[Central-Electronics] CE20A VFO drive level

[Jim Candela]

Hi Jon,

   In addition to the good stuff that Ed says, many folks make the mistake where 
they use the crystal (at operating frequency) and then are dismayed that the CW 
mode is all that works. So to transmit phone (AM or SSB) on 3.880 for example 
you need a crystal at 5.120 Mhz instead of 3.880 since 9.00 - 5.12 = 3.88. The 
20a could be used by Novices back in the day with crystals on the transmit 
frequency. That kept them from using phone mode!

   I'm just waking up (night shifter - so check my math), but I remember that a 
solid state 1 watt amplifier for your signal generator will put out about 10v 
peak into 50 ohms. So here you don't need a step up transformer, but instead a 1 
watt amplifier driven to 1 w output that is terminated into 50 ohms at the 20a 
VFO PL259 plug

Regards,
Jim
WD5JKO. 


----- Original Message ----
From: Ed - K9EW <k9ew57 at gmail.com>
To: k6jek <k6jek at comcast.net>
Cc: central-electronics at mailman.qth.net
Sent: Tue, April 12, 2011 3:04:42 PM
Subject: Re: [Central-Electronics] CE20A VFO drive level

Hi Jon,

The crystal oscillator stage in most tube rigs is also used as a
buffer for an external VFO.  This stage usually requires about 9Vpk-pk
for adequate drive.  You can use a toroidal transformer (5t pri and
30t sec twisted together on a T50-2) to boost your signal generator up
to that level, or you can use an active stage or two.  If the active
amplifier isn't broadband, it will require tuning to peak it at the
desired operating frequency.  A CATV integrated circuit amplifier
(both stages of an LT1253) can be used without tuning.

Hope this helps.

73,
ed - k9ew
www.k9ew.us


On Tue, Apr 12, 2011 at 2:52 PM, k6jek <k6jek at comcast.net> wrote:
> How much signal does a 20a need from the VFO?
>
> I have the 20A working with a crystal but the 458 VFO is a mess.  I thought, 
>what the heck, use a signal generator to get on the air.  The 1V my signal 
>generator delivers isn't doing it.  Should it?
>
> Thanks,
>
> Jon
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