Tube Socket Wiring

[idsnowdog]

While looking over a Matchless Spitfire schematic I noticed a difference in the way V1 is wired. The picture on the left is the Spitfire and the right is from a Fender Princeton. Is the Spitfire only using one-half of the 12AX7 or is it series vs parallel?

 

[jeremy]

its wired in parallel. i have an amp my friend an i built. one 12ax7, both sides in parallel->longtail pi-> cathode biased pair of 6v6. it sounds amazing

 

[idsnowdog]

its wired in parallel. i have an amp my friend an i built. one 12ax7, both sides in parallel->longtail pi-> cathode biased pair of 6v6. it sounds amazing

So the socket on the left is using both sides of the 12AX7. I'm more used to seeing each side wired separately like on the right.

 

[jeremy]

correct. a 12ax7 is two triodes in one glass enclosure. most of the time you use them independently. such as a typical bf fender amp, input->1st triode->volume/tone stack->2nd triode. the pins that are joined on the right diagram are the heaters (pins 4&5). for the left diagram, the heaters are also connected but so the two plates are connected, the two grids are connected, and the two cathodes are connected.

 

[idsnowdog]

correct. a 12ax7 is two triodes in one glass enclosure. most of the time you use them independently. such as a typical bf fender amp, input->1st triode->volume/tone stack->2nd triode. the pins that are joined on the right diagram are the heaters (pins 4&5). for the left diagram, the heaters are also connected but so the two plates are connected, the two grids are connected, and the two cathodes are connected.

I intend to build a Matchless Spitfire clone. I would like to have B/M/T controls. Would the B/M/T controls be better in between two triodes like with a Fender?

 

[jeremy]

not sure. my amp only has volume and tone. how did matchless do it on the spitfire? a buddy of mine has an old one and its a great little screamer of an amp. i know matchless used a parallel wired 12ax7 on the chieftain and mojave did it on the coyote too if i recall

 

[idsnowdog]

The Spitfire has the volume/tone in between V1 and V2 which is the phase inverter.

 

[jeremy]

i believe my amp is wired the same. v1 in parallel->volume/tone->pi

usually t/m/b eq has more loss than just a tone though