[Amps] older 3k

[John Becker]

> Based on minimal information and assuming you have checked the fuses, my first suspicion is you have  3-500 tubes and the solder has melted off the filament pins... Very common with Henry 3K (I've been there a couple of times)
> If so, you need to beef up the air flow to the bottom of the tube after resoldering the pins...
> 
> denny / k8do

Years ago I experienced similar problems with a Hunter Bandit 2000, 
which used a pair of 3-400Zs. One of the tubes appeared to go bad but 
was fixed by re-soldering the filament pins. Sometime later, the amp was 
losing power output and I found cold solder joints on the lugs at the 
ends of the filament choke. After re-soldering these connections, the 
amp was putting out more power than when it was new!

I also recently resurrected the CRT in a Heath HO-10 monitor scope by 
re-soldering the filament pins, and just three days ago I fixed our 
microwave oven which had cold solder joints on the control board in the 
circuit feeding AC power to the magnetron's power transformer.

Cold solder joints are not uncommon in circuits carrying significant 
current after long usage!

73,

John, K9MM