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Heathkit SB-200 Restoration & Problem

Sep 16th 2014, 15:33


Joined: Mar 9th 2012, 17:06
Total Topics: 0
Total Posts: 0
I just restored a Heathkit SB-200 linear amplifier. I installed the Harbach power supply and soft-start circuit. (The soft-key circuit was already in the unit when I acquired it last month.) I installed the Harbach power supply that is made for 240V operation. (The only difference are the 20K power resistors as opposed to 10K.) However, I am currently running the unit with the transformer primary configured for 120V operation because I wanted to initially perform some tests with it connected to my isolation transformer and variac.

The preliminary tests were good. The next step was to connect it to my Kenwood TS-530S transceiver in CW mode. (I am no longer using the variac. I plug it into a 120V wall outlet.) . I made a cable going from the DIN connection on the back of my TS-530S to the SB-200 ALC and Ant Relay RCA jacks. I wired them according to the diagram in the Kenwood manual. Pin 6 of the DIN goes to the ALC center connector on the SB-200. Similarly, pin 4 of the DIN goes to the SB-200 Ant Relay center connector. Finally, pin 2 of the DIN is the shield that goes to the outer ground connector on both RCA jacks.

I connected the SB-200 RF Output to a dummy load and the SB-200 RF Input to the output of my TS-530S. I was able to tune up the TS-530S straight through the SB-200 for full exciter power.

I turned on the SB-200 and observed 2400V HV at 90ma. idle current. Then, the big moment came. I keyed the TS-530S, heard its relay and the relay of the SB-200 click, but the SB-200 meter and the dummy load meter both only measured 100W! That's only the exciter's power output. I looked at the plate current and it indeed increases from 90ma. to approximately 300ma. during excitation. Nonetheless, the power output still measures 100W on the SB-200 meter and the dummy load's power meter.

One other peculiarity is that the SB-200 relay will only remain actuated if I use the VOX on the TS-530S. If I manually throw the SEND switch on the TS-530S, the SB-200 relay will not remain actuated during my CW characters. I can certainly live with this behavior if it's expected, but mention it as a possible hint to my problem.

The cable that I made from the DIN to the RCA jacks has continuity and no shorts. The only possible error could be the pin connections. I went by the TS-530S manual and assumed that the DIN plug shown with pin numbers was the external side of the plug. Moreover, since I hear the relay being thrown, I assume that the Ant Relay connection is correct.

This is the first linear that I have ever owned and a piece of history, in my opinion. Any help in getting it back online would be greatly appreciated. (You can see my station on QRZ. I am KA2KNX.)

Thank you.

Sep 16th 2014, 15:43


Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
What frequency are you using? Is the SB200 band switch set correctly? Did you try tuning the amplifier? The straight-through operation bypasses everything.

If that's all OK, it sounds like the SB200 antenna relay might not be switching, especially if the amp tuning has no effect.

Good luck & 73
(Keep one hand in your pocket!)

Martin AA6E
Sep 17th 2014, 02:09


Joined: Mar 9th 2012, 17:06
Total Topics: 0
Total Posts: 0
Thank you Martin. It turns out that the ANT RELAY was NOT switching correctly - just as you expertly suggested. The reason was the way I wired the DIN connector from the exciter. The Kenwood TS-530S manual illustrated the pin numbering from the solder side. Therefore, I had mirrored the connections. I found this out when I decided to manually short the ANT RELAY leads. That keyed the amp. After rewiring the DIN connector, I tried the full feature set of the amp and all worked really well. I restored this electrically and refinished the cabinet as well. It looks like it just came off the shelf and performs that way too. Thank you for your help. 73, Steffen (KA2KNX)

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