I just received a nice wooden table-model.. 1945 Westinghouse WR-209 five-tube set acquired from Ebay for $65.

http://www.nostalgiaair.org/PagesByModel/267/M0024267.pdf

Wow this thing is built like a battleship!
It instantly gives you that old "Cadillac"-like feeling of solid quality.

It is very heavy and seems very well designed mechanically as well as electronically.

Everything works so solidly.. the dial/tuner just seems so solid...y'know?
.. And beautiful sound (6" speaker) too
...and silence between stations and very sensitive too.

It uses a 6F7 as the RF & osc stage. (triode/pentode)
I haven't seen this tube very often.

Is it considered superior to a 6a7 or not?

Could it take the place of a 6A7? (Pentagrid converter)
I mean is the 6F7 similar enough that perhaps with a few re-wires the 6F7 could be used in place of the 6a7?

BTW:
It's kind of funny to see in the parts list those items that were the most expensive at that time in 1945.

6" Speaker = $6.00
Transformer $3.80
Variable Condenser = $2.45
Field Coil $1.75
IF Transformer $1.75

If, in the original 6A7 circuit, the cathode was part of the oscillator circuit (not held at a constant voltage by being tied to the B- line), this would allow for adequate coupling in a 6F7. If the traditional grid-plate circuit was used, there would need to be a link between the oscillator plate and the RF pentode. You could remove all wires from pin 3 and connect pin 3 to pin 4. However, normally in a heptode there is an electrostatic shield between the oscillator and RF sections, formed by the screen grid. This would remove that feature and allow the two circuits to act on eachother, so it probably isn't a good idea. If you could tie the oscillator plate to the supressor grid, leaving the screen grid connected to its normal power source, that would probably be the better option. However, with that tube it isn't possible.

There are other options, too, like linking the two plate circuits by various means.

The 6F7 is somewhat better than a 6A7 because, from what I have read, mostly, a separate oscillator is more stable, especially at higher frequencies, than a heptode oscillator/mixer. I do have a couple of radios with very high short wave frequencies that use only a heptode oscillator, though, and they seem to perform well enough.

T.