen grid resistors. It was OK in Pentode or Triode Mode but was unstable in Ultralinear Mode. Increasing the screen grid resistors to 1K fixed that instability.
Cheers,
Ian
The "grid stop" function is VERY important when using Ultralinear connected outputs. I had a parallel push pull EL34 Amp which ran 150 Ohm Screen grid resistors. It was OK in Pentode or Triode Mode but was unstable in Ultralinear Mode. Increasing the screen grid resistors to 1K fixed that instability.
Cheers,
Ian
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Im sorry I have been somewhat absent lately, the internet has been sketchy, ( I hear there is some internet out west somewhere -shameless southpark plug...)
At any rate, I am running SED Svetlana Winged C tubes in the Heath.
@ polk monitor 10 dude- I tested mine with the multimeter and the resistance across the terminals was about 4 and a half ohm.
I have 499 on the plate and about the same on the screen.
A friend of mine has given me some 1k Resistors for the screen but I havent had a chance to install them yet, as I run the amp about 12 hours a day.
This friend also informed me that I could drop in some 6v6 tubes instead, but I'd have to measure plate current to properly bias them as their power consumption is a little different than the EL34 fire bottles.
Just trying to avert a potential problem here...
6V6 is a much less powerful tube than EL34.
- 6V6 can only dissipate 12W on its anode, a couple more (maybe) on its screen.
- EL34 anode dissipation is 24W (double the 6V6 rating), screen dissipates a few watts more.
- 6V6 maximum voltage on anode is less than 400V.
- EL34 rated maximum anode voltage is well over 400V.
As you can see, totally different. Please don't plug 6V6's into that circuit. It's likely you'll burn those 6V6's up really fast, and might damage other parts at the same time. Besides, if the circuit was designed for EL34, you should use EL34, unless you're ready to properly re-design the circuit.
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6V6 is a much less powerful tube than EL34.
- 6V6 can only dissipate 12W on its anode, a couple more (maybe) on its screen.
- EL34 anode dissipation is 24W (double the 6V6 rating), screen dissipates a few watts more.
- 6V6 maximum voltage on anode is less than 400V.
- EL34 rated maximum anode voltage is well over 400V.
As you can see, totally different. Please don't plug 6V6's into that circuit. It's likely you'll burn those 6V6's up really fast, and might damage other parts at the same time. Besides, if the circuit was designed for EL34, you should use EL34, unless you're ready to properly re-design the circuit.
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I wonder if your friend meant 6L6 instead of 6V6? 6L6GC would be close to an EL34 under some bias and supply conditions.
IIRC, the plate to plate impedence of the output transformer's primary is 8K ohms, so NOS american 6L6GC, 7581, 7027A, or NOS KT66 will work well with this transformer in UL connection.
You will have to put more negative bias on these tubes to get the same idle current as the EL34's have now.
Hell, you might even like the way these tubes sound over the EL34's!
Daniel
You will have to put more negative bias on these tubes to get the same idle current as the EL34's have now.
Hell, you might even like the way these tubes sound over the EL34's!
Daniel
Just watch pins 1 & 8.
EL34 has Pin 1 = G3, pin 8 = K
6L6 has Pin 1 nc and pin 8 G3 and K.
You may not have to make any changes to go from EL34 to 6L6, but going the other way you would have to.
Just FYI.
EL34 has Pin 1 = G3, pin 8 = K
6L6 has Pin 1 nc and pin 8 G3 and K.
You may not have to make any changes to go from EL34 to 6L6, but going the other way you would have to.
Just FYI.
yes the above is ringing bells, 6l6 must be what i was trying to say.
In my Amp, pins 1 and 8 are already tied together.
I have about -55v in the bias supply. IDK if that is enough. There are no resistors in series with the bias rectifier, so it is wide open already. if the -55 isnt enough, I'd probably have to get a different power xfmr.
In my Amp, pins 1 and 8 are already tied together.
I have about -55v in the bias supply. IDK if that is enough. There are no resistors in series with the bias rectifier, so it is wide open already. if the -55 isnt enough, I'd probably have to get a different power xfmr.
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