" The manual notes more than 80ma of "idle current" is a Zener diode failure
(D2) which appears to be in the power supply, but I'm not clear on what
"idle" means - it doesn't indicate current in Standby"
Idle current is that current that flows when the amp is "keyed" (switched on
by the relay in the exciter), but no RF is going into it - like if you are
running CW and you you are not sending, or you are transmitting SSB and you
don't talk (and there's not a lot of hum and stuff...)
The zener is probably in the grid bias circuit. Failing changes the bias
and the idle current changes.
-Rex-
K1HI
Rex Lint
Merrimack, NH
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Tom Mandera
Sent: Tuesday, March 10, 2009 1:46 AM
To: amps@contesting.com
Subject: [Amps] SB-1000 - 100ma minimum plate current.
I'm new to QRO, but bought an SB-1000 (aka AL-80, sporting a single
3-500z) last week that belonged to a well regarded SK.
Finally wired things up tonight, bringing 240V to the amp.
I have the original Heathkit manual and I'm trying to follow through the
correct tune-up procedure, but I'm having difficulties.
I have 3400V with power on.
I dial back the exciter (TT Paragon II) as far as it'll go (less than
10w indicated, roughly 5w), set the band switches to match (80M in this
case), and find the initial settings from the manual.
I have no current in Standby mode.
I switch to OPR and key the exciter. I'm supposed to see 50-80ma of
plate, but I see 100ma immediately.
I then can't apply more drive and reach 50ma of grid without exceeding
200ma of plate. I reach 40ma of Grid and 200ma of Plate. I then adjust
for peak.
I'm then instructed to switch to the Power reading and adjust for peak
power again.
I heard the (tube?) sizzle (sounds like a good weld, not a good thing in
a radio) while attempting to increase the exciter drive to hit 125ma of
grid, and never reached it.
The manual notes more than 80ma of "idle current" is a Zener diode
failure (D2) which appears to be in the power supply, but I'm not clear
on what "idle" means - it doesn't indicate current in Standby, but with
minimal drive from the radio, it doesn't go below 100ma. Is this a
failed diode?
I don't have any ALC hooked up, just the antenna (less than ~1.6:1 swr
at the test frequency) and the relay control from the radio.
Do I need to dig inside and have a look at the diode, or is there
something else I should examine first, or adjust in my operation, or
should the tube really sizzle (doubtful!)
Thanks,
-Tom
KE7VUX
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