Browning Mark 4 and 4A

[bossman327]

I wanted to get some help from you guys that are doing the hi fi audio with Browning Radios. NightCrawler has helped me tremendously in the past and i was hoping he would chime in here with the rest of you guys. I wanted to know what the mods would be to bypass the transmit audio clipper circuit or either direct inject audio from my rack gear into a 4 or 4A? I would also like to know how or if its possible to widen the receive on the receiver to pass hi fi audio. Thanks for all your help! Bossman

[Night Crawler]

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.

[bossman327]

NightCrawler you are the man! Thanks again for your help! Do you have any mods for the receiver that will open up the receiver to pass more audio? Thanks Bossman

[dirtyjob]

interesting, ill be watching this thread for your results.

[bossman327]

Hey Dirtyjob I did the mod that Night Crawler gave me for the transmitter on a transmitter of a Mark III and it is awesome! Wide audio thru glass is the way to go!

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Wed May 15, 2013 9:24 pm

Would I need more output from my rack if I direct injected the audio NightCrawler? I see that would be bypassing the 12ax7 which is the pre amp tube if I'm not badly mistaken. Would I need more output from the rack gear to drive the 6bq5? Thanks again for our help. Oh yeah also clipping c220 before or after the point that it goes to c219? Thanks. Bossman

[dirtyjob]

sounds good, ill have to make a note of this

[Night Crawler]

Would I need more output from my rack if I direct injected the audio I see that would be bypassing the 12ax7 which is the pre amp tube if I'm not badly mistaken.

Yes you would.
You can inject the audio from the mixer into the 12AX7 through the mic jack but the interstage coupling capacitors C213,C214 and C215 determine the frequency response of the microphone stage those can be changed to a .01uf or a .05uf to improve frequency response.

Try it both ways and see what works best for you, also R219 will be your mic gain control and R603 the clipping control will not longer function after the modification.

Clip C220 before C219.
C218,C219 and L601 are used for the high frequency filter for the clipper so you don't want anything connected to that circuit.

[bossman327]

Thanks again Night Crawler!

[grimace]

so is this wright for 3 and 3AM
mark4 v204 c220 L601 c213 c214 c215
mark3 v8 c53 L6 c45 c46 c49
mar3am v4 c28 L6 c17 c20 c23

[KOA4705]

I wanted to get some help from you guys that are doing the hi fi audio with Browning Radios. NightCrawler has helped me tremendously in the past and i was hoping he would chime in here with the rest of you guys. I wanted to know what the mods would be to bypass the transmit audio clipper circuit or either direct inject audio from my rack gear into a 4 or 4A? I would also like to know how or if its possible to widen the receive on the receiver to pass hi fi audio. Thanks for all your help! Bossman

Bossman,
My friend Marc asked me if his Browning Mark 3 transmitter would be a candidate for high fidelity audio on AM. The Mark4 uses the same audio amplfier circuit. After reviewing the schematic it looked encouraging, for one thing the transmitter is plate modulated. The first thing in order was to sweep the audio chain and a Step response with a audio function generator. Looking at the audio response at the output of the transmitter with a scope. The stock response was 400 to 2800 Hertz with phase and amplitude distortion, this is telephone quality. The first two audio stages use a 12AX7 which are straight forward. The 3rd and 4th audio stage is a voltage clamper circuit. This limiter circuit clips the input signal which distorts the audio signal and produces odd order harmonics. Which is then put through a low pass filter to remove the harmonics and have a so called reconstituted signal. The final drive stage uses a 6BQ5. By making a few simple changes to the 1st, 2nd and driver stage and eliminating the clipper circuit and reducing the equivalent capacitance across the secondary of the modulation transformer. This will greatly improve fidelity and eliminate distortion of the transmitter. To my surprise the modulation transformer frequency response is quite good. The low end does suffer a bit because the Modulation Transformer lacks inductance but remember this was designed for communication audio. Output response was 60 to 15,000 Hertz (-3DB) with low distortion. I might still incorporate a loop of negative of negative feed back from the secondary of the modulation transformer to a earlier audio stage to see if any further improvements. I also have provided a line level input so you drive the transmitter directly from a audio chain. I do have wave file to demonstrate the results. The phone jack output from the receiver was feed directly into digital recording. Can you post a audio file here?
Joe

[Smooth912]

Just stumbled across this while searching. Great post, exactly the info I was looking for. How exactly is this connected from my rack gear? Direct to c220 on the mk4? How about the shield/ground wire?
How wide does these transmit? I am used to running my Kenwood 850s, directly injected however want to try some plate modulation!

[KOA4705]

Just stumbled across this while searching. Great post, exactly the info I was looking for. How exactly is this connected from my rack gear? Direct to c220 on the mk4? How about the shield/ground wire?
How wide does these transmit? I am used to running my Kenwood 850s, directly injected however want to try some plate modulation!

Smooth912,
Sent you a PM
Joe

[masterplan]

Hey I am new to this Forum and stumbled across this thread. I am wanting to do Hifi on a Mark II Am transmitter? I assume the audio section is similar? I have a transmitter that is ruff looking but works good I want to experiment on. Any help or suggestions? thanks in advance..

[dirtyjob]

hiya Toby

[masterplan]

Hi Mark,


I wonder if anyone know how to give the Mark II AM unit Hi Fi audio? I have a Mark III but I want to do the mark II cause I have a extra transmitter.. ANy help would be appreciated