Finding Bargains at an Electronic Salvage

[cminor9]

A friend of mine was telling me about an electronic salvage shop in town. I was thinking of going there to see what kind of goodies I could get. Specifically, I was looking for transformers since those are the most expensive parts (and thus what is preventing me from completing my amp build).

I have a good idea of how I can test a power transformer using a AA battery and a multimeter. But any ideas on how one could test an output transformer? Am I just concerned about the ratio? Or are there other things to look for that might not be stamped on the transformer?

[tubeswell]

Hi cminor9

The only way to really test a tranny is with a variac. However a multimeter will tell you quickly whether the windings are open and/or directly-shorted.

Output tranny impedance evaluation is explained here:

http://www.radioremembered.org/outimp.htm

Basically you need variac and you hook it up at a known VAC to the secondary and measure the VAC at the primary to get the VAC ratio - which will be the same as the turns ratio. Then you square the turns ratio to get the impedance ratio.

[black_labb]

you need ac to test a tranny, so the battery wont work.

[Enzo]

Go over to RG's Geofex site and look at his transformer tester.

Expect that you are not the first person to look the place over for audio parts.

Are you expecting parts on the shelf? or is this old equipment to tear down for parts. Output tranaformers tend to serve the same few tube types. 6L6, EL34, 6V6, EL84, and older stuff maybe 7591 or even 8417s. But if you see a transformer on a chassis with 6L6s, then that is likely what it was intended for, and how it would be if use to you. In other words, if I buy a transformer intended for a 100 watt Bassman, I don't need to determine the relative impedances, I already know they suit the 6L6 quad.

[cminor9]

you need ac to test a tranny, so the battery wont work.

Duh, good point! Well, I guess I sure didn't think that one through

[cminor9]

Expect that you are not the first person to look the place over for audio parts.

Are you expecting parts on the shelf? ... But if you see a transformer on a chassis with 6L6s, then that is likely what it was intended for, and how it would be if use to you.

Good points, all. I thought about the first one, but the second point I sure didn't. I guess the "context" would give me a clue how to use the tranny.

As for the first point, I considered that but the thing is since I have gotten into building tube amps, it's amazing how many friends tell me they saw an old tube radio in the alley, they just threw one out, etc. I was thinking many (not all, obviously) people simply think anything with tubes in it is obsolete and therefore junk. Now, maybe the people running an electronic salvage yard would be a bit more saavy, but still...seemed like it was worth checking out.

If I find any bargains, I'll be sure to share the news...

[Enzo]

Oh I love surplus places.

When I was starting out back in the 1950s and 1960s in Washington DC, there were a number of surplus joints. I was a regular. Lots of world war 2 vintage stuff being discarded then. I used to buy old radar terminals and such by the pound. Times have changed, but if you have surplus outlets locally, very cool.

Check these people out, they often have neat stuff:
http://www.fairradio.com/

I think the old tube radio deal is simple. To most folks a radio is a radio. If an old tuber breaks, where can they even take it to get fixed? And if they found me, they wouldn;t want to put the $80 into it for the rebuild it needs anyway.

Here where I am we have Michigan State University - very large school. They have a salvage yard - a depot where anything remotely of value that some part of the school wants to toss, it goes to the yard for sale. Tons of working computers by the way, all hard drives blanked. I find old test equipment including scopes. other electronic odds and ends. Also a great place to buy file cabinets and things like doors.

I think most large schools have similar facilities. Something to check out at your local colleges.

[Don Moose]

I found a really nice vintage stereo in a used furniture store in a ... less affluent part of town ($20 - see thread in Music Electronics section)

There was also a lovely 1930's vintage radio at a Goodwill for $60.

The surplus stores probably know what it is and will be pretty proud of it. It's the places that don't know what's up that are worth visiting every couple of months.

Hope this helps!