Page 1 of 1
7S7 triode + heptode for preamp?
Posted: Tue 04/04/06 8:39 am
by engels
I hope you will understand me when I say I don't want to see those 12AX7's in the preamp anymore. They're probably the best sounding preamp tubes but I want to have a bit more fun with my project, so here's the question:
I've got a loctal 7S7 tube from a radio. It's like this:
and here's the datasheet:
http://frank.pocnet.net/sheets/049/7/7S7.pdf
Is it possible to adopt it to preamp slot?
Is it possible to wire heptode as a triode?
Is it suitable for audio signals?
The grids of both halves are connected so I was thinking about something like Spitfire's first stage with both triodes connected like this -
But maybe there's a better way to use the heptode?
Posted: Tue 04/04/06 12:28 pm
by markh
IIRC, heptodes were used for a combined oscillator/mixer/amplifier section in the standard five-tube radios of yore. I don't remember them being particularly linear. One 'grid' was really the two support rods,
for example.
--mark h
Posted: Tue 04/04/06 3:12 pm
by zaphod_phil
You could make a great tremolo preamp stage with one of those tubes. Use the triode side for the trem LFO, and the heptode side for the preamp stage. Any non-linearity in the heptode should help for a coll tone too. The only problem is the tube might be microphonic. RF tubes often are.
trem
Posted: Wed 04/05/06 9:02 am
by engels
do you have any example of trioode-heptode based tremolo stage?
for some reason I cannot find one.
Posted: Wed 04/05/06 9:30 am
by zaphod_phil
This is a radio tube. There are no designs like that in existence yet.....
cool
Posted: Wed 04/05/06 5:30 pm
by engels
ok, I'll be the first and I will inform you how it'll progress.
btw, my champ with 7B7 preamp is not that bad at all.
Re: 7S7 triode + heptode for preamp?
Posted: Fri 07/25/25 10:39 pm
by TriodeLuvr
My sincere apologies for resurrecting this ancient thread. I'm about to embark on a project using a heptode (AKA pentagrid converter) for audio. It's a hi-fi thing, so the work might have only limited applications in a guitar amp.
One common variety is the 6BE6. The Brimar data sheet shows G1 and G3 being used independently to create an audio mixer. Then there's the 6BY6, another heptode. The Tung-Sol sheet includes data for standard characteristics of the two input grids, such as typical values, transconductance, etc., and also triode-mode plate curves.
Before I start with this on the bench, has anyone here ever pursued the use of these tubes?
Jack