JJ6V6 in 6L6 amp

[ultra-gain]

Hello,

I'm wondering if it is safe to put JJ6V6 into my Peavey triple X amp. I have a plate current probe and will have a plate voltage probe soon. Any danger?

thanks again.

[glebert]

Do you know what the plate voltage is?

[R ski]

Yes there is a chance of melting down the 6V6 tubes, they can only dissipate 15 watts while 6L6 can dissipate 25 watts. The higher plate voltage from the amps design would probably be to high, and the plate side output transformer impedance would be to low. The bias supply would need to be increased to dial down the bias current, can be done, takes some skill at modifying the bias circuit. If the power amp is fixed, heavy resistor to govern the bias current, that value of resistance needs to be increased.

All in all, the installing 6V6 isn't worth while, it will probably damage those tubes and components in the amp, expensive repairs to recover

[ultra-gain]

with a single tube removed from a set of four it reads 504VDC. I'm assuming it will come down a bit with all the tubes in place. I'll have a plate voltage probe soon.

Is it all that I should be concerned with is the plate voltage?

[TomCarlos]

You also have different specs for the Load Resistance. I believe the 6L6 is half the resistance of a 6V6. So this could affect matching to the Output Transformer? And I believe Raa is dependent on the Plate voltage? Can someone confirm this for me?

[ultra-gain]

thanks R ski, this amp has a convenient negative bias adjustment potentiometer handy next to the output tubes. I think it should be able to deliver -60VDC to about -25VDC negative bias. Do you still feel the same way?

[TomCarlos]

BTW.... are we talking Triple X 100 head?

[ultra-gain]

yes sir

[TomCarlos]

Ok... and here is the schematic.

[ultra-gain]

thank you

[glebert]

Here is the datasheet for the JJ 6V6s. https://www.jj-electronic.com/images...s/pdf/6v6s.pdf The Ua=500V is plate voltage and Ug2=450V is the screen voltage max. Seems like you are going to be pretty close to the max.

Actually, taking a look, these ratings are the same as their 6L6GC tube. Raa is double on the 6V6s (10k vs 5k)

[ultra-gain]

Here is the datasheet for the JJ 6V6s. https://www.jj-electronic.com/images...s/pdf/6v6s.pdf The Ua=500V is plate voltage and Ug2=450V is the screen voltage max. Seems like you are going to be pretty close to the max.

Actually, taking a look, these ratings are the same as their 6L6GC tube. Raa is double on the 6V6s (10k vs 5k)

thank you. I should had thought to cross reference the 6L6 tube data sheet. Besides the Raa doubling would there be any other concerns?

[Justin Thomas]

Yes. The plate dissipation is only 14W on the 6V6 instead of 30W on the 6L6. Be aware that wven as you bias for less current in order to not exceed plate dissipation, your plate voltages will rise, possibly exceeding specs.

There is a certain amount of play for ams that may not already be running the tubes near their limits, but since your amp is already close to the voltage limits of even a 6L6, it may not wprk out as you would like. The whole thing with current, dissipation, and voltages works as a system. A change in one will change the others, and as everything is alrwady close to borderline, it may not get you where you want it.

If you're trying to lower volume, I'd look for other means. But on the plus side, at least JJ6V6s are cheap (relatively), so if you blow a few tubes you won't be put out too much...

Justin

[glebert]

Odd to me that they don't put a "half power" switch on this amp. Would be easier than trying to switch tubes.

So with the higher Raa of the 6V6s would it be recommended to run the output impedance switch at 1/2 of what the actual speaker impedance? This is the same question people thrashed on for 20 pages regarding if this should be done when pulling two tubes.

[Enzo]

Well, to be honest, on that amp a half power switch would be like a half power switch on a drag racer. The XXX is a loud stage amplifier, not a bedroom warrior. If one wants a quiet amp, one should not buy a XXX.

And if half power is all you are after, why fart around with 6V6 tubes? Just disable two of the power tubes. Open their cathode leads.