Thought also about building a quad four.
Think carefully about that. Getting 4 1625s to be stable in grounded-cathode is not going to be easy. It can be done but you have to be very careful with layout, bypassing, shielding, and neutralizing. If all you want is 160, 75 and maybe 40, you may be OK. Note that the pi-net output values will include lots of C and not much L.
Half the gird bias for two so 1/4 for four I guess.
No! Same bias voltage, four times the current.
Seperate parasistic suppressors for all with a common tie point. Make a Rf plate choke to handle all 4 and a gimmick cap per tube for neutralization issues.
No, one big neutralizer for all 4. Not a gimmick, either.
They cant be all bad. The Arc 5 has only two tubes ahead of them . A vfo and a buffer I guess of sorts.
The ARC-5 uses a 1626 power oscillator to drive a pair of 1625s. No buffer, though many hams modified them to include a buffer because they can chirp and FM pretty bad if you don't.
There is a parallel pair of 807 in the ARRL book. Specs are not a whole lot different then a plain jane 6146 except I dont think they like higher freqs like the 6146.
Max power input of a 6146B is 120 watts. Max power input of a 6146 is 90 watts. Max power input of an 807 or 1625 is 75 watts. (Class C maximum ICAS ratings).
Hams used to beat the tar out of 1625s because they could be had surplus in almost unlimited quantities for 19 cents each. That's not the case any more, and those old bottles should be treated with more respect.
btw, in AM linear a quad of 1625s is only good for about 50 watts carrier output.
73 de Jim, N2EY