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Where to find cool tubes?

nick parkin

nick parkin

Well-Known Member
greetings all!

I have a bunch of NEC 12AD7 tubes salvaged from a Sony TC500a reel to reel.

Apparently these are some pretty good, low noise tubes.

This got me thinking. What inconspicuous products (reel to reels and other vintage devices) can I find some nice tubes in? Preferable $100 or less? Or even good output transformers?

The TC500a has fantastic output transformers, tubes, and speakers and I doubt anything will be as much of a gold mine as the Sony is, however I wanted to see where I can find some secret gems.
 
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Generally most scopes use good tubes,,, I was at a hamfest last summer, I guy was cleaning out his Dads estate... had a PU truck and a trailer full of old gear... was giving scopes away free at the end of the meet,, couldn't sell em !!!
 
nick parkin said:
What inconspicuous products (reel to reels and other vintage devices) can I find some nice tubes in? Preferable $100 or less? Or even good output transformers? I wanted to see where I can find some secret gems.
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Well, the secret gems are . . . uh, secret. :rolleyes:

Seriously, though, just about anything with tubes and a power transformer (not being run on line voltage) can be a good source of tubes and parts. Console stereos, reel to reels, organs.

That said, my definition of cheap is much less than $100. In most cases I don't think it's worth paying even half that for a handful of used tubes that may or may not test good. And, unless you're already familiar with the equipment, you don't even know what type tubes are in it.

I've purchased two R2Rs in the past few months for a total of $23 but I did some research to find out what was inside first. Since then I came across another one but passed on it. A lot of these are very difficult and time consuming to pull parts from.
 
Older Wollensak RTRs (the kind you may remember from school) have a pair of 7591s nestled under a screen on the bottom.
 
The Akai M8 RTR amps have some good tubes in them, but those are pretty well-known already, so may be harder to find at bargain prices.
 
electronjohn said:
Older Wollensak RTRs (the kind you may remember from school) have a pair of 7591s nestled under a screen on the bottom.
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Well, again, you really need to know which model numbers to look for because not all Wollensaks use those tubes.

I have two of these that I bought many years ago and they both had a pair of 12AB5s as outputs. They are nice tubes but new ones are only about $3 - $4. I assumed the circuit was SE because they were labelled as "stereo" but that was because they had a stereo preamp section which could feed a separate amp.

I considered using the PT and OTs for projects only to discover that the PP OTs have a 1.5k primary, which is useless for most stuff. It shouldn't even be right for PP 12AB5s, which are basically a 9 pin version of a 6AQ5, but I can't say I understand R2R designs.

I was considering using the PT in a preamp but it is only good for 10mA, yes 10. It was used to power the input tubes only and the rest was run off rectified line voltage. So if the preamp only drew 5ma or less per channel, it would be useful but that limits it a bit. And it would not be easy to remove. It might be more useful as a filament transformer since it also has a 12.6v and a 6.3v winding.

The third transformer turns out to be an interstage with a slight stepdown: 1.2 : 1. Maybe I'll experiment with it someday. At least it is easier to remove since it's mounted with screws instead of rivets.

7591s and 7868s, which are electrically the same, are more common in organs, whose transformers are more useful too if you're building from scratch.
 
There's a ovalish screen on the bottom of those Wollensaks...the tube tops are clearly visible as are the markings. I've picked up a bunch over the years...some for as little as a buck or two.
 
nick parkin said:
Do you know any scopes in particular and what types of tubes they have?
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You should try and find and make friends with the local ham radio guys. A lot of them have tube equipment. Also radio stations usually have back up tubes that maybe still in storage even though they don't have any tube equipment. Many times a "score" is pure luck but you need to keep your eyes open.
I used to go to the local Salvation Army which had a weekly auction of items that were broken or unfit for sale in their store. Sometimes tube stuff would be up for auction. Mostly you need time to be able to cruise around and check out leads, garage sales, estate sales. I found that "older" neighborhood estate sales to be more likely to have items of interest.
 
When I was in high school, the electronics shop got in a few old heart monitors as a donation. Each one had some ribbed plate Telefunken 12AX7s inside. Kinda doubt there's too much tubed medical gear left in the wild, but who knows... :idea:
-Adam
 
A guy I know has a couple of Tek 513 scopes in his junk pile. Not a whole lot of useful tubes in them, a ton of 6CB6 tubes but I can't find a cross reference to any audio tubes.
Martin, your going the opposite direction. Most folks here gut scopes for the useful audio tubes.

BillWojo
 
I'd also be inclined to make the argument that a good scope is more useful than a fancy tube or two for audio gear. The build quality in those old Tek scopes puts most hifi gear to shame.
 
I was about a month too late checking Into an old repair shop that had been closed for years. The children of the original owner just tossed everything and sold the building. I knew the owner and he had soooooo many years of stocked parts. He used to do warrenty work for many major brands. At one point I used to deliver parts to him. Lots of good tubes went to the dump.
 
These 513 Tek scopes were in an outbuilding with a leaky roof for years. When I saw them they were outside covered in leaves and debris. Way past fixing them. He said he is digging stuff out of his attic, when it cools down some I'm going to stop by again. Who knows what might be hiding in this old house.

BillWojo
 
fair enough, thats scrap / parts donor condition. It just sort of irks me when people take really nice condition working test gear and scrap it just to filch 2 tubes and the little roll of silver solder.

save the solder out of those, its nice stuff. The ceramic terminal strips are also really cool if you're planning to build an amp. Have to use the special solder though otherwise the contacts get damaged.
 
Before thinking for parts from a Tek you must be fit enough to build like a Tek.
I have seen hundrets of Audio amplifiers looking inside like one of the old Wood Radios.
The heart of old engineering is the mechanical plan how to build a large system, straight forward, short wires, center grounding, easy to service and high in the quality.
Please let me see what you have done with your Tek parts but don`t make me crying.

here is my "Audio Amplifier", made without Tek parts. It runs a dozen tubes.
I made also the plan where you will find in seconds each solding point, each part, each test point.
And it have "wires binding", hand made. The solding stripes are selfmade from epoxy.:)

greetings
Martin

imperator-37.jpg
 
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