Hi All
I bought a Knight 93 SX 670 amp and when I received it the the out side of the chassis was ok for its age but when I took the cover off the plate that holds all of the components had been pushed in so I cut it out and rebuilt it . The opt is original but had made separate 5volt 6.3 volt and ht transformers made re did the lay out for the tubes as they were all very close to each other generally made it neater and easier to work on and all new components . The problem is as it warms up about 5 minutes the volume increases so does the distortion to the point where the volume pot is turned right down .It happens on both channels .
Have swapped all the tubes but no change . The transformers get barely warm and I am at a bit of a loss at what to do next .The only change I made was to swap the input tube from a 6SC7 to 6SL7 . Can someone please help.
Thanks
Nigel
I bought a Knight 93 SX 670 amp and when I received it the the out side of the chassis was ok for its age but when I took the cover off the plate that holds all of the components had been pushed in so I cut it out and rebuilt it . The opt is original but had made separate 5volt 6.3 volt and ht transformers made re did the lay out for the tubes as they were all very close to each other generally made it neater and easier to work on and all new components . The problem is as it warms up about 5 minutes the volume increases so does the distortion to the point where the volume pot is turned right down .It happens on both channels .
Have swapped all the tubes but no change . The transformers get barely warm and I am at a bit of a loss at what to do next .The only change I made was to swap the input tube from a 6SC7 to 6SL7 . Can someone please help.
Thanks
Nigel
Hi Jane
Thanks for the reply . I have rewired the grid and cathode . The amp works and sounds good for a lunch box amp all except for when it warms up . All the components are new except the opt . When its cold the volume is quite low in comparison to when it warms up .
Nigel
Thanks for the reply . I have rewired the grid and cathode . The amp works and sounds good for a lunch box amp all except for when it warms up . All the components are new except the opt . When its cold the volume is quite low in comparison to when it warms up .
Nigel
Hi DF96
I have pulled out the input tubes no change pulled out the phase inverter seems to stop there will try and post the schematic .http://music-electronics-forum.com/attachments/3619d1227882411-picture.jpg
I have pulled out the input tubes no change pulled out the phase inverter seems to stop there will try and post the schematic .http://music-electronics-forum.com/attachments/3619d1227882411-picture.jpg
If you are still getting sound through with volume pots at zero then you have a wiring error or faulty pots. My guess is that you forgot to ground the zero end of the pot, so the valves have no grid bias. This would do strange things as the valves warm up.
As I said, DC voltages will tell us what is really going on.
As I said, DC voltages will tell us what is really going on.
Thank you for your advice DF96 it's been running for about twenty minutes now and all is fine . I will put the phono circuit back in and have ordered some better quality pots , these one's don't even fully turn off . I have made two two amps and a active crossover from scratch all of them worked so have not been able to develop any trouble shooting skills . I now can put my nos 6L6G's to see how they sound .
Thanks Again
Nigel
Thanks Again
Nigel
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
- Home
- Amplifiers
- Tubes / Valves
- Volume increases as amp warms up