no Name tube amp acting strange

[bluespower]

Home made, great sounding amp, with very odd characteristics;

-> but the buzz and hum are outrageous when the volume is on zero....
-> volume increases and buzz/hum when bass pot is in the middle, less when volume and hum when bass is full on or full off.
-> treble acts the same, buzz/hum and volume increase in the middle of the dial, less when full onor full off.
-> there are two toggles that only say "up" and don't seem to have any effect on the tone.

It has ; New tubes, new three prong cord.

opinions are welcome.

[Rob Mercure]

First off my sympathies for your being in Cincinasty - try and avoid the porkopolis blues. Worked for a while there as the Senior Tech at Buddy Roger's Music - strange working with radical right wing conservative rock musicians (still sound like an oxymoron) but BRM treated me well and still employs one of the best guitar repairmen in the country.

Secondly, how old is the amp? Sounds like dried up filter capacitors - is this of such recent build that this seems unreasonable? Generally they last at least 15 years but if someone started with caps that had been setting on a shelf for 15 years then all bets are off.

Hey, did they ever get the Sam Adams brewery going in the old Hudepohl building?

Rob

[bluespower]

Yeah Cinci is moslty right wing reactionaries who fear change. I've been working part time at Willis Music since I retired from teaching (history). Which Buddy's were you employed ?

Inside, it reads, built by Joe Stenger in 1974, and has two 6L6, two 12AX7, treble , bass, volume. there are stand by, on / off toggles, and two other toggles that just say "up".

why does it get louder when the bass or the treble is half on?

When volume is all the way up, and treb and bass all the way down there is the least amount of hum and buzz.

I could send you a picture of the internal wiring though email?

[Béla]

Hi

I'm not sure that this'll help but I noticed that the same thing happens on passive guitars when the shielding of the cable between the output and the amp is not good enough (cheap cable, or unshielded speaker cable). The noise is the highest when the volume pot on the guitar is in the middle. The same problem doesn't happen when I use a better cable, with good shielding.

I think the reason is that the output resistance of your tone stack or the volume knob is the highest when the knobs are in the middle and that makes it easier for EMI and power supply interference to crawl into the signal.
So I suspect the problem is that the wire going from the pots to the next buffer/gain stage is either too long, not shielded well, or too close to the power supply transformer.

[Rob Mercure]

BP,

I worked in the Fairfield store which has been closed I believe. At that time the guitar and electronics repairs were in F'field while the band instrument repairs were in College Hill - they've been consolidates at CH now. Cinty has the odd distinction of being the 2nd "most German" city in the US and one of the most Catholic so my theory is that you wind up with the worst aspects of both (and I was raised Catholic so I understand 1/2 of it). The one thing I truly hated was the predjudice against folks from the Appalachians - they didn't call us "hill billies" as most folks do but "hill jacks." Even though the folks I worked with knew I was proud of my origins/ancestry after a while they would forget and slur someone with "hill jack" - and my blood would boil. Cinty is the only city I'm aware of that passed legistlation making it illegal to discriminate against people of Appalachian origin. Lotsa of bad long institutionalized predjudice coupled with periodic race riots (first one in the 1830s). But you probably know all of this poop - I'm just venting. Lotsa places are down on Appalachians but Cinty is the most blantant.

Hey, ever read a SF novel called "Queen City Blues?" Strange and interesting especially when you know the places where the action happens.

As far as the amp goes (you really didn't post just to get my rant did you <grin>) I still think that replacing the filter caps is the first thing to do and them work out the other issues. Bad filters can cause all sorts of gremlins (good German word) and odd symptoms that make other diagnosis difficult.

Rob

PS: Ever play "corn hole" with your little sister on a Sunday afternoon? <grin>

[bluespower]

Believe it or not, I got in touch with the original builder from 1974. He is going to inspect it tomorrw and says he can get a diagnosis, and fix it for under $45.00.

I'll keep you posted on the results.

I'm transplanted from Chicago, and the "Cornhole Tournament" always concerns me just a little bit.