SB-201/200 no output on any band

[Paul]

Tom

Have you checked the SWR of the input circuit to make sure that it matches
the band on the plate side of the amp?

Have you verified the T/R relay is working correctly? Is the amp actually
connecting to the antenna when the T/R relay is energized? Is the input from
the exciter actually reaching the tubes? You can test these paths without
turning the amp on and simply pressing down on T/R relay and checking with
an ohm meter.

Good Luck with your problem

73
Paul K5RT





-----Original Message-----
From: Heathkit Owners and Collectors List [mailto:HEATH at LISTS.TEMPE.GOV] On
Behalf Of Tom Chesek
Sent: Saturday, October 18, 2008 4:41 PM
To: HEATH at LISTS.TEMPE.GOV
Subject: SB-201/200 no output on any band

I have an SB-201 which was converted to an SB-200 equivalent with a complete
bandswitch swapout. I cannot tell you if it ever worked after the swap. This
amp has the Harbach power supply mod and antenna relay including the
resistor change that comes with the relay kit. The tubes are a pair of
Cetrons which are soft but verified as working in my other SB-200 amp. Using
the Taylor tubes from my SB-200 make no difference at all. There is no
output on any band. I've cleaned the bandswitch with Deoxit, verified that
the wafers are aligned with each other corectly, and verified that each
contact has good wiping action. I have verified the -2vdc bias by measuring
with a DVM and get a reading of -1.78vdc. The filament voltage measured at
the tube side of the bifilar choke measures 6.72vac. The HV reads just under
2400vdc on the built in meter. The idling plate current reads about 98ma.
PC1 & PC2 both have NOS carbon resistors. R21 and R22 are new also.

I've tried drive on each band from 30 watts to 100 watts with no output
measured on the amps' meter or on the watt meter inline to the 50 ohm
antenna load. If I drive it with higher power, such as 100 watts, the tubes
will start to "cherry up" in color if I keep the key down for 30 seconds or
so. It almost appears to the that no rf is passing beyond C24 but I have
swapped that cap with the one in my working SB-200. All screws have been
tightened to be sure the ground paths are intact. 

Nothing is going up in smoke so where is my output? This is driving me nuts!

73 and Tnx,

Tom K3TVC

ps: for what it is worth I know that at one point this amp was modified for
11 meter use and then changed to the current SB-200 configuration.


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