Tweed Twi-Luxe, Gonna Do It! Need Help?

The Ballzz

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Well folks,
Before digging in to building a JTM45, I need to get this project done and off of my bench. If it turns out like I hope, it may negate (for a while, at least :rolleyes:) the need for said JTM45! :D Its gonna be a low powered Tweed 5E8-A Twin preamp into a cathode bias Tweed 5E3 Deluxe power section. I do have a few questions to answer though, concerning the input stages. Here's a "married" schematic:

Twi-Luxe-5E3-A-Schematic copy.jpg


My re-work of the inputs duplicates this jack arrangement, if using a Y-Cord into the #1 inputs of each channel of a 5E8-A, as below. If I plug into the top #1 input of my Twi-Luxe design I feed both channels and as soon as I plug anything (even a dummy jack) into the lower #2 input it disconnects the two channels from each other. I still haven't yet determined my input resistor values.

Twin-5E8-A-Inputs jpeg.jpg


Notice that at the inputs, there are no grid stop resistors and that when using the #1 input of either channel, we get an effective grid "leak" value of 500kΩ and that input parallels to both triodes of that tube/valve. My plan is to also parallel to the input #1 of the other channel. My questions concern what value I should use for a common grid leak? I will leave open the ability to add grid stops later, if it seems appropriate.

My thought process here is that by the time the signal gets to the grid of V3A of the cathode follower pair, the signal will be quite strong, but with lots of harmonic and tonal character. I'm guessing the paralleling will not produce an overly high amount of gain (especially with such likely low input impedance), but instead a very strong and wide ranging signal? Getting my voltages right will likely be a challenge! The transformers are Classictone 40-18085 PT,
http://www.classictone.net/40-18085.pdf
MPS OT20PP-VC87, 8K/6K6
And Mojo777 choke
https://www.mojotone.com/amp-parts/Filter-Chokes/Filter-Choke-for-6L6-Amps

I'm not sure if I'm going to actually use the choke at all and if I do, whether or not I should put it before the OT/CT or between that node and the screen node?

For reference, here's a link to a schematic for the complete, original 5E8-A:

https://cdn.shopify.com/s/files/1/2325/2729/files/Twin-5E8-A-Schematic.pdf?5926397210715640943

Notice how and where they use the choke and also that there is no separate node for the screens and no sceen resistors. I'm concerned that it's going to be difficult to keep the B+ up to around 370-ish and also keep the voltages of the earlier stages up at the listed values. I may even need to create an additional node for V1 & V2?

While I've got most of the hard components mounted, I want to get all my planning done before heating up my iron! Obviously, I may need to tweak and twiddle the resistors in the dropping string a bit!

Any and all thoughts and comments will certainly be welcome here.

Thanks Folks,
Gen
 

The Ballzz

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I seem to be over the current capabilities of the Power transformer on hand, at least according to:

https://thesubjectmatter.com/calcptcurrent.html

I do however question it's accuracy, as when I plug in other numbers from other amps I have on hand for testing the voltage is considerably higher than my known and tested readings? Also, the choke I have on hand is 3.5H/100ma/100Ω. Others have helped me calculate my current draw, as per tube choice in my updated schematic below, and we've come out to about 90ma. The ClassicTone 40-18085 specs at 630v/100ma:

http://www.classictone.net/40-18085.pdf

I've got no problem getting different iron, but how to choose the right one that won't be too stiff is a bit beyond my expertise. I've been led to believe that part of the magic of many Tweed designs is having just barely enough current available to get the job done without melting down! A 5E3 is one example. And while I want to minimize hum and ripple, to a point, reading this short article cautions me to not want to completely remove ripple in the power supply:

https://www.ampbooks.com/mobile/classic-circuits/class-AB-ripple/

I also want to be careful about "stiffening" all the response too much in the filtering, as I kinda like squishy, within reason.

Understand that I'm simply a guitarist who knows how to use a soldering iron and follow instructions, along with understanding safety precautions and how to take good measurements. I have a scope, good Fluke DMM, signal generator and dummy load It's late enough in my life that I don't really have time to study, experiment and learn a whole new trade of designing and building amps. On the other hand, I've played through enough 100s of amps to have noticed what I like and don't like, as well as being able to generally discern whether certain things are happening in the preamp or power section. Even though what I think I want isn't very complicated, nobody currently makes what I want! I just want to get to play through the amp I've come to believe is best for me! This is what has led me to this point!

