[R-390] OT Strange 5R4

[k2cby]

I recently acquired a Viking 1-1/2 transmitter (that's a Viking I with the
TVI suppression and audio mods from the Viking II).

 

Before I fired it up - and before I re-fastened the umpteen 6-32 screws that
hold the top shield in place - I thought I ought to check the tubes on my
trusty TV-7.

 

The power supply uses two 5R4 rectifiers.

The first one I popped in tested fine.

The second one didn't move the needle at all - not a flicker.

I said to myself "Well, that's obvious: open filament."
As I reached over to pluck the tube out of the TV-7 and throw it in the
trash I got a surprise - it was hot and glowing.
I then figured maybe there was a solder fault in one of the base pins, so I
sweated all of them and applied additional solder - no cure.

 

I never heard of a rectifier with a good filament that wouldn't conduct at
all.

 

Did 5R4s have an internal fuse?

 

Any other ideas?

 

 

 

Miles B. Anderson, K2CBY
16 Round Pond Lane
Sag Harbor, NY 11963
Tel.: (631) 725-4400

Fax.: (631) 725-2223
e-mail: k2cby at optonline.net