6V6 ECC83 push-pull amp project - Page 4 - UK Vintage Radio Repair and Restoration Discussion Forum

RogerLLL · 6th Apr 2023, 1:56 pm

I realised that I'd disconnected the 2.7k cathode resistor instead of the NFB - just s stupid mistake - which might explain why the volume dropped so much...!
I tried swapping the speaker wires, in effect so that the OT speaker ground went to the signal and vice versa. There was definitely more volume and distortion with the wires swapped. So I'm guessing that it was wired correctly originally for negative feedback.
Disconnecting the NFB properly this time, there was a definite increase in volume, but with more of a harsh sound. I tried with a 100uF cathode bypass cap and the volume increased further, but with a slightly smoother break up. While this most definitely provides more gain, break up starts at a much lower volume, so I have reverted to its original set-up with the NFB loop in place, as this provides an overall cleaner tone with more headroom. Nice to know the option is there though for higher gain if needed.
I actually tried replacing V1 with a 12AT7, which provides a cleaner sound with less breakup, but also lower volume, so It'll be interesting finding a balance with these options. I play mostly blues, folk & country, so I'm not necessarily looking for lots of overdrive.

Gabe001 · 6th Apr 2023, 2:33 pm

Looks like you're there, just fine tweaking to taste. When you're done, post a sound clip and a few pictures. Remember that you can keep tweaking forever, so at some point call it job done and enjoy it.

6th Apr 2023, 1:56 pm	#61
RogerLLL Tetrode Join Date: Feb 2023 Location: Shoreham-by-Sea, West Sussex, UK. Posts: 88	Re: 6V6 ECC83 push-pull amp project I realised that I'd disconnected the 2.7k cathode resistor instead of the NFB - just s stupid mistake - which might explain why the volume dropped so much...! I tried swapping the speaker wires, in effect so that the OT speaker ground went to the signal and vice versa. There was definitely more volume and distortion with the wires swapped. So I'm guessing that it was wired correctly originally for negative feedback. Disconnecting the NFB properly this time, there was a definite increase in volume, but with more of a harsh sound. I tried with a 100uF cathode bypass cap and the volume increased further, but with a slightly smoother break up. While this most definitely provides more gain, break up starts at a much lower volume, so I have reverted to its original set-up with the NFB loop in place, as this provides an overall cleaner tone with more headroom. Nice to know the option is there though for higher gain if needed. I actually tried replacing V1 with a 12AT7, which provides a cleaner sound with less breakup, but also lower volume, so It'll be interesting finding a balance with these options. I play mostly blues, folk & country, so I'm not necessarily looking for lots of overdrive.

6th Apr 2023, 2:33 pm	#62
Gabe001 Octode Join Date: Oct 2019 Location: Stockport, Greater Manchester, UK. Posts: 1,328	Re: 6V6 ECC83 push-pull amp project Looks like you're there, just fine tweaking to taste. When you're done, post a sound clip and a few pictures. Remember that you can keep tweaking forever, so at some point call it job done and enjoy it.