81 Rectifier

[Diy martin]

Hello Diy members,

I have two pairs of big st style 81 rectifiers and want to use them in my new 5842 dc 45/46 tube amp.
For the powersuply i want to use the Psu designer from Duncan ,but there is no 81 rectifier in the list .
Which rectifier can i choose who comes closest to the 81 .

Regards Martin.

[Witchdoctor]

TAccording to my RC-16, the type 81 is a half wave rectifier with a 7.5 volt 1.25 A filament. it's ratings are PIV 2000 max, Peak plate ma 500 max, dc output 85 ma max. Unfortunately it doesn't list any similar tubes. But At least you can find info on it, I have a Rodgers 2X3, that I can't find any info on.

[SHiFTY]

It is a half-wave rectifier, like a single diode. You will need both of them to build a power supply of course.

So you could possibly think of the pair as equivalent to a type 80, which is like a lower powered 5Y3 I think.

Nice looking things! Just don't go too much above 250V with the voltage and use a small input capacitor, should last for decades.

[Eli Duttman]

An idea: connect 2X 81 filaments in series, energize the series assembly with 15 VAC, and take the B+ from the junction of the 2 filaments.

An 80 is = 5Y3; the base is UX4. Max. value cap. for an 80 is 32 muF. 15 muF. should be safe enough for a pair of 81s, while keeping the rail voltage up.

[jlsem]

I have two pairs of big st style 81 rectifiers and want to use them in my new 5842 dc 45/46 tube amp.

These tubes have a considerably higher resistance (read large voltage drop) than almost any other rectifier. Look for a loss of 80-90 volts in your application. I don't like these tubes because whenever I would rummage through boxes of tubes at hamfests and swapmeets, I'd think that I had found a type 50 and it would always turn out to be a lowly type 80.

John