volume and gain pot issues

[dwilkins]

I had an amp built by a local person and am having problems with the volume and gain pots. They are very sensitive in that I can only turn either one of them about 1/4 to 1/3 of a turn to go from quiet to wide open. Not sure what steps to take to "stretch" this out to the full revolution of the pot.
Any suggestions would be much appreciated.

[Structo]

Do you know what values (resistance) the pots are and do you know the taper of the pots?

[dwilkins]

I do not, but I will check tonight and post a pic of the board also.
Thanks

[Leo_Gnardo]

What Tom's suspecting, me too, is your amp is equipped with linear taper pots. This concentrates all the "action" in the first quarter turn or one third. Past halfway up, there ain't much difference. That's why we generally use audio taper pots AKA log taper, for audio gain.

If you find it's audio taper pots, could pad 'em down with a series resistor to spread the useful control range over a wider area.

[roberto]

dwilkins, I'd ask to the "local people" to repair it for you.
I have the same feeling something went wrong with the A and B after the pot value...

[Stevem]

Where the pots always acting this way from day 1?

[dwilkins]

Sorry for getting sidetracked on this. We swapped out one of the pre-amp tubes for a 12ax7dw, and that actually made the amp much more usable. Its still a little touchy with the volume pot, and it was great until it just started blowing fuses. The person who built it says its the power transformer even though it shows good. It blows the fuse when turning from off to standby. The next question would be what would be the best power transformers for a 15 watt two 6v6 amp? It has a weber in it, but since I have to order one, I want to hopefully make sure I do not have this issue again.
Thanks,

[M Fowler]

You don't need to order anything, you need to wire that standby switch correctly and change those pots from linear B to audio A.

Doesn't sound like a very good local builder. If this amp is a Weber kit then download the schematic and layout from Weber Amp kits website.

[dwilkins]

Not sure what route to take at this point. May be easier to start over.

[hans-jörg]

o.m.g.!
Did you bought it so?
At first look I see several possibilities of shorting! Lot of blank wire, crossings, ...sorry, but ...
I fthe green twisted wire is the filament (and I´m quite sure it is) - wire it new (see other pics of amps).
I´m sure your fuse problem is not the tranny too, its the free floating chaos in this amp.


Sorry, but I would build this amp new - complete!

I feel your deep sorrow, but better for your health

Hans-Jörg

[tele_player]

I would certainly clean up the wiring, but I wouldn't call that a complete rebuild.

Seems to be two issues:
- blowing fuse: check power supply and standby wiring. Check fuse value and type.
- touchy volume: check wiring and pot taper.

I think 1-2 hours work is all it needs.

Robert

[hans-jörg]

I would certainly clean up the wiring, but I wouldn't call that a complete rebuild.



I think 1-2 hours work is all it needs.

Robert

Close to my words, or not

To be honest: there are a lot of blank wires, resistors etc. which are Close together, or to screws and so. With every touch into it you bend something to a wrong place.
I dont se any (ampbuilder) rule fullfilled exept of twisting the filament, but the routing of it (layout!) is .... strage. Only as example.

I apologize, but the layout is terrible and causes only Problems. Please take care and compare it with other layouts to find a solution.
To your pot problem: you will have quit a lot crosstalks, due wireing, wich cause them.
Jm2ct (if you are able to understand my english )

Best,
Hans-Jörg

[dwilkins]

Thanks for all the input. I did order a new power transformer and the builder installed it. That corrected the fuse blowing issue, but there is no sound and he says it probably is the output transformer. My question is that since there were no storms or surges around when the amp first blew a fuse, will a bad output transformer cause a power transformer to go out and/or will a bad power transformer burn out an output transformer? The output transformer was not new, but the power transformer was new.

[dwilkins]

Just heard back from the builder and he says it is fixed, so one caused the other I guess. I will look into rewiring it later if this fixes it for now.

[Phil_S]

Sorry...not meaning to pile on here, but my 2nd or 3rd amateur level build looked better than that. I'm not trying to be picky. Plenty of amps work well with build quality not so tidy. Nevertheless, I don't think it is honest to charge someone to build an amp for that level of workmanship. If you charge money, you need to offer good quality professional workmanship. Just my 2 cents.

I'm glad you have it working now.