Sansui 500a restoration questions

Yes, a .047 is the equivalent to the .05. No issue there as long as the voltage ratings are the same.

Haven't used a k75 so I'll let somebody else chime in there.


Thanks Dan, I have to say you have been a big help. Without your thread and parts list I would be really lost and would have asked a lot of questions :)


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One kink I found in nosirrah's unit was the bias trim pots.

One of them fell apart when I touched it.

You may want to source some new ones.

I snagged a bag of 10 off ebay that fit pretty well.



Given the number of caps in that thing, I worked in sections.

I re-capped the amp and power supply (main caps) first and worked into the tuner area later.


Yeah I've heard that. I'm going to attempt to use the ones on there, but I do want to replace them eventually to get easier adjustments.


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Hello everyone,

My parts from Mouser have arrived! Finally. They were supposed to be delivered a week ago but, something happened and they ended up being delivered today. I've decided tonight is a project night and I just picked up some fresh solder, so looks like I'll be getting to work tonight.

As a little contribution, I put together this spreadsheet and I think it might be helpful for anyone doing the 500a restoration. It has all the parts in there laid out in a fairly logical fashion. If you'd like it, PM me your e-mail and I'll send it off to you. AK won't let me upload a spreadsheet.

Next I'll be putting together an installation checklist for me to go by as I put the parts in (and to remember what work I did since I am doing it in phases). blhagstrom recommended to do each section - however, I am really a newb when it comes to reading schematics and I'm not really sure I'm able to separate each part of the unit; the tuner, power supply, pre amplifier, etc. Is this something I should definitely do or should I just tackle each cap from top to bottom?

Oh and before I forget - the 10ohm and 100ohm resistors - what function do these play? I read your thread danimal for that info but it only explained that it should be done. I wasn't sure if this was to swap the tubes to the 6p14s or if it was just a safety measure regardless.. thanks :)
 
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Sorry, I missed this post.

The 10ohm is a cathode resistor. Add that so you can easily measure the bias and help protect the circuit as well.

The 100ohm is a screen resistor. That is purely to help save your system in the event of a screen arc. I didn't actually do that to mine yet. I was gonna have to run a few wires and just didn't get to it. Guess I'm living on the edge.
 
Whew, what a piece of work this is!! This is definitely the most challenging work I've done to date. I've replaced 10 caps and 1 of the big filter caps.. And I've spent about 4 hours so far. You weren't kidding when you said take your time!!


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That's better than me. I would spend an entire evening and only do one little section. Some of those caps in the preamp sections are a real pain in the butt. I lost count on the hours I spent. But it's worth it!
 
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That's better than me. I would spend an entire evening and only do one little section. Some of those caps in the preamp sections are a real pain in the butt. I lost count on the hours I spent. But it's worth it!


I completely agree. When I was warming it up on the Variac I had some speakers hooked up to it and had a chance to hear it. If that is any indicator of what this 'Sui is going to sound like, it will be more than worth it. I managed to get the other filter cap replaced so I think next will be the tricky pre amp section.


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...and I just placed my second order, for all the coupling caps.

I bought mostly K40/K42 caps, except for the 0.33uFs which I bought K75s. No specific reason other than they were cheaper.

No idea how long those will take to come in, but hopefully soon.
 
Okay, some pictures!

The receiver itself is in decent shape and I'm sure you know what a 500a looks like, so I'll just show you my progress so far.

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What I have left is the 2 multi-can capacitors, all the coupling capacitors (12) and then 11 other capacitors. So far I have replaced 16, so I'm getting close to the halfway mark.


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I made a little more progress tonight, replaced the other 50uF/50v and a 5uF/12v..

Unfortunately when I was desoldering the 50uF cap, the leg to the bias trim pot came off and I don't know where it went. So I used part of the lead on the capacitor to hook it back up. Looks a bit crude but should work fine.

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I'm taking a break from this until the coupling caps come in. But I think I can say I'm about halfway done this recap.


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Thanks Dan! It's going pretty smooth so far, and I have to say your thread and parts list is a major help.


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Hi all,

One thing I forgot to ask about. When I was originally powering it up, I found the tuner did not work at all. Zero signal or sound. Not sure why this is.. I get "fuzz" through the speakers but it doesn't pick anything up, and the signal indicator shows the same.

Interestingly there is something written on the box for the tuner section (the metal box) which you can partially see in the second image I posted above.

I'm not totally concerned with making the tuner work.. if it doesn't, I'm not going to really worry about it too much.. BUT.. with that said it would be nice to get it working if it doesn't mean a world of trouble. I have at my disposal, an oscope, DMM, variac, and of course a myriad of tools. My question is - thinking worst case scenario, am I really going to want to bother with this? I'm an amateur when it comes to repairing any sort of electronics besides speakers, so, I would need to rely heavily on someone here at AK.

I'm also wondering if a bad tube could cause the radio to not work at all? I wouldn't think so but, who knows.
 
I have secured the funds for the third and final order! So I will be ordering from AES shortly meaning this project is going to be finished quicker than I anticipated.

I'm going to see if there are some other multi-can caps at AES that will fit the 40uFx2 cap instead, since I've decided I am just going to replace the 40uF/300v capacitor with a cap instead of running it off the multi cap. I like simple so this will work best for me.

Other than that I need 4 new tubes. I'm still looking around for a good source on some cheaper 6AQ8s, but being these are important tubes it might be a good idea to spend some money here.. Either way, it's getting close to the end! :)


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6DT8's are a direct fit replacement for 6AQ8's. Having said that, if there are any 6AQ8's on your Multiplex board, stick with the 6AQ8 there. My 1000A does NOT like 6DT8's there. Oh yeah the reason I mention 6DT8's is you can get 3 or 4 for the price of 1 6AQ8.

Yes The tube can affect the operation of the tuner. If all you are getting is "FUZZ" across the board, check out the 1st 2 tubes on the schematic (usually OSC and Mixer/RF-AMP). Sansui used the 6AQ8 freely so it's a good bet it's one of the 1st two tubes, and shot.

Looks like the 500A has the same front end as the 1000A. 2 6CW4 Nuvistors, and a 6AQ8. Bets are the 6AQ8 is bad. But it's not out of the realm of possibilities that one or the other of the 6CW4's has gone T.U. I'd bet on the 6AQ8 being bad.
 
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6DT8's are a direct fit replacement for 6AQ8's. Having said that, if there are any 6AQ8's on your Multiplex board, stick with the 6AQ8 there. My 1000A does NOT like 6DT8's there. Oh yeah the reason I mention 6DT8's is you can get 3 or 4 for the price of 1 6AQ8.

Yes The tube can affect the operation of the tuner. If all you are getting is "FUZZ" across the board, check out the 1st 2 tubes on the schematic (usually OSC and Mixer/RF-AMP). Sansui used the 6AQ8 freely so it's a good bet it's one of the 1st two tubes, and shot.

Looks like the 500A has the same front end as the 1000A. 2 6CW4 Nuvistors, and a 6AQ8. Bets are the 6AQ8 is bad. But it's not out of the realm of possibilities that one or the other of the 6CW4's has gone T.U. I'd bet on the 6AQ8 being bad.

Ahh okay so it could be a bad tube. Yes, one of the 6AQ8s is bad in there.. that's for sure. I am just going to replace them all anyways with much better ones. Thank you Larry.
 
All right, phase 2 of this project begins, the coupling caps are in.

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