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Hi guys, I'm having an odd problem with the tremolo on my Kay. The amp works great for a little 5 watter. I'll turn the tremolo on and sometimes it works and sometimes it doesn't. Once its on, it works fine but then I'll shut it down and it won't work the next time I tun it on. I don't see a pattern. I've recapped every cap, cleaned the controls, cleaned off the oxidation off the tremolo controls and even changed the tube. Anyone have any ideas for this fun little amp?
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JPB beat me to it!
You tried swapping the 12ax7 tubes? Check for loose connections? Make sure the pots are clean? Looks like you did that.
So if the Tremolo is not working (or controls at 0), does the amp still have the same output level?Last edited by TomCarlos; 12-19-2019, 03:43 PM.It's not just an amp, it's an adventure!Comment
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That is the correct schematic, I didn't swap but I replaced with a new 12ax7. Yes, the pot controls were cleaned BUT I wasn't sure how to clean the dual function tremolo ON switch which piggybacks the INTENSITY pot, which i did clean well. Would it help if i posted a pic of that?Comment
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Spray some Caig Deoxit into the switch while turning it on and off with the reducer tube. It may not be a permanent fix but it will probably make it worse if that is indeed the problem. You should be able to read a voltage measurement on one side of the switch while switching it off and on.Comment
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You cleaned everything but did you VERIFY operation of the parts? On other words when the switch is closed, does it measure close to zero ohms? And with the switch open, measure resistance across the speed pot. Does it sweep from about 1 meg down to about zero smoothly? Same with depth control. Does it sweep down to zero and up to 220k?
Remember pots are usually VERY loose to spec, especially in that era, so the 220k could be 200k to 300k, but the question is does it sweep smoothly.Education is what you're left with after you have forgotten what you have learned.Comment
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..."Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." HelmholtzComment
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I am not sure why "R-6" appears three times on the schematic??
In any event, do what Dawg and Enzo recommend. I would also disconnect the pot and test it out of circuit. I'd give the shaft a tug and tap on the pot, to see if you have mechanical issues other than the value (the conductive material within) being in tolerance.It's not just an amp, it's an adventure!Comment
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Sounds good....if it is a bad pot/switch, what criteria do I need to know to replace with another? 1M with switch? Audio or Taper? Shaft length?Comment
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It could be all the above. You may not find an exact replacement. I experienced this with a pot coming out of a Marshall. If you have a problem finding a pot with a switch, some might suggest you drill a small hole and mount a switch. In addition to shaft length, is is round, D shape, Knurled Shaft? If you need to replace it, take a photo and we'll see if we can help you find a replacement.It's not just an amp, it's an adventure!Comment
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Let's find out what the problem is before we look for switches.Education is what you're left with after you have forgotten what you have learned.Comment
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It is an older convention. There would have been a list of parts used. On that list would have been 220k 1/2w resistors, type R-6. So they noted that by each such part. I see four of them. Note the four R-8 at the input. 22k. I see several C-2 ecaps. I don't get the two R-13s one is 10k the other 10 meg, or so it says. That 10 meg doesn't look right to me in general. Note C-4 with small arrows to three of them, and an R-5 with arrows to two of them.I am not sure why "R-6" appears three times on the schematic??
Yes, I find it a lot les useful than just numbering each part.Education is what you're left with after you have forgotten what you have learned.Comment
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The "list of materials used" was all over those ancient tube project books. And check some of the old Gibson schematics - I think they carried all the way through like that til the 60s.Originally posted by Enzo View Post
I feel like the "numbering each part" started with silkscreened PCBs? Earliest I saw it was in a 72 Ampeg GU12. I don't recall if it printed both designation and value on the PCB; I seem to remember it being designation only, so if the part smoked or exploded and you didn't have a schematic you'd be up the creek to guess. First I saw both value & designation was my Prosonic; also an early Vibro-King had both on the eyelet board.
Justin"Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
"Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
"All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -Comment
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[QUOTE=Enzo;545879]You cleaned everything but did you VERIFY operation of the parts? On other words when the switch is closed, does it measure close to zero ohms? And with the switch open, measure resistance across the speed pot. Does it sweep from about 1 meg down to about zero smoothly? Same with depth control. Does it sweep down to zero and up to 220k?
Remember pots are usually VERY loose to spec, especially in that era, so the 220k could be 200k to 300k, but the question is does it sweep smoothly.[/QUO
Clockwise, the ON/SPEED pot measures 166K-.8M. The STRENGTH pot measures 246k-130k. Both were measured in circuit, swept smoothly but neither goes to 0. I tugged on the shafts and both measured stable. I removed the pot and deox'd again, this time clicking on/off a dozen times. It seems to have resolved the problem but I'll try it thru the day & report back.Comment
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