Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: scstill on January 16, 2021, 12:30:28 pm

Title: Triode and Pentode tube comparison for a new build
Post by: scstill on January 16, 2021, 12:30:28 pm

So a new build will be a two channel 6v6 push pull to replicate 50's vintage designs
I am looking for advice on tube selection.

Channel 1 is triode stage like Fender 5c3
could I use a 6sq7 (single triode, 100gain, 1ma plate, 53kohm plate) instead of 6sc7 (dual triode, 70gain, 2ma plate, 85kohm plate)?
would single gain stage into PI be adequate?

Channel 2 is pentode like Gibson BR-6f
could I use a 6sk7 (instead of the 6sj7)?
would single gain stage into PI be adequate?

Phase Inverter
could I use 6sq7 (single triode like the Gibson EH125) as PI instead of 6sc7 (dual triode like fender) or 6sn7 (dual triode like Gibson BR6f)

Any thoughts on glass vs metal shell?

Title: Re: Triode and Pentode tube comparison for a new build
Post by: PRR on January 16, 2021, 11:08:41 pm

6SK7 is a variable-gain tube for radios. It "works" for audio but distortion may be high. (No, the variable gain function is untamable in simple audio.)

What kind of "PI" is that? Topology is at least as important as tubes. Maybe moreso because it determines the wiring; tube types can be changed much later in development.

Any way so fussy about tubes? Are these the ones you have in pocket? Preamp tubes are not usually a killer cost in a tube guitar amplifier. Budget is dominated by chassis, transformer, knobs.

Title: Re: Triode and Pentode tube comparison for a new build
Post by: scstill on January 17, 2021, 10:17:09 pm

The  build is going into a 40's Packard/Buick car radio, was a PP 6V6 with 6sq7 as PI, and 6sk7 first detector from Antenna. Thus my questions whether I could use those tubes. But you got me thinking that I should stay with what has worked before.
The base radio has provided all the knobs, chassis, sockets and OT. Replaced the lightweight 6x9 with a beefier Jensen. I sourced a PT from a webster reel. Also will use 6x5 from the webster as rectifier. I will share the circuit for comment once its drafted.
Couple of pics

Likely will go with 6sj7 for pentode preamp channel and 6sc7 or 6j5 for triode preamp channel. Will use either 6sn7 or 6sc7 for PI.

I like the idea of a post PI Master Vol. Just would need to add another pot somewhere