My Sansui 500a restoration

Danimal1969

The Tall Guy
Does anybody know if the two black power resistors are available anywhere? They are the ones next to the output tubes on the top of the chassis.

Thanks!


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Does anybody know if the two black power resistors are available anywhere? They are the ones next to the output tubes on the top of the chassis. If not available new, does anybody have a used set?

Thanks!


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What is wrong with the originals?

You don't want to fit 'used' power resistors anywhere - if you need to replace them, they should be available new from many suppliers.
 
They are melted. Best I can tell, a few of the coupling caps failed and allowed too much current to pass through. Tubes redplated (or so I'm told).

I can't recall the exact values (don't have schematic in front of me) but one of them is an odd value. I've looked at Mouser but can't find anything close to the same size and type. I figured an original that was still in spec would be ok to use.


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Ah I see, well you need to pin down the resistance value and with luck it will state the wattage on the schematic. OR there has been a few questions about another 500a restore recently in this forum. Once you have those pieces of info - you can look on suppliers websites armed with all the info you need - perhaps someone familiar with the 500a will chime in with some supplier part numbers for you?
 
I looked at the 500a schematic One is a R001 1Kohm (15W) and the other is R0002, a 3.6Kohm (30W). The 1K is fairly simple to find in many variants. The 3.6K in 30W will be hard.

You may have to go with a different style casing and mount differently.

1Kohm 20W Ohmite. 588-B20J1K0E (mouser link http://www.mouser.com/ProductDetail/Ohmite/B20J1K0E/?qs=sGAEpiMZZMtlubZbdhIBIKhgRMNKT3W3zVwcsBqRHTE= )

I can't find anything @ mouser in a 3.6K 30W or anything close. Nothing @ digikey either. Closest I could find is to parallel a few. Not 100% sure but I think You could parallel 3 10W 11Kohm to get a 30W 3.666K resistor.
3 of this ohmite would work if so. 588-80F11K
http://www.mouser.com/ProductDetail/Ohmite/80F11K/?qs=3cy5W7uMrzEUg3E9Ucd41Q==
 
The 1K I linked has the pass thru hole, the one you linked has mounting lugs on the end.

If the 3.6 isn't melted, keep using it. I've seen a couple of 500A's with melted 1K's but not any 3.6K's.

If you can't find an intact viable 3.6K you may have to parallel some to get the value.

Can you post pictures of yours???
 
Ok, I don't have mine in house yet...it's on the FedEx truck. :thmbsp:

However, I do have lots of photos. I'll post them at the end of this post. You can see the 1K is melted. Owner said that one output tube was red plating. From what I understand, and more from what I've read here, the likely failed part is one of the PIO coupling caps (the Elna's?) off the output tubes. That of course would draw more current through that 1K resistor.

So my plan of attack is as follows. Replace the spent power resistor, replace the coupling caps off the power tubes, and the caps in the bias section. Fire it up and test it out.

If it runs smooth and no longer red plates, then move on the PS/Filter caps and the rest of those PIO and electrolytics,

As for those 2 big power resistors, the 3.6K one does indeed look good and may be ok. I will need to test it.

My new concern is the 1K resistor because I was told today that that resistor is actually 2 resistors into one housing. A closer check of the schematic shows that is the case. There is also a 2.5K (15 watt) resistor in the circuit and it seems to be all in one case. I guess if I buy an Ohmite 1K I can also buy a 2.5K one and stack them. The sell double stack resistor holders, right? Then just run the wires down into the chassis and it will look pretty good.

As for the photos, here you go:




















 
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I was watching that receiver too. The 500a is on my bucket list, bucket probably get kicked first though. Keep us posted on results. Might be near ultimate in the all tube receivers.
 
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...
 
This is my first. I was thinking that I wanted a Fisher 400 or 500B/C but I just couldn't afford it. And I like the overall cosmetic condition of this. Just gotta fire up the soldering iron.
 
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...


Thank you for the info. I do plan to replace all of them.

What are you seeing that shows the can cap is almost dead shorted?
 
look at the schematic and locate the power resistor on it..

as I recalled, the power resistor is used to separated the can sectioned caps... the cap before the resistor is "almost shorted" to GND.. since those sectioned cap are in 1 can.. you need to replace that can... .... and all the caps..

if you have a capacitor meter, you can verify that bad sectioned cap..

if you simply just put on a new power resistor without replacing the bad can cap. the new resistor will be melting too.
 
