It is currently Sat Aug 19, 2017 9:19 pm

Is the valve heater/filament Really dud?

Valves, Transistors, IC's and Components. Bench test techniques, Test Gear - Valve Testers, Scopes, CRT Testers, Bridges, Sig Gens, Pattern Gens, Workshop tours etc
 
Posts: 7156
Joined: Sun Aug 14, 2011 11:02 am
Location: Co. Limerick

Is the valve heater/filament Really dud?

Post by Michael Watterson » Wed Jun 26, 2013 11:39 am

If a valve has a separate base rather than pins on glass or wire-ended (B8D, B5A etc) don't assume it's faulty till you have removed the base.

I had bought a 1D5 from an ebay supplier who checks the filament and I was sure I had checked it before giving feedback a few months ago. I decided to test it and the other valves used by my Ever Ready 5017 prior to repair/restore. A multisection capacitor is in the B5 location for the U4020 rectifier valve and the field coil speaker replaced by a normal one, both I think about 1965 or 1966 on this 1935 radio.

Anyway, the heater was open circuit. So I decided to see if it Really dead or just a corroded wire.

I soaked the base in boiling water which made glass come loose. I used my SMD heatgun and tapping to get solder out of pins. Then fresh solder (for the flux) and solder sucker on each pin. The base then came off.

1D5_parts_sml.jpg


The heater works!
1D5_parts_2_sml.jpg


The Anode wire was about 1.5cm too long! It must have caught on assembly originally. I discovered a shorter insulated centre tap wire which I added extension to for experimenting as there is an unused pin.

The pin order is unusual on B4 / B5, it's 1 3 2 4 (clockwise from separate pin, bottom view).

The valve was Anode - CT - h1 - h2 - Cathode on the Pinch (quite visible, but use a meter to check heater connections). I added some soft sleeving to all the wires and assembled the base (without glue) and soldered up the wires not too tight. The Anode wire I pushed back a little and cut off 1cm.

1D5_rear_2_sml.jpg

Reassembled view from "behind" valve label.

Testing is here.

I'll add a bead of epoxy or ersatz flour & lacquer later after the radio is restored.

 
Posts: 942
Joined: Sat May 26, 2012 5:41 pm

Re: Is the valve heater/filament Really dud?

Post by Valvebloke » Wed Jun 26, 2013 12:42 pm

Quite a common problem with GEC KT66s. I've had a couple with 'dead' heaters which turned out to be dry joints inside a base pin (Gerry at Crowthorne Tubes first alerted me to this possibility). It's a good day when you find the 'display only' one that cost you a couple of quid is actually fine, and now worth twenty times as much.

Balanced against this is the risk of snapping the stub of the pump-out tube when you remove the base. Generally it's OK to take the base off. But occasionally the blob of glue has run down into the base while still liquid and has then set around the stub. Loosening the base busts it :\'( . For this reason, I guess, Gerry's method involved emptying the heater pins of solder, scraping the wire end and the inside of the pin with the finest rat's-tail file you can find and then re-making the solder joint. If that doesn't work then you can take the base off since you now have nothing to lose.

VB

 
Posts: 7156
Joined: Sun Aug 14, 2011 11:02 am
Location: Co. Limerick

Re: Is the valve heater/filament Really dud?

Post by Michael Watterson » Wed Jun 26, 2013 1:28 pm

:thumbl:
Agreed and the important thing is never to force base. Unless it comes loose with solvent or hot water it's going to break something.

Less space in the end of these pins than octal base.

 
Posts: 2920
Joined: Wed Jul 27, 2011 7:13 pm
Location: Croydon

Re: Is the valve heater/filament Really dud?

Post by sideband » Wed Jun 26, 2013 1:32 pm

I had a humble 6K8 with what I thought was an intermittent heater. Tapping the valve brought it back on for varying times. Someone suggested running flux and fresh solder over the ends of the pins making sure the solder runs down inside. It worked and never gave any more trouble.



Rich

 
Posts: 224
Joined: Fri Jul 13, 2012 4:39 pm
Location: Dorset

Re: Is the valve heater/filament Really dud?

Post by Marconi_MPT4 » Wed Jun 26, 2013 5:28 pm

Hi, In its heyday Brimar 6U4GT appeared to have more than its fair share of intermittent heater connections so whenever encountered the connections were re-soldered as a matter of course. Same applied to the 25U4GT.

Often with these, when the heater goes out gently tapping the bulb will often be enough to make it work again and mistakenly conclude failed filament.
Rich

 
Posts: 818
Joined: Fri Oct 14, 2011 9:44 pm
Location: Nottingham

Re: Is the valve heater/filament Really dud?

Post by valvekits » Thu Jun 27, 2013 10:02 am

I have an old KT66 with the spigot missing that initially passed the heater test on my valve tester but then failed. Eventually I did manage to get it to run long enough to complete testing and it did test okay before the heaters failed again. I just assumed that the filament was making and breaking, It's the old grey type with KT66 printed inside a box - now I just have to find it.
Maybe this thread should be made a sticky somewhere?

Eddie

 
Posts: 2920
Joined: Wed Jul 27, 2011 7:13 pm
Location: Croydon

Re: Is the valve heater/filament Really dud?

Post by sideband » Wed Jul 03, 2013 8:21 am

valvekits wrote:Maybe this thread should be made a sticky somewhere?

Eddie



Stuck!

 
Posts: 16
Joined: Fri Dec 30, 2011 6:50 pm
Location: Lincolnshire

Re: Is the valve heater/filament Really dud?

Post by Techman » Sun Aug 04, 2013 8:58 pm

I've certainly had this problem in the past. It was with a PP3/250 output valve where the corrosion inside the base pin made the heater 'high resistance', so not a lot of heating was going on inside the valve. Careful use of a small file and a hot soldering iron soon sorted the problem out.


Return to In The Workshop



Who is online

Users browsing this forum: Bing [Bot] and 1 guest