66 Bassman head stock, low output normal, no output bass side

[pintail78]

Working perfect before, turned it on today and very low output on normal side, no output on bass side. Nothing obvious/loose in the chassis. Tubes are good, checked and changed both (pre-amp and power) them. I'm at 425volts and 48ma on both output tubes. I'm thinking its a bad cap or open resistor, I've looked at the schematic and checked what I could. I'm at a loss as to what the problem is. Any ideas?

[pintail78]

update

Everything checks out normal....but pin 8 (coming off the 25/25 caps, parallel 1500 resistors) on V1 and V2 are reading 350 volts instead of 1-2 volts.....I think have it pinned down to the area thats messed up but not sure yet. Any ideas???

[oc disorder]

Everything checks out normal....but pin 8 (coming off the 25/25 caps, parallel 1500 resistors) on V1 and V2 are reading 350 volts instead of 1-2 volts.....I think have it pinned down to the area thats messed up but not sure yet. Any ideas???

My gut reaction is to check with the amp off, that the the other end of the 25/25 and parallel resistor is grounded.

Then check the resistance of that 1k5 resistor. It seems to me you are getting the HT on the cathode.

[Leo_Gnardo]

Everything checks out normal....but pin 8 (coming off the 25/25 caps, parallel 1500 resistors) on V1 and V2 are reading 350 volts instead of 1-2 volts.....I think have it pinned down to the area thats messed up but not sure yet. Any ideas???

That IS bizarre. Obviously 350V across those 1k5 resistors & cap would have smoked them real quick. The ends of those cathode R's & C that should be grounded - are they? Sometimes the jumper from the board to brass bus bar behind the pots comes unstuck, and you can see that. One of our correspondents had an awful time with his Bandmaster until a good tech found those ground wires weren't making good contact with the solder surrounding them due to corrosion. If the ground jumper looks OK give it a good tug with needle nose pliers, you may find it slides right out of the solder blob on the bus bar. A couple times I've found the jumper never was well soldered to the eyelet on the board.

[Jazz P Bass]

Kind of hard to ascertain exactly what is going on.
The plate voltages of V1 & V2 should only be 220Vdc.

I would suggest double checking the readings.

[pintail78]

Funny last night I keep looking at that ground on the schematic just before bed......then I read all your suggestions. It was a bad ground, fired up perfectly after resoldering. I'm going to give all those grounds a yank with the needle nose today before I zip it back up. Thanks for all your help! John T.

[dumbassbob]

That was one of the problems with my 63 Bandmaster all that was wrong the ground wire to the buss bar had coroded under the solder joint..Kendricks amps got me for $1300 and never fixed it just pulled every thing else out.....If you can't find the problem send it to Skip Simmons amp repair,he fixed it in 10 mim and only charged me a few dollars...

[Silvertone Jockey]

$1300 and never fixed it? Damn 1300 ain't right even with fixing it. Personally my conscience wouldn't let me charge someone for troubleshooting something that I never repaired, other than the normal 1 hour bench fee. If I had that much time in it I would damn sure find the problem so I could charge for at least some of those hours, but that's just me

[Leo_Gnardo]

That was one of the problems with my 63 Bandmaster all that was wrong the ground wire to the buss bar had coroded under the solder joint..

That's you I mentioned in #4, DAB. And now a good reason for everybody who services Fenders to have a yank on all the ground leads, see if something doesn't come loose.

SJ, it's an old shaggy dog story around here, DAB was going thru hell with his amp and Skip finally found the real problem which was cheap to fix after lots of money & frustration at Gerald Weber's shop. You think the self-proclaimed "world's foremost authority" would know better, but no. Must have been 600+ postings, it would take a week to read it all. We're ALL very relieved it got repaired right.

[gui_tarzan]

$1300 and never fixed it? Damn 1300 ain't right even with fixing it. Personally my conscience wouldn't let me charge someone for troubleshooting something that I never repaired, other than the normal 1 hour bench fee. If I had that much time in it I would damn sure find the problem so I could charge for at least some of those hours, but that's just me

Mine either but there are a lot of crooks out there.

[Justin Thomas]

Hey guys,

Actually, The Man (Skip) who actually FIXED DAB's amp wrote aboout it in Vintage Guitar magazine... It was fun to see our saga here (no names mentioned) in a national publication. His advice was great: "get a second opinion!" And hopefully Bob can now drop the DA from his name!

Justin