On Thu, 24 Dec 1998 16:38:17 -0600 bob alexander <realex@flash.net>
writes:
>
>Howdy,
>I've been troubleshooting an SB200 and have gotten exactly
>nowhere. Measured operating conditions are:
>
>Plate voltage = 2100 indicated on front panel meter
>(I've measured 350 VDC +/- 10% across each filter cap)
>there is continuity between p.s. and plates (no open choke)
Should be 2500V but the likely culprit is increased value multiplier
resistors. No concern relating to ur main problem.
>
>Bias (measured between grid and cathode) = -125 VDC in standby,
> -2 VDC keyed
That is normal. How about the 200pf grid caps are they OK ? Ive seen
them partially resistive to completely blown away as a result of tube
arcs.
>
>Idle current = 20 Ma indicated
Way off, should be 90ma but could again be meter ckt problems and not
operational ones.
>
>Plate current = 100 Ma with 100 Watts drive
>
>Power output = 100 Watts max on any band
>
>Input VSWR between 2 and 3:1 depending on band
>
>Filament voltage = 6.31 VAC (center tap is grounded)
>
>All components check O.K.
Ive found many soldering problems over the years from kit amps. Carefully
check all connections and components from the bottom end of the filament
choke right up to the sockets....particularly those little wires at the
terminal strip at the cold end of the choke.
Next replace the input RF coupling cap C-16, Ive had bad ones. Anything
in the .01-.03 mF and 600V+ range will be OK for testing
Do a complete DC path check with an Ohmeter from the RF in port to C-16;
there is no DC on that side so you can check the relay also by keying the
panel jack to ground. An analog meter is particularly useful.
Sounds like no RF getting to the tubes, getting lost somewhere thru an
open or short.
>
>I get the same results with a second set of 572Bs
>
>Does anyone have any suggestions?
I need another SB-200 carcass for 6M conversions if you get the urge to
toss it out Bob!
73 Carl KM1H
>73, and Thanks
>Bob, W5AH
>
>--
>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
>
>
___________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]
--
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
|