6F6 tune vs 6V6 tube

With a reasonable plate voltage and suitable cathode resistor, you can... Try to match as best the datasheet specs.

AFAIR, the plate dissipation is 9W for a 6F6G instead of 12W for a 6V6G, meaning that a direct swap in a Champ of a 6V6 for a 6F6 may be dangerous for the 6F6's life, IMHO.

-tbln

 

I seem to recall that some metal tubes are grounded to their exterior metal shell...can’t swear to it, but sounds important .

 

Good research. I was just noticing Wikipedia says this under '6V6':

Following the introduction in July 1936 of the 6L6, the potential of the scaled down version that became the 6V6 was soon realized. The lower-powered 6V6 was better suited for average home use, and became common in the audio output stages of "farmhouse" table-top radios, where power pentodes such as the 6F6 had previously been used. The 6V6 required less heater power and produced less distortion than the 6F6, while yielding higher output in both single-ended and push-pull configurations.​

 

The metal 6V6 has the can grounded. The 6F6 is a generation previous than the 6V6, used in about the same applications. It can use a 7k output transformer in SE at 285V, as long as the voltage is not crazy high I would not concern myself too much about it.

 

Why? What about it being earlier makes it not worth the trouble?

Octal preamp tubes came before miniture 9 pin tubes like the 12a*7 series but you still see them used today in a minority of amps because they sound good. Hell, tubes in general are outdated and came before transistors (and op amps and DSP and assorted other blasphemy)... but here we are discussing them in this forum.

I'd give it a shot just to see how it sounded. The only real issue is you will want to go for somewhat lower voltages due to the lower max dissipation. The 6f6 datasheet I'm looking at shows it as an 11W tube with max plate voltage of 375v and max screen of 285v. So a slightly higher max plate voltage than most 6v6 datasheets, slightly lower screen voltage and slightly lower dissipation. So for your average single ended champ OT with say an 8K primary you could shoot for a B+ of about 320-330v and a plate voltage (plate to cathode) of something like 300v, maybe 20v lower on the screen, keep the dissipation under 10W and you should be good. It'll take some modification of the stock champ circuit, but nothing over the top.

 

I've found a Brimar 6F6G (coke bottle glass envelope) in an antique shop a few years ago and took it home and chucked it in a SE champ-style build and it sounded nice. A little cleaner than a 6V6, and they are an 11W tube (so the bias needs to be a little cooler - all other things being equal)

 

Think of them as needing the heater current and grid signal of a 6L6 but with the plate dissipation and power output of a 6K6GT. I have six tubes and a couple of P-P transformers for them. A field coil speaker as well. One day I will make a period inspired amp.

 

Many, if not most, are. Look at the data sheet and it should show the internal connection and which pin is tied to the shell. Even if that pin isn’t used or shown on the amp’s schematic, open up the amp and make sure the socket either grounds that pin or doesn’t use it at all.

Sometimes, someone will use an unused tube socket lug as a tie point for something like, oh... B+ voltage that you’ll shake hands with if you touch the shell.

 

The 6F6EG seems to be a purely philco thing. They used it for a few models as a single ended output tube in 1937, such as here in the 37-2620 radio. No Squat, No Stoop, No Squint.

 

Found a reference to a 6F6EG. on page 5, don't know how accurate it is, might be an idea to look at the tube pin connections.

https://nzvrshome.files.wordpress.com/2018/12/nzvrs-4-4.pdf

 

Here the pinout from the schem above.....and a 6V6 for comparison...so it appears to be the same.
=

 

same pinout