First Homebrew HF power amp

[AD5ZC]

Sorry everyone for the blow-by-blow, and I'm sure this isn't rocket science to anyone. Just hope this helps anyone else looking to re-vitalize 4-400 tubes... I'll get back to actually building the amp very soon...I promise!

73,
-Vern

R U Kidding?
Don't stop.
All the arcing, smoke and explosions...
Fascinating.

[N7GTB]

R U Kidding?
Don't stop.
All the arcing, smoke and explosions...
Fascinating.

LOL!! No problem!

[N7GTB]

The second 4-400A may yet be toast, since during the filament test (with 5VAC, not high voltage), it smokes a bit inside the tube. The smoke terminates as soon as power is removed, circulates out, down and then back inside the anode where it doesn't reappear... Strange thing is, the hi-pot test shows no evidence of gas. I can run it all the way up to 9.99KV DC without any indication of leakage current... Weird...

This tube appears to be unusable. No amount of plate voltage (up to about 1500) would get it to go. The filament continued to burn, but no plate current, zip, nada... There's also a greenish colored residue covering the outer dome of the anode. Not sure what it is, but it wasn't there before I applied power to the filament.

...will put it away for the day when either someone comes up with a slick way to regenerate it, or I decide to build a table lamp... -V.

[N7GTB]

...Just setting out some components to get a feel for layout...

initial_layout-halfsize.jpg

The large white rod in the center is the Delrin form I plan to use to build a plate choke. Also note the lantern globe for chimney. I used it along with the blower on the test fixture. Seems to work pretty well, so picked up a second one today...

[AG6K]

...Just setting out some components to get a feel for layout...

initial_layout-halfsize.jpg

The large white rod in the center is the Delrin form I plan to use to build a plate choke. Also note the lantern globe for chimney. I used it along with the blower on the test fixture. Seems to work pretty well, so picked up a second one today...

 Delrin has too high of a D-factor to use in high-V RFCs -- i.e., it may melt down. A more RF-friendly material is G-10 epoxy/fiberglass tubing. I use 1/16" wall G-10 for HV-RFCs. Example:
http://www.somis.org/PBox_top_inside.jpeg

[N7GTB]

 Delrin has too high of a D-factor to use in high-V RFCs -- i.e., it may melt down. A more RF-friendly material is G-10 epoxy/fiberglass tubing. I use 1/16" wall G-10 for HV-RFCs. Example:
http://www.somis.org/PBox_top_inside.jpeg

Rich,

Is this still an issue if jacketed wire is used? I was planning to wind it with #22 awg (stranded) wire that has PVC insulation... The site I found this used actually calls for teflon coated wire, but I think used smaller gauge wire... Or is this an issue with the Delrin material absorbing RF energy and thus becoming hot?

Thanks,
-Vern

[N7GTB]

 Delrin has too high of a D-factor to use in high-V RFCs -- i.e., it may melt down. A more RF-friendly material is G-10 epoxy/fiberglass tubing. I use 1/16" wall G-10 for HV-RFCs. Example:
http://www.somis.org/PBox_top_inside.jpeg

Rich,

Is this still an issue if jacketed wire is used? I was planning to wind it with #22 awg (stranded) wire that has PVC insulation... The site I found this used actually calls for teflon coated wire, but I think used smaller gauge wire... Or is this an issue with the Delrin material absorbing RF energy and thus becoming hot?

Thanks,
-Vern

[N7GTB]

...sorry for the double post. Not certain why that happened. I only hit submit once...

[AG6K]

Rich,

Is this still an issue if jacketed wire is used? I was planning to wind it with #22 awg (stranded) wire that has PVC insulation... The site I found this used actually calls for teflon coated wire, but I think used smaller gauge wire... Or is this an issue with the Delrin material absorbing RF energy and thus becoming hot?

Thanks,
-Vern

 Vern: RF is not like DC in that it's effect does Not stop with any insulator. IME, teflon insulation will help reduce the heating of the Delrin® but it will not eliminate it since the distance improvement is small. . . I like G-10 because it is easy to work with, strong, and it is quite good around HV-RF. However, G-10 is hellish on saw blades and it is not inexpensive. .
RE: PVC has a high D-factor. Several lower D-factor plastics are styrenes. ABS is very good.

[N7GTB]

Not a lot of progress, but some. More to come...

rf_deck1_small.jpg