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Old 3rd August 2009, 03:21 AM   #1
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Default Stromberg-Carlson ASR-433

Hello Everyone,

I've had this amp sitting in my basement for about ten years and have decided to put it to use. It looks like everything is original including the S-C tubes. The schematic is conveniently glued to the inside of the bottom cover and is in great shape.

I'd like to use it and possibly restore it but have no idea what to expect. I've read on-line that it's not a good idea to power-up an old tube amp that has been sitting around for a long time.

I know nothing about electronics but am handy with a soldering gun. I replaced the PCB of my Dynaco ST-70 and also did a Curcio mod to my Dyna Pas-3 but that's the extent of my experience.

Any suggestions would be greatly appreciated.

Thanks in advance, BK
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Old 3rd August 2009, 01:34 PM   #2
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It's a well-regarded amp. The coupling capacitors probably are leaky, electrolytics are dried out. The circuit breaker will fall apart if you look at it cross-eyed (I've replaced with a clip type fuseholder underneath - it's tight but I insulated it with Nomex).

If you want to power it up first... put a 100W light bulb in series to limit the current. ANY positive voltage on a grid pin is a sign of a leaky cap, certain death to an output tube...

The big can cap may measure good, but I wouldn't leave the room with it running if it hasn't been replaced. You can disconnect it, leave it in place and put separate caps on a terminal strip underneath.

Instructions and service info are on my Stromberg page: http://www.audiophool.cjb.net/MadeInRoch.html
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Old 24th August 2009, 02:22 AM   #3
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Default S-c asr 433

Tom,

Thanks for your advise. I hope to dig-in to it late this fall. I'll post before and after photos.

Your website is fantastic! A great resource.

BK
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Old 27th September 2009, 03:11 AM   #4
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I went over to my warehouse today to look for something that I could use for as a chassis for quickly building a Simple P-P amplifier. I found a Stromberg Carlson amplifier with no model number. It had places for 10 tubes, but only 3 tubes were present. The output tubes (all missing) were 6BQ5's so the iron would likely be good for a Simple P-P build. I remember dragging this home from a hamfest at least 10 years ago and probably never hooked it up. I brought it home with the idea of using the chassis and iron.

I removed the bottom cover and found the schematic and the model number ASR-333. I remembered this thread because of the model numbers similarity to an old Teletype that I used to own (ASR-33). After visiting Toms web page it became obvious that this was an ASR-333 but someone had added a magnetic phono preamp. I don't know if they copied the ASR-433 design or not. Some capacitors have been added in parallel with the can cap. One looks as old as the amp (an old Sprague Atom) but the other is much newer, so it may have been worked on 2 or 3 times. All other components and circuitry is original (including the coupling caps). The next thing that became obvious is that this amp uses a solid state voltage doubler so the power transformer would not be compatible with the Simple P-P which uses a 5AR4. I have plenty of OPT's so it doesn't make since to part this amp out for its iron to build a Simple P-P.

OK, what do I do with it? Well the answer to that question may become clear if I had a better idea of the amps condition. If the power transformer was toast, I would have no problem gutting the whole thing and using the chassis.

Since this amp had no special meaning to me, and I am inherently impatient, I decided to do exactly what you shouldn't do, just plug it in. Leaky coupling caps (usually the case) will make life short and unpleasant for the output tubes, so I dug up some junk tubes. 4 different tubes made in 4 different countries. Yeah these are a matched quad, honest! I had no idea what to put in the unmarked socket for the added phono stage, so I popped in a pair of 12AX7's.

I was convinced that there would be some smoke, maybe some guts spewing from the electrolytics, or at least a bright red glow, but nothing, no smoke, bang, or fizzle. OK, hook up some speakers and try again. Maybe there will be a loud hum or some snap crackle pop. Nope, just a faint hum. Could this thing actually work? I connected up a CD player, put in a CD, and......YES, it does work, It isn't even distorted. The controls work even the tone controls. I played a few tracks through it and decided that it sounded pretty good, but isn't a Simple P-P, but then my Simple P-P's are made with all new parts and use much bigger OPT's and good tubes. I decided to hook up my turntable. OK, I found something wrong. The phono stage works, but there is some hum and the amp motorboats if the volume and the bass controls are advanced to nearly full. Even in this condition I played a 10 minute track from an Al DiMeola record and it was listenable. After almost an hour of listening the can cap became quite warm. This is bad, very bad. Experience has shown me that it will explode if not replaced. These do not vent, they go bang. The cap is bad, and is possibly the reason for the motorboating.

