[Buzz]

Hello:
I am restoring this Zenith 5R312. I got it working, but i can only get 1 local station and the signal from my SSTRAN comes in very good. While contemplating getting a set of new tubes, I noticed that it has a 6K8 as the 1st det, while the schematics says it should be a 6A8G. Is this tube
interchangable? It is not listed as a subsitution in Nostalga Air web site.
Can anyone shed some light on this?
Many thanks,
Buzz

[BrendaAnnD]

They are not interchangable. In some circuits, I think the 6K8 will sort of work, but get yourself a 6A8. This all presuming someone hasn't modified the circuit to use a 6K8. You can tell whether this might be an off model by looking at the tube socket from the top. That's something Zenith was always good at, printing the tube number on the socket.

[Buzz]

Hi Brenda:
Thanks for answering. I looked at the tube socket and indeed it does say 6A8G .The bottom of chassis looks original. I'm amazed this 6K8 tube even worked, hope it didnt damage anything. Cant believed it worked with the 6K8. Anyone else have this happen?
Buzz

[BrendaAnnD]

As I said, in some circuits they will 'sort of' work. One of these, I believe the 6K8, is a two section tube, with a heptode(?) and a triode. The other is a pentagrid converter.

[Arran]

I would get another 6A8, I don't know if brand Z ever used 6K8s, the 6A8 is what is known as a pentigrid converter, the 6K8 is a triode-hexode. I've never had a set that used a 6K8 but have heard of some communications sets using them, some RCA sets, along with my Philco 40-180 used a 6J8 which is a triode-heptode, the heptode section has one more grid then a 6K8.
Regards
Arran