My Sansui 1000A Restoration

[angelaudio]

A few weeks ago I started a thread asking for advice on ordering parts for my first ever audio amplifier restoration and some great members of AK heeded my cry for help.

Here we are now a few days into the new year and I have before me the parts necessary to begin the work. I have the single pot version of this amplifier and I intend to modify it to have an individual bias adjustment for all four 7591 tubes after I get it powered up and verify it is fully functional. I was told this unit has not been powered on in over 50 years and though I did verify that the output transformers are good I do want to get a little more familiar with the circuitry as I progress and complete the basic recap.

My first order of business will be to restuff the 200uf can caps with 330uf 400v nichicons, as per Larry D’s suggestion. This cap looks like a multisection cap sitting up on top of the chassis but it has a plastic wrap to it and I will attempt to re-stuff it if possible. Which leads me to my first question, are these types of “can” caps re-stuffable? If so what is the best approach?

 

[capbeefheart]

If there is no metal cans under that plastic I don't they are going to be easy to stuff. Some cut the cans but I like to lift the crimp around the bakelite/phenolic wafer, screw a screw through the vent, heat it up and pull the sections out. Once stuffed just re-crimp the edge down over the wafer and it looks perfect once installed. If there are cans under that plastic I would rip the plastic off and buff/polish the metal, it will look nice. Honestly I don't think those are going to be stuff-able.

Aren't they single sections? I.e. Each one of those is just one capacitor? If that's the case then I would order some snap-in or screw terminals radial types that have a diameter that fits the clamp.

 

[angelaudio]

Can I replace the SW-05 diodes

with 1N4007 GW diodes?
If so, is the silver end of the 1N4007 positive or negative?

 

[angelaudio]

If there is no metal cans under that plastic I don't they are going to be easy to stuff. Some cut the cans but I like to lift the crimp around the bakelite/phenolic wafer, screw a screw through the vent, heat it up and pull the sections out. Once stuffed just re-crimp the edge down over the wafer and it looks perfect once installed. If there are cans under that plastic I would rip the plastic off and buff/polish the metal, it will look nice. Honestly I don't think those are going to be stuff-able.

Aren't they single sections? I.e. Each one of those is just one capacitor? If that's the case then I would order some snap-in or screw terminals radial types that have a diameter that fits the clamp.

They are in fact single section cans. Just desoldered one. Going to inspect and post pics of what I find.

 

[angelaudio]

The single section cans are aluminum underneath the plastic. I’ll appreciate any pointers on re-stuffing as I don’t see any crimps around the base.

 

[capbeefheart]

They are made by taking the black wafer and guts and sliding it into the aluminum can then a machine crimps the edge down and around the wafer holding it all together. That one has a large dimple around it which may make it tough to pull the guts out. The ones I typically do have a shoulder that actually comes out, not in like the dimple so there is a big wide opening to pull the guts out of.

I only stuff multi-section types. If I were in your shoes I'd just replace them with something like these and be done with it: https://www.mouser.com/ProductDetail/Nichicon/LNT2W331MSEC?qs=kArNe9LFxXkZtqNiEQrp2Q==

 

[TriodeLuvr]

That's a doubler supply. The negative lead of one of those caps is elevated to almost +250V. If you don't re-insulate the can after stuffing, be sure the innards are well isolated and can't possibly touch the can.

Jack

 

[angelaudio]

That's a doubler supply. The negative lead of one of those caps is elevated to almost +250V. If you don't re-insulate the can after stuffing, be sure the innards are well isolated and can't possibly touch the can.

Jack

View attachment 2757996

No part of the capacitor should be touching the can or just make sure the leads aren’t touching the can?
Would hot glue be an acceptable way to insulate?

 

[gadget73]

If you know the diameter on those, its very possible that a cap exists that will just fit in the clamp, no messing with re-stuffing required. IMO that would be the better way to go, but I hate re-stuffing cans.

