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My Sansui 1000A Restoration

As I’m soldering these new caps in I’m concerned that soldering to the old capacitor leads may not be the best way to go. soldering the caps to the terminal lugs may have been possible but I already did most of them. I didn’t want to desoldered all the components from the terminal for risk of heat stressing them, but I’m wondering now how good of a connection will I have now with the way I soldered them in. Good? Bad? Acceptable?
 
J hooking the leads is a old and common practice. So long as you make a good connection its fine. Bend a J in each lead, hook it together, and snug them down with pliers before soldering.
 
gadget73 said:
J hooking the leads is a old and common practice. So long as you make a good connection its fine. Bend a J in each lead, hook it together, and snug them down with pliers before soldering.
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I think I made good j hooks on most of them but didn’t crimp them together as tight as I should have. Hopefully it won’t be an issue.
 
I have a question about the screen stability resistor wiring.

This is how it is wired currently:
B0EBF177-7CBE-4370-9FA0-27AF8BFA1700.jpeg


And this is my understanding of how it should look when it the screen stability resistors are added:
E208283E-D52A-4B09-A390-41A142DBA1CA.jpeg




The lines between pin 4&8 are solid wire and the orange wire is the screen B+

Is my drawing correct? Can I use 20AWG 600V wire for this application?
 
I’m installing the multisection caps but I am not sure if the negative tabs are ok to touch the chassis
A4337D77-A65C-4774-8C72-534BA95D6509.jpeg
I circled one of the tabs in red but there are three others. Three of the tabs have eyelets and one is solid. As it is I’m having some issues mounting the cans properly because the CE can is thicker at the base than the old one so the clamps need to be widened more. This causes one of the tabs from the clamp to shift and I therefore can only screw it in on one side as such:
4199733D-C6ED-424F-A900-9E140378CE74.jpeg

I figured that wouldn’t be an issue as long as I could fold the tabs over on the bottom of the can to fit snug over the chassis, but I am uncertain as to whether this is an acceptable practice.

For reference, the original multisection can cap did not have tabs and does not appear to have been grounded to the chassis but I may be wrong. Here is a picture:
05EE803A-920A-4C11-A80D-752F32554418.jpeg
 
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You wired the screen stab ressitors correctly.

On the original can cap the Ground comes out the bottom as one of the leads, and is connected to a wire that goes to a ground lug. IIRC I got new sized clamps from AES withthe can's and drilled one hole to in chassis per clamp, tapeed and used the existing screws. Then with the cap centered, and clamped, ran the ground wire to the outer lugs (ground to can which is grounded internally).
 
larryderouin said:
You wired the screen stab ressitors correctly.

On the original can cap the Ground comes out the bottom as one of the leads, and is connected to a wire that goes to a ground lug. IIRC I got new sized clamps from AES withthe can's and drilled one hole to in chassis per clamp, tapeed and used the existing screws. Then with the cap centered, and clamped, ran the ground wire to the outer lugs (ground to can which is grounded internally).
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Thank you Larry. So just to be certain, the ground wire that went to the old can cap can be soldered to any of the available outer lugs? Additionally, is it acceptable to fold those lugs down onto the chassis if nothing is connected to them?
 
I was taking resistance measurements on the speaker terminals just now and realized that the speaker on-off switch is problematic. If I toggle the switch to the “off” position and then back to the “on”position, the resistance reading shoots up to the Mega Ohm range. I then have to wiggle the switch around until it finally gets into the right position and the resistance drops down to 1ohm. Is there any way to get inside this switch to clean or repair it?
 
Not sure if the case is riveted or crimped to the base plate. (been quite a few year since I opened mine up. Easiest is to take off the Front cover, and shoot some DeOxit inside (right at the toggle pivot), let it sit for a while then toggle the living hell out of it. Then spray again with Faderlube. It may or may not clear up. Do all of them while you're in there.

On the resistor the 1/8W it looks like a Temp de-rating. 70C is 158*F, while 85*C is 185*F. And they are rated to 250V. TOO LOW for Screens on a 1000A, which run nominally @ 420v. Better off with a 500v rated resistor. Only one with a 500v 1/4w rating I can find @ mouser is this one. Expensive? Sure, but it won't blow due to excessive voltage. https://www.mouser.com/ProductDetail/Vishay-Dale/PTF65100R00BYBF?qs=OcxjBg3m64jn%2Bd5ThUsPBA== $5.11ea 8 in stock at time of writing this.
 
@larryderouin getting the last few parts soldered in tomorrow when the parts arrive. Can you tell me if the 10ohm cathode resistors I posted right above are ok? I already soldered them in but I’m not sure if they can handle the job they’re meant to do. Thank you for your help, Larry.
6167B291-C7CA-4AB4-826B-38F9134CF80E.jpeg
 
Well I installed all the remaining parts and I fired it up. Brought it up slowly on a variac and noticed my left channel output tubes were red plating so I shut it off. It turns out I installed an electrolytic capacitor backwards. I pulled it and installed a new one. The electrolytic capacitor that I installed in the wrong wrong orientation was the one going off the left channel bias pot. ( I originally thought this was a single bias pot 1000A but found another bias pot).

I then brought it up on a variac again with the output tubes pulled and set it at 100V AC and my bias levels on both channels were at about 19.8 VDC.
My Plate voltages were about 438 VDC. I adjusted the Variac to 117 VAC and my plate voltages seemed quite high at around 529 VDC. The schematic shows that plate voltage should be 470VDC.


What could be the reason for this high plate voltage?
 
are the output tubes adjusted to flow any current? -20v with old production 7591 should be pretty near to cutoff, so no current flow. When that happens the supply voltages go way high because its not being loaded down.
 
gadget73 said:
are the output tubes adjusted to flow any current? -20v with old production 7591 should be pretty near to cutoff, so no current flow. When that happens the supply voltages go way high because its not being loaded down.
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I was measuring without the output tubes. My bad. Once I put them in and they started to conduct the plate voltage went down but it’s still somewhat high at around 480VDC with variac set to 115VAC. Tubes are biasing right at around -22VDC. What is the ideal bias voltage for the 7591? Sounded good through speakers playing a record.
 
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Thanks to everyone who helped and encouraged me along the way. I finally finished the rebuild and it sounds great.

I had to order parts like 5 times but it was a good learning experience. This amplifier was a lot of fun to work on because it was bone stock and in excellent condition. The most difficult part of the rebuild for me was probably getting the power supply rebuilt. All of the other caps were fairly accesible. I didn’t align the AM or the FM because it is beyond the scope of my ability at this point in time but at some point in the future I will attempt it if need be.

I hope I never have to part with this receiver as it is the first one I have ever restored and did I mention it sounds pretty dang good too? Well it does and I’m looking forward to doing a lot more listening with it.

Thanks Audiokarmians you guys rock :rockon:
 
Sorry this is late. Been busier than a 1 legged ma at an ass kicking contest.
480V is ok. Mine runs at 478 plate voltage with the tubes biased to 75% of max dissipation. 10% variance from schematic value's is acceptable due to component tolerances.

The 10ohm resistors are fine. You're not getting more than a volt or so across the cathode to ground (if it goes higher than .5v your chances of redplating go up exponentially).

Measure across the 10 ohm resistor on pin 5. You'll get mv. Divide by 10(resistor value) to get ma. Set the bias to read .330v (330mv). Subtract 3ma for the screen dissipation. New value is .300v(300mv). divided by 10ohm = 30ma. This works out to 14.4Watts per tube which is right about 75% 480 x .030=14.4W.
 
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