Realistic TRC-457 Talkback?

[Mr. Fortyfive]

Hello Everyone!

I just got a hold of a Realistic Navajo TRC-457 the other day. Can a talkback
mod be added to this radio? I want to use an echo mic with it. Also like to
run an amp with it and just wondering if there is a way to add a swing mod
to this radio. Would any appreciate any advice and info.

Good Day and Happy DXing!!
Mr. Fortyfive

 

[liquidh8]

For the Washington & TRC-457 (858pll), you can connect a resistor from the modulation transformer output where it connects at the relay, then the other side of the resistor to the positive side of C103, which also connects to the relay, C103 is a DC blocking cap for the speaker as this is also the modulated DC line for the driver & finals for AM mode. You will have to experiment with resistor values, somewhere between 330 ohm to 680 ohm or so. A 330 was too loud when I tested it, and a 680 was close, so experiment.

This gives talk-back in AM mode, but does not work for SSB, but not many people use echo on SSB anyway, so no big deal I guess.

 

[mackmobile43]

For the Washington & TRC-457 (858pll), you can connect a resistor from the modulation transformer output where it connects at the relay, then the other side of the resistor to the positive side of C103, which also connects to the relay, C103 is a DC blocking cap for the speaker as this is also the modulated DC line for the driver & finals for AM mode. You will have to experiment with resistor values, somewhere between 330 ohm to 680 ohm or so. A 330 was too loud when I tested it, and a 680 was close, so experiment.

This gives talk-back in AM mode, but does not work for SSB, but not many people use echo on SSB anyway, so no big deal I guess.

Can he add a toggle switch in that circuit without any IF issues?

 

[giboni]

Okay,

An old thread. Just maybe 399 might have some information !

I purchased off FleaBay a talkback speaker with hookups. Works fine on the Cobra 19 VI

which is a test jig for Mosfet finals. Works on an old Uniden Pro 510 that I use as a test

fixture for NPN Bipolar transistor finals.

But not on the Trc 457,458,139xlr,Washington 858.

I'm leary of the above Mod. Is this the only known Mod?

I guess I can do the Mod with a 680 ohm or larger. Add a small $2.98 Audio Amp

into the speaker enclosure. Have two volume controls. I don't connect the PA red plug.

Then I have to filter the 13.8v to the mini amp. Can wind a 10uf choke on a torroid.

Obviously the above Mod is taking a portion of the signal that drives the finals it seems.

Seems to be plenty to spare though with a Turner +3 and power mod on the

858 chassis audio circuit. I detailed this Mod. on another thread.

73s Best John