[Amps] SB220 step start blows fuses
Warren Volz
warren at warrenvolz.com
Tue Jul 4 17:58:43 EDT 2017
Ron,
Thanks for the reply!
> On Jul 4, 2017, at 3:51 PM, Ron Youvan <ka4inm at gmail.com> wrote:
>
> Warren Volz wrote:
>
>> 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
>
> Tube pins 2, 3 & 4 should all measure zero Ohms in any direction.
Correct, they are zero Ohm (after the meter settles) in any direction.
>> 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?
>
> Zero Ohms is a good reading across a 5 Volt 30 Ampere transformer
> winding.
>
>> 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!
>
> You do not say if the filaments light or start to light when you turn
> on the power. You do not say if you have the unit in the high power or
> low power mode.
>
> I do not know anything about the step start circuit, but it is suspect.
When I had the fuses blow the meter lights did not turn on, but I can’t comment on the filaments. I was being a little paranoid and was several feet away when I first turned it on. Unit was in the low power mode when I tried it before.
-Warren
More information about the Amps
mailing list