help with identifying the cause of preamp problem

[ekirts]

hello
i asked this on another forum but this forum has a dedicated tube section so should have posted here first
anyway the one and only reply i got was take to a tech because of its age tehre's potential elec & fire hazard ect. i know i should
but i just want to identify what could be causing this problem and learn something on the way first and it takes the fun away

i started to have a problem with the tube preamp like 2 days ago until then been using it with no problems
the preamp is SANSUI CA-303 and since i think it still has all the original parts and it being way older than i am i'm not surprised its having problems.
it doesnt help at all that i dont have a schematic of it though
the power amp it was outputting to was also a tube luxkit A3500 not SS
if that makes any difference
the power amp probably needs checking too tho....

the problem is that the preamp works ok but after a while the left channel starts to distort but when i stop the music no noise and sometimes it cuts off completely or goes very quiet that i can only hear the right channel. when this happens there's noise from the speakers when i turn off the preamp. works ok for a while when restated till it repeats. and no i havent been using the preamp since this started btw

i'm thinking it could be the tube itself or one of the capacitors.
there were 0.01μF 'suzuki oil jcp-a' on the pins of the tube socket and rest of the large capacitors were ELNA the oil ones said cp-c i think and few 'elyt' ones which i guess is electrolytic.
there were few elyt which i think is really bad and when i measured across it it measured less than 1V its the one with the rubber thing sticking out seems like its leaking too
damn camera seems to have focused on the big cap
hard to see but see the yellow thing on the cap where its legs come out
Imageshack - dscf9004.jpg
Imageshack - dscf9003k.jpg

.....o wow after looking at it on this it looks REALLY bad..

and when i measured across one of the elna 400WV 3μF rated oil cap it measured around 60V this big one
Imageshack - dscf9005w.jpg

anyway it uses 4 of 12AX7 and 2 of 12AT7 tubes but stupid me forgot to remove the shield thing before taking a photo
Imageshack - dscf9010r.jpg
no idea which tube is used for what or for which channel :S
but they seemed ok

i havent tried swapping the tubes around yet to check if it moves
i guess the screwed up voltage could be a possible cause?

could there be another cause for this
hopefully its not one of the few transistors on that thing.....

the only equipment i have is A/DMM tho lol so that doesnt really help either

dont know why i found this so funny but
Imageshack - dscf9002d.jpg

thanks in advance

[gingertube]

Not much help - BUT....
I have repaired/restored quite a few Japanese Tube Amps. Most of them had those Suzuki Oil Caps in them and in 80% or more the cause for the failure was those caps being leaky. These days when I get an old Japanese amp to restore/repair and I see that it has those caps in it, I just rip them out and replace them without even bothering to test them. Past experience has suggested that more than half of them will be bad and its quicker to just change them all for a modern polypropylene caps than actually go through and test each individual cap.
Cheers,
Ian

[gingertube]

I think you should be able to download the service manual free from here:

Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics

It looks like its in 2 parts so you will need to download both parts.

Cheers,
Ian

[ekirts]

o ..WOW
i searched for it but couldnt find anything on it so
thankyou so much this should help me understand the circuit a lot more

ok i'll definitely replace those caps they looked dodgy but i wasnt sure, too bad the k40y caps my dad had were only rated at 200v :S was the same capacitance too lol

Not much help - BUT....

lol no i think that is important and helpful especially with your past experience them

anyway thank you again for the link to the service manual and your input on your past experience with the suzuki caps

[gingertube]

I did download the service manual (out of curiosity). One of those 2 files is busted but the entire service manual is in the other file. It is a ".rar" file which is a compressed file. I installed 7zip which is freeware from the net and quite successfully used that to decompress the ".rar" back to a pdf.
Cheers,
Ian