[Milsurplus] BC-9: A Big Road Block

[David Stinson]

----- Original Message ----- 
From: "AKLDGUY ." <neilb0627 at gmail.com>
Subject: Re: [Milsurplus] BC-9: A Big Road Block


> The key is the switch symbol above and to the left of meter M,
> isn't it?
Yes it is.

>How come it shorts meter M when pressed?
> Is there
> no indication of plate current when sending?
The meter is there to monitor and test for receiving
oscillation and is marked in tenths of milliamps.
On transmit, this meter would be slammed.
I suppose they didn't want to pay for a second meter
or make the case larger.

>
> 73 de Neil ZL1ANM
>
> On Sat, Jan 21, 2017 at 4:57 AM, David Stinson 
> <arc5 at ix.netcom.com> wrote:
>
>> By using an external tank coil in place of the loop and 
>> link-coupling, I'm
>> getting good, sensitive receive and
>> am able to get a good Watt of power
>> out on 80 Meter CW.  https://goo.gl/photos/SthdKR1rmwxXkZ6z6
>>
>> I had this dream of making a few contacts with it during 
>> Novice Rig
>> Roundup.  But now there's a big problem I should have seen 
>> coming.  Take a
>> look again at the diagram:
>> https://goo.gl/photos/THcWRvYScQfnp5gg9
>>
>> The RF stage is regenerative through the plate
>> resistor, R5.  This reduces the plate voltage on
>> the RF tube during receive from 120 VDC to
>> 70 VDC.   To transmit, the plate resistor is shorted,
>> the full 120 VDC is applied resulting in a strong
>> oscillation for transmitting.  And here's the rub:  What 
>> happens with a
>> non-
>> crystal tube oscillator when one raises the B+
>> from 70V to 120V?  Right- the transmit freq
>> jumps higher by several KC.
>> Some movement is to be expected, but I suspect
>> that the original VT-1 didn't move as much as
>> the substitute 6AQ5; otherwise the rig wouldn't
>> have stayed in service for a decade.
>>
>> Irreversable changes are absolutely forbidden.
>> Not sure how I'm going to address this.  Always
>> feel frustrated if I don't get at least one QSO out
>> of a rig.   Perhaps something can be done in
>> the substitute tube mounting.  I'm open to suggestions?
>>
>> TNX OM ES 73 DE Dave AB5S
>>
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>
>
>
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