Thank you for the replies. I had some time to circle back to this today and
checked a few things.
- With the tubes removed, it looks like they have no shorts but the grids
measure ~0 ohms (maybe it’s too low for my meter?). Is that expected?
- Checking the filament transformer I see (All are while in circuit with the
power switch off)
BLK-BLK/YEL = 3.2 ohms
BLK/GRN-BLK/RED = 4.1 ohms
RED-RED = 10 ohms
GRN-GRN = 0 ohms
GRN/YEL-GRN = 0 ohms
Am I correct in assuming that 0 ohms across the GRN/GRN winding is not
a good sign?
- Checking the anode to chassis resistance without tubes and the HV interlock
defeated I see ~750 Kohm, is this normal?
When I rebuilt this, I did the following modifications:
- W7RY board with fuse option installed
- ES4SB220 filter capacitor board installed with new electrolytics
- RM220 replacement metering board installed
- Grids grounded
- Molex connector on the HV transformer primary windings
As I mentioned previously I think the fan isn’t working, but I haven’t had a
chance to verify that yet. I only have one more replacement set of fuses so I’m
trying to be smart about my testing until I can get replacements (likely later
this week). I can easily disconnect the HV transformer. Am I correct in
assuming that if the fuses blow after disconnecting the HV primary I can assume
the filament transformer is bad?
Thanks again for your help!
-Warren
> On Jun 25, 2017, at 11:54 PM, Warren Volz <warren@warrenvolz.com> wrote:
>
> All,
>
> I’ve been restoring a SB220 and finally got to the testing stage this
> weekend. When I turned it on, the HV went up to ~1kV and then started to
> drop. Successive cycles of the power switch did nothing. Oddly, the meter
> lights and fan never started running. I looked at the bottom of the amp
> tonight and the 3A fuses I added to the W7RY step start board blew. What
> areas should I look at now to determine what is going wrong? I have both
> tubes in, and I believe I previously checked them for filament shorts. I’m
> worried the HV supply has an issue.
>
> Any advice would be very much appreciated!
>
> Thanks!
>
> -Warren
> KD5YPH
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