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Capacitors replacement for tube stage
Capacitors replacement for tube stage
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Old 24th January 2019, 07:02 AM   #1
Breezio is offline Breezio  United States
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Default Capacitors replacement for tube stage

Dear community,

I am reviewing an old modification (very poorly executedÖ) that was done on the two tubes modules representing the final stage of my hybrid AMC CVT3030 amp.

I donít have those modules anymore and I am thinking of applying the same mod to the present ones since itís only about replacing four capacitors and one resistor.

I highlighted in the schematic the components that were changed and I am adding also some pictures.

Could you please take a look, possibly indicate if the changes make sense to you and which capacitors I should buy?

For instance, I could not find online the green Russian caps but Iím sure there are good alternatives.

C507: 10k100 white bulky cap, no idea what that is
C502: 3u3 400vdc +/- 3% Mundorf MCAP
R520: 12k
C505 / C506: K71-7 0,1 mk +/- 2% 250B8604 green Russian caps

Thanks a lot in advance

Fabrizio
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Old 24th January 2019, 10:18 AM   #2
Kay Pirinha is offline Kay Pirinha  Germany
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This modification appears to be executed by an overzealous audiophool who didn't really know what he's being doing. Waaay too bulky capacitors with waaay too long leads! I suppose he has solved non existing issues by introducing new ones.
If the original non-polarized caps were film caps, and the polarized ones were 'lytics of good quality and in good shape, I don't see any necessity for altering anything at all. And there's also really no necessity to replace a - most probably - wire wound resistor by a sub-par carbon composite one.
Perhaps you might want to desolder those EL34's and put them in appropriate sockets?
Best regards!
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Old 24th January 2019, 10:33 AM   #3
huggygood is offline huggygood  France
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and while doing so, take the el34 out of their heat sink and put them vertically, turn this ridiculous connector and replace it with wires.
this amp (and for having had more repair) is a nightmare of engineering and is even ridiculous given the size of the box.
if you want to do something good, look at the diagram, put the original components back and change it to remove the sinks and connectors
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Old 24th January 2019, 10:45 AM   #4
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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C502 should be a small electrolytic 4u7F 350volts; Aluminium Capacitors | RS Components
C507 10uF 63v ; Aluminium Capacitors | RS Components
C505/6 100nF 250v ; Polyester Film Capacitors | RS Components
And R520 15k 5W ; Through Hole Fixed Resistors


All samples are to give you the type of component required. Mouser will carry stock.


Don't forget to make good the burning connector, (pin 4) is probably for the heaters and is being over loaded.
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Last edited by JonSnell Electronic; 24th January 2019 at 10:50 AM. Reason: Comment .....
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Old 24th January 2019, 10:45 AM   #5
Eli Duttman is online now Eli Duttman  United States
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C505/C506 are polystyrene. Good stuff, but heat sensitive. This listing is exactly what you're looking for.

The schematic clearly shows (via the + sign) that electrolytic parts are OEM for C502 and C507. C502 is a PSU decoupling part. The silly expensive Mundorf part is (IMO) a bad idea, if only for mechanical reasons. This part should be (electrically) an improvement over OEM, without creating as many problems as it solves. C507 appears to be part of a NFB loop and a film part makes sense, but size and cost operate strongly against that selection. Working with PCBs leaves little "wiggle room". Once again, a high grade 'lytic, like this, may be the best way forward.

The photo suggests that a 10% tolerance carbon composition part is OEM for R520. This part is a definite upgrade (less noise/no drift).

I agree with the installation of sockets suggestion, for the EL34s.
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Old 24th January 2019, 10:46 AM   #6
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Join Date: Dec 2012
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C502 should be a small electrolytic 4u7F 350volts; Aluminium Capacitors | RS Components
C507 10uF 63v ; Aluminium Capacitors | RS Components
C505/6 100nF 250v ; Polyester Film Capacitors | RS Components
And R520 15k 5W ; Through Hole Fixed Resistors


All samples are to give you the type of component required. Mouser will carry stock.
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Old 25th January 2019, 07:39 PM   #7
Breezio is offline Breezio  United States
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Thanks everybody for the suggestions!
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