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TRC-440

Aegir

Member
Jun 27, 2013
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0
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I have a TRC-440. It's a back up radio, but sounds good & is a good performer.

I'm interested in making some minor modifications to this radio:

1.) Replace Squelch circuit with an RF Gain using the same Pot on the front of the radio.

2.) Upgrade Finals

Attached is a schematic. I'm a novice tech, but have already perfromed the rudimentary adjustments/tweaks found on the web - notable L102 L104 L106 adjust.

Can someone tell me which final transistors to upgrade to, & which resistors I'd have to change as a result?

L102 is stuck - I'd like to just replace this part. It's an RF transformer, but looks different than L104 and L106 - not your typical ferrite coil in a threaded form with copper wire around it. It looks smaller & is sitting atop a plastic base. It may be tapped? Dunno.

73's & thanks for reading.
 

Attachments

  • TRC-440 Schematic.pdf
    67.9 KB · Views: 90

Addendum

Just a quick addendum - I replaced both large caps on the power supply PCB with larger values to help filter out the AC, but still get significant AC hum with the volume turned down audible through the speaker. I also soldered a 3 prong AC cord, with the ground to the terminal marked GND on the AC side of the PCB. Do I have to go ahead & replace all the rest of the electrolytic caps? Thanks.
 
yes, a hum in the audio is many times caused by a bad filter cap in the power supply, but that is not always the case.

there could be a bad cap in the audio section of the radio that would also cause that condition.

if it were my radio i would replace all of the electrolytic caps just to be sure.

there is no point in replacing the final and driver transistors.

no one would notice one single bit of difference in your signal if you were suddenly able to swing up to 25 watts instead of 16 watts.

to gain a 1 S unit increase in someone else's receive, you have to quadruple your power output.
that is not my opinion, that is a fact.

if you key up with 4 watts deadkey, and hit someone with an S-5, to get to S-6 you will have to deadkey 16 watts.
100 watts out of your radio gives them S-5?
you will have to put out 400 watts to get to S-6.

thats just the way it works.

if you want to get some additional modulation in that chassis, try messing with the value of R134.
i like 1.5K ohms, but if you are looking to experiment, try anywhere from 470-3.3K ohms and see what you like best.

do not clip the diode or other part that the "internet instructions" tell you to.
it will make the audio sound terrible.

if it is clipped, solder it back together.

i would not mess with L102.
it wont gain you much at all, and the chances of breaking it are very high.
if it breaks, you will probably put out much less power than before, and you'll have to buy another 440 to get a replacement.

if you just must try it, you might be able to loosen it by carefully holding your soldering pencil on the ferrite slug, just long enough to heat up any glue that may be holding it in place.

again, my advice is to leave it alone, but i know how folks love to tinker, especially if its a "backup radio".

PS- you should have the green wire (ground) of that AC cord going to the actual metal chassis of the radio. the other two wires just get connected to the wires that went to the old two wire cord.

good luck,
LC
 
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I have a TRC-440. It's a back up radio, but sounds good & is a good performer.

I'm interested in making some minor modifications to this radio:

1.) Replace Squelch circuit with an RF Gain using the same Pot on the front of the radio.

2.) Upgrade Finals

Attached is a schematic. I'm a novice tech, but have already perfromed the rudimentary adjustments/tweaks found on the web - notable L102 L104 L106 adjust.

Can someone tell me which final transistors to upgrade to, & which resistors I'd have to change as a result?

L102 is stuck - I'd like to just replace this part. It's an RF transformer, but looks different than L104 and L106 - not your typical ferrite coil in a threaded form with copper wire around it. It looks smaller & is sitting atop a plastic base. It may be tapped? Dunno.

73's & thanks for reading.

I know this is a old post. But this was one of my favorite radios back in 1979.
The modulation adjustment is not R134. Its R135. Changing it to a 1K will get you around 100%. Don't clip it it will sound like crap. These radios sound full and natural with a D104. I remember the first time Inheard a local using one.
I was shocked at how good it sounded. I rushed off to Radio Shack and got the last one half price. $69.95. I just purchased a NOS and recapped it.
Sounds great.
 
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Reactions: tecnicoloco
the regulator section offers a lot of ripple rejection if it is working correctly.
yours may not be.
probably due to dried out caps.
if you want to use this rig in the long term every lytic needs replacement.
iirc this is a cybernet chassis.
been a long while since i have seen one.
 
I know this is a old post. But this was one of my favorite radios back in 1979.
The modulation adjustment is not R134. Its R135. Changing it to a 1K will get you around 100%. Don't clip it it will sound like crap. These radios sound full and natural with a D104. I remember the first time Inheard a local using one.
I was shocked at how good it sounded. I rushed off to Radio Shack and got the last one half price. $69.95. I just purchased a NOS and recapped it.
Sounds great.
OLD thread, but looks like you have experience with TRC-440!

For the audio limiter, so far I've seen R135, R136, R139, or D107, D108, and D109 from Secret CB.

Which is it?
 

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