hello, would It be possible to swap out the 12au7 in a Browning mk3 transmitters audio circuit for a 12AY, AT or AX7 for more transmit audio?
Thanks
Thanks
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Mark 3 tube swap
- Thread starter Van Lifeson
- Start date
The 12AU7 clipper circuit takes the place of the modulation limiter in this radio.
Oddly enough, the lower the gain of the tube in this circuit, the higher the audio level you'll get from it. The 12AX7 used in the mike-preamp stage has an amplification factor (mu) of about 100. The mu for a 12AU7 is around 20.
Don't know of a compatible tube with a lower mu.
If you put the higher-gain 12AX7 in that socket you get less audio, not more. I know, sounds backwards. You can try making the resistor between cathode and ground a higher value. Should get you a little more output from the 12AU7.
Are you trying to drive the 6BQ5 modulator harder? The stock circuit will hit it pretty hard with the mike gain turned up.
Or are you trying to modify the tone balance? A clipper circuit requires filtering out bass tones. If you're looking for more bass, bypassing the clipper will be necessary.
73
Oddly enough, the lower the gain of the tube in this circuit, the higher the audio level you'll get from it. The 12AX7 used in the mike-preamp stage has an amplification factor (mu) of about 100. The mu for a 12AU7 is around 20.
Don't know of a compatible tube with a lower mu.
If you put the higher-gain 12AX7 in that socket you get less audio, not more. I know, sounds backwards. You can try making the resistor between cathode and ground a higher value. Should get you a little more output from the 12AU7.
Are you trying to drive the 6BQ5 modulator harder? The stock circuit will hit it pretty hard with the mike gain turned up.
Or are you trying to modify the tone balance? A clipper circuit requires filtering out bass tones. If you're looking for more bass, bypassing the clipper will be necessary.
73
Nomad, so I tried a 12at7 in place of the 12au7 in both my mk3 and mk2. The audio got louder. Why? This is contrary to what you said in the above post.
Not to go off track but why LOUD!! Seems a lot of people look for LOUD. why not articulation? Clarity? Fullness? As a kid I had my D104 wide open, amc and alc clipped, fan in the background, I was LOUD! Now when I hear that I either shut it off or change the channel.
The 12AT7 should clip the audio at a lower level. However, it will do this more aggressively. More clipping would get you 'loud' and a bit fuzzier both. I need to try this while watching on the 'scope. It's the one thing I trust more than my ears.
I would expect to see a lower peak power on the wattmeter, but a more-intense and distorted sound from the mike audio. Speech-clipper circuits always introduce some distortion.
Only way to tell is to try.
73
I would expect to see a lower peak power on the wattmeter, but a more-intense and distorted sound from the mike audio. Speech-clipper circuits always introduce some distortion.
Only way to tell is to try.
73