Great Design

Yes it is : PNP (Ge)

3 year MTBF doesn't mean that it *will* fail in 3 years !

Nice story, anyway.

That's right. It could be much less than 3 years. ;-)

Al

Could be.

I guess these units were stored for a long time before someone found them and decided to threw them away ?

I don't believe they would function continuously at 45W for 50 years.

225 mA? (I know you didn't mean 225,000 amps!) Maybe they were insufficient for the previous owner's needs, or maybe he died. (I once got a spectacular deal on a one-owner car whose owner had presumably died. It was about 15 years old, and almost cherry.)

Cheers! Rich

How you run a bit of power semiconductor has a huge effect on the MTBF (more properly the MTTF) -- derate it so that it runs cooler, and it'll last a lot longer.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

The transistor is rated at 3A max. In this application it was current limited to 225mA. The heatsink is the entire chassis. What is more amazing is that the large filter capacitor has not failed. It may not be effective. I'll have to check the ripple later to see what's what. And that one is easily replaced.

Al

Last year I needed another audio signal generator and retrieved a HP

200AB from my garage, (SN 1651). It was one of the first HP instruments, introduced in 1952 to replace the older 200A and 200B. It had been unused for over fifty years. I was worried about the electrolytic capacitors, and debated about starting it on a Variac to "re-form" them if needed. Running the rectifier at low filament voltage might cause more damage. Instead, I just plugged it into 120 V AC, after replacing the line cord, on which the rubber had deteriorated. (LA smog!?)

It worked perfectly; even the calibration was within a couple of cycles at the 60Hz where I checked it. There's no 60Hz hum in the output, so the filter caps most be OK!

They don't make 'em like they used to!

--
Virg Wall, P.E.

A lot of modern PC PSUs wouldn't last 50 weeks sitting on the shelf before the capacitors start leaking.

.

I hope it didn't smell strongly of industrial cleaners / deodorizers................

Still it wouldn't hurt to replace the paper capacitors. The degrade from the high acid paper that was used, and develop leakage. That model on had one electrolytic.

C6, C9, C10 and C11 will change the bias on the four tubes, causing them to draw more current. That can damage the tubes, and change the value of their plate resistors.

has the manual, if you need a copy. It is in DjVu format.

--
You can\'t have a sense of humor, if you have no sense!

My SN 1651 has a 20microfd and a 40microfd electrolytic in the power supply, with an 800 ohm resistor between them. The supply for the output

6K6 tubes is taken ahead of the resistor.

I did have one half of the 6SN7 driver go bad. I replaced it with another, and for a while thought I'd forgotten all I knew about vacuum tube troubleshooting, as it didn't fix the problem. A little more probing with my trusty VM showed the replacement 6SN7 had the same half bad! I'll check the paper condensers next time I open the case, but the tube currents seemed OK when I looked at them at that time.

Thanks for the reference; I already have a copy.

The first thing I did, when I retrieved the oscillator, was to download the manual. Although it's for SN 7725 and above, it seems to be accurate. I had to go back to WinXP to print out the .djvu format. One of these days, I'll get around to installing a .djvu program for Linux.

The only thing that's missing is the leather handle, which had rotted and broken. It's in the parts list, but probably not available.

--
Virg Wall

Find someone selling custom leather belts at a flea market and see what they want to make a replacement. I knew one who would, but he died a few years ago. For some things you can use the modern replacement suitcase handles. I have a dozen or more of them, but haven't added them too my website yet. They are the right size for some tube testers.

--
You can\'t have a sense of humor, if you have no sense!

I didn't say the guy died INSIDE of it; it had been parked in his driveway for some time; every little nook and cranny on the outside was littered with tree debris, notably the heater/defroster air intake and the gap between the body and bumpers.

But it had that old-guy green plastic thing across the top of the windshield, and several VFW-type stickers in the back window. And the brake pads were so worn that one of the front disks had a huge gouge, and the guy had parked it on a hill, using only the parking gear pawl, like he'd never even used the parking brake.

I drove it from CA to MN one time, with 20-50 oil, in the winter. The next morning, it wouldn't even crank - it was like tar in the crankcase. So, I filled it with 10-40 and drove it for some years until it threw the timing chain. I sold it to some salvage guy for less than the price of its new tires. (I had finally got the front end tie rods, A-arm bushings, Pitman arm, and idler arm all fixed so it had stopped eating tires.) )-;

Thanks Rich