Fixing a Realistic TRF radio's scratchy volume control the easy way

Realistic TRF 655 AM long distance portable radio, as it was when I bought it a few years ago at a thrift store -- this is before I fixed the volume control.

The Radio Shack, Realistic TRF is a well-known Long Distance AM band radio (known among radio nuts as a "DX radio") which was made in the 1970's. Some can still be found at garage sales, online, or at thrift stores -- where I got mine a few years ago.

A COOL THRIFT STORE FIND

I got my Realistic TRF 12-655 at a thrift store. The person who had it before must have been a painter, or had done some painting, as there are a few tiny specks of white paint on the case.

No sooner than I put batteries in the radio I found it worked great. The only glitches were two points on the dial where it will pop slightly if I tune across them very fast (common to older transistor radios with plastic mesh tuner capacitors), and -- well -- the reason I've written this article: the Volume Control was noisy.


This problem is one that is common to older radios, and especially common to older radios with slider potentiometers: scratchiness from use and internal wear in the slider.

In fact, the volume control on mine was so scratchy it was difficult to use with headphones, sometimes painful. It would pop. I found myself not ever using the radio.

The tone slider, however, was clean as a whistle.

SOME BACKGROUND ON THE TWO REALISTIC TRF MODELS

Before I go into how I fixed my volume control, I'll write a little bit about the TRF itself, because there are still radio distance-listeners out there who have these radios, and there isn't a ton of information out there about them.

The TRF came out in two different models, the 12-655 and 12-656 (there was an earlier variant in the 1960's apparently, I know very little about that one).

The 12-655 is the more well-known of the two, and many believe it is the better performer. Both radios have your standard RF amp - Converter - IF amp - IF amp - Detector - AF section radio circuitry. The main difference is that the 655 has a ceramic filter in front of the first and second IF amps, and the 656 has an extra IF can in between them instead.

Realistic TRF model 12-656, with slightly different styling, slightly different circuitry, and a tone switch.

A Realistic TRF 656 with its back off. This is the TRF model that came out after the one in the top picture. The shorter antenna and slightly different components can be seen. This is not the radio that needed the tone and volume switches re-wired -- photo just put in here for comparison.

The AF section in the 656 is a chip, the 655 has four discrete transistors.

The antenna in the 656 is shorter than the one in the 655 (as can be seen in the above photo). The 656 has a tone switch, and the 655 has a tone slider. The 655 has 'narrower skirts' in the selectivity, the 656 has wider skirts. That means, basically, that with the 656 you get a little more treble in your listening, but in the 655 you can tune to a weak station that is right next to a strong station, and hear it better.

The 655 seems to have an overall edge in performance, much of it due to the larger antenna and the selectivity may give it a slight edge as well.

The Realistic TRF 655 with the back off (after I fixed it). The loopstick antenna is about 180mm long or so, and fairly thick -- which pulls in signals quite well. You can see the yellow coded IF can with ceramic filter in the middle of the radio's PCB. It's a large metal 'can', which has the IF coil and ceramic filter all in the same enclosure.

IT WAS AN EASY FIX, ACTUALLY

Just before last winter's lousy Long Distance / DX season, I decided to fix the problem with my TRF's Volume Control. Not having any spare slider potentiometers handy, I did the next best thing: I swapped the wiring between the two sliders (tone slider and volume slider). That way the clean tone slider would be used for the volume, while the scratchier volume slider would be used for the tone, which I used less, anyway.

It wasn't that difficult to do -- in fact, it only took about 15-20 minutes, including disassembly, re-assembly, double checking to make sure I wasn't messing up the wiring, etc.

This is how the TRF's two slider controls, tone and volume, looked before swapping the wiring. The way the radio is wired at the factory, the tone slider is on the left hand side of this picture, the volume slider is on the right hand side in this picture. After being  re-wired, the new volume slider will be on the left side of this picture, and the new tone slider will be on the right.

The wiring swap is very simple: you just remove the wiring from the volume control and apply it to the tone control, and vice versa... and you must move the green capacitor in the picture above to a different pair of terminals. You don't have to know radio circuitry to do this fix.

WHEN REWIRED, THE CONTROLS ARE REVERSED

Now that the controls are reversed, and they also work in reverse: Full volume is when the slider as at the bottom of the radio, not the top. Full treble is when the tone slider is at the bottom, not the top. It's not that difficult to remember. The easiest way to remember is to make sure and shove the controls all the way back to the top when you're done listening to the radio.

(You could also swap the actual controls themselves, which would allow for them to work exactly in the same direction they did before fixing the problem -- but that would take a lot more work than just swapping the wires and remembering that the controls and direction you slide them is reversed).

The Realistic TRF's tone and volume controls with the wiring swapped. Now the old tone slider is the new volume slider, and the old volume slider is the new tone slider. Note the new position of the green capacitor -- it was on the top of the two controls, now it is on the bottom. Full bass and low volume are now when the sliders are all the way to the top. You now push them downwards to get more treble, and more volume.

So, if you do this fix the way I've shown it here, as soon as you're done -- push both knobs to the top. The tone will be on full bass (muffled), and the volume will be all the way down.


Otherwise, as soon as you turn on your TRF, it will be at full blast. You don't want that.


The Volume control will now be on the far right side (actually, a more convenient place for it, especially if you're right handed), and the Tone control will be on the inside, nearer to the speaker (also more convenient, as most people use the volume more than the tone control on these radios).

The original tone slider on these radios is linear taper, and the original volume one is audio taper. With the wiring swapped, that isn't all that much of a problem. You just have to use finer increments in setting the volume than before, that's all. It's not a problem for me at all. There still is enough play in the Volume control to make it very usable

With the wiring swapped, the new tone slider on mine works fine (with no noise) and so does the new volume control. 

WAITING FOR THE NEW LONG DISTANCE AM/MW SEASON

Last Long Distance ('DX') listening season was a stiff, of course. Consequently, I haven't DX'ed the AM band probably in nine months now. But I will haul my TRF out of the closet this October or so, plug in the headphones, and give the band a listen, and see if there is anything worth listening to.

The Realistic TRF is a very capable radio. I've heard Radio Rebelde from Cuba, about 2770 miles away, on just the internal antenna of my 12-655 (the radio pictured below) more than once. It works great with an external loop, too (also shown in the picture below).

A recent picture of my Realistic TRF as it is now. The volume control is now on the right side, and when the control is all the way up, the sound is all the way down. Where I have the volume set in this picture is where I usually have it. It's plenty loud. The tone control is now on the left, and where I have it set in the picture is a nice mix of treble. The circular thing to the left of the TRF is a Select-A-Tenna, a loop antenna that boosts signals to the radio. The dial in the middle of the Select-A-Tenna 'tunes' it to the radio. You just set the Select-A-Tenna next to the radio, turn the dial until the signal peaks, and you can hear AM radio stations on Mars! :-)

THE TRF's SOUND

Through the speaker these radios sound -- well -- like medium sized transistor radios. They have volume, especially the 12-655 model. But tone wise, they are a little bit thin. OK for talk radio, though.

But through headphones you get a much richer sound. The best way to Distance listen ("DX") with a TRF is using headphones. It's the best way to get the most out of these remarkable old radios.

A pic of me a couple years ago, a bit heavier and with a beard. The camera I used in this pic was a $20 digital snapshot camera.

Hope everyone is having a good October. Here it's 60+ degrees almost daily, and decent weather. The big-leaf maple trees here are getting orange leaves. Hopefully it will hold until the end of the month. I have been taking photos of them -- will put them up in a post soon. Thanks for reading!

CC 10-18-2014