[AMRadio] Initial settings 20V-3

Bob Maser bmaser at tampabay.rr.com
Mon Jan 31 22:42:20 EST 2005

I tried grid dipping the tank circuit without finding any dip even remotely 
close to 75M.  I never have any luck with that thing.  I tried putting a 
2400 ohm resistor across the final plates to ground to simulate plate load 
impedance and that gave me resonance somewhere near 3200kcs using an Autek 
RF Analyst.  I set the C1, C2 to what they should be (125pf & 615pf), 
checked the 2 L's and they measured 18uH & 5.5uH, just like Bill's book says 
they should be.  Enough of this predicting stuff.  I put the power cutback 
at low power and fired her up.  Got 1000V on the plates and 400ma.  No RF 
out at all and no dip anywhere. Tried it again with the power cutback set to 
"medium" and now I get 2000V at 800ma, still no dip, no RF.  The R197 in the 
Plate voltage circuit, which is supposed to 1K ohms I notice has been 
changed to 2K back in 1971.  I figure that is the reason why the volts are 
measuring low.  At this point I'm  getting tired of this so I turned it off 
to play with some more tomorrow.
Any suggestions?

----- Original Message ----- 
From: "David Knepper" <cra at floodcity.net>
To: "Bob Maser" <bmaser at tampabay.rr.com>
Sent: Monday, January 31, 2005 4:35 PM
Subject: Re: [AMRadio] Initial settings 20V-3

>I would strongly suggest that you grid dip the tank circuit after changing
> the taps on the coils.   Remember that you have to readjust the tank 
> circuit
> by repositioning the coil taps.
> When I converted mine to 160 meters, I had to change the taps on both the
> loading and input coils.
> It is not a matter of simply adjusting the tuning and loading variable 
> caps.
> Good luck
> Dave, W3ST
> Publisher of the Collins Journal
> Secretary to the Collins Radio Association
> www.collinsra.com
> Nets:  3805 Khz, Monday/Wednesdays 8 PM EDST
>          14250 Khz Saturday, 12 Noon EDST
> ----- Original Message -----
> From: "Bob Maser" <>
> To: "AMRadio" <amradio at mailman.qth.net>
> Sent: Monday, January 31, 2005 6:21 PM
> Subject: [AMRadio] Initial settings 20V-3
>> Can anyone give me the initial settings for the Tune and Load capacitors
> for
>> 75M?  I am just about ready to put the power to the dummy load.
>> Thanks,
>> Bob W6TR
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