>A friend of mine has loaned me his SB200. If I can get it working again,
>I get to use it (for a while anyway :=)
>
>From what he told me, and by inspecting the amp, it looks like RFC2 is
>burnt out. From what I've been able to gather from a schematic and
>partial manual found on the internet, cut-off bias voltage from the power
>supply bias circuit is applied through the coil of the T/R relay, a
>resitor, and RFC2 to the grids of the tubes (on RX). On TX, the Ant Relay
>jack grounds the grids of the tubes through RFC2 and a couple of
>resistors. (RFC2 is is parallel with a 1Watt 3.3K resistor.)
>
>The schematics show RFC2 = 28uH. How critical is this value?
Not very. 15 - 50uH will work. The problem was not that the choke went
bad. Something made it go go bad. Unless one discovers what this
problem was, an instant replay seems possible. What is the actual
resistance of the grid resistors and the suppressor resistors?
- Editorial. If this were my sb200, I would convert to resistor-cutoff
electronic bias switching (not RF-actuated), high-speed relays, and lower
VHF-Q parasitic suppression -- especially with the newer, higher-gain
tubes.
>Can I just
>go through my junk box and use any old choke that's close in value? Wind
>my own? If not, does anyone have a suggestment for a replacement part
>(supplier, part number, etc)?
>
>Thanks in advance!
>
>73,
>
>Chris VE3FU / VO2AC
>
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>http://lists.contesting.com/mailman/listinfo/amps
>
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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