I've never seen an *SA412* but with your amp the ONLY thing that is some semblace of HiWatt is the PI topography ,,,datz it.
AFAIK,, No Hiwatt used the extra front end. It's dumb noise prone stupidity.
Marshall hot rodders found out the fatal flaws of wiring up the extra triode like that. they just osscilate and any extra gain is rendered useless.
My advice for you is just loose the first AX7 and wire the preamp back up to standard hiwatt specs,, you will thank me one day.
If you wish to underatnad how hard it is to get that many stages to work without issue then download the *Carvin Legacy* schematic and have a squizz at the Hot channel and count the triodes. ALL heaters are DC,,, only way you can make it happen.
Cheers phil.
AFAIK,, No Hiwatt used the extra front end. It's dumb noise prone stupidity.
Marshall hot rodders found out the fatal flaws of wiring up the extra triode like that. they just osscilate and any extra gain is rendered useless.
My advice for you is just loose the first AX7 and wire the preamp back up to standard hiwatt specs,, you will thank me one day.
If you wish to underatnad how hard it is to get that many stages to work without issue then download the *Carvin Legacy* schematic and have a squizz at the Hot channel and count the triodes. ALL heaters are DC,,, only way you can make it happen.
Cheers phil.