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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