Surplus store purchase

[E biddy]

I found this interesting thing at our local university surplus store. My initial though was this would make a cool chassis for an amplifier.

]

I opened it up and found this.



I'm thinking I could make a pretty cool amp out of all of this.

The power transformer is a UTC R-112. What I've found online is that it is 350-0-350V@120mA, 5V @ 3A and 6.3V@5A. I checked it out and ran it up to 120v. It measures 400-0-400V. It also has a tap on it that measures 25V?

Tubes

(3) 5814A (substitute for 12AU7?), a 12AX7 and a 12AT7. I tested the 12ax7 and 12at7 in an amp and they both work fine. I don't have anything to check the 5814s in. I'm hoping I could us a 5814 for a phase inverter.

It also has a pair of 6AC7. I can't seem to find out if there is anything I can do with this.

It also has some relay and diode tubes.

It has a bunch of sockets with shields and some switches and pots, 2 chokes (16H 50mA and 2H 200mA.).


I'm thinking I could make something Marshallish, with a pair of EL34s on the output.

I'm also wondering how useful these caps would be. I pulled one and it measured right on.

[nevetslab]

Is the power transformer the one on the right, near the filter cap cans, or the much larger xfmr at the lower left bottom. That one looks like a small Sola constant voltage transformer, but, of course I can't make out the labels. Take a look at the date codes on the cap cans. It's normally a 4-digit code, like 5714 (1957, 14th week), or 6442 (1964, 42nd week) and so on.

What are the two tall tubes near the bottom on the 2nd image? The 6AC7's look to be the two black shielded tubes. Could be a useful find, if you're looking for a chassis & some usable transformers to begin with.

[E biddy]

Good eye! What is this for?



The cap cans are 6340 and 6345. The voltages test correctly, but is there any chance that these are still good after 55 years?

The two tubes are 2050.

[eschertron]

I was just mentioning the 6ac7 in another thread 6AC7
https://music-electronics-forum.com/...ad.php?t=48762
a low power pentode, with questionable audio applications. I have some, haven't tried them out yet.

edit: In my humble IN-experience, I think of constant voltage trannys as overbuilt (way too much iron) transformers that resist voltage changes due to spikes and noise. I could well be wrong though. A typical application is for industrial equipment - think transformer and line reactor in one. A real engineer will correct me here...

edit: So what is this thing? Power supply? RF receiver? Welder?

[nosaj]

I was just mentioning the 6ac7 in another thread 6AC7
https://music-electronics-forum.com/...ad.php?t=48762
a low power pentode, with questionable audio applications. I have some, haven't tried them out yet.

edit: In my humble IN-experience, I think of constant voltage trannys as overbuilt (way too much iron) transformers that resist voltage changes due to spikes and noise. I could well be wrong though. A typical application is for industrial equipment - think transformer and line reactor in one. A real engineer will correct me here...

edit: So what is this thing? Power supply? RF receiver? Welder?

What ever it is, I'm sure Juan has used something similar, he is pretty well versed in off the wall stuff

nosaj

[Enzo]

COnstant voltage transformer is more or less an AC equivalent of a voltage regulator. The mains comes through this thing before hitting the actual power transformer. I forget now, but seems to me the Sola works with a cap.

The row of black caps may measure OK to value, but that tells us nothing about leakage, ESR, or a host of other things. I worry a lot more about leakage than value.

2050 tubes? Isn't the 2050 basically a tube version of a triac? We used them in jukeboxes to trip solenoid coils. A thyrotron:
https://www.radiomuseum.org/tubes/tube_2050.html

How about close up views of the control panel? How are the controls labelled? What does the surplus yard sticker call the thing on the white tag?


I would not count on any of the caps being good, they might be, but I sure won't bet on them.

[E biddy]

edit: So what is this thing? Power supply? RF receiver? Welder?

I'm not really sure.

[E biddy]

[Enzo]

Photovolt still exists, contact them and ask if they have any historical stuff on this old piece.


As to the integrator itself, I am going out on a limb here and guessing this thing is part of a chart recorder. Pen drive suggests the pen dropping to the paper roll so it can record a trail of squiggles, like a lie detector. They have a steady stream of Grass Labs stuff over there, and that is all basic lie detector stuff. They use it for research.

