I need help with a '63 Fender Concert

[War Admiral]

The amp sputters\crackles when I power it up and then stops but intermitently continues afterwards. It cracks badly when I get the volume up to 4 or more while playing.
I took all the preamp tubes out except for the PI and powertubes and it still sputters on startup. If I leave all the preamp tubes in with the powertubes but take out just the PI tube it stops sputtering.
I swapped PI tubes but it makes no difference. This problem in the PI section of the board?

So far:
I changed the PI plate resistors(82K and 100K)
I changed the PI grid resistors (1M 820 1M)
Changed both PI caps (.1's)
Changed the PI tail cap (.1)

Hasn't fixed the problem. Crackles on startup and can't play past 4 without it crackin badly. I'm stumped.

[Firestorm]

Blackface? (Cool amp, btw). Fender used 1/2 watt plate resistors on the preamp tubes on all of these, and while technically adequate, these guys begin to develop a lot of "contact" and "shot" noise as they age. Most of this noise will be present whether there's a preamp tube in the socket or not. Fender eventually replaced all of these with 1-watt resistors, which reduces noise significantly. Start there.
You might also want to replace the 1K and 4K7 1-watt dropping resistors in the "doghouse" as these can contribute a bit of noise, too (though is usually more "hissy.") Finally, the Standby switch is under a lot of stress, switching B+ as it does. Every time that switch is thrown, there is a tiny arc between the contacts leaving carbon deposits behind that can eventually get very noisy. You could try giving it a good shot of contact cleaner (everything OFF, UNPLUGGED and DISCHARGED), but a better approach might be to replace the switch.

[War Admiral]

Thanks man. I've replaced the plate resistors in the PI but not on the preamp tubes. You think it would be a good idea to replace all of them?
I've also replaced all the power caps in the doghouse and the 2 powertube sockets as well.

[Firestorm]

The preamp plate resistors can get noisy. And since what ever they do gets amplified 2 or three more times, they can be WAY noisy. But don't overlook the standby switch as a noise source.

[War Admiral]

I chopsticked the hell out of the resistors with the volume up and I couldn't get a bite anywhere. Didn't change the noise.

I sprayed the standby and I think it seemed to help. I had it going a couple off times on startup with no noise and even played on 6 without it sputtering out. Then it came back! Damn.

It actually could be the source off the problem tho. I just might have to get another switch. Any special switch I need to replace it with?

[War Admiral]

I was screwing around in the dark if I could see an arc by taking it out of standby and I noticed that the pilot light didn't come on sometimes when I turned the power on. The heater filaments wern't on either and when I did get it to powerup,(by poking the ''on'' switch) I only had a little over 3 volts on the heaters. The heaters are supposed to be 6.3 volts right. If the amp is not getting it proper powersupply(120vac), it could be causing this problem?

[Phil_S]

How are you metering the heaters? One side to ground is 3V. Across both legs it will be 6V.

Some may consider it heresy, but I would replace all the plate load resistors with metal film type. There is no "tone" on the plate load resistors, so you will only be doing yourself a favor, as these can be hissy and contribute other noise.

Heaters should be on with the first power switch. You might want to check for a cracked solder, or just reflow anything suspicious. I do not think, however, it will fix your noise problem.

Since you've shotgunned the PI, I'd check around the tube before the PI.

Have you check your pots? Maybe a bit of contact cleaner would make a difference?

[War Admiral]

Thanks for the reply. As for the pots, jacks and sockets, I cleaned them all.

The only other thing I've noticed is that the wire coming off of pin7 of the tube before the PI is quite microphonic when I tap on it.

[roadkingbluzs]

I would suspect pwr filter caps, inspect condition or replace. But also replace pwr resistors.

[ampdoc1]

Use some coolant spray on the resistors and caps. This will show up a lot of components that have problems. You can use the cheap computer keyboard
cleaner spray by turning it upside down to spray. The propellant is very cold.

ampdoc

[Firestorm]

I chopsticked the hell out of the resistors with the volume up and I couldn't get a bite anywhere. Didn't change the noise.

I sprayed the standby and I think it seemed to help. I had it going a couple off times on startup with no noise and even played on 6 without it sputtering out. Then it came back! Damn.

It actually could be the source off the problem tho. I just might have to get another switch. Any special switch I need to replace it with?

You can get replacement Carling SPST switches from Antique Electronic Supply: part number P-H495. They also have a heavier duty version (not Carling) that's even cheaper: part number P-H495-T.

These can be a source of noise, but so can a lot of other things. If the filter caps are old and leaking current, they'll pull too much current through the dropping resistors which can A) burn them up and B) make them noisier.

[Firestorm]

The only other thing I've noticed is that the wire coming off of pin7 of the tube before the PI is quite microphonic when I tap on it.

Odd. That's part of the tremolo oscilator. Not actually in the signal path.

[War Admiral]

Thanks for the replys.

Well I just took some voltage readings and somethings screwy.
V1 1 202
2 0
3 1.4
6 212
7 0
8 1.5
V2 1 207
2 0
3 1.5
6 209
7 0
8 1.5
V3 1 Irratic reading up and down continously between 150 and 215. Pins 1 and 6 are tied together with a resistor and 1 and 7 are jumped.
2 0
3 1.5
6 334
7 same as 1
8 same as 1
V4 1 2 3 not used
6 282
7 24
8 65
V5 1 317
2 0
3 3.3
6 311
7 0
8 3.3
V6 1 285
2 18
3 29
6 282
7 20
8 29
V7 3 443
4 443
5 -39
6 443
V8 3 443
4 443
5 -39
6 443

[Firestorm]

Yeah. A little bit screwy. Based on what you say here, this appears to be a 6G12-A Concert rather than an AA763. So it's actually even cooler than a blackface concert.

The big issue is lack of voltage on V1 pin 6. That probably means your plate resistor is open. Could be a busted lead or a cracked resistor body. It is makes intermittant contact, that will be way noisy (and since it's after the volume pot, it will make noise whether there's a tube in that socket or not).

Since this is a 6G12-A, the preamp voltages are about right (they'd be low if it were a blackface, but with six preamp tubes, it ain't).

V3 is the oscillator for the tremolo and the readings are supposed to fluctuate all over the place, so don't sweat it. The fact that pins 1 and 7 are tied and pins 1 and 6 connected by a resistor is pure Brown Concert (6G12-A). This guy has the unusual phase shift tremolo that requires so many preamp tubes, Fender gave up on it right quick.

[War Admiral]

Thanks firestorm, you've been a great help. Yeah, it is a 6G12-A with 6L6's instead of the 5881's. I made a typo and the actual voltage on pin 6 V1 is 212. I rechecked and they are all right except for V1 pin 6. Sorry.
Chris.