 

[kvflyer]

If it is a single section (I didn't go look at mine), would this work?

https://www.tubesandmore.com/products/capacitor-jj-electronics-385v-220-f-electrolytic

 

[James Cox]

When I did mine I found replacement caps that fit almost perfectly in the old claps. I think I went with jjs mostly and just upped the capacitance like 20% or so to find values that were readily available

 

[nerdorama]

It's been a few years, but I found snap-in style caps of the same diameter that fit the clamps. It's now gone to a friend so I can't measure them.

 

[hogwylde09]

Yes, JJ’s worked in my 500a. Just had a 1000a gifted to me.

 

[angelaudio]

I checked the dimensions of the suggested JJ cap and it is 1/8” too small and the clamp would not close down on it so I came up with a simple solution. I wrapped the 330uf caps with electrical tape at the base like suchA little bit Mickey Mouse but it does the job.

While I’m in this part of the chassis I’m going to go ahead and change out a pair of caps and diodes. I remember reading in another sansui 1000a resto thread about changing the SW-05 diodes out but I can’t remember what replacement was suggested. I have some 1N4007 diodes on hand, can I use those?

 

[TriodeLuvr]

You can't reuse the original cans? That would result in a much more professional repair. Also, it's hazardous to leave the upper doubler cap with the metal exposed on top. At the very least, this should have a circular insulator set on top and the cap covered in heat shrink tubing. The tubing will curl over the top when it shrinks and hold the insulator in place. You can cut the insulator from fish paper without special tools. One more thing - those caps are more than 50% larger in value than the originals. I would change out the two doubler diodes (SD-1A in the schematic above) with 3 Amp fast recovery types to be sure the peak current isn't exceeded.

Jack

 

[nerdorama]

I believe I used UF5408 diodes in mine. You should be able to buy snap-in style caps that will fit the clamps.

 

[angelaudio]

You can't reuse the original cans? That would result in a much more professional repair. Also, it's hazardous to leave the upper doubler cap with the metal exposed on top. At the very least, this should have a circular insulator set on top and the cap covered in heat shrink tubing. The tubing will curl over the top when it shrinks and hold the insulator in place. You can cut the insulator from fish paper without special tools. One more thing - those caps are more than 50% larger in value than the originals. I would change out the two doubler diodes (SD-1A in the schematic above) with 3 Amp fast recovery types to be sure the peak current isn't exceeded.

Jack

I tried removing the old capacitor from the old can but didn’t have any luck, it’s stuck in there pretty good. I was considering drilling it out but the smell and debris from cutting off the end with a grinder was already bad enough so I’m thinking drilling will be worse. Now that you mention it, a few layers of heat shrink tubing around the length of the entire cap with the rice paper on top would look much better.

As far as the fast recovery diodes go, would the 1N4007 fit the bill?

 

[gadget73]

something I can tell you from dealing with electrical tape that is exposed to heat, the adhesive melts out of it and it makes a nasty mess.

and yes that exposed top will shock the BS out of you. Found that one out the hard way on my big Bogens. Not sure if the can is directly tied to negative or if it was just leakage but on that one it got 1/2 B+ right across my hand, all 350 volts of it. It did not feel good.

 

[TriodeLuvr]

rice paper on top

I'm hoping you meant to say "fish paper." Rice paper is very porous and not suitable for use as electrical insulation. Here's an example with a set of three large caps. The cap on the right has more than 700V on the top. The clamps are also insulated to protect against punctures into the cans. If not for the fact this assembly is under a semi-permanent cage, I wouldn't have even trusted fish paper. I sometimes cut circles out of .020" FR4 for this.

 

[angelaudio]

You can't reuse the original cans? That would result in a much more professional repair. Also, it's hazardous to leave the upper doubler cap with the metal exposed on top. At the very least, this should have a circular insulator set on top and the cap covered in heat shrink tubing. The tubing will curl over the top when it shrinks and hold the insulator in place. You can cut the insulator from fish paper without special tools. One more thing - those caps are more than 50% larger in value than the originals. I would change out the two doubler diodes (SD-1A in the schematic above) with 3 Amp fast recovery types to be sure the peak current isn't exceeded.

Jack

Should I stick with the original value? I was under the impression this cap value needed to be increased due to the increased wall voltage of 120V as opposed to 117V of the late 60’s