Volume knobs on 12 make no sound

[gtownblues]

My first post. I built a Mojo 5e3 kit and after some small problems with high PT voltages have things in the ballpark. One persistent problem is in the volume pots. They sound fine and sweep fine but about11 1/2 to 12 the volume goes out like a quiet fuzzy short. No popping or any thing, it just dies. At first I noticed it on the Normal channel only then I found the same problem with the Bright channel. Any ideas? Thanks.

[Leroy Beal]

Both of mine do the same thing. One of the quirks of the 5e3 design.

[Chuck H]

Both of mine do the same thing. One of the quirks of the 5e3 design.

Nonsense. It's most likely a parasitic oscillation due to poor lead dress.

[gtownblues]

It doesn't sound like parasitic oscillation, there is no increasing bug like sound. Everything sounds fine up to about 11 1/2 then cuts out from there to 12. I did include the Paul C mod in the build and ran RG147(?) from pin 2 of V2 and connected the hot lead to the right terminal and the coax ground to the left terminal of the Normal channel Vol. pot. It did the same thing with the regular cloth covered wire initially installed.

[Jazz P Bass]

Maybe the pot is bad.
You can check the resistance from the middle leg to the outside leg as you are rotating the pot.
If the reading drops out at 11 1/2, it is bad.

[wyatt]

My '60 Tweed Deluxe did that, it's considered normal for 5E3's. Someone once explained to me why it does that, but it's late and I forgot.

[MWJB]

Alpha 1MA pots per chance?

[Chuck H]

What's wrong with Alpha 1MA pots? Did they fail to catch a bad batch or something? I've used a bunch without any trouble. Well, if you over heat the lugs they may fail. But not just at full up.

[MWJB]

I have quite a few that decline in ohms value near the end of their sweep, so they effectively turn off at the end of their sweep.

[Wittgenstein]

I have noticed the same on a few 1meg alpha pots that I tried in my 5E3 circuit. I have been using alpha pots becuase I thought they felt more smooth then other cheaper pots I have tried, and I don't want to drop the cash on high end ones.

[NorCalTuna]

MWJB I have a similar issue with some alphas I bought! They reduce in resistance at the end of the sweep, and one of them has 16k when it's supposedly all the way up. Nothing as drastic as the OP though-

[Resonator Guy]

This won't add much to the discussion, but I finally got around to testing my Mojo 5E3 at 12 (never played that loud for years) and it works fine. No parasitic oscillation or anything like that, just louder mistakes.

[jmaf]

Well yesterday I trusted an 1M 24mm Alpha pot into a build. Before testing, I soldered its back, etc, did all the work trying to keep it neat and when time to test came the thing seemed to be in random scale, volume would shoot up early like a linear pot, then behave normal up until 6 and simply completely turn on from 7 or 8 till 10. I substituted for another Alpha within the same lot, all went ok....

[gtownblues]

Thanks for all the posts from everyone. I checked and rechecked everything I don't know how many times, then got a bad case of bronchydous(sp?) last week or so. Long short of it laid out no work. Got back to it today check pots in place and got .988M at 0 position and.2K at 12 position. Checked some other Alphas I have and have similar readings. Had high bias voltage with 250 resistor (24.8 V) so changed out to a 330 5% 10 watt and am now getting 23.4V. Plates at 363 and Screen Grids at 340. For some reason (not sure) the pots are acting correctly, interacting and not fritzing out on 12. Sounds great through the '62 P12Q recone I got for $50. Maybe it was raising the bias that affected the preamp section. Thanks for all the help.