OK, so now what? I can't justify killing off a working amp just for the chassis. I don't need any more amps since I can't use all of the ones that I have made. Does this amp have a warm place in someones heart, does someone out there jest have to own it. If so email me. If I don't get any interest I will probably list it on Ebay next month. As noted the can cap needs to be replaced or eliminated and the power cord has some bare spots. The front panel is also bent.
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Old 29th September 2009, 07:21 PM   #5
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i have this same amp & i use it daily. it is connected to my computer & i listen to online radio with it. i use a pair of Polk Audio bookshelf speakers with it. all i can say is that this is a real sweet sounding amp.
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Old 30th September 2009, 02:06 AM   #6
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I couldn't bring myself to kill it, so I took it back to the warehouse, but it must find another home sooner or later. Warehouse rent keeps going up so I must again downsize. I plan to cut my rented space in half again by next year. I just took a pickup truck full of electronics to a scrap dealer (no audio stuff).
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Old 30th September 2009, 04:29 AM   #7
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The old S-C stuff does have a following and it might sell well on eBay or not... Last week I managed to sell a pair of very good vintage GE VT4C for just $79, yes you saw that right.. Might not be the best time to sell..
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Old 30th September 2009, 09:39 PM   #8
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I saw the ASR-333 in my warehouse maybe 2 years ago when I first started cleaning out the "stuff". I started watching Ebay and I saw one go for around $60. It was the only one that I have seen on Ebay. I decided that I would rather salvage the iron, which I still may do. There are a few more old amps in there that I haven't got to yet.

Quote:
Last week I managed to sell a pair of very good vintage GE VT4C for just $79
I would have given 80! I try not to look at Ebay since I might be tempted to buy something. I used to keep a list (mostly tube #'s) that I searched for weekly but I kept buying stuff, so I avoid the temptation. VT4C, 211, 845, 833A ASR-333 were all on my list. I have several 833A's that I will sell as soon as I test them (some have been bad). These seem to fetch anywhere from $20 to $100.
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Old 1st October 2009, 12:18 AM   #9
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Quote:
Originally Posted by tubelab.com View Post
<snip>


I would have given 80! I try not to look at Ebay since I might be tempted to buy something. I used to keep a list (mostly tube #'s) that I searched for weekly but I kept buying stuff, so I avoid the temptation. VT4C, 211, 845, 833A ASR-333 were all on my list. I have several 833A's that I will sell as soon as I test them (some have been bad). These seem to fetch anywhere from $20 to $100.
Hi George,
I think you must have evolved a bit beyond me, OTOH you probably have a few more tubes than I do already.. I still have the list, and I still do the weekly search, but sadly at current prices I am not that tempted.. These days I seem to do better at antique radio shows and hamfests.. I guess the novelty of eBay has worn off (or it's the higher fees) but I have the impression that these once apparently doomed shows are doing better. Certainly a lot more fun than bidding on eBay. (Actually that is no fun at all and I mostly look for BINs - so tired of being sniped.)
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Old 1st October 2009, 03:22 AM   #10
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Quote:
OTOH you probably have a few more tubes than I do already
Well, yeah!

I have an old friend that has been in the surplus business since high school. I used to go shopping with him at Homestead Air Force base, back in high school. He would occasionally call me to assist him loading, unloading, or moving "stuff" in exchange for some of what he would have sold for scrap. He now lives about 200 miles away.

What would you do if an old friend called and said "you can have all of the tubes if you help unload the truck?" Well I got a call like that 3 times in a year. One time there was two semi trailers full of "stuff." I wound up with about 100,000 tubes (estimated by weight). Lots of transformers too. Almost all loose, unboxed, and unsorted tubes. About 1/4 of them broken. I had to rent more warehouse space which eventually added up to $6K per year. Well now these "free tubes" have become expensive. Thus the serious effort to eliminate "stuff" including tubes that I will never use in my lifetime. I have been selling tubes and "stuff" by the pound, giving them away, and even trashing a few. I have eliminated enough "stuff" to cut my rent to $4K/year, and I need to be at half of that by the end of the year. I would guess that there are about 25000 tubes left.

This has been a long slow process, and I now realize that it wasn't worth it. At first the tubes were packed in boxes floor to ceiling comletely filling a 10X20 foot by 12 foot high warehouse. It took 2 years before I ever saw the back of the warehouse. I have been through every box, although I have still got about 10000 tubes left to sort.

Quote:
I still have the list, and I still do the weekly search, but sadly at current prices I am not that tempted..
There were only a few things on my list that I wanted to buy. About 6 or 8 years ago I collected about 20 45 tubes, some as cheap as $4. I snatched up every 6LW6 that I saw for under $12. You don't see them for that price anymore.

I agree on the hamfests. Hamfests seem to be dying off, so get what you can when you can. Make the Dayton trip at least once in your life. It does take two days to see it all. Orlando is good too, I try to go every year.
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