ST-2 Rectifier

[dpm309]

I have a ST-2 8-pin tube shaped metal rectifier that came out of a Gulbranson Organ conversion I did some time ago.  The original schematic called out for a 5U4GB Rectifier tube but must have been replaced some time ago.  I have attached a photo of it.  I can not find a lot of information on-line on this rectifier and was wondering if this would be a good substitute for a 5U4 as I would like to use it in one of my future builds.  Would this give the same performance as a tube rectifier or would it perform more like a modern solid state rectifier?  Is this even worth keeping?

Dan

[phsyconoodler]

They have some on E-Bay for 14.00. I bet it's just a solid state rectifier in a can.I would check into the voltage by using it in another amp and compare it to a 5U4.
  I don't know about the reliability factor.Someone will pipe in I'm sure.

[HotBluePlates]

The "I  R" on the item in your picture stands for International Rectifier.

I can't find info for it, but there is a 75% chance it is an early solid-state replacement for a rectifier tube. Probably solid-state diodes in it, maybe also some resistors to drop the output voltage in a similar way to a tube rectifier.

[Colas LeGrippa]

I am pretty sure it is a real tube. I have a couple of those metal tubes from early 50's like 6L6, 6SN7. The metal shield acts like the one we use on preamp tubes. Correct me if I am wrong

Coca Colas

[sluckey]

It really is a solid state rectifier. Think 40 year old Weber copper cap.   

[dpm309]

Sluckey, that is what I suspected.  The original 5U4 must have been replaced with this some time ago on the organ.  Could I use this in place of a 5U4 in one of my builds to see if it makes any difference in the sound or would I have to do any modifications to the circuit?  When I received the organ amp, all of the tubes were bad with some evidence of red-plating on the power tubes.  Could this have been caused by the rectifier substitution?

Dan

[HotBluePlates]

Could I use this in place of a 5U4 in one of my builds to see if it makes any difference in the sound or would I have to do any modifications to the circuit?

You could probably use it without problem. We just don't know the spec's on the ST-2.

If it were me, I'd clip a voltmeter's leads on the first filter cap after the rectifier (clipped in place, so I don't have to hold them there), then flip on the power while watching the meter, tubes & power supply for smoke. Be prepared to switch the amp off immediately if needed.

When I received the organ amp, all of the tubes were bad with some evidence of red-plating on the power tubes.  Could this have been caused by the rectifier substitution?

Maybe, but only if the output voltage from the rectifier was way too high, as a result of not voltage drop across the rectifier. If this happened, I'd expect to see filter caps failing due to over-voltage. You hadn't mentioned this being the case.

I would think it more likely that if the rectifier failed or caused a problem, that there might have been shorting of the rectifier, which would pop the fuse.

I'm thinking it's a good gamble to at least try the ST-2 out and see how it works in your amp.