[Heathkit] SB-200???

[Carl]

----- Original Message ----- 
From: "Paul Kraemer" <elespe at lisco.com>
To: <heathkit at yahoogroups.com>; <heathkit at mailman.qth.net>; 
<heath at lists.tempe.gov>
Sent: Wednesday, August 19, 2009 10:39 PM
Subject: [Heathkit] SB-200???


> Working on a SB-200 for a friend (really)
> I only have the download copy of the manual and note the following
> discrepencies:
> The grid resistors are 22 ohm 1w instead of 33 ohm 1 watt. One of them
> appears original, one was changed
> The grid choke rfc2 looks "funny" to me. Too new and a 3 pi style. 
> Measures
> 2.5milli henry not 28 micro henry
> There is no 33 ohm 1 watt in the antenna relay line and doesn't appear 
> there
> ever was
> There are a new matched pair RF Parts 572-B installed but I am taking this
> carefully repairing the obvious first, like the HV meter resistor already
> replaced once before and open alc bias resistor. The filter caps all esr
> test perfectly ---surprise---but I'll be cautious with a variac first and 
> no
> tubes.



> Questions:
> Was there a early or late version for the 22 ohm 33 ohm grid resistor?

No, only 33 was used. It serves as a rudimentary method of forcing equal 
current sharing as well as an aid to stability.


> Is the bias provided by the 33 ohm in the relay coil circuit beneficial?

It has nothing to do with bias. It is used as a current limiter to minimize 
contact welding problems in exciter relays. Up to 100 Ohms can be used with 
some rigs.


> Is the choke in the grid bias critical? If it is then I am looking for a 
> 28
> micro henry rfc

The choke needs to be non resonant over the full operating range, a 2.5mH 
choke doesnt do that. Give me an address and I'll send you a good used 
original. Be sure R-23 is across it.

Carl
KM1H


> Thanks in advance for your helpful suggestions
> Paul K0UYA
>
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