Unknown radio. Identified as a Murphy A34.

[ms660]

The mixer valve that's fitted probably has the same pinout as a VP4b pentode, heaters (pins 4 & 5) paralleled to the AC/HL heaters, g3 (pin 3) connected to the AC/HL's cathode and to pin 6, the valve holder looks to be of the anti-microphonic type and was made by Telsen so far as I can make out.

Lawrence.

[LyntonP]

Originally Posted by ms660

the valve holder looks to be of the anti-microphonic type and was made by Telsen so far as I can make out.

Lawrence.

The extra valve holder is a Junit HT. Not sure if this means anything.
The connections are small thumb screw terminals, not soldered.
Lynton

[ms660]

The name on the B5 valve holder doesn't mean a lot, it all looks a mess to me, I would get rid of that and the Telsen B7 and revert to B9 and AC/TP if possible.

Lawrence.

[LyntonP]

Spent some time cleaning the chassis and considering what to do with this ‘valve adaptor’. Came up with a plan to mark all wires and extend wires through the adaptor so I could replace them if required. Had one last firm tug at the adaptor and it moved. Continued slowly and got the surprise of my life! As the photos show the connections to the original valve sockets were secured by matchsticks! Clearly I am now going to install an original valve. Can anyone point me in the right direction to find an AC/TP?
Lynton

[ms660]

Try Langrex if all else fails:

https://www.langrex.co.uk/stocklist/

Lawrence.

[cathoderay57]

Hi Lynton, I can definitely provide an AC/TP. I will get one out of the spares box, test it and post the test results. I will send you a PM with price. Cheers, Jerry

[LyntonP]

Originally Posted by cathoderay57

Hi Lynton, I can definitely provide an AC/TP. I will get one out of the spares box, test it and post the test results. I will send you a PM with price. Cheers, Jerry

Wonderful thanks Jerry.
Lynton

[cathoderay57]

Hi Lynton,
I found an AC/TP brand new in box. See pics. On the valve tester it tests as follows (spec values are in brackets):

Triode section: Ia=1.7mA (1.5); gm=1.3mA/v (1.4)
Pentode Section: Ia=5.2mA (5.5); gm=1.5mA/v (1.6)

As you can see it tests very close to spec. You have a P.M. Cheers, Jerry

[LyntonP]

Do the pin outs for older valves (AC/TP)etc follow the same numbering convention as more modern examples? ie do I read the pin numbers as normal from the underside of a valve holder?
Spent some considerable time cleaning the Murphy chassis, and am working my way through the wiring following the circuit diagram.
The normal items have to be replaced in fact the reservoir and smoothing capacitors have been cut out of the circuit previously but the aluminium cans left in place on the chassis. Nothing looks in very poor codition, but time will tell.
Also many thanks to Cathode Ray who kindly supplied me with a new AC/TP valve.
Lynton

[ms660]

Originally Posted by LyntonP

Do the pin outs for older valves (AC/TP)etc follow the same numbering convention as more modern examples? ie do I read the pin numbers as normal from the underside of a valve holder?

Yes, same method, the pinouts as viewed from underneath for B9, B7, B5 and B4 can be seen in this link amongst others:

https://tgale.home.xs4all.nl/antradio/vchar2.html

Lawrence.

[LyntonP]

Thanks Lawrence

[LyntonP]

Still working my way through the circuit diagram, most of it is fine but I cannot make sense of the connections to the final output valve. It is supposed to be a Mazda AC2/PenDD. A Mullard valve has been substituted at some stage but I cannot read the I.d. number. Looks like ??W4DD ? The circuit diagram shows the cathode common to one of the heater pins but the valve holder has been wired with the anode common to a heater pin. I hope this is visible on the photos. I looked for alternative valves on the valve museum site but none seem to match the Mullard. Can anyone help please?
Lynton

[LyntonP]

Further examination of the Mullard valve revealed a ‘code’? Etched on the glass.
150.0. 6BQ. Not sure if this means anything?

[ms660]

Originally Posted by LyntonP

The circuit diagram shows the cathode common to one of the heater pins but the valve holder has been wired with the anode common to a heater pin. I hope this is visible on the photos. I looked for alternative valves on the valve museum site but none seem to match the Mullard. Can anyone help please?
Lynton

Looking at the 3rd photo, pin 1 is the furthest to the right, which two pins are connected together?

Lawrence.

[LyntonP]

Hi Lawrence I have turned the image around so that pin 1 is at the top. Pins 2 and 4 are connected together.
Lynton

[ms660]

That would be correct for a PEN4DD:

http://www.r-type.org/exhib/aad0138.htm

EDIT: link added.

Lawrence.

[LyntonP]

Blimey more sabotage! Anode and cathode in different places. No wonder I couldn't make sense of it. I assumed that the correct valve was in place as I couldn't read the valve number. I assumed that a direct replacement had been fitted, but bearing in mind the fun and games with the previous 2 valves it was a poor decision.I may sleep tonight!
Thanks for your help
Lynton

[PJL]

The bias conditions seem to be about the same so it should not have required any other changes.

[LyntonP]

I will leave the current valve in place for initial tests, but may try to obtain an original replacement if things are going well. Obviously the tech who made the changes knew what he was doing!
I now need to order various capacitors to move the project forward.
The set has rather a messy connection for various HT connections (wrapped in old fabric insulating tape)! is there a supplier for terminal strips that I could tidy these up with? I have tried the internet but all the suppliers are in the USA.
Lynton

[Nuvistor]

Is this the sort of terminal strip you need, the do a 10 way type as well.

https://www.cricklewoodelectronics.c...el-Plated.html