President Washington Talkback

#318099

So I have this beautiful Pres Washington. I want to put talkback on it. I have tried the jumper from the PA to the ext speaker jack, didn't work. I opened it up and soldered a variable resistor between the pa and ext speaker, didnt work. Not sure why, any ideas? anyone ever done this mod to the president Washington?

#318104

420 mobile wrote:So I have this beautiful Pres Washington. I want to put talkback on it. I have tried the jumper from the PA to the ext speaker jack, didn't work. I opened it up and soldered a variable resistor between the pa and ext speaker, didnt work. Not sure why, any ideas? anyone ever done this mod to the president Washington?

Which chassis is the radio? Does it have 4 or 5 pins at the Mic jack? If it has 4 pins, then the relay radio chassis will not work using a resistor from the receiver pin to ground.

Respectfully,

#318112

ya its a 4 pin. Is there another way of making talkback? I thought i read some place you could make something where it picked up your voice off the coax while you transmit.

#318115

420 mobile wrote:ya its a 4 pin. Is there another way of making talkback? I thought i read some place you could make something where it picked up your voice off the coax while you transmit.

Hi 420 mobile,

You will have to pick up the audio at the relay and feed it to the audio chip. I haven't done one in a long time, so I will have to go through my notes. I know you will need a resistor and a capacitor in series. The components' value will determine the volume of the talk-back.

I will get back to you after the kids are in bed......

Respectfully,

#318159

that would be fantasic! thanks alot, Looking forward to learning a few things.

#326043

Did the kids go to bed yet?

#327040

Lol, I am looking to do the same thing! I'll have to search some more!

#327058

Well I did a quick look at the schematic for the Realistic TRC-449 which is about the same for the Washington with the 858 chassis & the TRC-457, (I own both the 858 Washington & the TRC-457).

The speaker switching is a bit different in these radios.

Looking at the schematic it appears the speaker is unhooked from the modulator circuit in transmit mode by the relay, effectively unhooking the positive connection from the speaker. The negative speaker terminal is always connected to ground which is why the typical resistor across the speaker jack & pa jack ground does not work.

For the Washington & TRC-457, 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.

I will include a picture of my TRC-457 so you can see where to install the resistor, this applies to the President Washington 858 chassis, Realistic TRC-457, TRC-458 & any other radio that uses the same board.

I installed a 100-ohm resistor for the picture since I have a bunch & it was small enough to make the connection points of where it solders to visible, but you will have to experiment with values as stated above.

It seems to work fine; it gives talk-back in AM mode anyway. Hope it helps.

Here are the pics of the MOD, & yes my radio is not in very good condition, it has been worked on by a couple techs over the years & who knows how many more before that.

#327077

Thank you for the reply! Have you done any of the other mods floating around for the 858 chassis? I seen something for a microphone and transmit mods, I just got mine and dunno if I should do anything or leave it alone, lol, I guess I could always put it back!

#327302

Mine has had the channel mod & 10Khz jump done, & the modulation circuitry modified.

I added the channels many years ago, but another local that repaired the TRC-457 for me many years back did the modulation mod. The radio always seemed to perform well & always got good reports on it. Always got compliments on SSB too.

Personally I don’t think that any of the MODs will make enough difference to worry about doing, & if your radio is pretty clean a simple tune-up & alignment may be all that’s needed. I think the most important thing is to make sure your antenna setup is as good as it can be, & if you really need to get out further an amplifier would make the most difference rather then getting crazy inside the radio.

All that was done to mine from recollection was D21 & D22 cathodes were lifted & a jumper soldered where they were lifted from on the board. Some of the internet mods say to use a 4.7K resistor, but the guy that did this just soldered in a jumper, it has worked fine for many years & again got good reports on it. I did this to my Washington since it was done to my 457 & it worked fine on that one too.

That’s about it on mine. But again, if your radio is in decent shape I would not do much too it, they perform well without anything done.

352 Smiley · #327323

wish i chould help sorry

#345276

Pioneer621 wrote:Well I did a quick look at the schematic for the Realistic TRC-449 which is about the same for the Washington with the 858 chassis & the
For the Washington & TRC-457, 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.

THANK YOU!!

This worked for me on my Robyn SB-520D using a 160 Ohm resistor, and talking on the stock mic.
I searched for 4 hours looking for this exact data and finally came across this post during my internet search!

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