TWEED TWI-LUXE, FINISHED!

[Gene Ballzz]

Gene, I believe the switch you have there has been discontinued. I ad others have been using this instead.

https://www.amplifiedparts.com/products/switch-rotary-1-pole-3-position-0

Thanks for that confirmation, as that's the one I also found. I was aternatively thinking of opening up the hole and using this 8/10A rated unit:

https://www.tubesandmore.com/products/switch-rotary-impedance-selector-replacement-marshall

Even though it's rating is good, I'm wondering if folks have had any problems with either of those?

Just Wonderin'
Gene

 

[Gene Ballzz]

Well the executive has made another decision! Given that the two speaker jack holes and the impedance selector hole are the same size and evenly spaced, I'm simply gonna use three speaker jacks, 4, 8 & 16Ω.
There! Just Fixin'
Gene

 

[Gene Ballzz]

The TWI-LUXE has been mostly finished and fired up! A few issues, "I"s to dot and"T"s to cross, etc, but it sounds amazing! The girth, clarity and harmonic response that sits somewhere between a well tuned 1959 at it's sweetly cranked spot and a great Blackface Fender Showman at the same spot is breathtaking. Maybe even more like plugging into both both at the same time! All this out of a 14-ish watt cathode bias amp with 6V6 power tubes! And yes, even with the clarity, it can bark and distort, with glorious feedback, etc! Most of my suspicions of what this circuit could do have been confirmed! Remember, we all want "BIG BOY" amp sounds and feel at "little boy" volume levels! It's a new world!

There is a problem with a very high pitched whistle, around 10-12khz or so, under certain circumstances. I think I know what it it is. See if anyone can notice it in the voltage chart below?

Remember, this build includes a completely passive effects loop with a Master Volume (intended mostly as a return level for the loop) just after the effects loop and just before the driver stage of the cathodyne phase inverter.

And yeah, it looks a bit messy, but I'll clean up the lead dress as I sort out the oscillation and there's not a lot you can do with the extra tranformer wires when thay both have multiple primaries and scecondaries, except cut them off! I don't want to do that, as I might want/need to repurpose the iron, at a later date.

Also, please pay no never mind to that "janky" cap series on the bass pot. I forgot to order a 0.005uF cap and didn't want to wait on fire up for one to arrive, so I simply put two 0.01uF in series, for the time being!

Thanks For Playing Along!
Gene

 

[Gene Ballzz]

Well folks,
The amp is done except for finding a good source for 12AY7 tubes (it needs three) and checking the actual cathode bias, for dissipation percentage. I fixed the high pitched whistle/oscillation I mentioned in my previous post, by swapping the OT leads to the power tubes. The amp sounds absolutely amazing! Truly BIG BOY sounds at little boy volume levels. The passive effects loop works perfectly as planned for my use. And oh yeah, the amp is dead silent, even with piles of overhead flourescents in my shop!
Thanks Folks,
Gene

 

[Mcentee2]

What was the noisy whistle ?

 

[neikeel]

What was the noisy whistle ?

Positive feedback in power amp due to reversed primary wires.

 

[Gene Ballzz]

TWI-LUXE current, temporary home:



It is easy to get in/out of this box, for mods, tweaks, etc! I need to ascertain whether it will be a "go to" amp, before mounting it into a Tweed Super 1X12 combo cab that I have waiting. I also need to decide how much I like it, prior to spending the $$ on proper face and rear panels for it! FWIW, it is already out and on the bench for said mods/tweaks! I'm gonna bring the PI and preamp voltages up a bit and swap a resistor in the tone stack. While it sounds amazing for many things, it sure could use a tad more gain! Given the location of the Master volume, I can confirm that absolutely no distortion/overdrive happens in the preamp, but instead, all of that currently happens in the power section!
Thanks Folks,
Gene

 

[Gene Ballzz]

Well Fine Folks, the word "Finished" in the thread title was kind of a misnomer.

First> The Voltage survey above incorrectly showed a 5U4 rectumfryer, but was actually a 5V4. I have since bumped up all the voltages with a GZ34, as well as adjusting the dropping string to provide a bit more voltage to the screen, PI and preamp nodes.
Next> I changed one resistor in the tone stack to eliminate "mid range scoop" unless both Bass and Treble are nearly floored. Treble around 8 or 9 and Bass at about 3 or 4 yields a fairly flat response and I simply add in a bit of the normal channel to thicken the bottom end. And yes, this amp loves being close to fully dimed!
Next> I found that the passive effects loop send was just a bit too hot and upgraded the loop to a Granger unit. It works flawlessly and is as inert and transparent as could be! It didn't even shave any more than 1 volt off of the power rail and is dead silent. I can easily use the send as a "preamp out" to the effects return/power amp in of a different amp or use the effects return as a power amp in on this amp. Lots of cool options!
Then> The springy, bouncy character of the touch sensitive feel and response is absolutely amazing! It doesn't lose highs when the volume of the guitar gets rolled back, but simply softening picking attack works gloriously well also! I can go from clean to dirty to clean without touching a knob or stomping on a switch. It puts all control right in my hands, where I like it!
And Finally> The Master Volume is somewhat of a "white elephant" for now, but works as expected. It may find a use down the road, should I ever need to replace my Lexicon MX300 delay/reverb unit for something else. Did I mention that this amp provides no distortion in the preamp, but puts out a VERY strong, clear signal? I may monkey with splitting the V1 & V2 cathodes to color those two channels a little differently, but for now, This amp is truly amazing and exactly what I was shooting for!

Thanks Fine Folks!
Gene

 

[Guitar-Rocker]

Glad your amp is finished. Did you try lifting the NFB to see if that had any effect on the amp?

 

[George Dickens]

Looks like a nice clean job!
For me I wouldnt have the twisted wires so perfectly symetrical -
I think a bit of hap- hazard randomness in the twistes makes for less noise-
or potential odd noises - JMHO

 

[Gene Ballzz]

Looks like a nice clean job!
For me I wouldnt have the twisted wires so perfectly symetrical -
I think a bit of hap- hazard randomness in the twistes makes for less noise-
or potential odd noises - JMHO

Well, that's the whole purpose of an amp and guitar, to potentially make "odd noises" eh?

That's My Intention Anyway!
Gene