Cathode bias 6L6s, Voltage rise(50v) on one power tube when treble is turned up????

[Enzo]

Cosworth, we actually welcome new voices here. Having said that, no one expects anyone to prove what they know instantly. Likewise, sometimes it pays to read a forum for a while to see what voices seem to have something behind them.

As to the whack-it "mentality," would it sound better if I suggested using a rubber mallet - sold in any hardware store - to apply mechanical shock to the chassis to reveal intermittant connections?

Point is that hitting the amp with your hand is about the same as using a rubber mallet, and God gave it to you at birth, you don;t have to go buy it. it is a perfectly legitimate way to expose loose connections. And if you think about it, if the amp won;t withstand a fist-whack, then it most likely won't handle the trip to the gig in the trunk of the car either.


And just for the record, my whack it mentality has been soldering for over 50 years now, and my shop has been authorized my most of the major brands for 25 years. So we both have resumes.

[Chuck H]

Thanks for stopping by

[Steve Conner]

I have an old book, "Radio Receiver Repair and Servicing", or suchlike, from the 1950s. It actually recommends giving the "set" a "smart slap" to help diagnose intermittent faults. It is pretty much standard practice if you suspect a loose connection: poke the wiring and circuit boards, wiggle the tubes if the equipment has any, turn pots back and forth, flip all the switches several times, and yes, give it the odd whack.

I asked earlier whether the amp still showed the same oscillation symptoms when the meter lead was removed from the plate. Obviously you can't measure the original symptom any more, which was a rise in plate voltage. But you can see if the other observations that correlated with the rising plate voltage are still present. (Excessive B+ current draw, odd noises from speaker etc.)

Sometimes one of those electrician's screwdrivers with the neon lamp inside will show up really bad parasitics. If you wave the end with the lamp in it near your circuit, it may light without even touching anything.

If we're looking for resumes, I have designed about a dozen scientific instruments for various companies. We have a guy like Cosworth working for us as a contractor just now, doing PCB layout so I can concentrate on design and firmware. (He uses PADS too.)

[MWJB]

OT is good to go. Glad you got it sorted.

[kg]

It actually recommends giving the "set" a "smart slap" to help diagnose intermittent faults.

i do that with my wife from time to time.

her reaction depends on her mood.

[Enzo]

Depends on if she gets a loose connection.

[Chuck H]

Depends on if she gets a loose connection.

Your not suppose to hit her, uh, it hard enough to cause loose connections. Just hard enough to detect existing ones.

Any one that hits an amp hard enough to cause loose connections needs anger management.

[billyboy]

Mr Cosworth, My apologies if you feel like I ignored your post. I wondered myself if that little fella on the treble control was mucking up stuff and I had pulled it and it wasn't passing 9v battery dc and i put a bit of ac thru it so I assumed it was OK. I know leaky dc can throw off the next stage. Your nomenclature of "gate drive" and "capacitive coupling" sort of bounced off my head and I was having a little trouble with asking an intelligent question. I understand the gist of what Mr. km6xz is saying, people like me not understanding cause and effect, which I agree, i don't always, but I didn't understand if he was talking about your idea with the grid resister or me adding grid resisters and suppression resisters on the 6l6s or because I changed all the e'lytics . One of the main fliter caps was up to 85mf, which you don't want hanging on a rectifier. My local TV tech, retired, former designer at NASA, who has built amps says Why do you want to change those? Guys in the trenches say its maintenance which I agree with. I have had one explode on my bench. You can't tell by looking if they need changed. My tech buddy said adding screen and suppression resisters certainly wasn't a bad idea or I wouldn't have done it just to get rid of parts in the drawer. One thing I know for sure, Fools are not suffered lightly on this forum, as it should be. Thanks for your reply.

[kg]

billy, fwiw, i don't think cosworth was getting riled up at you.