Where best to locate the variable resistor for the 5150 bias mod

[7 DYing Trees]

OK, so I have all my parts, I have one old in need of some repair (but not too much) 5150 and how to do the simple bias mod.

Now, my question is, where is a good place to locate the resistor. Ideally I'd want to be able to adjust it without removing the chassis, so how would you guys advise me on:

- Where to place it

- I'll need to drill a hole, right?

- How do i mount it reliably this way?

Sorry about the n00b questions, but I got the 5150 cheap, so have decided to use it as an experimentation amp so I can put to use the electronics I did at university and actually relearn it, and then actually learn how to apply it again!

Thanks for all responses in advance!

[7 DYing Trees]

...and as an afterthought, i need to replace the rythm gain and the lead post gain pots on the amp. Any idea what they are before I open it up and find out just to save a little time so I can do everything at once?

That and is it worth retro fitting audio taperr pots to the post gains to make the volume range more usable or will that seriousl impact the way the amp sounds? (ie log instead of linear)

[Enzo]

Do you know where the bias control is located on the 5150-2? I usually mount them in the same spot - on top of the chassis near the corner of the transformer. You have to remove the rear grille to access it, but you had to do that to change the tubes anyway. The spot is pretty close to where the bias supply circuit is on the main board.

[7 DYing Trees]

Do you know where the bias control is located on the 5150-2? I usually mount them in the same spot - on top of the chassis near the corner of the transformer. You have to remove the rear grille to access it, but you had to do that to change the tubes anyway. The spot is pretty close to where the bias supply circuit is on the main board.

Nope, never seen a 5150 II, but do currently have a JSX, would that be in a similar position?

How do you run the wiring to and from it? Do you drill holes or just us the existing holes in the chassis for the transformer and run it out via those wires?

[Enzo]

The wires don't leave the chassis, I don't need holes. Only hole I make is for the control shaft bushing. The body of the control is inside the chassis like all the other controls. The wires run maybe two inches over to the circuit board.

I don't know where it is located on the JSX.

[7 DYing Trees]

The wires don't leave the chassis, I don't need holes. Only hole I make is for the control shaft bushing. The body of the control is inside the chassis like all the other controls. The wires run maybe two inches over to the circuit board.

I don't know where it is located on the JSX.

Ah cool, so as I understand it you drill one hole to expose the control shaft (the screw on the variable resistor) into the chassis?

How do you attach the control pot, hot glue or by some other means, just don't want it coming loose, and seeing how gravity gets in the way of stuff staying attached to the top of the chassis!

THank you loads for all the help so far as well, it is greatly appreciated!

[Enzo]

Oh I see.

No, I mount a real live pot there. Not a trimmer. A real pot with a threaded bushing. Think Fender Twin Reverb or something similar - like that. You can find a pot with a screwdriver slot shaft - like used on the Fenders - or just mount a pot with a shaft. Once the grille is in place, no one will be turning it anyway.

You could mount a trimmer. If it were up to me, I'd solder it to a small piece of pc board, and then mount the pc board to the chassis with a couple of standoffs, and have a hole over it. Of course than you have to find the little slot down in that hole. Not my style.

Some guys like the 10-turn pots. I don't, bias is just not that critical an adjustment. DO I really need a couple whole turns to affect current by 1ma?