Bias Trim pot value… 10k linear or 50k linear ?

[bluesrx]

Hi All…
Long time “lurker” here. I have found these forums invaluable and am very appreciative of the sharing of information and knowledge. Here’s my question.

I’ve built a few 5e3’s and a couple of 5f6a’s. My current project is another 5e3 with fixed adjustable bias instead instead of the stock cathode bias. I’m using a Weber kit with a few upgrades.

The PT has:
120v and 125v primary’s
45v bias tap
270-0-270 & 340-0-340 secondary’s

I plan on using the 125v primary and the 270-0-270 secondary. My question is which value trim pot should I use? I’m thinking the 10k with a 470 ohm range resistor and a 27k “buffer” resistor.

I’d like to get this right the first time. I have Parkinson’s and soldering is not the easiest thing to do.

Thanks in advance for any and all info…. Much appreciated!!

[sluckey]

Just copy the AB763 Deluxe Reverb bias circuit.

[WimWalther]

Just copy the AB763 Deluxe Reverb bias circuit.

If a given bias supply circuit uses typical resistor values, a 50K pot will tend to produce way too much adjustment range, with associated loss of control resolution (control will be too touchy).

To keep the resolution high, you want the minimum possible voltage drop across the control that still allows sufficient range to cover any tubes you're likely to plug in.

[Latole]

I sometimes use 20-25K
Often Cernet pot, so easy to adjust with their many turn.

Folow Sluckey advice.

[WimWalther]

I sometimes use 20-25K
Often Cernet pot, so easy to adjust with their many turn.

Folow Sluckey advice.

If you have multi-turn pots available, then I suppose that's a different matter.