PP Amplifier output impedance matching

[Mike Watterson]

Thin tip large blade screwdriver, clamp part of laminations in vice and lever out end E

[Refugee]

I did that to get the first lam out of a transformer but not without clamping a power resistor to it for half an hour to soften the lacquer.

[Amie]

Thanks Mike, Refugee.

Maybe an induction heater would work? The school has one in the science lab, I'll ask teach.

Amie.

[Diabolical Artificer]

Edcor do decent cheapish SE OPT's as does Hammond. A good valve to use with a 12k OPT is the QQV03-10, two beam 5w pentodes in one bottle. For class A you can move the load line about a bit, it's best to try and get it through or above the knee, see - http://www.valvewizard.co.uk/pp.html .

Andy.

[Mike Watterson]

Maybe an induction heater would work?

You don't want to heat the windings. It comes apart easily after the first couple are out.

[boater sam]

Amie, you have a new PM.
Sam.

[ppppenguin]

Amie, you also have PMs from me.

[Amie]

Thanks guys!

Replies in your in-boxes

Amie

[Amie]

Maybe an induction heater would work?

You don't want to heat the windings. It comes apart easily after the first couple are out.

Teacher wouldn't allow it anyway..........I asked.

[Amie]

In a pushpull output, does the transformer need to present an Impedance on its entire primary to match the individual R.a. of the valves used, or does it need to match the R.a. in each half of the winding?

The texts I've so far read on the subject have been written with ambiguity.

Easy part first - in Class A push-pull, you need the transformer to match double what each individual valve would require.

So if a valve single-ended requires 6kΩ, then two valves in push-pull would require 12kΩ anode-anode. This is because you have the same current as a single valve, but double the voltage swing between the two anodes. (If you had connected them in parallel, you'd need half the individual or 3kΩ, makes sense because you'd have the same voltage swing as a single, but double the current).

I was stuck indoors yesterday, and did some experiments, based on what I've read in several books on the subject, or, what I understand of what I read, I should say.

The quote from "Kalee20" is the concise answer to my original question, its a more difficult subject to completely understand than I can manage at the moment......the valve wizard articles posted by Diabolical Artificer are the easiest texts I found to understand.

Amie