My Sansui 500a restoration

1/4w for the resistors, both screens and cathodes.

Yeah you could do that.

See the differences between the 7189 and 7189A

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Power Resistors for a 500a

Couple more questions as I try to finalize my parts orders.

1) the rectifier and bias diodes seem like a good thing to replace. They are marked Sw-05. What would you recommend for a modern replacement? Would a 1n4007 be ok?

2) several of the Suzuki PIO caps are rated at 250v. The ones used as coupling caps I was planning to replace with some k40y's. Would I be okusing 200v rated caps? The 400v are just too big.

Btw, for the output coupling caps I'm going to try Auricaps.
 
Couple more questions as I try to finalize my parts orders.

1) the rectifier and bias diodes seem like a good thing to replace. They are marked Sw-05. What would you recommend for a modern replacement? Would a 1n4007 be ok?

2) several of the Suzuki PIO caps are rated at 250v. The ones used as coupling caps I was planning to replace with some k40y's. Would I be okusing 200v rated caps? The 400v are just too big.

Btw, for the output coupling caps I'm going to try Auricaps.

Danimal1969:
I have a need for your used SW-05 rectifiers...don't cut it too short and destroyed it
please PM me...

thanks
 
Couple more questions as I try to finalize my parts orders.

1) the rectifier and bias diodes seem like a good thing to replace. They are marked Sw-05. What would you recommend for a modern replacement? Would a 1n4007 be ok?
According to my sources the SW-05 is rated for 3A. 1n5406 or 5408 would be better.

2) several of the Suzuki PIO caps are rated at 250v. The ones used as coupling caps I was planning to replace with some k40y's. Would I be okusing 200v rated caps? The 400v are just too big.
NO! NEVER go lower on voltage. You can find K40's in 250V although I haven't seen them too often. You can stuff those 400V in there. I've got 630V .33uf Orange Drops in my 1000A. Like stuffing a Semi into an 8ft culvert pipe. It can be done. OR find some 400V K42's or K73's.
Btw, for the output coupling caps I'm going to try Auricaps.
Just make sure the voltage is same or higher.
 
After 3 or 4 nights of reading schematics, checking component locations, and searching all the vendors, I think I have my final parts list. I already ordered a set of Russian 6p14p tubes and some K40y/k42y caps from fleabay. Next couple weeks I'll put the Mouser and AES orders in.

If anybody is interested, here is what I came up with using Excel.
 

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Am I just asking for trouble using CE cap cans on this amp? At 55C degree rating that just seems crazy on a Sansui, no?
 
Maybe. The 7189's don't put off as much radiated heat as a 7591. Also proximity to the tubes, transformers, and those power resistors has a lot to do with it.

If it were mine, i'd at least stuff the original cans with 85*c if not 105*c caps. Or spend the extra and get some custom made caps from HAYSEED. His are rated to 105*c. This way you get the values/voltages you need in the cap, uprated to today's standards against 1964 standards.

Larry
 
Maybe I'll try stuffing the caps in this amp myself to see how it goes. If that works out well, I'll do the same with the Fisher. If I fail, I'll call Hayseed.

I was just happy that CE actually makes the right caps for this amp. That is the easy solution but I didn't realize the temp issue on them.
 
Finally put my order in for the parts to get this restoration started. Waffled a few times on the cap can thing, as well as the power resistor replacement. Stay tuned to see how it turns out...
 
Yikes!

very common problem for sansui tube design with this age..

your power supply can capacitors.. the one that the "melted" resistor is on. is almost "dead shorted" and that power resistor took most of the "shorted " current pass.

at this age of the receiver, all of the electrolytic caps need to be replace.... the big can caps and all of the grey one...

ALL those PIO (Paper In Oil) capacitors have to go! :yes:

Mark T. :music:
 
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Ok, here is where I'm at. I finished recapping this 500A. See my thread here: http://www.audiokarma.org/forums/showthread.php?t=586236 where I restuffed one of the cans. The others I replaced. I ordered two voltage doublers and I had the correct cap for the other can (it was one I bought for an old Marshall guitar amp and never used it). As you can see, for the electrolytics, I used a variety of Sprague, Nichicon, etc. The PIO caps were replaced with mostly Russian K40/K42Y's. Jumped pins 6 and 9 on each output tube, moved the 47K to pin 2, and added 10ohm cathode resistors as well. Now I can run the 6n14n Russian tubes. Replaced the melted R001/R003 resistor with an adjustable 50watt one. Had to drill one small hole in the chassis since it was longer than the original. I think I got this all done the right way with good quality parts.

I just need to retention and clean the tube sockets, clean the pots, and get it biases. That is what I need help with now. Can somebody walk me through the process of firing this up?

I will leave the output tubes out of it, run it up with my variac, but then what? Where should my voltages be on the output tube sockets (without the tubes)? Once I'm sure that is correct, I will install the tubes. What should I set these too? I will be measuring voltage across the cathode resistors for each tube, correct?

Anything else I should inspect of do *before* putting voltage to this thing?

Thanks,
Dan























 
I would defer to one of our 1000A/500A experts for your specific request - but just to say that looks like a pretty neat job you have done there :thmbsp:

Well Done Dan. ;)
 
I would defer to one of our 1000A/500A experts for your specific request - but just to say that looks like a pretty neat job you have done there :thmbsp:

Well Done Dan. ;)

Thank you sir!

There was more than one occasion that I lost my cool trying to get some of those caps fitted. But I persevered. :D
 
Well, I tried to give this a shot by myself. Without the output tubes installed (all others in place), I turned it on and measured some voltages. On pin #2 of the output tubes I had approx. -16 to -18 volts dc. Pin #6/9 had 350 volts dc. Pin #7 had 447 volts dc. Per the schematic, I adjusted each of the bias adjusters till there was -17 volts at pin #2 of the tubes. By then, I could already feel the two big "log" resistors getting HOT.

Installed the 4 output tubes and fired it back up...

The good news...sounds good!

The bad news...I rechecked the voltages and noted the voltages at pins 6/9 went up to 370volts dc. I checked the current draw of the tubes (across the cathode resistors I installed) and two were running 52ma (52mv), one at 39ma (39mv), and one at 36ma (36mv).

At this point I plugged in my ipod to the AUX input and tested that. Played a song for a couple minutes. No obvious sound issues, but oh yeah, those resistors are so hot I can't touch them!

So, what's my next step? Please help me out guys!!

Dan
 
If your talking about the power resistors-They will get pretty dang hot. On my 1000A you can't even hold your finger on them. I guess from what I've seen --That is normal.
 
Ok, that's fine about the power resistors. Thanks for the heads up.

Still, how do I adjust the bias to be in spec? I know I'm running way too much idle current.

Also, can someone tell me about my tubes. I bought the 6p14p-k tubes with the Russian cppt/star logo. Are those capable of handling the 450 volts I'm tossing at them?

Dan
 
you will be measuring the voltage across the cathode resistors for each tube..

in mili Volt...

what is the cathode resistors that you have installed ??

you have a 4 Pots unit... 1 pot/tube.. that will make adjusting the idle current very easy..
 
I have 10ohm resistors installed.

I understand that each tube has its own adjustment, but I guess I'm a little confused as to what I should be setting them to.
 
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