[Amps] SB220 step start blows fuses

Merv Schweigert k9fd at flex.com
Tue Jul 4 20:17:41 EDT 2017

If this is the first time you turned it on since doing the mods,  you
can bet 99 percent that you messed up something when doing
the mods,   check all the mods and wiring you changed etc.

> 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
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