Gec 5441

[singlepentode69]

I have recently purchased a GEC 5441 wireless I have printed off the trader sheet for 1952 but the valve line up is totally different .It does work of sorts on one wave band but gets a better reception when you touch v1 what could be causing this and is this the reason for getting no reception on the other wave bands
Regards
Robin

[Skywave]

When you say "touch v1", do you mean you simply touch the glass valve envelope or a particular pin (or top cap - if fitted) of v1 ?

As for "no reception on other wavebands", two avenues to explore come to mind:
1. Check valve electrode d.c. voltages;
2. Check that the oscillator is running by using a 'scope.

All of the above obviously assumes that you have connected the set to a suitable aerial - probably a 'longwire' in this case.

Al.

[singlepentode69]

When I touch the glass envelope the signal gets stronger.i do not possess an oscilloscope is there another way to test if the oscillator is working
Regards robin

[singlepentode69]

I have been using a price of wire running along the fence regards
Robin

[Joe]

Could be a bad contact in the valve base. Give that a clean and inspection. The other thing to rule out is the wave change switch.

If it's the BC5441 I'll scan you the R&TVS info tomorrow.

- Joe

[singlepentode69]

I will try that joe it is the BC 5441 with u50 rectifier thank you the trader sheet includes the 5442 and neither match my model
Regards
Robin

[Skywave]

When I touch the glass envelope the signal gets stronger. I do not possess an oscilloscope. Is there another way to test if the oscillator is working?
Regards robin

Assuming that the local oscillator is a triode - which is most usual, although what follows should apply to a pentode - measure the voltage on the control grid with a high impedance d.c. meter: you will see a negative voltage - typically between -2 and -10 v. - if it is oscillating.

Al.

[Yorkie]

Firstly, as always, you're better off using the maker's service data than the Trader Sheet as they're invariably more comprehensive. The GEC BC5441 Maker's data run to 8 pages - the Trader Sheet only two.

As to the valve line-up, there were two. Early production sets used:

V1 X6M
V2 W61/KTW61
V3 DH63
V4 KT61
V5 U50

Later sets used:

V1 X79
V2 W77
V3 DH77
V4 N78
V5 U78

If any of your valves are different from any of those it would be worth checking to see if someone has, at some time, fitted an equivalent.

For example:

KT61 = CV1438
X79 = CV5115
N78 = CV3711
DH77 = 6AT6, CV452, EBC90
U78 = 6X4, EZ90

If you get any stations at all on any band, if only weakly, that suggests that the local oscillator is working, at least after a fashion. The lack of stations on other bands could be due to dirty switch contacts. The IF is 470kHz, so you can check if the local oscillator is running by placing another set with the same IF close to your BC5441 and tune across the band around on your GEC around the same frequency. If the local oscillator is working, you should get a strong heterodyne ('whistle') on the working set at that frequency. If you don't, that suggests that the local oscillator on the GEC isn't running. If the oscillator is indeed working, the low volume might be due to a tired audio valve, so you can check the audio stage output by scratching a screwdriver on the centre tag of the volume control and if the audio stage is OK, should get loud crackles from the speaker. If only feint, that points to problems in the audio stage. If you've got a signal generator or injector, you could of course just inject a 1kHz tone at the volume control centre pin.

Although the set has an internal aerial, if you haven't yet connected one, it would be worth plugging in an external aerial to give the set a fighting chance - just a few feet of wire laid on the floor would be good enough. Incidentally, if you haven't already done so, the least thing you should do is the change the AF coupling capacitor ('that cap') which on the Trader Sheet is marked C18 (0.02uF) from the slider of the volume control to the grid of V3. If you don't, you risk stressing the output valve and output transformer. If the cap is leaky (in the electrical sense), it won't block the DC from getting on the grid of the valve.

It goes without saying that it makes good sense to check the voltages at the various points as indicated in the maker's data (anodes, grids etc) to see if they're fairly close to the maker's figures. They'll be higher if you use a digital meter of course, as compared to one with an analogue meter with a low input impedance such as an AVO8, which is only 20,000 Ohms per Volt, though will doubtless have been used to check the voltages when the set was designed.

Everyone has their own approach to fault finding. Personally, I use a signal injector/tracer as you can check with the tracer at the slider of the volume control to see if any signals are present there, and if you can tune stations in. If not, I work back to the front end to see if anything is getting to the IF stage. If so, but not at the IF output to the AF stage, that points to a problem in the IF stage. If there are signals at the spider of the volume control, but nothing out of the speaker, I inject a signal into the volume control and use the tracer to follow that through the AF stage. Anything at the output transformer primary? If yes, but not at the secondary = OPT suspect. If a tone at the secondary but nothing from the speaker = speaker is suspect.

I was trained to do as much diagnostic work with equipment unplugged from the mains, rather than live testing. In a radio set a great deal of testing can be done that way. For example, continuity of coils, switchery, transformers, valve heaters etc. Also, check the value of resistors to see if any are way out. Many carbon resistors go high in value over the years, and anything over about 50% can, and probably will, degrade the performance, if not stop the etc from working altogether.

I don't know how much you know or what equipment you have Robin, so I hope none of the above will sound as though I'm 'teaching my granny to suck eggs' or stating the blindingly obvious.

Hope it helps a bit.

Good luck with the set!

[Aerodyne]

Check the level of HT voltage, as a low emission rectifier could be at the root of your problem.
Tony

[Joe]

Information now in The Archive: http://golbornevintageradio.co.uk/forum/attachment.php?aid=10827

- Joe