Arvin 4080T

[miniman82]

Didn't want to post about this till I knew if it was worth saving or not, and as it turns out it's definitely worth some effort.

This was sitting in a pile at the museum, looking rather forlorn. CRT socket nearly ripped off, cabinet had been dropped, it was sort of a mess. But it grew on me the more times I walked past it, it's got this funky little 8" metal cone CRT with a triode gun in it for nerd appeal (8AP4). I made Steve an offer, and took it home.

Tried to variac it, but all that got me was hot capacitors and nowhere near enough B+ to spool up the horizontal section. So I plugged some lytics into it and tried again, this time it showed signs that it was waking up so I decided the chassis was probably salvageable. But that left the question of the CRT...

I can't get a reading on it with my tester no matter what I do since it's a triode and to make matters worse, the socket was about to fall off AND it has a cathode/G1 short indicated by DMM. I carefully removed the base and tried the short clear function on the tester, but it didn't do anything. Knowing that feature simply discharges a capacitor through the short to try and burn it open, I tried the same thing with different value caps up to around 600 volts but nothing happened- it still read 300k ohms on my DMM.

Deciding I had nothing to lose, I went for broke and rigged up a variac, momentary pushbutton switch, and a 1.6kv microwave transformer. I tied the secondary of the transformer to the G1 and cathode on the tube and slowly advanced the variac, then hit the button. Nothing happened the first few times, but eventually I got halfway up the variac dial and got a sharp <snap> when the button was pressed and a flash of light. Hoping the tube wasn't destroyed I disconnected everything and checked with the DMM again, this time I read no short so apparently it had cleared- but that still didn't mean it was good! I could have destroyed the cathode in the process.

I glued the base back on with sensor safe silicone, came back the next day after it dried and soldered the pins. Then I put the tube back into the chassis and let 'er rip. I was rewarded with luma stairs!





It still needs a lot of work- there's some old caps that still need changing, most of the pots are crappy, and it's short on vertical height. Over the next few days I'll see if I can't clear those remaining issues up, hopefully it returns to how it should be. Sure is a cute little bugger.