MCI Tube Compressor(now with some gear porn)
- Thread starter pucho812
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Jean Clochet
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Post removed.
pucho812
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testing 1, 2, 3.
today started testing with a 1 K sine wave. unit behaving badly.
If I scope the output the tone is not constant volume it pulsates in volume from big to small and back to big. Fairly quickly I might add. then I tried to adjust the threshold pots. They arced something fierce, then shorted out. the 6aq5 pulsate exactly as the scope is showing.
clearly more work is required. and off I go.
today started testing with a 1 K sine wave. unit behaving badly.
If I scope the output the tone is not constant volume it pulsates in volume from big to small and back to big. Fairly quickly I might add. then I tried to adjust the threshold pots. They arced something fierce, then shorted out. the 6aq5 pulsate exactly as the scope is showing.clearly more work is required. and off I go.
pucho812
Well-known member
to keep people updated, I am waiting on a parts order of a few items I could not get locally.
pucho812
Well-known member
After a kidney transplant, the unit has a clean bill of health. original jan 6386 tubes, jan 6005(6aq5) ad jan 6072 tubes to boot. time to test with music and such.
pucho812
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In time.... I will provide one. maybe a point to point layout and or a pcb as well
dustbro
Well-known member
pucho812 said:
Nice!
pucho812
Well-known member
well so much for the kidney transplant. Put in 2 brand new multican caps a week ago. unit tested well at that time. I could flip it into gr mode and it would come up to 0vu or close to 0 and meter adjustment would do the rest. It sat for a couple of days in the shop with no use. Then from their the intern took it to install in an audio rack and all hell broke loose. The unit would not show anything in gr mode any more. So I took it back down to the shop for work/testing. Then it started to behave as it did previously before the recap, plate voltages were not steady and their was about a 30V difference in measuring the plates between the 2 X 6386 tubes. I can't figure out what happened since other then maybe the caps went bad. I would hate to think so. The original caps were labeled for 500wv and I put in 475VDC caps. shouldn't be a big deal especially since there is roughly 300VDC before the caps.
back at it...
Put in 2 brand new multican caps a week ago. unit tested well at that time. I could flip it into gr mode and it would come up to 0vu or close to 0 and meter adjustment would do the rest. It sat for a couple of days in the shop with no use. Then from their the intern took it to install in an audio rack and all hell broke loose. The unit would not show anything in gr mode any more. So I took it back down to the shop for work/testing. Then it started to behave as it did previously before the recap, plate voltages were not steady and their was about a 30V difference in measuring the plates between the 2 X 6386 tubes. I can't figure out what happened since other then maybe the caps went bad. I would hate to think so. The original caps were labeled for 500wv and I put in 475VDC caps. shouldn't be a big deal especially since there is roughly 300VDC before the caps. back at it...
Sounds like a bad connection somewhere, since moving it made the problem return.
Joe
Joe
MagnetoSound
Well-known member
joe-electro said:
Yes. You will need to check all B+ lines and ground paths for integrity.
Some of those pesky plate resistors may still be suspect too.
I expect the new caps are all just fine.
You may want to "freshen" all the point-to-point connections with a little fresh solder. My "Frank" LA-2A unit is point-to-point and developed some intermittent connections over time. This type of work is what interns are for!
Joe
Joe
pucho812
Well-known member
joe-electro said:
indeed. I am however going to replace to ob2 tube socket as the pins are loose.
pucho812
Well-known member
faulty joint to ground of the ob2. now plate voltages are steady but still 30V difference between plates of the 6386 tubes. I also got gr meter steady as well and working on channel one sans issue. Channel 2 is still faulty. interestingly enough the voltages before a set of resistors is good for both channels. after the resistors it's off but all resistors test good and are with in .1Ω difference of each other. not bad... so hmmmmm.
now before cj says anything I am thinking out loud and not doing a fecking diary or blog of my mci compressor.
now before cj says anything I am thinking out loud and not doing a fecking diary or blog of my mci compressor.
Check the voltage ratings on your coupling capacitors. I had the same issue once with a Sta-Level I rebuilt. Turns out the capacitors looked identical but the voltage rating on one of them was too low and it didn't fail but it leaked at a consistent rate. Took me forever to find it because I was sure the brand new caps were good.
Also measure the voltage across the cathode resistors. From there you can calculate the current through the tubes. Compare that current with the current flowing through the plate resistors by using the same procedure. If the currents aren't the same through each corresponding plate and cathode resistor you've isolated which section of the tube is causing the problem. If it's not a leaky coupling cap it has to be a bad connection, bad tube or bad resistor.
Joe
Also measure the voltage across the cathode resistors. From there you can calculate the current through the tubes. Compare that current with the current flowing through the plate resistors by using the same procedure. If the currents aren't the same through each corresponding plate and cathode resistor you've isolated which section of the tube is causing the problem. If it's not a leaky coupling cap it has to be a bad connection, bad tube or bad resistor.
Joe
pucho812 said:
pucho812
Well-known member
thanks for the advice joe. Will press forward. Might even replace the coupling caps just because some suggested sozo caps for mojo. :
Will press forward. Might even replace the coupling caps just because some suggested sozo caps for mojo. :
pucho812
Well-known member
working it down from big to small. I have arrived at this. If I connected the 6386 on the working channel, voltage between the 2 plates of the 6386 is almost identical. ON the non working channel, If I connect just plate on the second triode, I got around 105VDC. The moment I connect in the plate on the first triode stage, the voltage to each plate on that tube is even but way low. More over both plates are fairly even in voltage on the non working channel. Then this takes me back to one working channel and one non working channel with a 30VDC difference in plate voltages between the 2 X 6386 tubes at one per channel.
I hate tested all the grid resistors, all the surround caps etc and cannot seem to find any issue either in wiring or component failure. I am beginning to suspect that although unlikely, the tube socket for the 63686 tube is shorting out and or has become conductive. it's the only thing else I can think of. i have been through all of it triple checking every thing I can't find anything else wrong.
hmmmmm?
I hate tested all the grid resistors, all the surround caps etc and cannot seem to find any issue either in wiring or component failure. I am beginning to suspect that although unlikely, the tube socket for the 63686 tube is shorting out and or has become conductive. it's the only thing else I can think of. i have been through all of it triple checking every thing I can't find anything else wrong.
hmmmmm?
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