re-capped fender twin silverface and modded to blackface

[Curranproducer]

OK I am getting ready to do the Merlin FX Loop to the silverface tomorrow!!!!!!!!!!!!!!! I am looking over somethings and I believe I should wire this in before the .001 cap going into the phase inverter. this seems to be the correct spot to splice into the circuit. IF it is not anyone feel free to pipe up! WOO HOO!!!

[Curranproducer]

OK FX Loop is in and working great!!!!! one weird thing though. the amp has a low level noise that comes and goes in the amp. like a hiss/crackle thing. I did not replace every cap in the amp. only the blue drops, the power filters, and the silver mica's on the bright switches and two silver mica's on the board itself. it has new tubes that are biased, and sounds amazing. except for this come and go noise in the amp. It is very low in the amp but it is there for sure

[Curranproducer]

So I replaced all the the plate resistors across the entire amp, and i still have the crackling in the PI, I also have a problem with the FX Loop being to quiet. All of my voltages are about 25 volts higher than the silverface schematic says it should be. Could the board be inductive at this point in the amps life, it is bent up and curving both the main board and the power circuit card as well. The new resistors are actually metal film Not CC.

[tictac]

the amp has a low level noise that comes and goes in the amp. like a hiss/crackle thing. I did not replace every cap in the amp. only the blue drops, the power filters, and the silver mica's on the bright switches and two silver mica's on the board itself.

Sounds like a tube socket could be your problem. Cleaning & retensioning the sockets may help....

The signal caps in the Fender amps, molded blues and ceramic disc, are one of the things that made them sound so good....

TT

I had read too many Torres articles about getting rid of the stock parts. My 100% Stock BF Pro Reverb lost the magic sound once I did that. (but I did get all new parts from Torres so at least he made out)

[Curranproducer]

I had to recap the internal with orange drops, the blue ones where a mess every where in the amp. It sounds amazing as is except for this noise in the amp

[Structo]

Do you have access to an oscilloscope?

If so trace the signal through the amp to see what stage the noise is coming in.

[Curranproducer]

I do have a scope and the crackling comes and goes through all the stages of the amp. I am ordering a new set of filter caps since I Did install one backwards at the time of the recap. I did replace the one i put in wrong with a new cap BUT I am going to redo this entire part of the amp. I am also going to get the CC resistors out if the drop down section of the filter caps and make them metal film

[66tele]

If you still have the carbon composition plate load resistors, try replacing them with metal film or metal oxide. Carbon comps absorb moisture and can cause hissing, crackling and popping noises.

Good Luck!

[Curranproducer]

yeah I already replaced all of those with metal film

[ToneMerc]

Take a hairdryer and warm that board while monitoring for the crackling noise. There's a possibility that board is conductive, worst that board will need to be replaced.

TM

[Curranproducer]

yeah I've been told that the board could be conductive and that I may want to try lifting the board out and spraying the back side clean with brake solvent

[67plexi]

Your board could be conductive unscrew it and remove the insulator board
look for green corrosion on it. Next on your bias capacitor up the voltage
rating from 50uf @ 75v to 47uf @ 250v it makes a big difference kills the hum and hiss. If your voltages are to high adjust the dropping string resistors easy. of course check your solder joints close use a non conductive probe. Check your input primary voltage your power transformer was designed for 120VAC that would explain your +25 volts.

Steve.

[Curranproducer]

my bias capacitor is the cap that is coming off of the B+ and going to the bias pot on of the amp correct? Because I have two of the same value in that section of the amp and I could redo both for the hell of it. What is the hairdryer trick do? does this dry out the CC and speed up the thermal drift that CC can exhibit to try and force the crackle/hiss stuff out of the amp?

[martin manning]

The hair dryer is used to heat the board to drive moisture out of it. The bias cap is circled. I can see hum reduction by increasing it's value... dunno about hiss.

[Curranproducer]

ah ha!