|[AMRadio] 6BA7 mixer Oscillator Drive|
b.gaz at comcast.net
Tue Jul 2 19:56:03 EDT 2013
Add another small filament transformer?
I always disliked running things at max.
I do not know the answer to your question, maybe prototype it outboard and
I did experiments when building my home brew receivers with the amount of LO
signal going into the mixer.
I varied the LO plate voltage to get a little or a lot of signal to the
mixer, but I forget the results!
My 6C4 osc circuit would oscillate from about 10 volts on the plate on up.
I ended up running it at 90 volts I think.
Too little signal and bad things happen, and if you want something that
works well, you need to be able to adjust everything for the best results.
If you have something up against the wall, how are you going to fine tune
----- Original Message -----
From: "Byron Tatum" <bjtatum1 at att.net>
To: <AMRadio at mailman.qth.net>
Sent: Monday, July 01, 2013 8:52 AM
Subject: [AMRadio] 6BA7 mixer Oscillator Drive
In a homebrew dual conversion tube receiver I am building I must resort to a
solid state osc to supply a 2.155 Mhz signal for the 6BA7 second mixer,
which is converting 1.700 Mhz to 455 KHz. I just cannot support another
miniature tube on my small power transformer, even a 0.15 amp such as 6BH6.
I have chosen a 2N5484 osc circuit that is very similar to the tube-type
tuned-grid/tuned plate osc circuit. There will be a resonant circuit at the
crystal freq of 2.155 Mhz in the drain (output) of the 2N5484. My question
is: Am I going to have the proper osc drive to the 6BA7 from this single
transistor osc? The output (from the drain/ tuned circuit) of the osc
circuit I chose shows a 10 pF coupling capacitor. I noticed on the Collins
75A-4 circuit for both 6BA7 mixers there are 100 pF capacitors coupling the
crystal osc or the VFO. I am thinking that I should build a buffer amplifier
but thought I would ask first.
Thanks, Byron WA5THJ
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