Scarce rectifier tubes...

soundmotor

super modified
My re-org of garage / storage / decades old mess continues on the way to a clean & functional shop. I found these stuffed away in one of the recesses. They are a Genalex U52 (5U4G) & U77 (5AR4), Mullard GZ33 (super 5AR4), and an RCA 5690 red base (derated & indirectly heated 5Y3). The 5690 a real odd duck and looks like a fatboy 5692. I do miss the old Sunday morning school cafeteria hamfests...

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The 5690 is a 12.6v rectifier. I guess it was made ultra rugged for missles or aeronautics. I got a handfull of them but not really useful in commercial audio and probably only seen in military. If you were designing your own amps they would look impressive, which is why i bought them. But specs wise they are not as good as 5ar4
 
The 5690 is a 12.6v rectifier. I guess it was made ultra rugged for missles or aeronautics. I got a handfull of them but not really useful in commercial audio and probably only seen in military. If you were designing your own amps they would look impressive, which is why i bought them. But specs wise they are not as good as 5ar4

I'd forgotten that about the filament voltage, what a weird tube. I got it pre-internet and it was a long time before I found out much on it. You are the only other person I've come across that had any. For a long time I looked for another but never found one and stopped. As far as ratings, I'd bet derating applies to the current spec on it like many military electronics items. It may ahandle more and the parameters are not the actual but well less of it. Agree it is a cool tube, maybe in a preamp someday with some 5692s.
 
I have have had 3 or 4 of those RCA 5690s for decades. Lots of cool things can be done with them thanks to separate cathodes. Full wave bridge, tube voltage doubler, etc.

Did I ever do any of this....no! I just hoarded the tubes.

I seem to recall that the WE 412A is set up like this as well.
 
Did I ever do any of this....no! I just hoarded the tubes.

I seem to recall that the WE 412A is set up like this as well.

I spent yesterday grouping all the tubes in one spot and last night at Target putting the unified tote theory into practice. I can't believe the quantity amassed from back when.

Easy to do when they were ~$1 each.
 
Very good point KV. It is knowing how to manipulate what you have to work with that will allow you to get the most out what you are using.
 
What other tube did you uncover?

It's not a huge stash of stuff but I was surprised by some I'd forgotten about. Here's a few, WE 211A & a 102F -

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I don't know what the A1757 is. The 439A is a trochotron, 10-line in switch tube for a decade counter or early computer -

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Yup. Palate cleanser after that disappointment, NU 5Y3G, pre-war w/ ribbed plates. Cryptic chicken scratch runes (mine) from decades back give hope these are OK.

If so, project bound! I've never seen another set before or after these.

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Euro 5y3 GZ30/32 from WW2 era are also very interesting/different construction.
 
I think that you will find that the 5690 is two separate rectifiers in one envelope. Both heaters could be connected in parallel for 6.3 volts.

I don't think that works because the heater resistance is designed to heat based upon the operating voltage. With the two heaters (resistors) in parallel, the cathode temperature will be far below what it should be because each heater is operating at a lower voltage. While the circuit impedance is now correct, the heater temperature is not.

This is a different situation than wiring two heaters (resistors) in series since each drops 6.3 V for a total of 12.6 V. In such circumstance each heater would be at the correct temperature.

String heaters do have issues, of course, because the string forces current through a heater which is already at operating temperature. If the string is small this issue is smaller. This is why string heaters are designed to have identical warmup times, although individual variations can force current through a high-impedance heater, damaging it. Remember, the tungsten has a PTC so its resistance increases as the heater temperature increases. That's why the heater does not have thermal runaway.

So parallel heaters to match the lower operating voltage will likely not work as the heaters will both be too cool for proper rectification.
 
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