[AMRadio] 6BA7 mixer Oscillator Drive


Brett Gazdzinski 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 
try it.
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 
it?

Brett
N2DTS

----- 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


Hello-
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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