Cutler Duo-Control

[Andy Le Blanc]

Today's project start is an amp to explore a "Cutler Duo-Control".
Nothing crazy, simple front end, self-balancing para-phase inverter.
It be a 6v6 power side with around a 8K load presented to the tubes.
Its from the RDH4, I'll noodle with the thing with common bench values.

[Andy Le Blanc]

here's the start of the chassis.... ink on metal, oh boy.

It's important to plan ahead for the break...

[Andy Le Blanc]

Holes.....

[xk49w]

Today's project start is an amp to explore a "Cutler Duo-Control".
Nothing crazy, simple front end, self-balancing para-phase inverter.
It be a 6v6 power side with around a 8K load presented to the tubes.
Its from the RDH4, I'll noodle with the thing with common bench values.

Andy, I think you might have discovered where Bob Crooks got that first preamp network in the 25L15, the one after the first preamp stage. It looks very much like your first figure of the Cutler duo-control (fig 15.46 in RDH4). It makes even more sense if you look at the original version, the one with the 220k resistor crossed out.

Good find.

[Andy Le Blanc]

I've been looking at the same thing in old gibson scheme forever, too.
It's half way to wah filter, parallel "T". figured I'd try it out, I like simple
tone controls, it makes the dress easy, and it won't sound like a fender.

[Andy Le Blanc]

pretty...... bent, A sheet of paper in the break keeps it from marring.

[Andy Le Blanc]

Old knobs made to shine. An buff wheel on a arbor adapter works fine.

[Andy Le Blanc]

Some times its works well, some times not so much.....
Both control elements actually work pretty well buy them selves, but
together they tend to wash the other out in a less than practical way.
If they were used to dial in a a tone, and everything was "just so", and then
left as filter its useful. I've seen them in only a few places, old Gibsons
made use of this as tone control, but it was just not all that practical as a
treble and bass control in a guitar amp. Frustrating, but a good way to play
with a "T" filter. And that seems the best use.... so far.

The rest of the project is up and running despite the set back.

I got frustrated enough to try a another duo control, one of the simple Hiwatt
treble bass affairs.
Very practical little thing and it not too bad a "duo-control". Not the same
feel as the fender one.

I had the opportunity with this one to use all "black cat" caps in the signal
path. I found an old deviation meter in my sister in-law's garage last summer
and finally got back around to it off the bone pile. Its a simple amp but it
should be just fine. The old circuits do better for a clean tone and the dirt
is softer and more colorful. Old para phase inverters and zero bias make
enough of the right flavor of distortion all by themselves, even when its clean.

[Wayne]

The filter network in your drawing above looks halfway like the twin-t network used in some of the Traynor Guitarmates.

Are those circuit values straight out of RDH4? If so, wouldn't they be more likely to be aimed at full range (i. e. playback) tone control rather than guitar? Perhaps a re-voicing is in order, or maybe you've already done that.

I'm all for deviations from the Fender/Marshall norm...

W

[Andy Le Blanc]

The Traynor is another duo-control, but its two filters that mix post.
The Cutler is an attempt to get two controls out of one filter.

Pg 664. figures 15.44A thru 15.46 in the RDH4. It was hard to convince myself
the the cutler would be practical, it wasn't the values, one control would make
the other less effective at the extreme of its range, and thats not what a
guitar player would want to deal with.

Consistency is the hob goblin of the simple mind.

The fig. 15.44B, just above the cutler on the same page looks neat.
Its described a treble/bass boost control. But... in the figure it driven by a pentode.
I might try that next before I button up the project, I'll have to see is a
12ax7 has a high enough impedance to drive the thing, in a practical sense.
All the pot.s are 1M. Always nice to keep parts to a minimum.

[Andy Le Blanc]

More shots, I went with that Hiwatt treble/bass for giggles.
The black cats sound nice. Phat classy amp. I'm thinking I'll pair it with
this 10x15 speaker, it'll be neat to hear. I really like old paraphase amps.
They're never clean, never suffer fender-itis, nice tone......

[M Fowler]

Andy,

Looks good, like you salvaged and old organ amp chassis complete with surface rust.

[Andy Le Blanc]

I'd like to say spilt beer, but it came from the local hardware store like that.

[Andy Le Blanc]

yeah..... the holiday's is done.

...should be done today, not but to cut a logo.

[Andy Le Blanc]

Nice to be nearly there...

The speaker is brighter in tone than I expected, the volume is lower than expected.
It's still running on bench tubes, fresh tubes should help, if its not that then I
might have to rethink the losses associated with the tone stack.

Tomorrow I'll have a logo fabricated, that's always fun.

Fabrication with a fairly simple amp like this, from sheet metal to logo,
can be squeezed into just three days. Built with what you got, no investment,
even the wood is left overs. I spent 6$ on handle's down at the hardware store.