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Sansui Model 500: My First Tube Amp

David Weaver

David Weaver

AK Subscriber
Subscriber
I've refurbished several solid state Sansui's (AU-555a's AU-888's, QS-1, QS100, 350 to date) but I never had a tube amp to refurbish; until now. Recently, I acquired a Sansui Model 500 that is in pretty darn good shape at least visually. The only thing I can see that is broken is the AM antenna case. However, I know this is an entirely different animal and I don't want to screw it up. I'm looking for some advice/guidance on how I should approach getting through the first fire up, best practices and things to do and pay particular attention to.
I made a DBT some time ago and I just bought a variac. Any advice would be greatly appreciated!

Model 500_1LR.jpg Model 500_2LR.jpg
 
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A DBT can be used with the variac to power up the unit; note that tube amplifiers should never be powered on without a speaker load. If the unit has Suzuki PIO capacitors, these should be replaced as they have invariably failed at this point.
suzuki pio.jpg
 
Leestereo said:
A DBT can be used with the variac to power up the unit; note that tube amplifiers should never be powered on without a speaker load. If the unit has Suzuki PIO capacitors, these should be replaced as they have invariably failed at this point.
View attachment 2541855
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Ahh, the infamous Suzuki bombs!
I replaced a lot of those in a TEAC reel to reel.
I’ll replace them before first power-up.
What do you think about the combo caps?
 
The combo's (mainly the 3 in the back) are a crap shoot. Most likely the 2 Voltage doubler can's and a 3 or 4 section, with the one in front being a 3 or 4 section. (I'm going on it being a smaller sibling to the 1000A and having a similar topology and 2 years older than the 1000A. Between the tube heat, transformer heat, and running them near max voltage (working voltage or W.V.) they're most likely dried out, like the 1000A. Re-Stuff them with upvalue, upvoltage, 105*C rated low leakage caps (Nichicon UPW, UHE series), or try and match them @ AES (tubesandmore.com).
 
Thanks Larry!
I read and bookmarked one of your threads where you noted a source for the combo cans. (Also about using a dummy load on startup.) I may try stuffing them for the experience, if for nothing else. If that doesn't pan out I'll order them CE Dist.
Here is a pic of the caps in the unit. The pic on the left shows the first two by the power supply, the second pic, the third cap in the back row and the pic on the right is the the cap front center.

M500 Ecaps.jpg

Any guidance on how far I can up-value the capacitance?
 
PIO's on Sansui's were de' Rigeur back in the 60's. Just replace them with equivalent value films but bump the voltages up (if 250V bump to 400v). Orange Drops are generally too large in the bigger voltages (250V and up.) WIMA's, Cornell Dublier DME series, Panasonic ECQE's, and Illinois Yellow Axials (or the generic axials from AES) are fine.

Now for the can's. You could go up to 330 on the doublers and 33uf on the others, but costs come into play here too. With can's I like to stay with the original values, accounting for the change to modern equivalents. So in that vein.......

C35/36. 220uf @350V or 400v (This takes care of Surge voltages and gives you some headroom to account for todays higher wall voltages)
C120/127 & C102/107. 22uf x3 or x4 @ 350 or 400v whichever is higher than marked surge voltage on the original cans.

C35/36. You'll end up stuffing. As they are single caps, Its fairly easy. https://www.mouser.com/ProductDetail/Nichicon/UPH2G221MHD?qs=9yqDzKQ6jsnMpPQ0W/KWJA==

C102/127........ https://www.tubesandmore.com/products/capacitor-ce-mfg-450v-202020-f-electrolytic

C102/107........ https://www.tubesandmore.com/products/capacitor-ce-mfg-475v-20202020-f-electrolytic

OR if you want fancy Chrome can's with custom caps (Nichicon individuals) inside the can, get with Hayseed Hamfest and list the can's. I figure about $ 1-1/2 Ben Franklins for the 4.
 
Thanks again Larry!
No, I don't think I'm gonna go for the Chrome "bling" cans. In fact I was wondering why stuffing caps is done at all, other than to retain an OEM look?
To me, placing multiple encased caps in another encasement is counter intuitive in an already heat intensive environment.
With heat being a major concern for the longevity of the components, it would make more sense to give them as much cooling potential as possible.
With that in mind, I'd like your (and others) opinion on my alternative:
3D printing cap holders to fit in the existing clamp using the following Nichicon caps:
https://www.mouser.com/ProductDetail/647-UPZ2W330MND9
https://www.mouser.com/ProductDetail/647-UPZ2W330MHD

ComboCap.jpg

I would also like your opinion on my over-zealous purchase of the two 470/ 400 caps for C35/36. (https://www.mouser.com/ProductDetail/647-LGR2G471MELC50)
I was on Mouser last night and they only had three left so I pulled the trigger on two of them. If you think they are too large just let me know and I will write them off as a lesson on impatience!

The underside is going to be the challenge. There are no lead insulators on anything and making sure any work I do does not make inadvertent contact with anything else is critical.
I'm going to take my time there!
 
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