[Heathkit] DX-60B HV DC Output

[Mark K3MSB]

Hi Wayne

Thanks for your comments.  I follow your math,  but I still can't see how
you arrive at  -115 volts in the driver stage.

I'm convinced the -115V bias value from the schematics on the driver in AM
is wrong.  Page 40 of the manual says -95/-85   I'm measuring
-55/-48.....    The radio works. and all the resistors in the bias circuit
are within range (out of range ones were replaced).   I think I'm going to
take this as a win in the "bias war".

Power output is 80 - 10:   50,45,42,30,22 W going into a dummy load.   All
at 150 mA Ip and 2.5 ma Ig.   I was using an 80M crystal for 80M,  and a
40M crystal for the other bands.

40M Seems intermittent.   I lose grid drive all of a sudden which is
evidenced by spiking Ip.   I need to investigative that some more.  Doesn't
happen often, but it does happen.

73 Mark K3MSB

On Fri, Jul 23, 2021 at 7:18 PM <hwhall at compuserve.com> wrote:

> 1. The 6146 in class C draws in the neighborhood of 4ma (per datasheets),
> so R30, R11, R12 (total ~22.4K) can drop almost 89 volts for that current,
> leaving ~40 volts for the grid. Close enough to  your measured 38 volts,
> given that we don't know the exact grid current or the ohms tolerance +
> drift on the resistors.
>
> 2. The 6CL6 control grid (pins 2, 9) is biased -115V which is likely
> nearly to or past cutoff (datasheed wasn't specific), hence very little or
> no grid current, & hence very little voltage drop through the resistances
> feeding THAT control grid. But R10 & R30 are also dropping voltage due to
> V1's grid current. As an approximation, R30+R10+R6 seem to be (per your
> measurements) dropping about 15volts, so the 6CL6 grid current is less than
> 0.5mA.
>
> Make sense?
>
> Wayne
> WB4OGM
>
> -----Original Message-----
> From: Mark K3MSB <mark.k3msb at gmail.com>
> To: Wayne Hall <hwhall at compuserve.com>
> Cc: heathkit at mailman.qth.net <heathkit at mailman.qth.net>
> Sent: Fri, Jul 23, 2021 2:34 pm
> Subject: Re: [Heathkit] DX-60B HV DC Output
>
> The -38 is on the 6146 and the specified -115V is on the Driver.
>
> Mark
>
> On Fri, Jul 23, 2021 at 5:12 PM <hwhall at compuserve.com> wrote:
>
> >You can't go from the same source voltage through 22K to the 6146 and
> have
> -38V,  and through 22K and then 18K + 4.7K and have -115 volts.<
>
> You might, if those 6146 connections are to different pins (i.e.,
> different tube elements) because (for example) plate current differs from
> screen grid current which differs from control grid current which differs
> from cathode current. Different current drawn through different resistances
> will result in different voltage drops. I note that your concern  is
> different pin voltages at different pins - aren't those different elements
> in the 6146?
>
> Wayne
> WB4OGM
>
> -----Original Message-----
> From: Mark K3MSB <mark.k3msb at gmail.com>
> To: Heathkit List QTH <heathkit at mailman.qth.net>
> Sent: Fri, Jul 23, 2021 11:42 am
> Subject: Re: [Heathkit] DX-60B HV DC Output
>
> Making progress.    I have a question on the schematics.
>
> I measure the bias at -130V at the junction of C37/C38.    If you go
> through R30 (22K) to Pin 5 of the 6146 the bias voltage is supposed to be
> -38V as indicated on the schematics.  We can ignore the parallel
> combination of R11 and R12 as R30 is significantly higher.
>
> Now, If I go through the same R30,  then R10 (4700) and R6 (18K) to Pins
> 2/9 of V2,  the schematics say -115 Volts.
>
> You can't go from the same source voltage through 22K to the 6146 and have
> -38V,  and through 22K and then 18K + 4.7K and have -115 volts.
>
> Is the schematics incorrect?
>
>
> Mark K3MSB
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