National DE-631 any info? - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

paulsherwin · 8th Apr 2009, 11:31 am

What a terrific find! Japanese radios were just starting to be imported into Britain at that time, and they are effectively Japanese spec (i.e. no LW). It looks to be in very good condition.

As Nick says, a tiny bit of leakage will be enough to light a neon screwdriver, so this isn't necessarily a matter of concern. Just be aware of it and take sensible precautions.

It's not impossible that the 6AR5 heater has failed, but this is fairly unusual so check that there isn't a problem with the valve pins or socket first. If the heater is open circuit, there will be infinite resistance between pins 3 and 4. A hundred ohms or so means the heater is OK.

If you really do need a new valve, a 6AQ5/EL90 or EL95 should work too, though you may need to adjust the cathode bias resistor.

Good luck, Paul

Derminator · 8th Apr 2009, 8:40 pm

Thanks Nick and AJS for the advice on earthing, I'll look into that. I had another look at the output valve earlier. I slid it in and out of its contacts a few times, powered up, and it spluttered into life! Slightly embarrassed that I hadn't done this before now but, hey, I am a newbie! Anyway its picking up loads of stations, way more than I expected on SW1 and SW2. Nice sounding radio. There's still work to be done though, the pointer isn't travelling the full extent of the dial and the dial lamps are blown etc. etc.

Derminator · 8th Apr 2009, 9:35 pm

Thanks for the info Paul.
I've just tested the voltage from the chassis to earth with a multimeter and got a reading of 0.1V so I guess that's alright then! I still intend to earth it though.

8th Apr 2009, 11:31 am	#21
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,965	Re: National DE-631 any info? What a terrific find! Japanese radios were just starting to be imported into Britain at that time, and they are effectively Japanese spec (i.e. no LW). It looks to be in very good condition. As Nick says, a tiny bit of leakage will be enough to light a neon screwdriver, so this isn't necessarily a matter of concern. Just be aware of it and take sensible precautions. It's not impossible that the 6AR5 heater has failed, but this is fairly unusual so check that there isn't a problem with the valve pins or socket first. If the heater is open circuit, there will be infinite resistance between pins 3 and 4. A hundred ohms or so means the heater is OK. If you really do need a new valve, a 6AQ5/EL90 or EL95 should work too, though you may need to adjust the cathode bias resistor. Good luck, Paul

8th Apr 2009, 8:40 pm	#22
Derminator Pentode Join Date: Feb 2009 Location: Crystal Palace, London, UK. Posts: 118	Re: National DE-631 any info? Thanks Nick and AJS for the advice on earthing, I'll look into that. I had another look at the output valve earlier. I slid it in and out of its contacts a few times, powered up, and it spluttered into life! Slightly embarrassed that I hadn't done this before now but, hey, I am a newbie! Anyway its picking up loads of stations, way more than I expected on SW1 and SW2. Nice sounding radio. There's still work to be done though, the pointer isn't travelling the full extent of the dial and the dial lamps are blown etc. etc.

8th Apr 2009, 9:35 pm	#23
Derminator Pentode Join Date: Feb 2009 Location: Crystal Palace, London, UK. Posts: 118	Re: National DE-631 any info? Thanks for the info Paul. I've just tested the voltage from the chassis to earth with a multimeter and got a reading of 0.1V so I guess that's alright then! I still intend to earth it though.