[Amps] 3-500z - intermittent filament

[n4zr at comcast.net]

I'm sure John is correct about both the risks of resoldering and the ideal solution, but what to do if you have tubes that have already failed from this cause?

Using some of Rich Measures' silver solder and packing the area around the glass seal with wet paper towels, I have successfully repaired several tubes.  Last time around, operating on the theory that the spring clips on the filament pins might have lost their temper, I swapped them for those on grid pins from the same socket.  I also made a point to polish the inside of the socket contacts and the filament pins in the hope of reducing the resistive heating at that point.  These fixes have so far been effective in intense CW and SSB contest use for several years.

73, Pete N4ZR

-------------- Original message -------------- 
From: "John E. Cleeve" <g3jvc at jcleeve.idps.co.uk> 

> I would advise caution in resoldering the sleeved pins of the 3-500 et al 
> tubes, for the Eimac spec. and the late Bill Orr, warned that the melting 
> point of the solder used, could be very close to the temperature which 
> would destroy the glass to metal seal of the filament pins..........more 
> effective electrical contact, between the tube filament pin sleeves and 
> sockets, with more effective directed forced air cooling of the tube base 
> sockets are the routes to follow.....but this has all be said 
> before.....regards, John G3JVC. 
> 
> 
> ----- Original Message ----- 
> From: "Steve Thompson" 
> To: 
> Sent: Thursday, February 08, 2007 12:15 PM 
> Subject: Re: [Amps] 3-500z - intermittent filament 
> 
> 
> > 
> > 
> > terry at g4amt.com wrote: 
> > 
> >> The pins are riveted over on the tube side of the `former` so they cannot 
> >> (?) be removed; they are of `split` construction. The only way I could 
> >> re-solder them was to use a solder sucker to extract the old solder - put 
> >> a 
> >> couple of drips of flux in the hole and re-solder with silver solder; 
> >> heating the pin with a mini-blowlamp ... 
> > 
> > A question as to what should be used here? There's 'silver solder' as 
> > used with a torch for brazing. There's also standard pcb solders with 
> > added silver content to give them a lower melting point than straight 
> > tin/lead. 
> > 
> > Steve 
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