Allen
It does sound suspicious that somehow, you have a sneak path for bleeder
current to ground. The bleeders and the entire HV PS should be floated and only
the neg lead should be brought back to your multimeter switch, and your 25 ohm
to ground. If there is another ground inside the power supply, the current
through it may show up deflecting your grid I meter, since that meter goes to
ground. I am not completely understanding the problem, though, without more of
a schematic. Odd though, that the tubes are even pulled, so it almost has to be
bleeder current.
John
K5PRO
> Date: Thu, 13 Mar 2008 11:25:42 -0700 (PDT)
> From: Allen Jones <w9dz@yahoo.com>
> Subject: [Amps] Metering Problem Heathkit HA-10 Amp
> To: Glowbugs <glowbugs@piobaire.mines.uidaho.edu>, Heathkit List
> <HEATH@LISTSERV.TEMPE.GOV>, amps@contesting.com
> Message-ID: <621389.78902.qm@web37301.mail.mud.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> For the last two weeks I have been wrestling a
> Heathkit Warrior around on the bench installing a new
> plate transformer and modifying the grid circuit.
>
> The amp originally bypassed the grids to ground with
> capacitors and metered grid current directly. I have
> bonded the grids to ground using braid and metering
> grid and plate current at the center tap of the
> filament transformer. A 20K 25W resistor and a 5.1V
> zener are in series with the filament CT to ground.
> The resistor is shorted out with a relay when the amp
> is keyed. The negative end of the supply is held 25
> Ohms above ground so as to meter plate current there.
> The plus side of the multimeter is connected to anode
> of the zener and the negative is switched between
> ground to read grid current or B- to measure plate
> current. Pretty much a standard Handbook arrangement.
> I am doing my testing WITHOUT the 811A's.
>
> When I power up, the meter is pinning (not hard)
> negative and I see a small upward scale deflection
> when I switch to the plate position. I pulled the
> solid state 866 replacements (the fil xfmr for the
> 866's has been removed) and see no current flow so I
> assume that somehow or another I am reading bleeder
> current. I verified this with the temporary addition
> of 100K in series with the existing 60K bleeder. The
> deflection of the meter in both positions is less.
> The grid no longer pins but still deflects negative.
>
> Anyone have any ideas? Could a leaky component be at
> fault.
>
> Thanks
>
> Allen, W9DZ
>
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