MM 2x12 HD130 bad low volume/distortion
Just picked up an early grey labeled, Phase inverter tube, 2x12 HD130 combo.......sounded amazing. All original....had a non name PI tube, TAD EL-34b power tubes. Played great at the used music store.....got it home.....sounded awesome for a one hour session! Quiet as a mouse at idle! Play always on low power to save power tube life.
Then, played tonight for about 10 minutes, left the room....came back to play...heard static....scrambled egg sounds too. Now all I get is no volume and LOTS of distorted sound. Also had a the dreaded "scrambled egg sound" thing going occasionally....replaced the PI tube with several none good tubes; same. I do not have spare EL-34's...these are lighting off fine and are not glow platting or looking a funny color...
Any ideas as to what this might be before I take her to a tech?
Bad power tube or tubes(s)? Something in the power amp part of the amp gone bad?
HELP?
Member for
11 years 2 monthsMember for
11 years 2 monthsMember for
11 years 2 months1993 MM silouette Albert Lee
Member for
10 years 2 monthsMember for
11 years 2 months
Member for
11 years 2 monthsMember for
11 years 2 months
Member for
11 years 2 monthsMember for
11 years 2 months
Member for
11 years 2 monthsInteresting, cleaned all the
Interesting, cleaned all the inputs and speaker jack with deoxit.....cleaned power tube sockets with deoxit. Played her again last night....
Started the distorted low volume stuff again, and I turned the master volume to 10, and it cleared up...
Sooooo, Master Volume pot dirty maybe??
Member for
11 years 2 monthsMember for
11 years 2 monthsMember for
11 years 2 monthsWhat else?
Hi Woody, The cleaning process you've done has hopefully made the master volume pot less scratchy. This is a routine maintenance procedure and not always a fix for intermittent problems. It was worth the effort. Intermittent "features" like you describe can be a pain, but they usually can be traced to something mechanical in nature, that is expansion and contraction caused by heating and cooling. So the question is: does the amp work OK when first tuned on and then get nutty after it's warmed up? If yes, start looking for loose solder joints and/or cracked or burnt resistor(s) in the power amp section. Also, if you have a DMM, test the master volume pot. It should measure 1Mohm from end to end. Also verify that it smoothly goes from 0 ohms to 1 Mohm at the wiper when you turn the knob through it's full range. Since it's an Audio Taper pot, the change in resistance won't be linear but it should be smooth and not jumpy. If it tests good, move on to visually checking for cold/loose solder joints. Also check each resistor with your DMM and gently tap them to see if the readings jump around. Hang in there. Let me add one more thing. Do the tests I've described with the power off for safety. -mgriffin
Member for
11 years 2 months
I'm afraid you are going to
I'm afraid you are going to have to get it into failure mode and chopstick it. It sounds electro-mechanical-bad solder joint or corrosion SOMEWHERE. It's in the power section from your description so you are going to have to have it apart, get it to fail and then start tapping components SAFELY with an isolated tool (plastic, wooden dowel-NOT an pencil) and see if you can get it to muck up. If you had a audio probe it might go faster but who knows. With no diagnostic equipment, you are going to have to meatball it. If you don't feel comfortable around 700v, DON'T DO IT. Get a person who is comfortable around these voltages. Knowing it's in the final stages helps some so start tapping the driver connections and later. Mike.
Member for
11 years 2 monthsMember for
11 years 2 monthsMember for
11 years 2 months
COULD be a bad pot with the
COULD be a bad pot with the track worn off. No amount of cleaning will cure that. IF YOU'RE BRAVE, you can short from wiper to input of the master pot and take it out of the equation. That will eliminate it from the process and it will be wide open for the test and see what it does. THEN you would know if it was the pot. Mike
Member for
11 years 2 monthsWell, I am back....this thing
Well, I am back....this thing just kinda worked itself out......Only rarely does that distorted thing when first cutting on from stby to on......rarely!. What I am hearing now is a SUPER CLEAN and wonderful sounding dry channel 1; and on the reverb side, channel 2, has at anything above small venue volume level, just a subtle bit of hair on it.....very, very subtle but it is there to the discerning ear. It sounds great, but not as super clean as channel 1.
Any thoughts about this?
Member for
11 years 2 monthsBack up, still problems with a bit of distorted tone!
Well, I am back....this thing just kinda worked itself out......Only rarely does that distorted thing when first cutting on from stby to on......rarely!. What I am hearing now is a SUPER CLEAN and wonderful sounding dry channel 1; and on the reverb side, channel 2, has at anything above small venue volume level, just a subtle bit of hair on it.....very, very subtle but it is there to the discerning ear. It sounds great, but not as super clean as channel 1.
Any thoughts about this?
Member for
11 years 2 months
Other than tracking it
Other than tracking it through the IC path and HEARING where it starts (or seeing it) the only thing to try in a shotgun format is to try swapping the IC's one at a time to see if it's one of them. OF just blindly replacing them but that MAY not work as one MAY be overdriven by a bad cap shorted or open. Using a audio tracer would be my choice. Personally, I like a little grit. It gives you the best of both worlds. By the way, does it change gritty level with the reverb or without and does it CHANGE as you add reverb? Mike.
Update, turned her on this
Update, turned her on this morning....now playing fine......
Help? Any ideas?