Potting for SS Rectifier

[Klugetone]

Hello all,
Finished building a 5E7 semi-clone. I am using a solid state rectifier and have built several for spares and other projects. Gutted some old octal-base tubes and soldered in two 1N4007 diodes. I want to pot these assemblies for safety and reliability but am unsure of what material might be best. I was thinking some 2-part epoxy or electronics-grade RTV (the non-corrrosive kind). The dielectric properties of the material would be the question. There are no internal resistors so heat should not be much of an issue. Anybody done something like this? I have a very old, (+35 years) octal-based SS 5U4 replacement that was commercially made. It looks exactly like what I'm making and is potted with a very hard, black epoxy type material. Anybody done something like this? Mine look pretty cool with the old tube mfr's logo still on the bases. Tung-Sol, Admiral RCA etc.

Thanks!

Oh, the roll of Kapton tape in the picture is used to seal the unused pin holes in the base when filling with whatever material I pour in there.

[JoeM]

Hello all,
Finished building a 5E7 semi-clone. I am using a solid state rectifier and have built several for spares and other projects. Gutted some old octal-base tubes and soldered in two 1N4007 diodes. I want to pot these assemblies for safety and reliability but am unsure of what material might be best. I was thinking some 2-part epoxy or electronics-grade RTV (the non-corrrosive kind). The dielectric properties of the material would be the question. There are no internal resistors so heat should not be much of an issue. Anybody done something like this? I have a very old, (+35 years) octal-based SS 5U4 replacement that was commercially made. It looks exactly like what I'm making and is potted with a very hard, black epoxy type material. Anybody done something like this? Mine look pretty cool with the old tube mfr's logo still on the bases. Tung-Sol, Admiral RCA etc.

Thanks!

Oh, the roll of Kapton tape in the picture is used to seal the unused pin holes in the base when filling with whatever material I pour in there.

I had a Fender RI Bassman that had a octal plug for the rectifier. Got it open and there were just 4 diodes (2 4007 on each side), no potting at all. Later I built my own the same way from the base of a broken rectifier. Didnt have any problems using it. I dont believe Webers copper caps are potted either. I do think you should use at least 2 diodes for each 'leg'.

[Klugetone]

Thanks!

Thanks Joe!
Certainly adding an extra diode on each side will provide a margin of PIV safety so it is cheap insurance. I believe I will pot mine though for safety reasons. Probably will use the flowable RTV as it is the easiest way to plug that big open base to keep dumb fingers out of. (Don't ask why I feel this is important.).

Thanks again!

[tedmich]

Thanks Joe!
Certainly adding an extra diode on each side will provide a margin of PIV safety so it is cheap insurance. I believe I will pot mine though for safety reasons. Probably will use the flowable RTV as it is the easiest way to plug that big open base to keep dumb fingers out of. (Don't ask why I feel this is important.).

Thanks again!

standard RTV is acetoxy based and you can smell the acetic acid (vinegar) while it cures, this is bad for many electrical components, causing some capacitors to fail. Electrical RTV uses a non-acid chemistry and costs more; I'd use 2 part epoxy IIWY. They won't be able to shed heat very much at all, additions like aluminum oxide and/or silicon carbide help the heat transfer in potting compounds, and don't conduct electricity. If potting without heat transfer help, I'd WAY overbuild using several HV diodes in series.

for a FWB these are great:

1200v/35A $1.80 at excesssolutions.com

[jrfrond]

I am still at a loss as to why you just don't solder the diodes on the back of the rectifier tube socket.

[JoeM]

I am still at a loss as to why you just don't solder the diodes on the back of the rectifier tube socket.

I've done that, but having a SS module you can change to a tube rectifier too.

[Klugetone]

I am still at a loss as to why you just don't solder the diodes on the back of the rectifier tube socket.

Ya' know, that is an excellent question in view of the fact this PT doesn't even have a 5V winding. Guess its because the chassis had a hole for a rectifier tube so I plugged it with a socket. I have a large number of them anyway and part of this exercize is to make a small dent in my parts collection. Thinking was that in the (unlikely) day when I swap PTs and want to use a tube recto, I would be all set. Also goes back to my days of restoring antique home radios and huge communications receivers. Always tried to make any deviations from the original circuit easily correctable. Old habits and all...
--------------------------

So, Joe, your thoughts about why I went modular are right on target. In this case I may just solder them under the socket to keep them cooler.

Thanks to both of you!

Dave