Dual Rectifier Solo Head

[carlosraj7]

Hi

I am new to this forum and am working on a friend's amplifier, Messa Boogie (Solo Head). He said the amp sounds dirty and crackling and had sprayed WD40 to clean the switches and pots but no difference. What I noticed is that, there is severe crackling, popping and weird noises from the amp even without any signal present. It is present on all 3 channels. It gets worst if I turn up the volume or gain on each channel. I have isolated and checked all the electrolytic and orange caps, they are all within range. I did not check the tiny (picofarad) caps. I tried replacing all the 12AX7 tubes , one at a time with a good working preamp tube with no difference. Cleaned all the pots, switches and sockets with CRC contact spray several times. I totally have no idea what is causing this problem. Can someone please guide me on what can cause such problems and what to check for.

I have tried switching from tube to solid state rectifier but no difference. I took the signal out from effects "send" to another amp and it is crackling, inserted an audio signal into "return", the signal was clean but when I turn up the gain or volume of that channel then the crackling comes in, So I guessed that the problem is in the preamp. Following the block diagram on page 1 of the schematic, the signal from input goes into V1a (grid pin2) then out of V1a (plate pin1) then into V2a (grid pin2) then out of V2a (plate pin1) and back to V1b(grid pin7) and out of V1b(plate pin6). I do not have a scope, so as an alternate I used my signsl tracer. Amp set to channel 1 (clean), probed pin 2 of V1, no crackling, then pin1 of V1, no crackling. From pin1 of V1 to pin2(in) of V2, no crackling. Now when I probed pin1(plate out) of V2a there is some slight crackling noise and the crackling noise want up about 3 to 4 times louder when I changed the switch from "clean" to "pushed" on channel 1. What I see the noise came in at V2a ( out) and was present also at V1b (in). I have tried replacing V1 and V2 with a good working tube but no difference. The noise increases as I increase the gain, the master volume has no effect, What could be the problem. Please assist.

Thanks

 

[user 41014]

Just to cross it off the list I would tighten the tube pin sockets individually with jeweller size tools or the end of a screw

 

[rarebitusa]

I'd try removing the Rectifier tubes and then test in solid state mode. Had a similar problem and found out with my Stiletto that switching to SS mode does not take the Rect tubes out of the circuit. Only removing the Rect tube finally revealed that it was my amps source for the noise.

 

[carlosraj7]

I did both, cleaned all the tube socket holes scraping using a tiny screwdriver and used fine sandpaper to clean the tube pins. Then I took out the 2 rectifier tubes, put in on solid state. The crackling sound is still there, at times it gives out some screeching or howling sound. I do not have a scope, but plan to borrow one from a friend. Where do I trace from? Please assist.

Thanks

 

[user 41014]

Another shot in the dark is bring the volume pot lugs to wet to assure the connection and check the board connects since that seems to be your hot spot. Burnt wires?

Obviously my guess is a bad connection if the tubes are good and the pots clean. I have no idea what using WD-40 on plastic or contacts does. I've not heard that one. I know it was out of your hands but wouldn't be using my PJ on anything in or around my amp.

The deoxit is the only thing I've used and a smart person on here said to use lube afterwards. I'm not sure but was guessing that to be fader lube.

 

[carlosraj7]

Hi

I did check all the electrolytic caps in the amp and they all check within range. Today I just wanted to try replacing all the electrolytic, and guess what.... After replacing all the electrolytic caps, the crackling noise disappeared. Many thanks to all those who provided some useful information.

Thanks