On Nov 10, 2023, at 3:55 PM, Gordon Gibby <docvacuumtubes@...> wrote:

So I resoldered ?everything back together again as carefully as I could. ?I had damaged the original 47 pF and I tried a couple of ways of replacing it, got confused when another problem popped up and ended up putting in a 47 pfceramic 3 kV

What confused me was a sudden loss of output power and the strangest voltages in the low pass filters I’ve ever seen, extreme high negative voltages like -150. ?

This took quite a while for me to wrap my head around and figure out that the reason the output power had basically disappeared and such incredible voltages were showing up was that L201 47uH which was not even touched, (and showed absolutely no visible signs of damage ) had picked this moment to open up. ?Measured the resistance across it and sure enough it’s an open circuit, how the heck did that happen? ?

I don’t carry things like that but I found a 60 micro Henry on a real core in an old bitx40 I had gotten from somebody— so I cannibalized the unit and got my radio working again!

Now I had what looked like good output, ?and I was able to run 2 spectrums on the problem bands, 15 m and 20 m, and they look real good. ??

<image0.jpeg><image1.jpeg>

How long I’ve been working on this thing! It looks like finally it is going to be really on the air!!

I do hope to change out the insulators on the finals but not sure when I’ll get to that.?

73?

Gordon Kx4z

On Nov 10, 2023, at 16:18, Gordon Gibby via <docvacuumtubes@...> wrote:

?Correction. I do remember that Asher had asked for another 470 ohm resistor to be added, in each of two places. ( You can see them in the photographs. ) Those are right in the area of the D 20 and D 21. Perhaps somehow in the process the diode’s got destroyed? ?Current from the iron? ?

That isn’t too hard to believe.

Gordon

On Nov 10, 2023, at 15:45, Gordon Gibby via <docvacuumtubes@...> wrote:

?Thanks Evan. I went all the way back up to the beginning of my posts and found that I had documented the problem on the very first set of measurements before I had done anything to the radio

<image0.png>

At that point the only thing I had done was open it up to insert the raspberry pi. ? I can’t say what the previous owner might have done but his assertion was that he had never transmitted with it?

He had received with it. ? He seem to think that it worked and I did also; ?when I received it , it appeared to be in fine condition. ??

I looked around for what causes diets to fail shorted and generally it’s too much current. It can be too much in either direction but if you have way too much current then it blows it completely open. The way it gets shorted is to just fuse the silicon with excessive heat. ?

These diode’s are connected to a high capacity 12 V source, but on the other side they really only have a 100 pF capacitor, and several 470 K resistors. ? ?(unless I’m missing something).?

They didn’t blow themselves; ?something caused it. ?

Once upon a time I wrote assembly language code for an Altera 8080 for Minnesota power and light. ?The system would fail after a couple of weeks. I was convinced it was hardware. My boss told me to keep looking. Eventually I found it, a software goof on my part . It took me a long time to figure it out. ?There’s usually a cause when something rare happens. ? I just may not be smart enough to figure it out. ?

But “whatever” would be hard-pressed to destroy those diodes again— with a 470 ohm resistor right there in series with them!!!

Now I have to start the work of putting this whole thing back together again so I can redo all the measurements

Gordon Kx4z?

On Nov 10, 2023, at 15:33, Evan Hand <elhandjr@...> wrote:

?

You need the 12volts when receiving and to start transmitting. ?There is no supply without the transmitter turned on.?

73
Evan
AC9TU