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Old 21st September 2013, 08:18 PM   #1
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Default Pioneer SX34

Anyone here wo restored a Pioneer SX34 and give me some hints what should be done first to restore this little beauty?

I can hear hum (right side more than on the left) and the hum noise is changing when turning up the volume. On 9h and 12h and 3h is the loudest position...between these positions the hum falls down a little bit and on full volume the hum is louder again and I can hear hiss as well.
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Old 22nd September 2013, 01:51 AM   #2
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Well, the schematic is always a good place to start.

ALL electrolytic capacitors need to be replaced. You're lucky that powering the unit up did no obvious damage.

Replace the noisy OEM voltage doubler diodes with UF5408s. As the volumetric efficiency of electrolytic caps. has greatly increased, a larger value in the doubler stack will be of benefit.

Clean all tube sockets with DeOxit and a periodontal brush. Retension the sockets, with a dental pick.

Along with the superb DeOxit contact cleaner, Caig Labs. also offers a pot. lubricant. That stuff may allow you to salvage the pots., after cleaning with anhydrous isopropanol.

Signal caps. may need to be replaced. The obvious candidates are Soviet surplus K40 PIO and 716P series Orange Drops.

After the "beast" is back in general good form, we can discuss modifications.
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Old 22nd September 2013, 12:00 PM   #3
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Hello Eli!

Thank you for your reply and the schematic.

The receiver was in daily use be the previous owner.
The two diodes and some of the electrolytic caps in the power supply
have been replaced. All the coupling caps and other electr. caps in
the circuits seems (except one coupling cap) to be untouched.

I have ordered some of the Caig's product right now and also 4 new cheap russian OTK stamped output tubes for further testings. Both ecc83 are brand new JJ's
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Old 22nd September 2013, 12:22 PM   #4
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This thread might be worth reading



1967 Pioneer SX-34, 11W, WORTH FIXING???
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Old 23rd September 2013, 10:09 PM   #5
rmyauck is offline rmyauck  Canada
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Yes , best to replace all the PS & coupling caps as you risk All The Transformers and Output Tubes. The hum is the warning!
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Old 24th September 2013, 08:03 PM   #6
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i put in cheap new preamp and power amp tubes. the hum is still there (but not very loud)

strange thing is: with the new tubes in the music on one side is much quieter compared to the other side

i think i should check now some voltages in the power amp section first am I right? (i.e. DC voltages at pin9 of each tube?)
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Old 24th September 2013, 09:01 PM   #7
kevinkr is offline kevinkr  United States
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Playing Russian roulette until you replace all of the supply and coupling caps. You could fry an output transformer or the power transformer, or experience the joy of an exploding electrolytic, and unlike modern devices these are not necessary vented properly and could end up spraying hot chemicals and shrapnel all over the inside of the amp.
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Old 25th September 2013, 08:36 AM   #8
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Quote:
Originally Posted by kevinkr View Post
Playing Russian roulette until you replace all of the supply and coupling caps. You could fry an output transformer or the power transformer, or experience the joy of an exploding electrolytic, and unlike modern devices these are not necessary vented properly and could end up spraying hot chemicals and shrapnel all over the inside of the amp.
you are right. but the amp was in use over the last years. a lot of caps have been replaced by the pre owner what I see. One of the multi section caps is still there. the others have been replaced. I see also some orange drops in the power amp section but there are still some old oil caps left in the rest of the amp in other sections....
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Old 25th September 2013, 02:49 PM   #9
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Quote:
One of the multi section caps is still there. the others have been replaced.
Mine were swollen slightly at the top as if under pressure so replaced them with individual caps. I've seen exploding caps on Youtube.......
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