Philips 274A No reception

[Old Sparky]

J have now ordered a new valveholder, which should arrive in the next week or so, but having, at Sam' suggestion, tinned all 5 pins of the o/p valve so that it's a tight fit in the valve socket, I'm now getting no sound at all, despite the valve being a tighter fit in it's socket than before, and am wondering whether I've managed to open - circuit an internal connection. Obviously it will be easy to check if the heater pins are o/c, but less so for the others.

[Murphyv310]

It's a possibility of course but unusual. Perhaps try to reflow the pins again just in case the internal soldering has gone dry jointed. It springs to mind that might be the issue all along?

[Mike Watterson]

I'd have thought the internal connections to the pins are all spot welds.

[Old Sparky]

Mike, you may be right, but I'll try again as Trevor suggested. It just seemed odd to me that the o/p stage was working albeit intermittently until Tinned/soldered the pins of the o/p valve, since then not a peep, even if I gently rock the valve in it's socket. I have a new 5-pin valve socket on order, so when it arrives, I'll change it, which should cure the proble. The output valve or any known equivalent(s) seem to be almost 'unobtanium', so I hope it's not faulty.

[Murphyv310]

I'd have thought the internal connections to the pins are all spot welds.

No. These are all soldered. I can't see how it would be able to be spot welded due to access. Mind its a 30s valve with wire ends fitted into a socket.

[Old Sparky]

I,m not certain how the internal wires are secured to the pins. Trevor. It simply occurred to me that I may have accidentally disturbed an internal connection when tinning/soldering to, the valve's pins, so I'll have another look at it and try re-flowing the solder in the hope that I then get a working o/p stage again.

[Old Sparky]

Having a short while ago 'revisited' the 274A, removed the o/p valve and checked that it's heater is OK (it is) as is the heater circuit connection at the valve socket. I again powered up the radio, still to be greeted with silence. A few quick readings taken with my DMM suggests that HT, etc., voltages are within spec., so I'm still scratching my head. I've temporarily mislaid my circuit diagram and notes about the 274A, so I'm probably missing something simple. Best to go back to it when I find the data concerned, I guess!

[Mike Watterson]

I'd have thought the internal connections to the pins are all spot welds.

No. These are all soldered. I can't see how it would be able to be spot welded due to access. Mind its a 30s valve with wire ends fitted into a socket.

Arrgh, I was thinking of connections INSIDE the valve.
Easy to check and redo the wires from a pinch base to pins on a bakelite base.

[Old Sparky]

Further checks earlier today revealed that the valve is drawing current as there is a voltage drop between the HT+ and the o/p valve anode, so maybe the fault is further back, except that it seems odd to me that I had intermittent noise if I 'jiggled' the o/p valve in it's socket.

[Murphyv310]

Quick way is to use a signal generator (audio) and work back to the RF stages, then obviously inject RF at the tuned frequency and see where you loose it.