I believe I read somewhere about changing some capacitor values to alter the transmit tone of a browning mark three. If anyone could steer me in the right direction to get a little more highs out of the transmit audio on this and a little bass I would appreciate it. Thank you
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More highs
- Thread starter Van Lifeson
- Start date
C45 is responsible for input audio bandwidth. Lower value - narrow. Higher - wider. I would try 1uF
Mike
Mike
The bass tones are removed on purpose. The Mark 3 uses a speech clipper circuit to limit modulation. If you feed bass tones into a speech clipper, the voice gets hard to understand.
The highs are filtered by C51, L6 and C52. This is done to remove the harmonic frequencies generated by the clipper circuit.
Short version, you'll need to do more than change the value of just one part to make much difference.
One last thought. If C54 is going bad, this makes the audio more "tinny" than it should be. If that part is original, it has no excuse to still be any good. If you just lose R78, and connect the positive side of your new C54 to pin 3 of the tube socket, this will get you just a little more "low side" tone.
73
The highs are filtered by C51, L6 and C52. This is done to remove the harmonic frequencies generated by the clipper circuit.
Short version, you'll need to do more than change the value of just one part to make much difference.
One last thought. If C54 is going bad, this makes the audio more "tinny" than it should be. If that part is original, it has no excuse to still be any good. If you just lose R78, and connect the positive side of your new C54 to pin 3 of the tube socket, this will get you just a little more "low side" tone.
73
I did this mod from Nightcrawler to one of my mkiv's. I can confirm that it works awesome. You will need to compare the 4 and 3 schematic and mark the locations on the 3 schematic. They are very similar.
To bypass the clipper refer to the schematic for the Mark 4 Transmitter.
1. Remove V204 the 12AU7 that tube is used for the clipper.
2. Find C220 and L601 on the schematic locate those parts in the transmitter.
3. Disconnect the end of C220 that's connected to L601.
4. Connect that end of capacitor C220 to pin 2 of of V204 the 12AU7 after the tube is removed.
5. Do not reinstall the 12AU7
The clipper is now bypassed also C213,214 and C215 can be changed from .001uf to .01uf for more low frequency response.
If you want to inject the audio directly to the modulator instead of connecting the one end of C220 to pin 2 of the 12AU7 connect it to your rack gear.
To bypass the clipper refer to the schematic for the Mark 4 Transmitter.
1. Remove V204 the 12AU7 that tube is used for the clipper.
2. Find C220 and L601 on the schematic locate those parts in the transmitter.
3. Disconnect the end of C220 that's connected to L601.
4. Connect that end of capacitor C220 to pin 2 of of V204 the 12AU7 after the tube is removed.
5. Do not reinstall the 12AU7
The clipper is now bypassed also C213,214 and C215 can be changed from .001uf to .01uf for more low frequency response.
If you want to inject the audio directly to the modulator instead of connecting the one end of C220 to pin 2 of the 12AU7 connect it to your rack gear.
So, if the highs are filtered by C 51 and C 52, would increasing or decreasing those capacitor values raise the highs?
Putting a potentiometer in parallel with L6 would probably have more effect. C51/52 reduce highs if made larger. Increase highs if you make them smaller.
73
73