Date: Sun, 28 Feb 2010 14:16:42 -0800
From: MIKE DURKIN <patriot121@msn.com>
Subject: [Amps] Mangian wire
Ok .. do you really need the Mangeian Wire from the B- of the Filter board to
the shunted amp meter??
## The B- from the HV supply, has to ultimately find it's way back to the
CATHODE.
I have my amp up and running with a GS-35b now and im sure that my bias isnt
working right .... mabey it is ... but as it sits now .. i should have 30V bias
keyed and im showing 60ma idle ... now this is why i think i still have a
problem with metering - when driving with 30W im getting an output of 600W
(carrier/cw -what ever) and the uA meter is showing only about 120 mili-amps of
plate current.
## are u sure the current isn't finding an alternate path ? You don't want
stuff like unwanted V drops turning on RVS connected safety diodes, and
diverting current through back door path's. Amp will work fine, just the
metering is screwed up.
Second question is do you need plate voltage on the plate to complete the bias
voltages (im talking through the tube) to the heater??
## YES. It's the cathode current [ = combined grid + plate current]
flowing through your zener's that creates the zener voltage.
My DC at the heater is 120VDC cutoff and 4V DC key'd state (no drive). My Bias
supply is not sagging and the collector of the pass transistor is tied to the
CENTER TAP OF THE HEATER TRANSFORMER ...... Please leave out comments about
using a center taped heater transformer and the differences of using a bifilar
wound rod for RF blocking - its simply what i have and plan on using for now.
## Maybe try a different meter, or remove stock meter....and bench test it.
Or temp substitute a Fluke 87 DVM. If the amp is functioning fine, the
current is flowing... somewhere... and only a portion of it may be flowing
through the meter. The current may well be flowing through multiple paths..
then back to the cathode. I'd be checking everything between the B-....
and the cathode.
Later... Jim VE7RF
If your wondering what amp again its a Yokagawa P93 blah blah blah.... i have
posted the schematic (a scan of it- and a poor one at that) . Im thinking that
the Bias supply needs to supply voltage at the collector via a blocking diode
and say a 1K 5W resistor so that when the emitter is pulled to ground the
Zeners are reversed by the Bias supply and not the tube leakage ..... at the
current configuration im thinking that the 30V zener that i used to replace the
pair of 4.1V zeners will never be properly reversed for the wanted 30VDC Bias
....
Mike
KC7NOA
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