I see. Thanks for clarifying. I do have a capacitance meter so I will check them out for sure. Like I said, they were on the list anyway, I just wanted to do it in stages if possible.
 
If you can find a 2.5K 15W (got to 25W on both) in the Ohmite with the center hole, you can series the 1K and the 2.5K on the rod, then wire them up as per the original. The replacements are small enough that you can install them in the original spot and still have alittle room left over.

Audiobee is right. These are interstage voltage dropping resistors. Each one is between 2 of the CAN CAP stages. Unfortunately SANSUI DID NOT number the can caps like everyone else (for example C81A-81B-81C-81D) they treated each stage as a different id number .

R001 is the 1Kohm 15W feeds the #2 grids for the outputs
R002 is the separate 3.6Kohm 30W feed for the FM B+
R003 is the 2.5Kohm 15W feeds the B+ to the amplifier tubes.

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Larry

Absolutely you must change out the coupling caps and all the PIO's in this unit before powering it up again. The SUZUKI PIO's have a really nasty tendency to turn into firecrackers.
 

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Power Resistors for a 500a

That's a good idea to use the two smaller Ohmites. I'll research that, but it should work.

As for the PIO caps, what brand do you recommend for replacements? I know that is highly subjective but I have nothing to go on.

I've worked on several old guitar amps and always used Sprague Atoms for electrolytics and Mallory 150 series for regular caps. Is that a good choice? Obviously, I want to keep it as stock sounding as possible. Is there a more popular choice??
 
PIO's just use a film cap of the same size and 600-630V. I used Orange Drops, Cornelll Dublier DME's in a lot of spots (they are small), and DMT's (a little larger).

As for Electrolytics, Nichicon UPW, UKL, UHE(radials), and TVX(Axials). These will be consistantly 60-70% smaller in size but work quite well in the sansui's. Plus the added bonus of less cost than Sprague atoms. UPW/UHE's for Power supply and non signal path, UKL for Signal path. Get 105*C caps. The sansui makes plenty of heat.

Some advocate the UFW/UKW series. Up to you tho. I don't hear a difference.

As for the can caps, you should be able to stuff the C003 and C004 (20uf/300V) voltage doublers with 470uf/450V caps (Nichicon). As they are single caps, no problem. The Multi-cap's I don't have a clue right now as the numbering is different from most I've seen. Most Co's you can look at the parts list and figure out real quick what you needs are. With the SANSUI you have to look at the actual cans to figure it all out. C-004/005/006/007 MAY be in the same can. If so you can use a 40-40-40-40uf / 525 V from CE (www.tubesandmore.com). But you'll have to figure out the can's on this one. I'm going from memory on the 1000A and comparing that with the 500a which is very similar.

In any event write down the value's/voltages of all the can's The two singles are the voltage doubler and could use some stiffening. (470uf/450v). If you can't find anything in current production that will work, www.hayseedhamfest.com makes custom value/voltage can's. I used them for the 4 section can on my 1000A. Took about 3-4 weeks depending on whether he had that combo in stock or had to have it built to order. TOM is good people and his product is good, prices fair. I get all my can's for my FISHER's from him.

Good luck

Larry
 
- for the single can capacitor, you can use 220us 450V there are plenty of modern replacement available with the same diameter can. it will be shorter.. like this one on the bay "171178532197"
check the diameter with the seller...
- for the multi section can, this one on the bay should work. 380604091699.
you will have to adjust and move the clamp higher . check the hts of this to make sure it will fit your unit. I have use this same one for the 1000a, 1000, 500 and au111. very good quality.
- for the PIO on the output coupling, the Russian military grade is an excellence choice with reasonable price like this one 290822917550.....221303837394
 
Thanks Larry, lots of great info. I realize schematics don't always match so I haven't even considered making a parts list yet. Just starting to wrap my head around the project and get a plan. Hope you stick with me since I know I'll have a lot of questions after I get this thing opened up.

That is a huge jump on the voltage doubler value. What does that increase do to the performance of the circuit? I trust your experience, but I just want to learn as much as I can.

UPW/UHE's for Power supply and non signal path, UKL for Signal path

Why is that? Just a price thing or are they just better for those applications?
 
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