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Olson Stereo FM Custom High Fidelity

Redboy

Redboy

a few good watts
I pulled an Olson Stereo FM tube tuner and amp out of a console this afternoon. The older gentleman selling it said it had been his mother's. He remembered that his father had ordered away for it, and purchased the console separately. Then he had "assembled" it himself, wiring in the drivers, turntable, amp and tuner. The guy was more than happy to help me dismantle the console, and got a kick out of the idea that some kid was going to get some use out of it.

The tuner is full of tubes, mostly Raytheon and Amperex. I see 6BE6, (2) 6BA6, 6AU6, 12AX7a, 12AU7, and oneTele ECC85. Being completely new to tubes, I've no idea what roles these individual tubes play.

The amplifier tubes are EZ81, (2) 6BQ5, and 12AX7a. My Eico amp has essentially the same tubes, but twice as many. I guess I don't understand how what looks like one "set" of tubes produces stereo sound. Can anyone enlighten me? Also, the speaker output is weird. I see three screw terminals only, wired red black green. Am I correct to assume that red and green are left and right positives, and the black is a shared negative? Any ideas on appropriate speaker impedance?

Google's given me very little on Olson stereo equipment, so now I call on the experts out there for more information about my newest toy... Is it worth playing with? Sorry about the crummy pics!
 

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Well, in your third picture, you can see two smallish transformers in the upper left corner: those are most likely the output transformers for single-ended EL84 awesomeness. Expect around 3-5 watts. That big can 'lytic closest to the power transformer deserves some looking into, possibly replacing, as it seems unlikely that it would have survived. Post some shots of the wiring next time, eh?
 
Here's the unders...

Some pics of the guts. I see that there are two small (pea size) blobs of black wax dropped out of the power transformer. They look old, not fresh. Is that okay/normal, or is it hemorrhaging? See how I worry? :worried:
 

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See that black gunk that is coating the PT wiring at the base. That possibly is not a good sign. If it were a cap then not so bad.

Im sure someone else will have a opinion on this one

RC
 
Yeah, definately re-cap the power supplys. The amp is stereo, tube-rectified and single ended. The power trannie leads may be an indication of a problem, but I've seen the same thing in many Fender guitar amps. Sometimes it's just from sloppy assembly by the trannie manufacturer. Remember there are HIGH VOLTAGES inside of tube chassis. Capacitors can store enough energy to cause you harm so, be careful!
 
Aside from billowing smoke and loud explosions, what would indicate total failure of the transformer? How do I know if it's shot, is what I'm asking.

The unit is currently operational. I know I'm not supposed to plug untested vintage amps in, but the seller said he'd used it just the other day. I figured any damage that might have been done would have been done then, and for $10 I'd only cry a little bit if it was smoked, so what the heck?

There's some hiss and static noise in there, though not the dreaded hum. I figure there are plenty of places in the tuner that might be a source of noise, too. Left channel output seems weaker than the right.

Recap?
 
Well, if it powers up okay and the power tannie doesn't get hot, it's more than likely ok. Caps that old are going to be weak though. Don't worry about any ceramic disc or mica caps. SE amps are Class-A and tend to go through tubes rather quick. The weak output could be a tube or again, a weak cap. Take your time and have fun with it!
 
What the heck is this thing?

I'm looking through the amp, trying to determine what needs to be replaced. Can anyone tell me what the red jobbers are between the power tube sockets? They're visible in the third picture of my second post in this thread. There are two of them, each about the size of a postage stamp. There are four numbered leads coming out of them, and the only markings are "848 PC81" - that's it. Are they caps? If so, are they a failure-prone type that need to be replaced? There are no value markings on them, either.
 
These are "integrated circuit" type devices containing resistors and ceramic caps, replacing discrete components in the circuit..usually they are pretty trouble-free.
One trademark for them is a "Couplate".
New electrolytics would be a good idea plus a fuse in the power line (2 to 2 1/2 amp) will protect the power transformer in case of a short.
I would just like to reinforce there are dangerous high voltages here (300 volts) so take appropriate precautions.

Tuner: ECC85 FM RF amp and mixer-oscillator
6BE6 AM convertor
6BA6 (2) IF amplifiers
6AU6 FM Limiter
The other tubes are used in the multiplex circuit (if used) and the audio pre-amp stages.
 
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Chad, thanks for the breakdown of the tube functions in the tuner unit! I don't know a 6BE6 from a 6BA6, so it's helpful. I'm still orienting myself to this language - it's like trying to crack some sort of secret code!

Tom, that link is helpful. Thanks. Good to know that I can probably leave them alone.

I popped the bottom cover off the tuner last night and was happy to see that there aren't really that many caps in there. This one's probably a good introductory project for me. A couple of questions, though...

Can someone recommend a good "one stop shop" for caps? I've had a little trouble finding replacements for some of the bigger electrolytics. For instance, one of the values on the big can is 60 uF 400v. The closest value I've been able to find is 80 uF 450v. Close enough? I've read that I can go as much as 80% higher (seems high!) or 20% lower than the stated uF values, but to never go lower with voltage values.

Where would I look for a schematic? Not much out there on Olson that I've seen.
 
There are 41 listings in the Sams Photofact index for Olson. Most of their tuners had model numbers starting with"RA..." Of course the Olson stereo tuner _I_ have isn't listed...
 
Redboy said:
Some pics of the guts. I see that there are two small (pea size) blobs of black wax dropped out of the power transformer. They look old, not fresh. Is that okay/normal, or is it hemorrhaging? :worried:
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I think that is from the manufacturing process. They dip the entire transformer, without the end bells, or maybe sometimes with them, into the potting coumpound. The transformer dangles by the wire leads when being dipped, and that would explain why the first couple inches of wire have the coumpound on them. So it's likely normal and okay. If the transformer runs not hot, then it should be fine.
 
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