18 watt question

[J Rindt]

http://el34world.com/Forum/index.php?PHPSESSID=5f292e24af653f4a37dba9688ccee2d1&topic=16826.0

The thread above reminded me to ask a question I have been wondering about for a long time. Would have asked sluckey  up there ^^^^^^^ he posted an 18 watt schem...but sometimes that is seen as bad etiquette.

S0.....in your "typical" 18 Watt Marshall...what Is/Was the reason for the phase inverter to be installed between the normal input and the trem input.?
In most cases, the PI is placed right before the power section....and shares power supply ground with the power tubes.
Is there anything "wrong" with swapping the PI and Trem tubes.?
Thank You

[sluckey]

S0.....in your "typical" 18 Watt Marshall...what Is/Was the reason for the phase inverter to be installed between the normal input and the trem input.?

That's the way the originals were wired. Who knows why. It was just a small practice amp so probably didn't have a lot of thought put into the layout. The original 18W Marshalls were Model 1974 (1x12) and 1958 (2x10). Same chassis. See attachment...

Is there anything "wrong" with swapping the PI and Trem tubes.?

None that I see. In fact, someone over at 18watt.com did just that.

[J Rindt]

10-4
I have only built one 18 Watt to date. I had a few problems with it.
I converted a Crate V18 into the Marshall 1974. Trying to make stuff fit the old holes made for a LONG Lead Dress.
I also tried to implement adjustable fixed bias...and along with the PI being in an "odd" spot...I had problems that I never was able to fix.
So I gutted the amp and built a Xits-10...Matchless Spitfire...Vox AC15, I cannot really remember. They are all kind of the same amp.
Anyway...have been thinking about trying the Marshall 18 again, and was wondering about that phase inverter.
Thanks for the info