[Amps] Heath SB-220 Soft Start

[Per Molund]

The PC board is single sided so it should not be very difficult to 
replace the relays (and resistors). However, a new board can be obtained 
from
https://harbachelectronics.com/shop/heathkit-sb220-sb221/ss-221-120-soft-start-module-copy/

73 de LA9XKA - Per

On 04.10.2024 05:52, Steve Harrison wrote:
> 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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>>> Amps at contesting.com
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>>
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