Hello every one I have a general sherman cb radio and would like to know how to peak & tune this radio and get the audio levels up can any one help me?
Thank You Molten1
Thank You Molten1
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sherman tune up
- Thread starter molten1
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Hello every one I have a general sherman cb radio and would like to know how to peak & tune this radio and get the audio levels up can any one help me?
Thank You Molten1
Remove TR24.....that disables the mod limiter on both AM and SSB. Cutting R131 will only disable the AM limiter. Adjust VR10 for the desired dead key wattage. You can adjust L38 for maximum swing but the results are usually minimal.
Cutting the limiter out of a Sherman, which is a Cobra 148 clone, is just fine even though some anal retentive people on this forum think removing a limiter will bring the end of the world.
There are other things you can do to get more swing watts but this info is short and sweet.
These radio sound perfect with the limiters CLIPPED.
1. found this on the web
2. Any modifications that you do - are done at your own risk !
3. The modifications page is for educational purposes only, many of the examples are
illegal in most countries!
TR-296 Series
1. Cut trace on PC board between Pin 1 of IC6 and pin 2 of IC4 ( MB3756 ). Next, install a .1uf mylar
capacitor at C136 and a jumper wire at J44. This corrects distortion on the SSB transmit audio:
2. Bypass or install a jumper across resistor R180. This resistor limits available current to bias
regulator transistor TR37 and causes final bias to go negative and limits power output and increases
distortion.
3. Install a 100 ohm - 1/4 watt resistor from pin 12 of IC5 to ground. This increases the gain of the
transmit mixer and is necessary when you do frequency expansion mods.
4. Change capacitor C163 to 3pf. This improves bandwidth of transmit bandpass filter. Change C41
to 3pf. This improves bandwidth of the receiver bandpass filter. These changes are necessary to
provide uniform performance over a wide range of frequencies on transmit and receive.
5. Remove capacitor C174. Install a 1000 uf, 25V capacitor, negative lead to negative side of C174
(on PC board) and positive lead to base of transistor TR41. Change TR41 to a 2N6487. These
changes make a tremendous improvement to AM transmit audio and modulation.
6. To tie clarifier on transmit and receive, remove diodes D52 and D75. Disconnect green wire that
goes from R44 to Rx 8 volt source at Rx 8 volt end (near front of PC board ). Reconnect to continous
8 volt source.
7. To modify clarifier for maximum frequency range on transmit and receive, remove diodes D44,
D75, and D51. Next remove resistors R44, R174, and R149. Move blue wire that comes from center
leg of voice lock to cathode side of D51 ( on PC board ), and move orange wire that comes from top
of voice lock to continous 8 volt source. Adjust L22, L23 and L59 to frequency with voice lock set to
the 12 O'clock position.
8. There are several ways to modify these radios for expanded frequency operation.
a. The simplest way is to install 2 SPST switches, connect them to pins 10 and 12 of PLL IC and
ground. This will give you coverage from 26.815 to 28.045 mHz.
b. The other way is to use a SPDT center off switch and connect as follows:
2. Any modifications that you do - are done at your own risk !
3. The modifications page is for educational purposes only, many of the examples are
illegal in most countries!
TR-296 Series
1. Cut trace on PC board between Pin 1 of IC6 and pin 2 of IC4 ( MB3756 ). Next, install a .1uf mylar
capacitor at C136 and a jumper wire at J44. This corrects distortion on the SSB transmit audio:
2. Bypass or install a jumper across resistor R180. This resistor limits available current to bias
regulator transistor TR37 and causes final bias to go negative and limits power output and increases
distortion.
3. Install a 100 ohm - 1/4 watt resistor from pin 12 of IC5 to ground. This increases the gain of the
transmit mixer and is necessary when you do frequency expansion mods.
4. Change capacitor C163 to 3pf. This improves bandwidth of transmit bandpass filter. Change C41
to 3pf. This improves bandwidth of the receiver bandpass filter. These changes are necessary to
provide uniform performance over a wide range of frequencies on transmit and receive.
5. Remove capacitor C174. Install a 1000 uf, 25V capacitor, negative lead to negative side of C174
(on PC board) and positive lead to base of transistor TR41. Change TR41 to a 2N6487. These
changes make a tremendous improvement to AM transmit audio and modulation.
6. To tie clarifier on transmit and receive, remove diodes D52 and D75. Disconnect green wire that
goes from R44 to Rx 8 volt source at Rx 8 volt end (near front of PC board ). Reconnect to continous
8 volt source.
7. To modify clarifier for maximum frequency range on transmit and receive, remove diodes D44,
D75, and D51. Next remove resistors R44, R174, and R149. Move blue wire that comes from center
leg of voice lock to cathode side of D51 ( on PC board ), and move orange wire that comes from top
of voice lock to continous 8 volt source. Adjust L22, L23 and L59 to frequency with voice lock set to
the 12 O'clock position.
8. There are several ways to modify these radios for expanded frequency operation.
a. The simplest way is to install 2 SPST switches, connect them to pins 10 and 12 of PLL IC and
ground. This will give you coverage from 26.815 to 28.045 mHz.
b. The other way is to use a SPDT center off switch and connect as follows:
I would never open up a clarifier on a radio that has no frequency counter built in. Heat and cold conditions will adversely affect the clarifier position.
My member isn't senior yet.
User control of modulation isn't new.
It can, as you say, result in "junk watts".
But it isn't inevitable with a clipped radio.
Get over it, it's CB radio, where 100+ percent mod is the norm.
"Clear" or "clean" modulation is considered to be loud, readable audio.
It's just the way it is, and disparaging posts won't change it.
User control of modulation isn't new.
It can, as you say, result in "junk watts".
But it isn't inevitable with a clipped radio.
Get over it, it's CB radio, where 100+ percent mod is the norm.
"Clear" or "clean" modulation is considered to be loud, readable audio.
It's just the way it is, and disparaging posts won't change it.
No need for a power mic with a clipped radio.
This works very well with a noise canceling mic.
The radio can archive full mod and still have it's power contained to its intended channel.
It's the "full right mic gain" mentality that is faulty.
If a radio needs a power mic to be loud then it is either a sub par model or the wrong golden screwdrivers have been in it.
the only time the position of the mic gain control comes into play and becomes especially critical is when the AMC is disabled.
http://www.firecommunications.com/amc.shtml
http://www.firecommunications.com/amc.shtml
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