HH Scott R326 Refurb...Capacitor choice questions

[Marty Socal]

I picked up this unit for $10 at my workplace's surplus sales department. Lights came on but otherwise dead, but in fairly good cosmetic shape, although very dirty and the knobs were hard to turn from all the dried up lube, etc. I figured it would be a cheap, fun project to get going again. Seems to be about 1977 vintage, 35W, IIRC, and made in Korea. Build quality is not up to par with the Pioneer SX-780, but it uses four TO-220 outputs instead of the STK's.

I was able to trace the fault to a bad main power cap that was causing the two internal fuses on the power supply to blow. While testing for power output, I disconnected the +/- 32VDC power output wires to the main amp board, and it stopped blowing fuses and the tuner functions came on (No sound, as the amp is not being powered). I was checking the 13V rails when one of the main caps blew up!!! The other cap was still stone cold, the 32V power was still there. After cleaning out my drawers, I had a couple used Elna 8,000uf caps that I had pulled out of my SX-780 I had recently recapped so i installed them in place of the 4700uf's. Fired it back up and let it run for 15 minutes with the 32V rails to the Amp board disconnected. All seemed OK, so I reconnected the Main Amp board and fired it up again, expecting the main fuses to blow again. Everything but a couple bulbs that are burnt out now worked and the fuses didn't pop!

Anyways, now I want to recap the whole unit.

The question about caps is what would be a suitable replacement in the Nichicon brand:

I followed Mark The Fixer's recommendations when I recapped my two Pioneers, and they worked out great. He recommends UPW for general replacements, and UKL's for the signal path. Pioneer was nice enough to list the preferred types on their units, so it's easy to decide which type to use in which location.

I was able to find the service manual for the R326, the parts list shows no part numbers for any of the capacitors, the only listing is in the schematic itself. As it turns out, every electrolytic cap on all of the boards including the two tuner boards is a Rubycon CE-W, all of them above 1uf are light blue, the few under 1uf are yellow, the main 4700uf caps are grey, if that matters.

Question 1: Should I use all UPW's, or should I use UKL's in the Tone, AM board, FM Tuner board and Eq boards, and UPW's on the amp and power supply boards?

Question 2:Since the difference in cost is minimal, should I just use UKL's in all of the positions?

I'm probably going to order ECQ/DSF series stacked film caps for the 1uf and lower ones. I don't need Nichicon part numbers, just your recommendations on which series would work best, where!

Another Question I have involves the main caps. The factory rating is 4700uf, 35 V, 35mm diameter x 40mm high, flat blade solder lug connections. Plenty of room to go taller. They fit in clamps, suspended over a hole in the chassis. My temporary replacements are the old 8000uf caps from my SX-780. The receiver seems to start OK with these in it, the lights don't dim on startup, etc. There is no protection or soft start relay in it. It does have four 2A diodes for the rectifier bridge.

Question 3:Would it be OK to use a pair of 8200UF 50V caps as replacements for the 4700uf 35V original main filter caps?

They are easy to get in 35mm and I should be able to solder the posts to the "Snap-in" terminals that most of them have. I can find 4700uf replacements if it's better to stick with the stock ratings. Also, there are 5600uf's out there with 35mm diameters, if only a small bump in capacitance is recommended. I'm thinking of using LKG series Nichicons here.

I took some pics of the unit, and as soon as I download them to my Photobucket account, I'll post some of them here, and link the album page. I even have a pic of the blown main cap as it's venting! It looks just like a volcano blowing up, and smelled almost as bad! :yuck:

When I'm done building a recap list, I'll post it here, too.

Thanks!

 

[larryderouin]

Q1. UPW in the Power Supply and Non signal path parts. UKL in the Signal Path.

Q2. Theorectically you could use the ULK's evrywhere. They are low noise.

Q3. Since you have the 8200's from a 780 in there, I'd say it's probably ok WITH A CAVEAT! Get a couple of CL-90's and put them in line before the Primary side of the transformer. This will slow down the INRUSH current as the caps are twice as large. Replacements should be no more than 25%. A 5600uf would be OK @ either 50 or 63V. Most guys would say Hell yeah go for the 8200's but i tend to be conservative when it comes to increasing capacitance and possible stress on components.

I looked for a UKL or UPW in 4700/50 or 5600/50. No such animal in the UPW or UKL. I've usedthe UVR series in my sx424/434/ and 790 without problems. Make sure the caps are rated for 105*C. The cap below is fine for the Filters.

647-UVR1H472MRD6 4700uf 50V leaded. Not snap in's. 25x30mm. lead spacing 12.5mm and you can stuff the original can's.

Larry

 

[Marty Socal]

Thanks, Larry! I'll look into the CL-90's and what it takes to mount them.

In the mean time, here are some pics!

This is what a HH Scott R326 looks like:

Nudie! Top side:

Nudie! Bottom side:

Here's the main filter caps:

The power supply is pretty basic, only two small Electrolytic caps:

The main amp board, only ten E. caps to replace here:

Here's the bottom of the filter caps, before one blew up! I notice now that the top one in the pic has a larger dimple than the other one:

Thar she blows! Pretty stinky, too! :yuck:

The aftermath, looks like the lower one now has an enlarged dimple where the other one blew out. Volts on the cap was +30.5 DC when it blew:

My temporarily substituted used 8000uf 50v caps that got it running, also note that I substituted some generic caps in the power supply:

Here's a link to the whole R326 Photobucket album if you want to see it:
http://s551.photobucket.com/albums/ii475/MartySoCal/Old Radios/HH Scott R326 Receiver/