Brownface Potentiometers

[strat100]

Just getting parts together for a brownface pro 6g5a build and having problems getting hold of the 10m ra pot, i can get the 3m ra pot quite easily so can i use the 3m ra pot instead of the 10m one and would i have to alter any of the components connecting to the pot?

Regards

[martin manning]

Here's one: https://www.tedweber.com/wp106ra/

[strat100]

Checked that earlier and they wanted $83.15 postage for a $2.22 part to the UK
but thanks Martin

[martin manning]

Checked that earlier and they wanted $83.15 postage for a $2.22 part to the UK :shock:

You didn't't say you are in UK ;^)

I would try this:

[strat100]

Thank you Martin that is exactly what i wanted just wish i had the brains to figure it out myself but alas its not my forte and have to rely on wonderful people like yourself so thank you once again.
Regards

[strat100]

Implemented the changes that Martin supplied but things are not as expected and the sound output is heavily distorted on volume 1 on both channels but the tremolo works as expected but heavily distorted, the voltages on v4 are not good either with 0v on pin 8(70v) and pin 6 showing 400v(295) the 56k resistor showing 404v on side and 400v on the other so only a 4v drop.The bias is causing me a problem too as i cant get the tubes hot enough got a range on pin from -50v to -60v but can only get it to 43% despite changing the input resistor to 220 ohms from 1k infact got up to 50% on a 470 ohm resistor.

[martin manning]

What if you pull the trem tubes out and try the normal channel? Pretty sure I checked out the 10M pot replacement with a simulation.

[sluckey]

The bias is causing me a problem too as i cant get the tubes hot enough got a range on pin from -50v to -60v but can only get it to 43% despite changing the input resistor to 220 ohms from 1k infact got up to 50% on a 470 ohm resistor.

If you want to bias the tubes hotter (ie, less negative bias on pin 5 of the output tubes) then you need a larger resistor before the diode.

[strat100]

Tried that and lost any volume now

[martin manning]

Have you made a voltage survey and compared it to the Fender schematic?

[strat100]

All voltages except V4 pin 6 at 404v(295v) V4 pin 8 at 0v(70v) and V6 pin 6 at 365v(290v) and pin 1 at 265v(295v) rest are within 10% of schematic.

[martin manning]

Looks like V4 is not conducting any current. Measure resistance from pin 8 to ground. You should see 57.5k.

[strat100]

And i get 58.87k both resistors measure ok. Pin 7 reads 57.4k

[martin manning]

There must be some wiring error, bad socket pin connection, or bad solder joint. You should see 60-70V across both of the 56k's. Based on the V6 voltages something is off in the phase inverter too.

[strat100]

Changed tube on V4 and now get on pin 6 307v and pin 8 65v will now have a look at the phase invertor. Strange that as thats the 4th tube i tried in V4 and all the others work fine in a 5e3.