successful installation of a gain stage in a Princeton style amp

[phsyconoodler]

 I have been experimenting with a gain stage added before an existing amps' circuitry and I got it right in a Princeton Reverb style build.
 I used a complete 12AX7 gain stage ala Weber's universal gain stage,and added it into a box a lot like Vox used to add the Top Boost mod to early AC30's.
  I had a Raw control on this amp that I used for the gain control and used a marshall style shelf divider;470k/470k/500pf for the grid on the existing V1 tube.I used shielded cables and the gain(raw) control was left at 250k.
  It's absolutely lovely sounding! It does higher gain than a JCM 800 and still allows you to get cleans if the gain is turned down.
Like Tubenit,I didn't use a 1 meg pot blindly,cause the 250k pot is more than enough for a gain control.
  I could even get away with a 250k for the volume control in this amp because there is so much preamp gain on tap.
I'll get some pics up of the amp today if I can.It's a tweed cabinet with a Weber 15: Alnico speaker.It shouldn't sound awesome with that combination but it sure does!

[Tone Junkie]

Cool phyconoodler it sounds like a lot of fun I too have found that a 1 meg pot is not necessary and will sometimes put in 500k were a 1 meg is called for when there is a lot of gain on tap. so what did the final schematic look like.

Bill                                   

[phsyconoodler]

Here are some crappy shots of the amp.
  The circuit is Princeton Reverb with the gain stage in a box on the side of the cabinet.

[archaos]

Very nice, congrats !!! 

[Tone Junkie]

Very nice looks good I love amp porn.     

[Willabe]

Yeah very nice phsyconoodler.

Is that a custom chassis?


         Brad     

[phsyconoodler]

yeah I had it made at a local aluminum shop.I rarely buy chassis unless I do a blackface Fender build.

[Willabe]

Looks strong, nice weld.


         Brad         

[zendragon63]

Nice work. Did it add much hiss being on the front end? Regards

dennis

[phsyconoodler]

No it doesn't hiss but it does add some hum at higher settings.Not near as bad as I thought it would be.It has TONS of gain on tap.
  I used the weber universal gain stage as drawn and the Marshall style shelf divider with a 250k gain pot.
You could easily use a 250k pot for the main volume as well and you would not miss the 1 meg at all.
  It's quite bright with the Weber 15" alnico speaker but it will cut through a mix nicely.Not overly bright at all.
The tone is quite remarkable.I am more than pleased with the results.

[zendragon63]

Thanks for sharing phsyco--got me digging out last year's goofy 5840 submini mid and treble boost project that didn't spontaneously combust with 'grail' tone.

Interesting you say that the 15" Alnico is "quite bright" with this. Regards

dennis