Seeking Valves

[Nowhere-Man]

Hello To All,
                 I've been having a spot of bad luck. I've been working on a GEC tube radio (about 1951). After building my silicon rectifier to replace the missing valve rectifier and after purchasing a new output tube (the original had been removed), I had no audio output at all. After some scratching of my head and investigating, I removed the screening cans and now I need to obtain valves. One is missing from the can and the others Kaput.

I've taken some time to investigate a range of valves that were used and here is what I have found. It relates either to Octals or B7 bases and if you happen to have any of these to sell, please let me know.

The Triode Hexode X61M should have a base size diameter 30 mm. It isn't as expensive a valve as the X78

The Double Diode Triode DH77 has a 19 mm base whereas the DH63 is bigger at 27 mm

If Amplifier Valve KTW61 and the W61 at 29 mm will be Octals and the W77 ought to be 17mm only.

Of course, I'm kicking myself for not having checked the screened can valves earlier on and I did consider whether it was worth the expense. Having said that, I suppose people have had clapped mains transformers or speakers so probably I'll probably push ahead. Unless it turns out to be really big bucks.

Also if you have any feedback over the quality of these valves and how you rate them, feel free to respond.

[AlanBeckett]

I'm sorry, I don't understand you. Are you saying that they are the Valves that the Service Data specifies? If so it's an odd mixture, even for GEC.

X61M is ECH35, which is International Octal. There's plenty of those about, along with it's 'CV' equivalent. A 6K8 would probably work as well although the Electrodes are actually different.

http://www.r-type.org/exhib/abh0083.htm

DH77 is 6AT6. Again, there's plenty of those available along with EBC90, it other equivalent. However, it's a B7G.

http://www.r-type.org/exhib/aaq0240.htm

Alan

[Ed_Dinning]

Hi If you can post the radio model number we can check with our reference sources and let you know what should be fitted as well as suitable equivalents.
As Alan said, it seems a strange mix of types.

Ed

[Nowhere-Man]

I'm sorry, I don't understand you. Are you saying that they are the Valves that the Service Data specifies? If so it's an odd mixture, even for GEC.

X61M is ECH35, which is International Octal. There's plenty of those about, along with it's 'CV' equivalent. A 6K8 would probably work as well although the Electrodes are actually different.
http://www.r-type.org/exhib/abh0083.htm

DH77 is 6AT6. Again, there's plenty of those available along with EBC90, it other equivalent. However, it's a B7G.

http://www.r-type.org/exhib/aaq0240.htm


Alan

This set was either made with all Octals or all B7. However, the service manual clarifies it may be a mix of Octal and B7s. I found a couple of tube supply firms and am now pretty sure what my Detector and Mixer will be. The Mixer has a bigger can than the detector so it ought to be the X61M by my reckoning. The only possible doubt I may have is over the IF Amplifier tube as this gives 3 possibilities, not just two.

It seems a bit crazy to discover the valves under the cans were history but I've always been reluctant to force old valves out of the chassis so I tend to leave them be. They can break easily in the process. In this case, I began to suspect something was very wrong so I forced the cans off only to find them damaged or missing. Perhaps I'll now be forced to check any future can but, for now, I'll just have to press on and fit the tubes.

[pwdrive]

Mixer/Oscillator valve possibilities:

X61 valve holder has 8 sockets (International Octal)
X79 valve holder has 9 sockets (B9A)
X78 valve holder has 7 sockets (B7G)

Detector valve possibilities:

DH63 valve holder has 8 sockets (International Octal)
DH77 valve holder has 7 sockets (B7G)

Lawrence.

[AlanBeckett]

I'm sorry N-M but I'm even more confused.
Terminology first: B7 is the old British 7-Pin Base. B7G is the modernish small 7-Pin Base. B9A is the modernish 9-Pin Base and Octal, of which there were two flavours, are 40s onwards 8-Pin Bases. There are Pictures on the national Valve Museum Website - http://www.r-type.org/search.php
Which are we talking about?
Are the Bases still in the Chassis? If so, what are they? A Picture would help.
If the Bases are missing then what size are the holes? If that's the case you're going to have some real fun deciding which wire goes where.
I have seen the odd Set where the Manufacturer fitted an 'Adapter Plate' in order to use a different Valve, but it's unusual.

Alan

[Nowhere-Man]

I'm sorry N-M but I'm even more confused.
Terminology first: B7 is the old British 7-Pin Base. B7G is the modernish small 7-Pin Base. B9A is the modernish 9-Pin Base and Octal, of which there were two flavours, are 40s onwards 8-Pin Bases. There are Pictures on the national Valve Museum Website - http://www.r-type.org/search.php
Which are we talking about?
Are the Bases still in the Chassis? If so, what are they? A Picture would help.
If the Bases are missing then what size are the holes? If that's the case you're going to have some real fun deciding which wire goes where.
I have seen the odd Set where the Manufacturer fitted an 'Adapter Plate' in order to use a different Valve, but it's unusual.

Alan

The bases are still there, yes. I had issues at first deciding whether to solder my silicon diodes to the base pins of the rectifier tube but, in the end, that's how I did it. All the other bases are fine. However, with regard to what you say about circuit wiring, the AGC decoupling capacitor had me baffled for close to 20 minutes when I was double checking it.

The GEC radio is the BC5243. You can access the schematic on radio workshop.uk. 2nd page gives a clarification for the possible valves used. These are:

X61M X78 or X79 Mixer
W61, KTW61, W77 I.F. Amp
DH63 or DH77 Detector
KT61 or N78 output valve (I already fitted the N78)

 I don't know why they didn't standardise but maybe somebody does have an explanation for that? I also noticed the valve data states the supply was 220 volts A.C. That had me curious and I was trying to find if 220 was standard in the early fifties.

I'll be ordering what I need tomorrow and the only possible doubt I have is between the W61 and W77.

I hope in the end it does work  although it will never be the same radio and it's been more of a project than a restoration (something to learn on).

[AlanBeckett]

Yes, but what Bases are actually fitted to your Chassis?
Taking the Mixer/Oscillator:-

X61M has an International Octal Base - http://www.r-type.org/exhib/abh0083.htm

X78 has a B7G Base - http://www.r-type.org/exhib/abc0040.htm

X79 has a B9A Base - http://www.r-type.org/exhib/aaq0065.htm

So which one? They're all different so it's easy to tell.
Picture?

Alan

[Mark Hennessy]

Hello N-M,

I must admit that I've been following this thread with interest, but I am also confused. I mostly put this down to my lack of experience with valves

For us to help you, we really need some pictures.

Pictures have already been requested earlier in the thread, but please allow me to add my vote to this. Apart from anything else, our interest has been piqued, so even if you're back on track, we'd still love to see what you've got in front of you

All the best,

Mark

[Mark Hennessy]

Hi again,

Is this the set?

http://s198.photobucket.com/user/langser...1.jpg.html