Using 6V6's on an a 'low level' output transformer.

[MaxDM]

What kind of issues, apart from current imbalance between windings, should I be looking out for, if I use a smaller 30K plate to plate line transformer with 6V6's?

The reason I would like to try it, is because I remember experimenting with such a configuration years ago and it had a sound that I thought was interesting.. not clean, mind you.

I can't remember if I was running them as pentodes or triodes

 

[abbey road d enfer]

6V6 recommanded load is 8-10k for max clean power. Tripling the impedance results in more gain, more distortion at max power, but used in a line output stage the expected power is less than 800mW (+26dBu into two 600 ohms loads). So there would be another 12-13 dB available from the tubes. The xfmr may not be up to the task, particularly at low frequencies, where the higher source impedance meets a lower inductance than expected...

 

[MaxDM]

That's interesting. What do you mean about the higher source impedance, as related to inductance? If the output transformer is 30K, shouldn't that carry across to the lower frequency spectrum as well?

How about loading the plates with resistors, as well as the output TX, to better load the tube?

What about using very low screen grid voltages? Is that a possibility?

Thanks for the help

 

[emrr]

There are RCA PP line amps with 30k:500 outputs. Nothing special or different. If the transformer works with a 30k source, as many/most old things do (spec for matching in old days) it should be fine here.

 

[MaxDM]

really? which ones?

 

[emrr]

PA-134’s.....you won’t find anything about them.....

Plug-in module similar to BA-1A format, 910Ω cathode resistor, pentode connection, 250V B+ through a 5K resistor.

 

[MaxDM]

Thanks for the values!

Any idea about the screen voltage? Are they connected directly to B+ ?

 

[emrr]

Through 120K from CT of output.

It's a custom Hollytran transformer, so no real specs discernable. I have not measured total current.

 

[MaxDM]

Thank you,

87 SEEMS a bit low, is the grid biased through a negative DC supply, or does it rely on the voltage drop of the cathode resistor?

 

[emrr]

Crap, sorry, looked too fast, it's a single bypassed 910Ω. The 87Ω are current measurement resistors in the plate circuit.

 

[MaxDM]

Ah, thought so!

Thanks!