First Act amp repair

[The Dude]

Both the volume pot that was removed and the pots I ordered are three leg, single output. I have a bigger problem now, the pot leg spacing on the replacements ordered are too small (not wide enough)

Does anyone have a stash of cheap linear 50K pots with the right lead spacing to swap?

You could always add some wire to the pot legs and solder into the board. Use the mounting nut to hold it into the chassis.

[jomama]

You could always add some wire to the pot legs and solder into the board. Use the mounting nut to hold it into the chassis.

Do you mean soldering wires to the pot legs and then making the connection to the board? I see two issues with that:

1. The board might flop around a bit because the wires won't be as tight.
2. I don't know how thick the wire should be and doesn't wire length change things?

So, what did you get as a replacement?

I picked up a Johnson 25B. It has much nicer cleans but has no distortion. A week later I picked up a DS-1 for $17. My total was $27 for the lot. I'm still learning how to get the same distortion tone with the DS-1. It seems much noisier than the distortion on the First Act but maybe it's just nostalgia. I guess the longer you play something, the more you get used to it so I don't think I'm imagining the difference. Maybe I am. I PM-ed you my address to send the 50K pot. I can return the smaller one(s) in swap if you include a return address. You'll let me know what you consider fair and we'll work it out.

[rjb]

I PM-ed you my address to send the 50K pot. I can return the smaller one(s) in swap if you include a return address. You'll let me know what you consider fair and we'll work it out.

DrGonz78 is the guy you want (see post #28).
-rb

[jomama]

Corrected, thanks.

[DrGonz78]

We *definitely* need pictures here, since we are on post#24 and still do not know what kind of pot you are talking about.
* 3 leg? ... check .
* "single output" ? ... what does that mean???
* you talked about ON-OFF and clicking. Standard 3 leg pots do not "click" nor turn anything ON-OFF
* "the right lead spacing" .... which would be? ....
* "the pots I ordered" .... I have no clue about what you ordered.

We need pictures showing old and new pots and pcb where it sits.
Also measure lead spacing on old and new.
And pot case diameter(s).

So we still need pictures that were asked about. I have a bunch of the 50k value pots but that does not help determine if any of them are good candidates for your amp. We need pictures to help determine what you need. In fact, we might see a picture and hunt down the exact replacement part for that amp.

[The Dude]

Do you mean soldering wires to the pot legs and then making the connection to the board? I see two issues with that:

1. The board might flop around a bit because the wires won't be as tight.
2. I don't know how thick the wire should be and doesn't wire length change things?......

Yep. That's what I meant. I'm not sure what you're dealing with (still no pics), but usually there are enough other pots and jacks to hold the board in (regarding the board flopping concerns). As far as wire length, I'm not suggesting leaving an extra foot of wire in there- just enough to make the connections, which won't make any difference at all.

[jomama]

The photo above is the pot that broke. You can see it's a 10mm spacing and it's out of the shell. Sorry it took so long. I used AWG 24 wire to connect the pot as suggested. The wire length is about 3". I tried shorter but it was harder to work with. It works now. The volume board that single pot normally sits on is separate from the main board and small/narrow. That was the reason I was concerned with flexing.

[jomama]

I think I spoke too soon. The amp blew a fuse last night. I left it on when I went out and came back to a dead amp. I'll pick up some fuses and try again. I don't understand what happened, it was working fine. What do you think the problem could be?

[jomama]

Three fuses blown. I only have one left so I'm not going to use it until I figure out what's going on. Is there any chance the added wire lengths on the pot are causing some kind of oscillation?

[J M Fahey]

You didnīt show the mounted pot nor the wiring so we canīt even guess.

[jomama]

I stated the lead wires were 3" long. I needed to use wire extensions because the pots bought had ~7mm spacing. The wires are not touching but they are bent to fit. I don't understand why photos are critical here to determine the potential for amp oscillation. DrGonz78, are you going to save the day here with the right pot?

[J M Fahey]

I stated the lead wires were 3" long. I needed to use wire extensions because the pots bought had ~7mm spacing.

and thatīs exactly whatīs puzzling me (and all others) from the beginning.
Typical modern pot spacing is between 7 and 8 mm ; you showed old one with apparently 10 mm spacing.

Simplest Math and Geometry tells us you need 2 or 3 (two or three) mm extensions.
Then you mention they are 3" long, which means 76 (seventy six) mm long ... WTF?

We are very interested on how did you manage to fit a tiger inside a cat sized box.

The wires are not touching but they are bent to fit. I don't understand why photos are critical here to determine the potential for amp oscillation.

Layout is *critical* for stability.
Since your description is not clear, we ask for pictures.

Extra long wires placed randomly can and do introduce cross coupling between amp parts which must be separated and definitely can be a cause for oscillation.

DrGonz78, are you going to save the day here with the right pot?

I suspect Dr Gonz does not have enough accurate data to suggest "the right pot", besides now we presumably have fresh layout problems.

[rjb]

You can see it's a 10mm spacing and it's out of the shell. Sorry it took so long. I used AWG 24 wire to connect the pot as suggested. The wire length is about 3". I tried shorter but it was harder to work with. It works now. The volume board that single pot normally sits on is separate from the main board and small/narrow. That was the reason I was concerned with flexing.

That would normally be called 5mm (pin-to-pin) spacing; the overall spacing is 10mm. I can't tell the shaft type or diameter from the photo. Would this fit the bill?
https://www.taydaelectronics.com/pot...ntiometer.html
https://www.taydaelectronics.com/datasheets/A-1931.pdf

On the fuse blowing: My uneducated guess is that the problem is more likely a physical short: flopping PCB; exposed wires touching something they shouldn't; random solder blob... something like that.

-rb

EDIT: I posted this before seeing #42.

[g1]

Guess who's back?

[rjb]

Yea, I noticed that too.