Testing 805...

[VE3GZB]

Well, I got a power supply built, at least a start!

I took apart the 300V power supply I made for the previous Xmitter.

I used the big Xformer of the 800V power supply I got for $5 (it had the two 5R4 rectifiers on it). I fabricated a set of mounting brackets out of scrap metal from the farm.

I gathered up 24 diodes, 1N4007, and put them in a bridge. (I don't have 24 resistors 1Meg Ohm, that might be next but so far it doesn't seem to need it). Luckily I had enough diodes! I asked my boss to order more for me and he's got it on order, they're like 11 cents each. no biggie.

I'm using choke input and a good Sangamo 4uF 2000V cap I salvaged over 20 years ago from some military gear. (I lucked out, I thought that was one of the many things I had to leave out west years ago but I didn't! He he!!)

For a bleeder I'm using 4 X 470kOhm resistors + 1 X 10kOhm. I can measure bleeder current across the 10kOhm and with a simple calculation determine my high voltage.

No load high voltage is about 1940VDC. Then I connected up the 805 and I'm using my alligator clip leads to give me the 0.8Ohm to drop 12.6VAC to 10VAC (good enough for now, will do better later on.) Under a load, pushing the 805, my HV drops to about 1500VDC.

I wanted to ground the grid of the 805 to get a better zero bias measurement but I found that I could make the tube oscillate just from G-P capacitance and lead inductance! Scope shows 1 full cycle occurring over 5 divisions at 0.005uS/division. That's 40Mhz!

I have no idea what the HV DC is then because all DC measurements get corrupted with RF and my meter pegs in the negavitve (that's how I suspected I was getting RF in the first place).

But I can leave it oscillating only for so long, just a few seconds. The bench light dims a bit when it oscillates, the Xformer hums and after about 10 seconds the 805's plate starts to glow red! EEK! I won't do that again!

I'm not leaving the 805 on the power supply board, this is just to load the power supply. I'm going to put the 805 onto the Xmitter board, drive it with a 1625.

I still need to find a good high voltage neutralizing cap.

[VE3GZB]

More pics...

[WBear2GCR]

Run the 805 standing up vertically only... you don't want the filaments to sag.

That plate voltage seems a tad high for the 805, but I don't have the book open right now...

                _-_-bear

[VE3GZB]

I downloaded datasheet for the 805.

http://tdsl.duncanamps.com/link.php?target=E2256764

From what I've read, as long as the filament is aligned with a vertical axis, it is permitted to operate horizontally.