>
>Gents,
? [guffaw]
>The Heathkit SB-1000 amp has a very small (tiny) coil in series with the B-
>and also has a 1N5408 in parallel with the B- right after the tiny coil with
>the anode side to ground. Component designations are L401 and D401 on the HV
>PS board. What are they for?
>
? D401 appears to limit the hv neg. potential to gnd during a glitch,
hopefully protecting the grid-current meter from damage. . Because
there should be no RF in this part of the circuit, I can see no purpose
for L401 being there. . Since no peak current-limiting glitch resistor
is used in the hv pos. circuit, I would be concerned that L401 might open
during a glitch. If I owned a SB-1000, I would add a glitch resistor,
short out L401, and add a 25-ohm cathode NFB R, just for starters. //
It seems a bit curious that a separate meter is devoted to grid-current
since the amount of grid-current plays no part in tuneup. A filament
voltmeter (and rheostat adj.) would have been way more useful than a
grid-current meter. // Have you measured the filament-voltage in
yours, Lane?
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|