SB-200

[Carlos Avellanet [kf4rrn]]

Hi again.

 I have received and overwhelming response to my request for advise and
information while I try to repair my SB-200.  Is along those same lines that
I please ask you all to reply to the reflector, not just me, so we can all
share the information being provided.  If you like to personal e-mail me,
that's fine.  I would just like everyone reading and following along the
benefit of the information flow.

Now, back to the 200...the one area I received the most advise on was also
the one I was most inclined to check; the 33 ohm resistors in line with
C-14.  Sure enough, though they still look good physically, the one on the
V-2 side was wide open.  These are 1 watt resistors.  Luck so have it that I
had a couple of 5 watts 33 ohm resistors in my tool box so I replaced both
of them even though the V-1 side was good.  I ohmed the rest of the
resistors and capacitors in the circuit and they all read OK.  Another
suggestion received via e-mail was a wise way to get around the lack of tube
tester--install one tube at a time in the amp and check it's performance
individually.  Well, being I found the 33 ohm resistor open, I replaced that
first before testing the tubes so I missed the chance to see what the
results would had been.  At any rate, both tubes, checking one at a time,
check exactly the same.  I set the FT-920 for 20 watts output and each
individual tube output was about 150 watts on CW.  I didn't even look at the
amps ma reading (should have).

Smoke test...350-400 watts SSB on 20 meters, 450-500 on 40 meters, 500 to
!POW! smoke and sparks on 80 meters!! Didn't get a chance to test 10 or 15
meters.  Inspection revealed blown 1 ohm 5 watt R-12 resistor on the power
supply board.  I didn't have a 1 ohm resistor but I did had a single 2 ohms
7 watts and I went ahead and replaced R-12 with it.  Before I try again, I
want to go thru the schematics once more and see what could have caused this
resistor to go.  However, I've been working this amp a good 8 hours today
already and I am not getting paid to fix my own gear, so I am quiting for
the night.

I'll keep posting updates for all of you who care.  Thanks for all the
e-mails and all the great suggestions and advise so far.

73,
Carlos. KF4RRN


>Hi gang,

>Here's an update on my SB-200 for all interested.  I replaced all 6 power
>supply caps and bleeder resistors. The amp turned on fine and was providing
>about 600w output on CW and about 450w SSB.  Shortly after capacitor C-14
to
>pin 3 of V2 blew out with a fancy flash and a trailing plum of smoke.  The
>amp still works but power is down to about 300w CW and around 150w SSB.  It
>seems it is working on only one tube, though both tubes light up. I double
>and triple checked my newly installed parts and inspected the board for
>other damage--none found.  I replaced the cap and the power output is still
>down.  I wanted to check the tubes but discovered my B&K 707 tester does
not
>support testing 572B's.  Troubleshooting is on hold until I can verify
tubes
>condition.

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.asp?list=HEATH
To post - HEATH at LISTSERV.TEMPE.GOV
Archives - http://interactive.tempe.gov/archives/HEATH.html