1965 Bandmaster hum

[Bombacaototal]

It's acetone. Give it a try.

Yup acetone, will do! Just ordered some new diodes as well

[gldtp99]

My #2 '65 Bandmaster had the black dye/paint on the diode solder joints, too ---- I just un-soldered the joints as usual and used my vacuum pump to clean out all the old junk ---- I removed the Rectifier/Bias board and backing board and cleaned up everything before i put it all back together with new components

So i installed a new AC Power Cord (3 conductor, properly grounded and with Power Switch and Fuse Holder on High side), New PT from CE Dist (made by Marvel in Chicago), and all new components on Rectifier/Bias board

Everything worked 100% on first start-up and is still the same years later

I installed new Filter/Bias e-caps and also the bypass cap for the Trem (Vibrato) cathode

I left the original other Preamp Bypass caps in place, as an experiment, because i'd read online that some folks don't replace them (for some reason) if they're not leaking goo all over the place ---- I'd replaced ALL e-caps in my #1 '65 Bandmaster and i wanted to see if it really made any audible difference

When i tested out the #2 Bandmaster, it had "That Special Something" that my #1 Bandmaster had ----- I've serviced many other BF/SF Bandmasters and no others had the superior tone qualities that these two '65's had

So the original preamp bypass caps are still in the #2 amp

I'm not sure if they contribute positively to the sound of the amp but, since the tone of the amp was "There", I didn't want to change anything else

Interestingly, I used to own a '64 BF Blonde Bandmaster, sticker said AA763 but the circuit was AB763, that always sounded "ok" but never as "Superior" as my #1 '65 Bandmaster

I spent lots of time rolling tubes, trying different Bias points, etc to get it up the tonal level of my #1 '65 Bandmaster but it never got there ---- Everybody else that played it loved it and never noticed anything sub-par (it sounded "good") ---- but it lacked that "Special Something" of my #1 '65 Bandmaster

When I first tested out my #2 '65 Bandmaster it had "That Special Something" similar to my #1 '65 Bandmaster ----- Even with the new aftermarket PT ---- And that's why I decided to keep it

[martin manning]

My #2 '65 Bandmaster had the black dye/paint on the diode solder joints, too...

Weird. Did any other eyelets have that treatment?

[gldtp99]

No, just the rectifier diodes ---- not on the Main Board

It seems like I've seen this black paint/dye on other old BF Fender amps, too

Maybe on the many Showman/Dual Showman amps i've owned or serviced

[Charlie Wilson]

That black paint is stock Fender.
CW

[martin manning]

Do you know the story CW? Why only on the rectifiers, and why only in the early years of solid state?

[Stevem]

I think where kinda off the rails here now with this string!

[Stevem]

One big point I forgot about these amps and there noise floor is that they are never as quiet as they should be when they are out of the cabinet.

When bolted up ( and grounded ) the steel mesh screen stapled to the inside top of the cabinet cuts down a lot on the noise floor of these amps, just like steel plates used on the floor of Marshall, Highwatt and a few other amps.

[Bombacaototal]

Just to give an update, I have replaced all 7 diodes (rectifier and bias) and also have replaced both tonestack filter caps. Hum is the same unfortunately

[johnnyreece]

Did you ever determine whether you had stray voltage from the fiber board?

[Stevem]

I too also question why he prefers to do the hard things first like change parts instead of taking some simple voltage measurements !

[gldtp99]

I must agree

If the OP's amp has Stray Voltage on the main Eyelet Board then no parts swapping will fix the hum problem until the Stray Voltage is eliminated

I'd also take a very close look at the grounding of everything on the front panel of the amp ----- Make sure everything is Clean, Tight, and Secure and that no corrosion has built up between the Brass Grounding Plate and the steel chassis

Eliminating flakey grounding is sometimes the cure for many old amp troubles

[martin manning]

I see nothing wrong with replacing parts that have possible reliability problems like old filters and old rectifiers.

Since the hum seems to be in the PI, see if its ground is good. It looks like you have reflowed the eyelets in that area, but put a clip lead on the bare wire as shown in this photo, and touch the other end to the chassis at the main filter ground. Any change in the hum?

[Charlie Wilson]

Make sure the 100 ohm in the PI has not broken free of the solder joints.
CW

[Bombacaototal]

Thanks everyone for the suggestions. Progress has been a bit slower than I'd like but today I had some time to go over a few things
1) 100ohms at the PI tail: I removed it and put it back in place. The leads that go to the eyelets are not short, so I'm pretty sure there is a good connection there
2) I have clipped an alligator clip to all the layout board grounds, one at a time. The grounds are the barewires going to the buss bar. First I did the PI, and clipped the other side to the input jack's, then the pre amp normal stack ground then the vibrato pre amp. No change
3) I measured the voltages on all the layout board ground points with the MM. They were all 0.000V DC
4) I measured many different places at the board itself with the MM (one probe to ground - ie buss bar, and the other at random places at the board). Around the PI plates, I had about 0.008V (pictured) at the board in between the resistors. As I moved towards the end of the board I had 0.004V. Around the 1M at the PI I had about 0.003V. After the vibrato and normal channel treble cap I am getting about 0.017V at the board