|10/17/13 - 230vac - first power-on
||Start checking out the interlocks and relays after wiring up
the harnesses to the drawers....
1) found/corrected my rewiring error in the tune-operate switch
2) the AM-CW HV relay was chattering - readjusted contacts & seems
3) brought up the bias/fil supply and adjusted the overload trip relays - found/corrected my rewiring error
4) brought up MV (600vdc & 1200vdc) supply to 1/2 voltage on a 115v variac, then full bore on 230 vac
5) couldn't get any AF in to speech amp - fixed a wire I had pulled loose on the 10-section mode switch - see below
6) hooked up TMC transmitting balun to convert FRT-17 600 ohm balanced output to 50 ohms coax to Bird dummy load
7) checked out the HV supply (up to 1kv) with the 115v variac
|The 10-section mode switch way back inside there
11/24/13 - with help for my buddy K4OZY, we started to tune up in CW mode with full B+....
|TUNE mode - 250ma final cathode current
||TUNE mode - 280 watts output
||TUNE mode - B+ about 2.4 kv
Screen voltage set to 640v per manual
|OPERATE mode - 350 ma
||OPERATE mode --about 600w output
||OPERATE mode - B+ about 3.1 kv
Screen voltage creeps up to 700-720v
|AM Troubleshooting - I see HV arcing on the scope at
both pos & neg modulation peaks.
Shows up on both modulator plates, modulated B+, and modulated RF. Fastest rise times appear on modulator plates.
Can't get above 30% modulation or so before this happens.
I have gradually tried to isolate it.
> Listened - mod xfmr buzzes a little when arcing appears on scope. Is this a direct or secondary symptom?
> Turned out the lights - can't see any blue glows anywhere.
> Disconnected leads to shorting relay for CW operation - no change
> Replaced modulator plate to mod xfmr wiring - no change.
>Disconnected PA screen winding on mod xfmr - no change.
>Disconnected PA plate/screen and connected 10K 300w resistive load to mod xfmr
AHA - no arcing with B+ disconnected from load, but arcing returns if B+ is connected.
>So I tried switching the mod xfmr secondary terminals
(hypothesizing that there is arcing from one modulator plate winding to the nearest (modulated) end of the secondary)
>And got no arcing! See scope photo .
>So next move is to wire the PA, etc. back up and keep my fingers crossed.
||temporary replacement modulator plate leads
||substitute resistive load 10k/300w
|Temporary mod xfmr connections
||HV scope probe on resistive load
||Oh yeah! - 1KV/division