LK72B - No volume, then scratchy low volume past noon

ballywho

New Member
Good day,

I've got an LK-72B that, inexplicably, went from fully functional before physically moving it to how I describe in the title, post move: I have no volume before say noon/1 o'clock on either channel, at which point it's just low power/low volume scratchy sound. I've swapped out all tubes and then back again, to no avail. I've also looked under the hood and can't see anything that looks fried. I've connected a voltmeter to the taps and get 0. That said, the voltage (and sound) have come back now, twice! I have absolutely no explanation for this...none.

Any idea what to make of this?

Thanks for your time,
Mark
 
Sounds like dirty controls/switches. Might the tape switch Have gotten jostled during its move.

Works the controls back and forth as well and see if anything comes back.
 
Sounds like dirty controls/switches. Might the tape switch Have gotten jostled during its move.

Works the controls back and forth as well and see if anything comes back.
Yeah, I did plenty of that, again to not avail. Thanks for the quick input, though, Fairlane.
 
Also, as I take it because of the lack of voltage going to the output tubes, they're relatively cool to the touch.
Do you have any spare preamp tubes to put in there?
Yep, did that too. Swapped between Bugle's, Tele's and Raytheon's (Japan). Thanks.
 
Can you say how extensive the move was? Something physical has been bumped or disturbed. When you say under the hood, do you mean from below, and how familiar were you with that view before the move?

Forget the speaker taps. First check that there is no visible fault like a loose wire or suspect solder joint, especially if this was a hobbyist build. Then check the voltages against those on the schematic, working from the power supply to the output tubes. I guess there is an assembly manual available. Sorry if I'm stating the obvious.

And, are the tubes all lighting up?
 
Can you say how extensive the move was? Something physical has been bumped or disturbed. When you say under the hood, do you mean from below, and how familiar were you with that view before the move?

Forget the speaker taps. First check that there is no visible fault like a loose wire or suspect solder joint, especially if this was a hobbyist build. Then check the voltages against those on the schematic, working from the power supply to the output tubes. I guess there is an assembly manual available. Sorry if I'm stating the obvious.

And, are the tubes all lighting up?

Hello, Dandy.

- I moved it from a rack and placed it on a shelf in another room while I tested out a friend of mine's integrated.
- I performed a repair, replacing a couple resistors a year and a half ago, thanks to the members here; I can't see any damage to anything else.
- I can see no visible faults like you state. And per your comments, it was indeed "restored" a number a years ago, per the person who sold it to me. Re: obvious statements - I appreciate any and all ideas/thoughts/inklings/suspicions.
- Yes, all the tubes light up...but the output tubes (though lit) are *relatively* cool to the touch.

Thanks so much.
 
So, I'm sitting here going, "Let me review this thing one more darn time." Well...sheesh...I found the source of the issue (thank gosh). One of the solder joints, although not obvious upon first inspection, from one of my previously replaced resistor's has come loose...to the point that if you were to move it enough one way or another would join or disjoin it. Okee dokee. Out comes the 'gun. See, all I needed was to toss it around with you all for a bit. Thanks for the support, moral and otherwise. :thumbsup:
 
The old dry solder joint trick. Great to hear that you found the culprit. Get yourself some flux liquid or paste for future soldering.
 
If you look at the HH Scott LK-72 in my avatar, it too had a problem. It would pop a few times whilst warming up, maybe for two or three minutes. I was the offender. When I replaced the bias supply filter capacitor, I missed soldering one of the lugs. Guilty as charged...

Glad you found and fixed the problem.
 
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