RGD R135 3 band radio

[Crackle]

I am having a problem with this little RGD R135 radio I recently bought off Ebay.
       
It was described as screws missing from back. The screws fixing the chassis to the front half of the case were also missing.
The radio only seems to work on FM and that is very very faint.
I have fed an audio signal into the volume control and the audio side seems to be working OK, so I believe the coils and trimmers have probably had a very bad case of twiddling.
   
Someone has also had a go at fixing the tuning dial cord but not done it correctly as it was not possible to get the full range from one end of the dial to the other.
That's now fixed after a lot of experimentation.

There is not a lot information that I can find on this RGD radio but I have at least got a 2 page service sheet.
I have discovered that despite its appearance the RGD R135 appears to have the same chassis as the early ITT Colt.
There is not much information on the ITT Colt either, but I should think that the RGD R150 is pretty close in alignment procedure if not circuit and layout..

So my problem is I am not very experienced in FM / AM sets and circuits and I am trying to identify the various coils.
So from the circuit diagram I think the coils are as follows;
   
FM RF = L302
FM Osc = L304
FM IF1 = L305
FM IF2 = L308
FM IF3 = L311
FM discriminator = L312

AM Aerial = L306 & L307
AM Osc = L315
AM IF1 = L309
AM IF2 = L310
AM IF3 = L313

I was wondering if somebody could please confirm the above inductor list and their use.

Thanks
Mike

[pwdrive]

Your inductor ID looks ok to me.

Lawrence.

[Crackle]

Hi Lawrence
Thanks for confirming that, I will go and have a go at alignment now.
The data for the R350 say start with the AM IF.
   
Mike

[Terry]

Be careful, Mike!

Those instructions have the AM pointer the wrong way round! If you look at your picture, 200m (HF) is on the left and 550m (LF) is on the right - same for LW.

Also, that 1650kHz frequency is suspect - it's more likely to be 1605kHz.

I think the colour coded cores on those inductors follow a standard code so it might help in the future to keep a record of which colour does what.

Unless you can see actual evidence of twiddling, I think your problem is more likely to be a fault somewhere in the IF strip.

[Crackle]

Hi Terry
I think you are right, although there are minor signs of the slugs being twiddled, that may have been from initial setting up at the factory.
There must be a fault somewhere, my first try after making a 85 turn coil "dummy aerial", as mentioned in the alignment instructions, proved absolutely nothing passing through the IF strip.
So I gave up with the coil and connected the signal generator to the base of T305 via a .01uf cap. Nothing.
I then started probing around with the signal generator and the only place I get any sort of tone is on the end of the detector diode connected to C336 & R327, and that is very faint, but the D303 tests OK on a diode test (whilst still in circuit).
Anyway given up for tonight as my back is aching.
I will have another look tomorrow.

Mike

[Crackle]

Not having much luck with this radio.
Can anybody tell me what type of component R350 is in the centre of this image and what/and how it does it..
It measures just about infinity on a DMM.
   

edit;
Is it a voltage dependent resistor (VDR) what is it protecting in this circuit


Thanks
Mike

[westcliff]

Hi Mike, there's one of these in this circuit. http://kbmuseum.org.uk/itt_service_manua...ny_Super_r&tvs.pdf

It's not some sort of fuse?

Gus.

[Crackle]

Hi Gus,
Yes, thanks, I came across that circuit as well when I was searching the internet. If it is a VDR they are supposed to be used for high transient voltages like lightning.
I have no idea what it is doing in this part of the circuit.
Can any one help.

Thanks
Mike

[pwdrive]

It's a VDR according to this schematic and components list:

http://nvhrbiblio.nl/schema/Graetz_301Hostess.pdf

Lawrence.

[Crackle]

So why is there a VDR in the circuit, what is it doing, how can I test it to check its working???
Also there are not many voltages marked on the schematic but the ones there, do they look about right. I am getting nothing like the ones given.
For instance;
T301 E 3.8v, B 3.1v C 0v
T302 E 3.7v, B 3v, C 0v
T303 E 3.7v, B 3.1v, C .5v
T304 E 0v, B 2.9v C2.5v
T305 E 2.4v, B2.9v, C 0v
For the above voltage readings I am measuring with the negative probe on point A which is the neg supply rail for the RF section, see schematic in post 1
I think I am going to have to dismantle an ITT Colt and do direct voltage comparisons between a working Colt and this R135.

thanks
Mike