Lovely GEC Valve Radio Repaired
This GEC Valve Radio, looks like, will be a frequent visitor to my workshop! The main reason for such temporary repairs is because of the customer’s unwillingness to spend too much money for repair! This was brought to me in December, 2013, when the customer bought it from some place, falling in love with its external beauty! On my inspection then, it was in shambles; Cabinet was shaky, with full of dirt and filth, none of the dial wheels were moving, and gang was stuck.Set was in dead condition, though the filaments were glowing.That time, after doing a thorough cleaning, I traced the fault to EZ80 rectifier valve, and a few burnt resistors and capacitors. Replaced all those. Surprisingly, the Can Capacitor was intact and working very well!
The ferrite core of one IFT was presumably broken, as the adjusting screw was freely turning. Since customer wanted only one local station in MW to be working, I did alignment to the extent possible and was surprised to notice that the Radio was working very well, with all the handicaps! So, I gave it back then, with the advice to the customer to keep using it. But that was something he did not and it was used only once in a while. Thus, this was brought to me again in September, 2016, with the same complaint, ‘dead’! The back cover was hanging, and I found a lot of cobweb, dust and filth once again filled in it!
After dismantling the chassis from the cabinet, I did a cleaning with brush and blower to the extent possible.Disconnected the speaker and kept the cabinet aside. Connected a test speaker and tilted the chassis on its side to examine the bottom side of the valves. Please see picture below:
Switched on the set and there was no audio at all, even when touched at the hot point of volume control. Checked DC Voltage at pin 3 of EZ80, and noticed that the DC was only in the order of around 178V in place of around 230 to 240 or even 250V. So, I replaced the valve with a good one. But still, there was no sound output. Checked voltages at pins of EL84, output valve amp. Voltages at 9 and 2 were ok. But there was no voltage at pin 7, which indicated that the output transformer primary must be open or some loose contact or dry solder. Switched off the set, discharged the high voltage capacitor and desoldered the primary of output transformer, checked continuity and noticed that it was open. I put a standby output transformer that I have in its place and reconnected the primary and secondary (that goes to the speaker) and still there was no output, except a low noise. Touched the pin 2 of the EL84 with a screw driver, holding it at the handle only, and could get a very mild 50Hz hum. Checked the voltages of EBC81 (preamp) and noticed that voltage at pin 1 was missing. Switched off the set, discharged the high voltage capacitor and removed the EBC81. Checked the 220K resistor connected between B++ and pin 1 of EBC81. It was open. Please see picture below:
Replaced the resistor with a 2 W 220K. Put the EBC81 back and switched on. Set was working perfectly well. Gave an aerial and tuned to stations in MW. Gave the transformer for rewinding next day and got it back after a delay of one week, since this place was closed for about a week for Onam Celebration (a typical festival in Kerala).
Connected the transformer, and output of it to its original speaker. I replaced the capacitor connected across the primary, as its value had changed, from .0068mfd to around 9 NF. Switched on the set and it was working perfectly well. I just tried putting its original EZ80 (Rectifier valve) back. The set was working well then also, though the volume output dropped a little bit. The DC voltage was only around 178 to 180 V! So, thatI saved the cost of replacement for the customer. Here you can have a look at various pictures of its inside, bottom (which has a square hole for trouble shooting without removing the chassis out), bottom with its cover, writings on the back cover etc. (The wire that you can see on the middle of the magnet of the speaker is a shield ground, joined at the speaker (-) terminal, which means that when you connect the two output wires of the transformer, we have to be cautious about this, i.e., + should go directly to one wire of the transformer and the other should be grounded along with the other lead of the transformer output.)
Here is the front side of the Radio in working condition, and its full back cover, after completion of fitting:
The customer did not want replacement of the ‘magic eye’ valve. Here are the pictures of the transformer, components replaced (including broken two pin plug), foreign articles found inside the radio (probably dropped in by children while playing):
Another work completed satisfactorily only to the customer! (Not to me, as I prefer to refurbish the Radio to the best possible extent!)
Here are the schematics of a typical Valve Radio Circuit for those who might be interested:
In the component list, the language used is in Malayalam. So, here is the translation: First column heading: Condens ers, Second: Resistors, Speaker, Third column: Transformers, Coils and Valves. C4 is a Gang Condenser. R7 is volume control. Speaker is 3 Ohms. Transformers are input, output IFTS, and output transformer suitable for EL84 valve, 80mA Power Transformer. Coils should be suitable for ECH81 valves. List of valves are as shown there. I have written the values of the resistors in the circuit itself.
This article was prepared for you by Parasuraman Subramanian from India. He is 66 years old and has more than 30 years’ experience in handling antiques equipment Valve Radio, Amps, Reel Tape Recorders and currently studying latest techs classes conduct by Kerala State Electronics Technicians’ Association. He was a BBA graduate, retired as MD of a USA company.
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You may check on his previous repair article below:
https://jestineyong.com/how-to-build-stk435-amplifier-ic-tester/
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Albert van Bemmelen
October 11, 2016 at 2:50 pm
Again good work Parasuraman since the Customer is happy! I noticed that the Loudspeaker probably does have a permanent magnet. Because I once had a reciever with a speaker so old that the DC input voltage was used to create an elektromagnet instead of using a permanent one.
Thanks for the article and the schematic.
Yogesh Panchal
October 11, 2016 at 8:15 pm
Sir,
Glad to see antique equipment still in the safe hand for repair.
Thanks for sharing.
Robert Calk
October 12, 2016 at 4:04 am
Good job, Parasuraman. I remember when I was a kid my dad always called capacitors, condensers.