GEC 4444 Receiver.

[clay shooter]

Just taken the chassis out of a gec 4444 portable that I've Just bought,( the dust and mummified lady bird came free)the wave change rotary switch appears to be almost seized, is it possible/advisable to try and free it off with the application of WD-40 type penetrating fluid ?.
I'm not surely that I have the physical ability after a serious hand injury last year to totally disassemble the whole switch.

[clay shooter]

Bought an unmolested GEC BC 4444 portable radio a couple of weeks ago, have been looking at the schematic and there's no recommend voltage listed with the capacitor values.

I intend to replace all 4 electrolytics along with the high value resistors before I power up from a battery(s). As it will run on 90V, would,say,100V rated capacitors be OK or should I go for 240V upwards?

Also one of the capacitor is a 250uf electrolytic, would a 220uf be an acceptable replacement as this value seems easier to find in a suitable voltage

Thanks in advance

[Neutrino]

If the old capacitors have voltage ratings marked on them, it is safe to use the same or a higher voltage rating.

Component numbers below are from “Trader” Service Sheet 1086.

C23 H.T. Smoothing 32μF: The nearest preferred value is 33μF. I think that 100V would be OK for battery operation. The Valve Analysis shows 95V on the anodes of V1 and V2. To give a margin, especially if the set might eventually be used on mains, I would select at least 160V.

C24 H.T. Smoothing 16μF and C25 H.T. Smoothing 32μF: These are not used for battery operation. There is no need to replace these if you are not going to plug into the mains.

C25 H.T. Smoothing 32μF: A minimum of 350V corresponding to the mains voltage x √2 is a very conservative estimate because there will be voltage drop in MR1 and the first segment of R19 (285Ω or 870Ω?). The Trader Service sheets states “the voltage across C25 was 194V”. This suggests that a rating of 250V would be adequate.

C24 H.T. Smoothing 16μF: 16μF is not a preferred value. 22μF would be suitable. R18 (1.5kΩ) and the three middle segments of R19 (560Ω+500Ω+870Ω) form a potential divider. A minimum of 250V which is about mid-way between C23 and C25 would be a very conservative estimate. The Trader Service sheets states that the voltage across C24 was 116V. This suggests that a rating of 160V would be adequate.

MR1 will probably fail if the set is connected to the mains. MR1 can be replaced by a silicon diode and a series resistor of suitable power rating adjusted to get the correct voltage on the valve heaters.

C22 Filament smoothing: 220μF is an acceptable replacement for 250μF. Electrolytic capacitors have a wide tolerance so values are not critical.

David

[Neutrino]

Originally Posted by clay shooter

__________________
If it ain't bust don't fix it

Are the capacitors faulty? You could try the set on batteries without changing the capacitors.

[clay shooter]

Due to its age , I think it's safer for me to change them they all look okay no, damage or leaks evident,but as it has a full set of original valves I'm playing Safe.
Thanks for your input

[clay shooter]

Looking at a gec 4444 portable at the moment and it's totally dead on both mains and batteries,none of the valves appear to light up but I've voltage at the heaters, only about 3.1/2 v though, I intend to change all the high value resistor and all electrolytics as a matter of course, although the tank capacitor replacement is being difficult to find being 32uf,+ 16uf,+ 32uf.
Would it be possible/advisable to replace it with 3 appropriate value/ voltage capacitor's ??

[Station X]

Don't change components wholesale without doing some proper testing with your meter.

References are to Trader Sheet.

Clean the contacts of the wave change/battery-mains switch.

Snip out C26 which may have blown. It's wired directly across the mains.

Replace C20 the audio coupling capacitor (that capacitor) to reduce the risk of damaging other components when power is applied.

Check the resistance of the sections of the dropper resistor R19/R20.

Check the valve filaments for continuity.

Apply power via a test lamp or Variac and check the heater voltages again.

[clay shooter]

Thanks Graham, I had already replaced c22 as it had ballooned and had started to leak ! .
When I get time in the week I'll replace c20 and clean out the rotary switch colecting switch cleaner on my way home tomorrow)and check out the rest , thanks for the reply.
I'll get back to give an update later this week

[clay shooter]

Having another probe about in this gec portable,( haven't touched it since before Xmas).
Have it connected up-to the batteries trying to find the fault(s) that are preventing it from working ,can't get the valve heater to Glow,while I was probing I found the LT batterys (5 AA in a holder) we're getting warm i checked the drain and it's about 55.3mv ,is this Normal ??, seems far to high to me.
Can anyone please steer me in the right direction?.

[Cobaltblue]

Originally Posted by clay shooter

Have it connected up-to the batteries trying to find the fault(s) that are preventing it from working ,can't get the valve heater to Glow,while I was probing I found the LT batterys (5 AA in a holder) we're getting warm i checked the drain and it's about 55.3mv ,is this Normal ??, seems far to high to me.
Can anyone please steer me in the right direction?.

Did you mean mV? the valves in series will take around 50mA so if its 55.3mA its in the right ball park.

You will struggle to see the valves light up you will need the lights to be low.

If you really did mean 55.3mV and that's across the battery terminals you have a virtual short circuit somewhere.

Cheers

Mike T

[clay shooter]

Sorry for the late reply, I didn't get a notification of a reply !.
Yes I'm stupid I did mean mili amp's ( been a long week).
If the drain on the battery is correct ,what would cause the battery's to overheat? Thought it might be a faulty cell but still got warm with a new set of batteries ( the 90v battery stays cool)

[Cobaltblue]

It seems odd 55mA heating up the battery.
The valves used in this set are 50mA types except the output valve (N18 or 3Q5) which has a tapped heater 100mA in parallel or 50mA in series as it is in this set.

You could try connecting a resistor in place of the radio across the batteries say 150 Ohm at 2W rating. Check your meter is reading correctly that should give you more or less 50mA with your 7.5V battery pack.

see if the battery pack still warms up (isolate the problem) looks like some kind of strange problem with the batteries or holder.

Cheers

Mike T

[clay shooter]

A quick update,
Had another probe this evening,changed c20 and c26 powered it back up and it sort of works, plenty of motorboating, will look at the decoupling caps later and after A few minutes a loud buzzing from the speaker , Will change the HT smoothing caps .
Volume is low and selectively is poor ,but, that could be due to the location of my cave ( just above the house consumer unit )
But it showing signs of life ,thanks for your help