L4B help

[vk8hlf]

Hi all, I am the proud owner of the drake L4B (near mint condition) I have had this amp for quite a few years without any problems except for the usual age related hicups,, however the other evening I noticed one of the bottles (3/500) was not working,, a visual inspection registered nothing,, so i swapped the tubes around,, both tubes were now working,, so i replaced them back into the original position,, result was same tube not working !!!
I have not performed a plate dip / load peak tune,, just thought I would throw it out their & hopefully get some response from a couple of drake veterens,,, cheers for now Greg

 

[W5LZ]

I'm not a Drake 'vet', but it sound like a missing point of contact between tubes and sockets. Or in the filament supply to the affected socket. ... Or the @#$ tubes figured out a way to 'pull your chain'! Gotta watch them @#$ tubes you know...
- 'Doc

If/when you figure it out, I know I'd be interested in knowing whats happening.

 

[vk8hlf]

Thanks for your interest Doc I'll keep you posted,, yeh I was thinkn somthing similar but im always open for suggestions from someone who has suffered befour me with a similar problem cheers mate Greg

 

[Bionic Chicken]

I'd suspect the tube socket clips. Check to see if they have any burnt or pitted spots on them. Also the solder connection from the bifilar choke to the socket. Inspect the tube pins to see if the solder is shiny and not grainy looking. Heat on the tube sockets will melt the solder out of the pins causing this problem.
BE CAREFUL WHILE WORKING ON THE AMP AS HIGH VOLTAGES ARE PRESENT!!!!

Good Luck on finding the problem.

 

[Captain Kilowatt]

I'll echo what Bionic Chicken said. By "not working" I assume you meant the filament would not light up? It seems that there may be a loose/poor connection somewhere and at 15 amps of filament current it does not take much to cause a problem. Carefully inspect the pins on the bottom of the tube as well as the pins on the tube socket itself and the filament choke. Any dull grainy looking solder is a sign of a problem. Give those 3-500's lots of cooling air or you will be plauged with loose/melted solder problems.

 

[Bionic Chicken]

The L4B is not as apt to have issues with the filament pins getting hot like a SB 220 does, but there is still the possibility. That is of course unless it has been ran real hard on AM and overdriven. It's a good amp and reliable. Some sockets have an extra "clip" on the outside of the filament clip to provide extra tension on the pin. Heat will take the tension away. If the contact surface of the clip is good you can readjust (bend) it to make a better connection. The best thing is to replace the socket if it has a problem. $25 for a new one and you don't have to worry about damaging the tube pins either.

 

[vk8hlf]

Hey Doc well I finally figured out the filament not lighting up problem & you pretty much hit the nail on the head with your comment,, one of the pins on the 3-500 was slightly smaller, even though i had all the clips nice & tight on the socket it still wasn't enough, so a retentioning on all the clips seems to have done the trick
cheers greg VK8HLF