Bassman is Crackling and Popping

[unhappybassman]

Hey I'm new to the forum, but not new to the Fender Bassman amp...I have a Silver Face Bassman that seems to have popping and crackiling when warming up. After about 10 minutes the popping seems to go away except for and occasional pop and crackle...I have stored the amp for the last year and this seemed to start just recently. I have checked the tubes and put new ones in and have opened her up and checked for anything burnt...but no luck. I have cleaned the pots and that didn't seem to help. Any suggestions on where to look....or check..?? Help if you can...

[pdf64]

This type of fault is most often caused (after the tubes) by the plate / anode resistors in the pre amp (100k ohm). To isolate which one, mess around with the tone / vol controls while it's doing it's thing, and note which, if any, affect the noise, to what degree, etc. Then try removing the small tubes one by one, starting with V1, the one furthest from the power tubes - switch on to standby when actually removing the tube, to avoid earth shaking noises. Replace any you remove, then go on to the next. Note which tubes have any affect on the noise. Let us know what you find.
Have a look for your amp's tech info at
http://www.ampwares.com/ffg/
Hope that helps - Peter

[unhappybassman]

O.K. Here we go.....

O.K. I went ahead and removed the preamp tubes 1 by 1 checking to see if there was a difference. No difference. I did notice that the amp is completely quite in with the standby switch on. I have turned all of the pots down and wiggled them one by one. No difference. The only thing that I'm noticing is that my bright switch seems to make no difference in the tone of the amp. Could it be possible to have the cap on the back of the switch go out and cause a short that I would here through the preamp? Would I need to discharge the Filter Caps before measuring the anode resistors on the preamp.. Any suggestions would be appreciated...I would just like the clean Fender sound back again from my amp...

[Satamax]

http://www.geofex.com/ampdbug/ampdebug.htm

[pdf64]

Nice find Satamax - follow the 'hiss' link for best fit to the problem, as I see it.
Are you sure the popping and crackling doesn't stop when the phase splitter tube, nearest the power tubes, is removed? Peter

[Satamax]

Nice find Satamax - follow the 'hiss' link for best fit to the problem, as I see it.
Are you sure the popping and crackling doesn't stop when the phase splitter tube, nearest the power tubes, is removed? Peter

If that's the case, i'd vote for arcing tubes or sockets. Could be a dry solder joint around there too. May be the G2 resistor, or this verry resistor which has heated up and melted the solder

[stokes]

Try poking the plate load resistors with a chopstick to see if you can get any noise.If you poke one and it makes noise,check the solder and or replace the resistor.Be careful,obviously, this must be done with the amp powered up.

[Amp Kat]

And try moving the tubes very gently mainly the preamp tubes and push down on them seating them firmly to make good contact. Could be tube sockets and I realize you changed the tubes but in this case usually it is faulty power tubes. They aren't Sovtek WXT's by chance are they ?

[Euthymia]

Regarding the non-functional bright switch, it's less likely that you are getting crackling as a result of a problem with it, but quite often the switch goes dirty/bad.

A shot of DeOxit Red or FaderLube often fixes the switch, if not, Radio Shack sells a drop-in replacement.

[unhappybassman]

Still Poppin

When the driver tube is removed no snap crackle pop....When another is replaced into the socket..Its popping all over again....And yes the power tubes are Sovetek's...The preamp and driver tubes are Mesa...I have the lights off and see no arcing..The article from the link say may be a arcing power switch and/or standby..Whats the likelyhood? I tapped on everything in the amp...still seems to pop on its own..Any ideas please...New set of tubes maybe....I appreciate any suggestions you all have been a great wealth of knowledge....

[Jag]

I would spray the switches, pots and sockets with cleaner first because it's the easy thing to do and is not a bad idea. If the crackling gets worse when giving a gentle wiggle to the 12AX7's be sure to retension the sockets. If it still crackles after that, my money would be on plate load resistors.

Since the crackling stops when you pull the PI, I wouldn't suspect the power tubes but you might want to replace them anyway.

[Satamax]

Well, if it's popping randomly i'd suspect a resistor and in the B+ rail, Preamp or PI since you say it's not popping when the PI is removed.

[pdf64]

OK, try thefollowing and report back
1/ power amp up and confirm noise is still there
2/ put amp on standby, remove the pre-amp tube (V1) furthest from the power tubes.
3/ with V1 socket empty, bring amp up from standby. Note what affect this has on the noise.
4/ put amp back on standby, replace V1 tube and remove V2 tube.
5/ with only V2 socket empty, bring amp up from standby. Note what affect this has on the noise.
6/ put amp back on standby, replace V2 tube and remove V3 tube.
7/ with only V3 socket empty, bring amp up from standby. Note what affect this has on the noise.
We already know that with no phase splitter V4, the noise stops, so no need to repeat for that one. The procedure should enable us to work out which circuit the fault is occuring in.
Hope that helps - Peter

[rf7]

I'm battling the same thing with a '66 Bassman. How are your filter caps? They may be part of the problem. I've replaced the filter caps and the 1K/1W B+ resistor before the PI tube and got rid of most of the problem. I also ended up replacing the 100k plate resistors and the 220K feedback resistors, but that did not help my problem at all. I've still got some crackling noise stuff going on, so I went whole hog, replaced the coupling caps with Orange drops, and replaced the tube socket, all to no avail. I even shotgunned the resistors on the tube grids. So now, I'm about to replace the cloth wires to the tube socket, hoping that does the trick. If not, then it could be a moisture problem with the eyelet board material that they use. I hope not. I hope your problem is not as stubborn as mine is. This amp is driving me crazy!

[Amp Kat]

I doubt it is the cloth wire but if it is the tweed disease you won't fix it until it's outta there and it is night and day and it does happen unfortunately.