[g1]

What he said ^^^^^.
Used in research lab measurement, biology and chemistry, etc.
google search 'photovolt integraph model 49 integrator' and you'll get lots of hits of old research papers.

[glebert]

If it is a chart recorder that is pretty much an amplifier right there, although probably of very low bandwidth. Moving a pen, moving a speaker, it is all the same thing, right?

[HaroldBrooks]

From my limited Experience, a limited number of can caps can work great after that long a time, for sure.

I have a several amps from the 1950's and 1960's that are still using the large Mallory can caps they came with. I've been told by some that it is an ongoing risk, but there is still good filtration with very little hum, and running another cap in parallel does nothing to improve the filtration, so it seems the old caps are working for now at least, and have been fine for the last 2-3 years of consistent use.

I think is comes down to how the amp was used early on, stored, etc... If the caps were sealed up properly and were used routinely, they may still be good. You can get a cheap ESR meter and check them pretty thoroughly, or just measure the capacitance with a multi-meter.

I use some protective circuits in my amps, like pre-rectifier tube 1N4007 diodes to stop AC to the filter caps in case of a rectifier tube short, and always use the proper size mains fuse. I also use TDK Varistors to stop voltage spikes cold on the incoming AC line, and Varistors after the power tube plates just prior to the output transformer (to eat any DC spikes). I believe that will protect most of the rest of the amp in case of a filter cap failure, and may reduce the risk of any catastrophic cap failure in the first place, but no matter what, there might be some inherent risk in using a very old cap that I don't understand (I am fairly new to this).

I've had bad caps that leaked on some other amps, and just replaced them when the amp started to hum. First perform a visual check to look for any leakage or bulge, and you can immediately cross off any cap that looks the least bit suspicious. If you decide to use the old caps add the protective diodes and Varistors I just described, and make sure you have the right fuse in place.

It's a risk I have been taking for the last few years, and it's worked out quite well for me on three different amps, so I will continue to use those very old caps as they have already proven they work just fine... still after all these years !

[nevetslab]

COnstant voltage transformer is more or less an AC equivalent of a voltage regulator. The mains comes through this thing before hitting the actual power transformer. I forget now, but seems to me the Sola works with a cap.

I never did look up how these Sola CV transformers worked, but found this link on the subject, which opened up one similar to what we see on this chassis:

https://www.antiqueradios.com/forums...c.php?t=133396

One of the quotes on how they work:

"They work by having a resonant secondary loosely coupled to the primary, with the secondary part of the core operating in partial saturation.

The resonating capacitance value is critical, too much or too little capacitance will fail to resonate at the line frequency and the output will not be properly regulated. Often the capacitors are connected to a separate secondary “tank” winding that is closely coupled to the output winding, but is wound for a higher voltage. Be careful with the covers off, there may be far more than 120 V in there! This higher voltage is determined by the economics of capacitor construction. Up to a point, the required capacitors are less expensive as the AC voltage is increased. "

I had installed a 5KVA model downstairs in an old house in the Hollywood Hills, which was being used as a band's recording studio (Hello People, late 70's, Todd Rudgren producing them). One of the nasty characteristics of these Sola Constant Voltage transformers is they are incredibly noisy, and run VERY Hot...no doubt Class C insulation system (180 deg C), but it sure solved the radical voltage fluctuation we had in that old house!

Some spec sheets on their current products:

cvs.pdf
opchars.pdf

[tedmich]

Integrating the area under an (often complex) curve!

Many ways to do this, this one worked with a chart recorder. This one may make umpteen many approximating trapazoids and add up all their areas.... no that was probably later...

The cheap ass way was to carefully cut out the curve and weigh it versus an uncut sheet, worked pretty well even without the special "highly uniform thickness" paper sold by several chart recorder companies (LOL good times!)

[glebert]

Integrating the area under an (often complex) curve!

Many ways to do this, this one worked with a chart recorder. This one may make umpteen many approximating trapazoids and add up all their areas.... no that was probably later...

The cheap ass way was to carefully cut out the curve and weigh it versus an uncut sheet, worked pretty well even without the special "highly uniform thickness" paper sold by several chart recorder companies (LOL good times!)

Had never heard of this technique, but seems pretty smart to me!