[Heathkit] DX-60B HV DC Output

Sat Jul 24 18:12:00 EDT 2021

The schematics show the key jack shorted which means the junction of R1,
R2, R6, and R10 are grounded.   That's the end of the string when key down.

R6 is 18K.   To get -115V at pin 2 of the driver, you'll need 6.3 mA of
grid current.   With -50 V (that I'm measuring), it takes 2.7 mA of grid
current.   I think my mistake was not realizing that node was grounded key
down.   So, based upon the schematics and the referenced page in the
manual,  the grid current of the 6CL6 must be between 5 and 6 mA.

On Sat, Jul 24, 2021 at 5:38 PM <hwhall at compuserve.com> wrote:

> >I still can't see how you arrive at  -115 volts in the driver stage.
>
> Well, if you start out with 130V at the filter caps, then attach a string
> of resistors, you can get any voltage you need as long as it is less than
> or equal to 130V at the other end of the resistors by varying the current
> through the resistors. It's just Ohm's Law at work.
>
> So... while it is at least theoretically POSSIBLE for there to be 115v,
> that isn't consistent with page 40 and if the radio is operating as it
> should then the rest is academic, I guess.
>
> 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: Sat, Jul 24, 2021 1:26 pm
> Subject: Re: [Heathkit] DX-60B HV DC Output
>
> 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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