6v6 stereo power amp build .

[Arbutt]

Yes chuck I have a pi circuit for each channel .

[Chuck H]

Thank you. I just wanted to be clear about it because so far "the" pi has been referenced. Which doesn't imply two of them.

I think the suggestion of using a LTP type phase inverter was a good idea. You can probably keep the NFB loop values the same, using the 1.5k cathode resistor value for the shunt resistor between the tail and ground.

[Arbutt]

Thank you Chuck . I will look at one later and post up when I want to use. And see what you guys think. I want to get this thing finished and off my bench.
Mr a

[Arbutt]

Morning . Had a read last night on AC and DC long tailed pair pi. On valve wizard web site As jazz p bass said. I sort of understood it .
I've decided to go for AC long tailed pair.
I'm going to start it later today- tomorrow hopefully .
If anyone has any suggestions
http://www.valvewizard.co.uk/acltp.html
Many thanks
Mr a

[eschertron]

We've been talking some time about the amp, as if it was only one channel. I never thought to ask if the "a little distorted" sound was on only one channel, or on both. I'm assuming both channels were wired up exactly the same way during any/all of the modifications that were made.

[Arbutt]

Both channels were wired the same and both channels were slightly distorted at a higher level . The bias was fixed and at 25ma per tube. Tubes are now stock Russian brand unknown. Tested ok on a tube tester. I did run one channel with a pair of used tubes and it was the same
I have removed everything for pi and going to work on one channel 1st and then do other when I'm Happy with the 1st one.
I have a clean slate to start again

[Chuck H]

Something like this might do:

[Arbutt]

Thank you Chuck. I had to look twice at this. Thinking it's my circuit . Thought you were taking the piss as the British will say
I will do this and report back

So I will leave you guys alone for a day or two.

[Chuck H]

I made a small edit above. I changed the inverting (input) side plate resistor to 91k instead of 100k. Better balance.

[Arbutt]

Many thanks to you all for the help.
I have done what chuck said and it's working perfectly.
Only think I haven't done is the 91k as I didn't have any.
I have ordered some and will change.. I'm yet to get on a scope and signal gen to give a full check and output wattage check..

Many thanks again you are all stars

Mr arbutt snitch

[Helmholtz]

Many thanks to you all for the help.
I have done what chuck said and it's working perfectly.
Only think I haven't done is the 91k as I didn't have any.
I have ordered some and will change.. I'm yet to get on a scope and signal gen to give a full check and output wattage check..

Many thanks again you are all stars

Mr arbutt snitch

The difference between 91k and 100k is smaller than the difference between the 2 triode systems in the same envelope/tube can be expected.

[Chuck H]

Absolutely true. Even with a perfectly "matched" tube the difference between the PI outputs just using a pair of 100k plate loads is only (gain) 26.93 to 25.45 (using an on line calculator). Changing to 91k for the inverting side get's you to 25.65 to 25.90. In dB the improvement is only from .48dB imbalance to .09db. But seeing as this is listening amp I was just doing my best