Parallel 12AX7 vs. EF86 (matchless clone design)

[elpops]

Hi all,

This is my first post here, thanks for reading it.

I am thinking about building a tube-recitified, 6V6-based clone of the Matchess Clubman circuit. My goal is to build a simple circuit with lower volume than the Clubman, with a LTP/cathode-biased/tube rectified power section amp, for small club and basement use.

I see on the schematic that the Clubman has a parallel 12AX7 in V1. My question is, instead of using the EF86 tube in the V2 position, what about another parallel 12AX7? Pros/Cons? I'm just not interested in having another kind of tube to stock in my bench drawer and am looking for a way around it.

Thanks in advance (PS>if the tube-rectified 6V6 won't sound right with this circuit, please tell me.)

Best wishes,

Pops

[Wombaticus]

Hi all,

This is my first post here, thanks for reading it.

I am thinking about building a tube-recitified, 6V6-based clone of the Matchess Clubman circuit. My goal is to build a simple circuit with lower volume than the Clubman, with a LTP/cathode-biased/tube rectified power section amp, for small club and basement use.

I see on the schematic that the Clubman has a parallel 12AX7 in V1. My question is, instead of using the EF86 tube in the V2 position, what about another parallel 12AX7? Pros/Cons? I'm just not interested in having another kind of tube to stock in my bench drawer and am looking for a way around it.

Thanks in advance (PS>if the tube-rectified 6V6 won't sound right with this circuit, please tell me.)

Best wishes,

Pops

If you would like consistent tube types, it sounds like a 12AX7 cascode would be a good option for replacing the pentode.

[tubeswell]

Or better still a 12AU7 cascode (or a 12DW7 cascode where the 'AU' triode is the bottom of the totem pole)

[leadfootdriver]

I wanna try a cascode. Who has a good one that I can use for the 1st stage in the amp? It could be an ECC83,82, or 81. I'd like more gain than a single triode with a 220k plate resistor.

[tubeswell]

[Gingertube]

The EF86 stage will have a gain of 150 or more.

Parallel 12AX7 stage will have a gain of half that (approx 70)

A cascode will match the EF86 for gain level, however, as Merlin B states in his book, the 12AX7 is NOT a good tube for cascode connection. The gain of a cascode is approximately equal to the RL (load resistor on top tube) x gm of the lower tube. For best results the lower triode needs to be a higher gm type, that is, NOT a 12AX7, so do as tubeswell suggests and use a 12AU7 or a 12DW7 with the low mu high gm triode on the bottom and the high mu lower gm triode on the top.

The Matchless Clubman schematic at Schematic Heaven shows an anode load resistor of 10K on the parallel 12AX7 input stage, hopefully someone here can tell you if that is correct, it seems very low to me (I would have expected more like 100K) and if it is correct then that input stage is going to have very low gain and you will need the 150 plus gain out of that second stage to drive the power amp to full output with some mild overdrive.

Cheers,
Ian

[jazbo8]

Also, after you changed the output tubes to 6V6 and cascode 12A_7 for the EF86, is it even a Matchless Clubman clone anymore? Just saying...

Jaz