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MG MGA - Radiomobile 50T

I've got an old 50T radiomobile radio in my car, not push button but the one with the turn knobs + earth LW MW and recently its gone off tune and won't hold a station. It was never very good reception but now it seems to prefer french radio stations -is this some kind of revenge, or is it possible I could retune it using one or more of the many small screws on the chassis that seem to invite turning. I'm not into radios but someone out there may be up to speed on such matters.
J H Cole

It sounds as if you may have changed your antenna. There is usually a tuning screw, but I don't know where it is. You might also open the case and see whether all tubes (valves) are firing.
mike parker

Yes Mike I've recently taken the aerial off and refitted it. I did not know that things were so sensitive -I will try and locate the correct tuning screw.
J H Cole

The aerial trimmer is normally accessible from the outside of the case. Twiddle at random with tuning screws inside at your peril.
Malcolm Asquith

I seem to recall it is sometimes on the front face, may be hidden behind a pull-off knob.

Steve
Steve Gyles

Is the radio still mounted? If so I have a 50T off the car if you need me to go and have a look. You can also send or take it to vintage wireless in Manchester who will add fm and a connection for something called mp3 etc? Not sure how much they charge these days, but I have a converted unit in my MGB and it works great.
Neil McGurk

I have attached a page from the factory installation instruction for the 40T (pushbutton). I assume the 50T is basically the same.
It says to adjust the aerial trimmer after the radio is fully fitted, so I assume that the trimmer adjuster must be on the front of the radio, or underneath.


Mick


M F Anderson

Neil, please see image showing the mounted radio and theres no sign of the trimmer on the underside. I can hardly see the sides but maybe its there. If you could check with yours it would be useful and save me possibly having to take the radio out. I did look into adding FM and I think the innards have to be pulled out and new circuitry installed. Somehow this seems a little drastic to me so I will settle for MW/LW as long as I can get a decent reception. MF, thanks for the ciruit diagramme it shows the aerial but theres no clue to where the trimmer might be.


J H Cole

I expect you have found it by now, but in case you haven't I attach a picture. The aerial (antenna) trim screw is towards the back on the right hand side of the case looking from the front. In the pic you can just see the brass adjuster in the middle of the second from bottom row of ventilation holes indicated by the black arrow. Although the ID has worn off the case I can vouch for the fact that this is the correct adjuster.

Andy


Andrew Dear

Mick and Andrew, thank you guys for your photos on this radio. I have a 1956 MGA and I have been wanting to add this original radio to my car but really did not know how. With your help I now feel really a lot more knowledgable on how to do it. Thank you for sharing your information. Sincerely, Tom Peotter
Tom Peotter

One of my earliest lessons in electronics, in the late '50's was not to "tighten" loose screws on a radio chassis. It turns out that I had completely ruined the adjustment for the IF or Intermediate Frequency used for de-modulating the AM received frequency from the antenna to audio frequency for the speaker. The repair involved using a signal generator and oscilloscope to reset the IF frequency. In other words;
1. Be very careful of what screws get turned on the radio chassis or the radio will have to be repaired and re tuned. On the other hand, new tubes for a tube radio and especially new capacitors for any old radio and a re tune can make a significant improvement in reception and power requirements of an old radio.
2. Remember that having the ignition switched on and the engine not running, for example to listen to or operate the radio, if the points are closed and Murphy makes this an 80% chance, the ignition wiring will be connected (shorted) to ground, melting the wiring (white wire black stripe) and possibly starting the (in)famous Lucas wiring fire. Under the hood or bonnet, out of sight until too late.
3. The antenna tuning adjustment used components like inductors or capacitors or combinations of both to tune the resonant frequency of the antenna (electrical length) to more closely match the (wave length) or resonant frequency of the broadcast frequency, tuning to maximize the received signal to the radio. If you have an adjustable length antenna, large changes to the physical length of the antenna can affect the received signal strength for AM or higher frequency signal. Long wave signals are just that, X number of meters from wave peak to peak, requiring meter length changes in antenna length or other elements in the signal path to tune for max signal.

Careful of the ignition switch.

Yup, far more than you really wanted to know.

Russ
Russ Carnes

This thread was discussed between 12/11/2008 and 17/11/2008

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