Wiring Heater String...

[Bob M.]

Hi,

I'm wiring the heater circuit of a conventional tube amp using 2x 12AX7A and 2X 6V6GTA tubes. What I can't remember is - what is the best way to connect the power tubes to the string -> Should pin 2 of the 6V6 connect to pin 9 of the 12AX7A and pin 7 of the 6V6 connect to pins 4 and 5 of the 12AX7A or vice-versa. What is the best way to wire this heater string?

Thanks,

Bob M.

[pdf64]

I can't see how it would make any difference, all else being equal?
Merlin's document on this topic is excellent The Valve Wizard

[Jazz P Bass]

Why would it matter?

As long as you wire them them in a logical manner, everything should be o/k.
Run one heater wire from output tube pin 2 to the next power tube pin 2.
The same with pin 7.
Keep the preamp tubes the same way.
4/5 to 4/5
9 to 9.
Symetrical.

I think where things go bad is when you start crossing things.

[Bob M.]

I don't know if it matters or not. But in past I have read somewhere, I can't remember if it was Kevin O'Connor or Gerald Weber or Dave Funk or Dan Torres but someone who had a preference as to how they've wired it and I guess it can't hurt to follow someone's advice who feels strongly about the topic. I know it's AC and I haven't done any comparative studies but I though I'd ask while I'd doing this today. The amp in question is single-ended so every little bit helps here.

Bob M.

[Tom Phillips]

I don't know if it matters or not. But in past I have read somewhere, I can't remember if it was Kevin O'Connor or Gerald Weber or Dave Funk or Dan Torres but someone who had a preference ...

I have found that it does make a difference if the power tube heaters are wired "in phase" or not. "In phase" being that all pin #2s and all pin #7s of 6L6s for instance are connected together. However, when a correction is made the audible difference is usually very subtle and often not noticeable at all. An interesting point is that I have always been able to measure the improvement using a wave analyzer. That is of course overkill for the standard guitar amp tech bench but it is cool to be able to correlate the cause and effect. I have never investigated the effect with the preamp tube heaters because I never imagined that it would make a difference unless you were dealing with a differential amplifier circuit.

Re: "...Kevin O'Connor or Gerald Weber or Dave Funk or Dan Torres..." Just doesn't seem proper to lump those guys together in any conversation.

Cheers,
Tom

[pdf64]

As the parallel SE power tubes are in the same polarity, it may be beneficial to wire their heaters with opposing polarity, ie 2 to 7 etc.
I can't see why crossing the heaters over for the pre-amp tubes should make any difference?

[66tele]

As the parallel SE power tubes are in the same polarity, it may be beneficial to wire their heaters with opposing polarity, ie 2 to 7 etc.
I can't see why crossing the heaters over for the pre-amp tubes should make any difference?

The OP said "conventional" amp. I would take this to mean a push-pull circuit rather than two parallel single-end amps. The output tubes should be wired pin 2 to pin 2 and pin 7 to pin 7. The preamp tubes are dual triode and therefore humbucking so the heater wiring doesn't matter.

[pdf64]

But then post #4 mentions 'The amp in question is single-ended'.

[Chuck H]

But then post #4 mentions 'The amp in question is single-ended'.

I'll get behind this. The cathodes emit electrons because they're hot. The phase of the heater doesn't matter for this. With tubes in parallel any noise from the heater should theoretically be canceled with equal, but opposite impressions on the OT in this case. Preamp tubes shouldn't matter, but, you might go ahead and elevate the filament CT. If the parallel 6V6's are cathode biased (and they probably are) you can fully bypass the cathode resistor with a cap and connect the filament CT to the power tube cathode pins for a 20+VDC elevation.