Mark III volume keeps dipping
- Thread starter fome
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Boogiebabies
Well-known member
It could be a bad effects return jack not making contact or losing contact when the amp starts to feel the rumble. It could also be a Master Volume pot that has a dirty or worn out contact. Cleaning the pots and effects return jack is a good place to start.
Run a small patch cable from the effects send to the return and play for a while. If the problem goes away, your return jack is dirty or bent and will need to be cleaned, adjusted or replaced.
The next place to look at swings in output are the preamp and then power amp tubes. Preamp tubes can exhibit odd behavior and power tubes generally either sound like crap or just plain blow out.
Your amp should be service every year with a full cleaning of the pots, tube sockets and check of the filter caps, tubes, jacks etc. I do a spring cleaning on every amp I have and get in. In a lot of cases of Boogie's with the SUS-4 mounting they let dust get in from the gap between the chassis and cabinet. It some cases after years of electrical attraction and the fan forcing dust in there the inner chassis can look like a vaccum bag exploded. In these cases I uses a micro fiber cloth and then clean all the dirty circuit traces with PCB cleaner or denatured alcohol and a Q-Tip. I use Caig De-Oxit on the pots followed with Ca-Lube and I use De-Oxit on all tube sockets followed by Caig Pro-Gold. I generally use a curved dental pick to gently scrub carbon and heavy oxidation. A good old fashioned pipe cleaner works great as well. I then use a straight dental pick to tighten the sockets. Finally I soak the grounds with De-Oxit and if they do not look clean enough I remove the star ground washer and scrub it with Scotch-Brite until it shines. Use Scotch-Brite pads to gently clean corroded buss wire and all 1/4 in jack contacts after a good dose of contact cleaner. So spending an hour with your baby once a year will lead to a seriously reliable and trouble free tone monster.
A tube job depends on how much you use the amp. I check the bias on the amps I use after each 100 hours of use to see if there is a big drift.
If one of the tubes had gone to more than 10ma of each other, or the whole bias point has gone up, I change them. Generally, I can get years out of even current production tubes. NOS, you can get a decade or more.
A freind of mine just changed the tubes in his 67 Twin Reverb. They were the tubes that came with the amp when he bought it in 1967. RCA Black plates with almost 30 years on them.
Run a small patch cable from the effects send to the return and play for a while. If the problem goes away, your return jack is dirty or bent and will need to be cleaned, adjusted or replaced.
The next place to look at swings in output are the preamp and then power amp tubes. Preamp tubes can exhibit odd behavior and power tubes generally either sound like crap or just plain blow out.
Your amp should be service every year with a full cleaning of the pots, tube sockets and check of the filter caps, tubes, jacks etc. I do a spring cleaning on every amp I have and get in. In a lot of cases of Boogie's with the SUS-4 mounting they let dust get in from the gap between the chassis and cabinet. It some cases after years of electrical attraction and the fan forcing dust in there the inner chassis can look like a vaccum bag exploded. In these cases I uses a micro fiber cloth and then clean all the dirty circuit traces with PCB cleaner or denatured alcohol and a Q-Tip. I use Caig De-Oxit on the pots followed with Ca-Lube and I use De-Oxit on all tube sockets followed by Caig Pro-Gold. I generally use a curved dental pick to gently scrub carbon and heavy oxidation. A good old fashioned pipe cleaner works great as well. I then use a straight dental pick to tighten the sockets. Finally I soak the grounds with De-Oxit and if they do not look clean enough I remove the star ground washer and scrub it with Scotch-Brite until it shines. Use Scotch-Brite pads to gently clean corroded buss wire and all 1/4 in jack contacts after a good dose of contact cleaner. So spending an hour with your baby once a year will lead to a seriously reliable and trouble free tone monster.
A tube job depends on how much you use the amp. I check the bias on the amps I use after each 100 hours of use to see if there is a big drift.
If one of the tubes had gone to more than 10ma of each other, or the whole bias point has gone up, I change them. Generally, I can get years out of even current production tubes. NOS, you can get a decade or more.
A freind of mine just changed the tubes in his 67 Twin Reverb. They were the tubes that came with the amp when he bought it in 1967. RCA Black plates with almost 30 years on them.
Thanks guys. One question: how will running a patch cable from the send to the return determine if the return is bad? Isn't this the same as having my effects in like normal? Your still sending the signal out and returning the signal to the jack, so I'm a bit confused.
Boogiebabies
Well-known member
The effects jack is shorted when the contact do not make an internal connection. It may be dirty or bent. A patch cable will complete the circuit because you are using the full 1/4 inch jack to make the same connection the loop would normally.
Trust the ways of the force.
Trust the ways of the force.
