OD3 voltage regulator

[rdrgtr]

Does anyone know about this tube?  I was just looking at an old Dukane tube amp and it had one in it.  Does it work like a standard solid state regulator?  If so, what voltage does it regulate, and why is it not used in guitar amps to control excessive B+?

Thanks

[sluckey]

It's a 150v regulator. Max current is 40ma. You could use it to regulate preamp voltages or power tube screens. Not much use for power amp plates though, unless you're gonna use it to drive some big series pass tubes.

[RicharD]

It's like a 150V 40mA Zener diode only it glows all purdy when regulating.  Here's a decent link:

http://mysite.du.edu/~etuttle/electron/elect27.htm#VR

[PRR]

> Not much use for power amp plates though

Actually it was often mis-used to anti-regulate power tube screens.

You want XX power a dollar cheaper than the other company bidding the school sound system.

You use cheap tubes then raise the plate voltage, but if screens are high and loading is bad they conduct way too much and die. Service call, tech-pay, truck gas, bad trip.

Use cheap tubes and high B+, then drop the screens down a constant 150V. Just for example, 400V plates and 400V-150V= 250V screens. On normal load it meets spec. On excess load the high load current sags the B+, say 400V to 320V. The screens now drop to 320V-150V= 170V. This large 250V:170V drop in screen voltage severely limits plate current. The sound is awful but the choked-up tubes don't die.

It makes an amp which will just-barely meet an exact spec, but faint when asked to do anything more. Good for clean un-clipped speech/music systems. Terrible for stage guitar amps which MUST overload GRACEFULLY.

> used in guitar amps to control excessive B+?

What is "excessive"?? Too much is almost enough, we always want MORE!

The wise designer can scale for pretty good power with acceptable tube life for any normal wall-voltage variation. An unwise designer can kill tubes with regulated voltage.

As a regulator, the 0D3 and kin waste more than they deliver.

As long as filter caps are large (to slow B+ variations lower than audio tones) and you are not running at the edge, there is no advantage to regulated power voltages, and real disadvantages.

They also hiss and oscillate.

They are handy in precision meters. My Boonton ACVM's needle might vary 4% for B+ from 130V to 200V. Instead it started from 300V into a big hot resistor onto a gas tube for a steady 150V, only some of that available to the meter amplifier. Since the amp only drew a few mA, this was acceptable.

[FYL]

Here's a decent link:

With some funny ideas such as using a magic eye as a triode...

[rdrgtr]

Thanks guys, I knew you would know.  If I do decide to rebuild the rack mounted dukane power amp in the future I will probably remove it.  I am looking for another one so I can have a set of mono blocks for a nice hi-fi- rig.  So many things to do...so little time.

[eleventeen]

I prolly got 50 of them, JAN NOS, in the garage of doom. They *never* go bad...I wish I could sell or trade them for something but they go pretty cheap and there's very little demand.

I was able to use an 0A3 (the 75-volt version) to advantage in my tube matcher, because the matcher uses a variac to change the power to the power transformer which feeds a voltage doubler. At the time I built it, I couldn't find an acceptable way to derive negative bias reliably or in a way I was completely happy with; After all, I didn't want to put costly 6550's, etc; into the thing and have the bias voltage crap out and fry the tubes. (I anticipated using the matcher to burn in tubes for long periods, as well) So I added another tranny which ONLY does bias. With such a regulator, I have a solid source of -75 volts and can slam any output tube hard OFF, talking ZERO pass current. I always start there and gradually dial up the tube current(s)