Another random popping and sizzling problem-1967 Pro Reverb

[Michael1]

Hi everybody-ive got a 1967 Pro Reverb that randomly pops and sometimes sizzles thats got me stumped. So far i have done the following:
                                Replaced both power tube sockets
                                Replaced all old resistors
                                Replaced all old caps
                                Resoldered every connection (including tube sockets)
                                Retensioned all tube sockets
                                Sprayed all controls and sockets
                                Swapped all tubes

It makes no difference with all controls at zero.  It will pop 4-5 times after standby switch is activated then be quiet till it gets warmed up. It will stop when i pull V3.   Thanx in advance for the help!

[eleventeen]

>>ALL<< old resistors?

Those evil 100K plate resistors have fixed this on every Fender amp I have ever dealt with, dramatically and immediately. Those 100K resistors arranged in that "V" structure? Replace all of them with 1 watt (2 watt = better) metal film resistors and you won't be able to tell if the amp is on or not. Yes, it's THAT dramatic.


I did this on my '65 BF Pro Reverb (which was a literal zoo/barnyard of weird noises) and SF Princeton Reverb and SF Deluxe Reverb. It killed the sizzle and rodent noises on all of them.

[Michael1]

Ill give that a try Eleventeen --sure has been a tough one !  I had changed all of them except the ones for V1-I dont keep a tube there so i thought it didnt matter on those. Ill change them all with your suggestion-thanx for the reply!

[p2pAmps]

>>ALL<< old resistors?

Those evil 100K plate resistors have fixed this on every Fender amp I have ever dealt with, dramatically and immediately. Those 100K resistors arranged in that "V" structure? Replace all of them with 1 watt (2 watt = better) metal film resistors and you won't be able to tell if the amp is on or not. Yes, it's THAT dramatic.


I did this on my '65 BF Pro Reverb (which was a literal zoo/barnyard of weird noises) and SF Princeton Reverb and SF Deluxe Reverb. It killed the sizzle and rodent noises on all of them.

Add checking and or replacing the 1M resistors on your inputs...

[eleventeen]

Did you go with [oversized, meaning 2 watt vs the stock 1/2 watt CC] metal films vs carbon comps with your plate R replacements?


In some ways I'd imagine it would not matter if you replaced them (the plate R's on V2,3, etc), because brand NEW CCs should be fine. They seem to acquire their noisemaking habits after being installed for a long time.


I don't want to steer you wrong, but we are talking about $3 in parts here, cheapest thing you can do to an older amp.

And yes, I would suspect that not having a tube in V1 would eliminate whatever noise comes from that tube, but again, $3, and the important thing to realize is that the preamp tube filter caps are probably exceptionally INeffective at shunting hiss-type noise to ground AND, in stock config, they are located far away, under the doghouse. They are good at 60/120 Hz, not so much with quasi-white noise = hiss.

[Michael1]

Yea i went with standard 1/2 watt resisters but will change those to at least 1 watt-i agree cheap enough. I didnt change the 68k resisters on the input jack either-searching for straws here lol! The hiss is not too bad in this amp--noise starts after being on awhile (other than the 4 or 5 pops it makes after standby switched on. It then starts the popping and will randomly start a sizzling sound for a while -then quit. p2pamps-are the 1megs your talking about at the PI tube? Thanks a million for all the help!

[super&plexi]

I'd say he's referring to the One Megs on the input jacks, and while there, it wouldn't hurt 2 check the tension and run a little Emery paper through those input Jacks either. Those shorting jacks complete a circuit, in effect closing the jack 2 interference if I'm putting it correctly. In my experience any of the old fenders that have Reverb are susceptible to all kinds of noises ( RCA connectors loose, cables frayed, Reverb tanks messed with, Reverb bag not screwed down, or nonexistent, and the simple addition of a couple extra tubes and parts introduced into the mix,e tc. ) and in the case of my super Reverb it was a combination of RCA, tube, & final culprit,  loose resistor in my turret board. I would fix one only to have the noise come back sometimes days later until I started pulling/testing every component 4 solidity. On the turret boards if you pull on a Wire and it feels like the dentist when he picks at your teeth, that sick squeaky feel, then you know you found it good luck!

[Michael1]

Thanx Super&plexi! I haven't messed with the input yet-ill definitely clean it up real good-the input jack resisters are 68k instead of 1meg on this model-may get to it tonight -thanx again!

[eleventeen]

The 1 Meg is the "grid leak" resistor. The general admonition is to replace the "high value" resistors when doing the MF search and destroy. It's not crazy to go a little overboard with the MF > CC replacement thing, especially when you are talking about the very first stages. And the end of the day it's cheaper to just replace them than to fret about whether it has a profound effect or not.

[p2pAmps]

Thanx Super&plexi! I haven't messed with the input yet-ill definitely clean it up real good-the input jack resisters are 68k instead of 1meg on this model-may get to it tonight -thanx again!

Repeating ( checking and or replacing the 1M resistors on your inputs...)

Never ever a bad idea, I use modern resistors here too as well as the 68K grid stoppers

[Michael1]

Great advice guys! Im going to get back on it tomorrow-Thanx a million!