[Amps] Heath SB-220 Soft Start

[Steve Harrison]

Actually, if one contact of that relay was burned, it sounds as if it
developed high resistance at that contact and failed to close
sufficiently as to short the resistor, causing the resistor to burn up.
Replace both relays and resistors and you should be back chasing pileups.

However, IIRC, those relays are soldered to the PC board, making removal
and replacement difficult. Might be better just to buy a whole new
replacement soft-start module. I forget who took over the Harbach line,
but somebody did... maybe the QRO guy in CT, KB1SEL??

And yes, test the repaired amp without the tubes first; cheap and easy
insurance (as long as you rember to unplug the amp and short the HV
before plugging the tubes back in!!).

Steve, K0XP


On 10/3/2024 8:41 PM, Victor Rosenthal 4X6GP wrote:
> If the soft start relay fails to close, then the resistor will burn
> up, because it is only rated to handle the full load for a short
> period of time. So you should investigate why the relay stayed open.
>
> 73,
> Victor, 4X6GP
> Rehovot, Israel
> formerly K2VCO
> CWops no. 5
> http://www.qsl.net/k2vco/
>
> On 04/10/2024 3:11, Larry Carpenter wrote:
>> Hi Folks,
>>
>>                  Its been a while since I posted anything but I do
>> enjoy reading messages on this group. I find them very helpful. I
>> just recently acquired an SB-220 with all the Harbach mods, soft
>> start, soft key, metering board and power supply board with new caps
>> and bleeders. I used this amp for a couple of days and it worked fine
>> with 3000 VDC in the SSB position with about 1100 watts out and about
>> 2250 VDC in the CW position. While sitting in a idle state there was
>> a flash and it immediately lost power. After some investigation I
>> found one of the wire wound ceramic resistors (20 ohm @ 10 watts) had
>> opened up and left a black zorch on the soft key board.  It also
>> appears that one post of the 48VDC K2 relay got really hot. It looks
>> like these resistors will be easy enough to replace but I am
>> concerned at what caused the resistor to open up. I am wondering If I
>> should replace the resistors and take the tubes out before powering
>> on and see what happens. Neither of the circuit bre
> ake
>>   rs on the back of the amp had tripped. Just wondering if anyone
>> else had run into this problem with Harbach Soft Start module. Any
>> advice greatly appreciated.
>> Larry Carpenter
>> AA4VI
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