Brownface tone control question

[hearforever]

Scratchy volume control and hum

Well I rewired the amp with the later Fender tone controls using the 500K pots that were already in the Masco. I used the Tone Stack Calculator to get the right capacitor values to compensate for the 500K pots. It sounds great!

Other than the fact that there's scratchiness on the volume pot. There's also some hum and hissing coming from the speaker when the volume is set at zero. I replaced some of the power filter caps and that didn't seem to help any. Any idea of what could be causing any of those sounds?

[Satamax]

Well I rewired the amp with the later Fender tone controls using the 500K pots that were already in the Masco. I used the Tone Stack Calculator to get the right capacitor values to compensate for the 500K pots. It sounds great!

Other than the fact that there's scratchiness on the volume pot. There's also some hum and hissing coming from the speaker when the volume is set at zero. I replaced some of the power filter caps and that didn't seem to help any. Any idea of what could be causing any of those sounds?

Scratchyness usualy is caused by bad coupling caps puting a litle DC on the pot.

[txstrat]

Correct me if I'm wrong, but when I think of brownface I usually have these 350K pot with a 70k tap in mind. Therefore the schematic looks different too. I know the 6G5 pro was the first brownface to come out but later versions also used the tapped pot.

Matt

[Paul P]

Could someone explain what properties the tapped pot gives to the tone
controls ? I have brownface tone stacks in my amp and put a 68K resistor
in place of the tap so I could use 250K pots. It's not clear to me what part
of the tone adjustment I'm missing out on. I don't believe Duncan's tone
stack calculator includes the tapped pots.

Paul P

[hearforever]

There are a couple versions of the Brownface tone stack

http://amps.zugster.net/articles/tone-stacks#Brownface

[Paul P]

There are a couple versions of the Brownface tone stack

I hadn't noticed this, thanks. I was referring to the later "-A" models and
just realized that you've been talking about the earlier ones which use 250k
pots.

Paul P

[hearforever]

Actually I ended up using the tone controls from the later Blackface amps because the Brownface tone stack isn't in the Duncan tone stack calculator and I'm more familiar with those later controls. it sounds good!

[hearforever]

Could leaky coupling capacitors causing DC voltage also cause the hum that I'm hearing?

How do I test for DC voltage across the volume pot with my multi-meter?