I recently inherited this pre-amp and got around to checking it.
After complete cleaning of controls with F5 faderlube and cleaning of connections / tube sockets with D5 DeOxit, and testing (good) all 8 tubes, I turned it on and found the following problems:
1. The tone-control-defeat button does not latch easily and one must push it in two or three times until it stays in (engaging the tone and contour controls). Is there any fix for this? Getting at / inside this switch looks daunting for either repair or replacement. It is one of about 5 buttons in a row and in an assembly of buttons.
2. The balance control does not work correctly - specifically, the rear pot does not track with the front pot when rotating to the right. I can see a little plastic part on the back of the rear pot that does not always follow the front pot when the dial is turned. With some fooling around, one can get the pre-amp in balance and the actual individual pots work correctly with no noise but the physical connection between the two pots is not working correctly. Can this be repaired or is a suitable replacement control available?
3. Hum, not super loud but needs to be fixed. I can work this some more; likely an issue with the PS and the documentation is pretty good, so I suspect I can fix this. May be subject of a future post.
4. No pilot light - easy fix.
I am concerned mostly about being able to fix the tone push button and balance control.
History:
A friend bought this new cc. 1976 or '77. In the mid eighties, I re-capped the audio circuits with Rel brand poly caps (the same type used by ARC in their '80s stuff) and metal film resistors. I also replaced the volume control with a stepped-Alps control sourced from ARC at that time. I did not touch the PS. The pre-amp sounded really great then and I gave it back to my friend and sorta lost track of it. Very recently, that friend pulled it out of the closet and just gave it to me. I see a sticker on it now that says it was repaired in 1992 and I see that a lot but not all of the PS caps have been replaced. I suspect that some of the caps not then replaced now need to be replaced and are the cause of the hum.
Other than the issues mentioned above, everything seems to be working. All 8 tubes have unreadable labels, and are not the ones in there back in the '80s. All 8 (16) measured within 1% of each other and good on the emissions test on my tube tester, so I think they're fine.
Hoping for advice from anyone experienced, especially on items 1 and 2 above.
Thanks,
After complete cleaning of controls with F5 faderlube and cleaning of connections / tube sockets with D5 DeOxit, and testing (good) all 8 tubes, I turned it on and found the following problems:
1. The tone-control-defeat button does not latch easily and one must push it in two or three times until it stays in (engaging the tone and contour controls). Is there any fix for this? Getting at / inside this switch looks daunting for either repair or replacement. It is one of about 5 buttons in a row and in an assembly of buttons.
2. The balance control does not work correctly - specifically, the rear pot does not track with the front pot when rotating to the right. I can see a little plastic part on the back of the rear pot that does not always follow the front pot when the dial is turned. With some fooling around, one can get the pre-amp in balance and the actual individual pots work correctly with no noise but the physical connection between the two pots is not working correctly. Can this be repaired or is a suitable replacement control available?
3. Hum, not super loud but needs to be fixed. I can work this some more; likely an issue with the PS and the documentation is pretty good, so I suspect I can fix this. May be subject of a future post.
4. No pilot light - easy fix.
I am concerned mostly about being able to fix the tone push button and balance control.
History:
A friend bought this new cc. 1976 or '77. In the mid eighties, I re-capped the audio circuits with Rel brand poly caps (the same type used by ARC in their '80s stuff) and metal film resistors. I also replaced the volume control with a stepped-Alps control sourced from ARC at that time. I did not touch the PS. The pre-amp sounded really great then and I gave it back to my friend and sorta lost track of it. Very recently, that friend pulled it out of the closet and just gave it to me. I see a sticker on it now that says it was repaired in 1992 and I see that a lot but not all of the PS caps have been replaced. I suspect that some of the caps not then replaced now need to be replaced and are the cause of the hum.
Other than the issues mentioned above, everything seems to be working. All 8 tubes have unreadable labels, and are not the ones in there back in the '80s. All 8 (16) measured within 1% of each other and good on the emissions test on my tube tester, so I think they're fine.
Hoping for advice from anyone experienced, especially on items 1 and 2 above.
Thanks,
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