To test my hypothesis, I've installed a passive effects loop (just two jacks) just prior to V2A in my otherwise stock 5E3. This has allowed me to drive various other amp's power sections with the 5E3 pramp as well as drive my 5E3 power section with many other preamps. It has confirmed that I love the way the 5E3 power section operates, even with all its warts, crooked teeth, crossed eyes and stray hairs. It has also confirmed that while the 5E3 preamp is glorious in many respects, it lacks some of the control I'd like to have over what it is sending down the line to the rest of the amp. It's not just about overdrive and/or distortion, but instead giving control "on board" the amp to shape the tonal color and character of that overdrive as it proceeds through the circuit. I've determined that these two dual parallel triode channels, also run in parallel with each other (and likely splitting the cathode pairs of each channel apart from each other), through somewhat of a Bandaxall style tone stack will probably get me where I want to go! And then on to my gloriously "farting" 5E3 power section, adding its own special color and character to the whole schmear!

And while I totally get what some folks have said about getting the input impedance too low decreasing the signal, that's what the four triodes in parallel will likely make up for. My plan for testing (once the amp gets fired up) is to put two 1meg pots in place of the input resistors to find the "sweet spot" measure the pots and install fixed resistors.

And then on the plus side, if it turns out that my "hunch" is full of poo, it's a walk in the park to remove a tube/socket and turn it easily into a cathode bias 6V6 5E7 Bandmaster, 5E5-A Pro, 5E4 or 5F4 Super!

Where I need the most help is getting my power supply in order, with enough wiggle room to experiment a bit! The power transformer I have is right on the edge of doing the job, but I'm just not sure! What's your take on my proposed current draw? FWIW, most of the voltages are in the ballpark of what I'm shooting for. The OT/CT B+ could go up a few and I may need to trim down the B+3/PI node a tiny bit.

Thanks Again,
Gene
 

The Ballzz

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I want to thank everyone for speaking up to help me! The replies to my very old "Oddball Inputs?" thread
https://www.tdpri.com/threads/oddball-inputs.1023832/
and the lack of interest and participation here and at other forums, prompted and inspired me to dig in to my own research and I'll be heating up my soldering iron shortly. I'll let you know (if anyone cares) how it all works out and there will be pics of the build!
Thanks A Bunch Folks!
Gene
 

Wally

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Subscribed, and I apologize for not having much to say. I am in no condition to analyze your design. But...I am subscribed. Having owned a 1956 5E8A Twin that was made as new as well as having owned and worked a a number of 5E3s, I would simply build a 5E8A per the schematic. I would prefer the sound of the Twin as built. Cathode Biasing can easily be added it wanted to lower the power. In a real 5E8A, one could expect about 26 watts output..maybe a bit more using two rectifiers. I would provide a switch to drop one of the rectifiers out of the circuit for a tiny power cut. See....you don’t want me to respond because I’ll get 8n the way!!!

Let’s hope some designers and analysts chime in....
 

jsnwhite619

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That calculator factors in a +10% safety factor, so whatever numbers you got are 10% higher than maxed out levels you should actually ever use/need. But, the 6.6k OT is what is raising your numbers for PT requirements. You basically have Princeton Reverb tube requirements, but used a Deluxe Reverb sized OT. Drop your OT to a 5e3 or Princeton Reverb 8k and you'll be closer to ok. As it is, you probably are going to be struggling to get the most out of anything designed to be a "Mini Tweed Twin". If you want lower headroom and more sag, maybe go ahead, but keep a check on the PT to see how hot it gets. The heater current is right on the edge too it looks like. An 8k OT or a Deluxe Reverb PT will be the either/or to get closer to "correct" numbers I think.
 

The Ballzz

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@jsnwhite619
Yeah, I'm already planning on using the 8K primary in my OT. And that calculator does funny things when you actual put in the R value for load. When you leave that blank, the Calculated current ends up more in line with what tube data sheets and math tell us it should be, around 91mA. Also, that calculator shows much higher voltages than measured in the real world! I've plugged in the numbers from several amps with know/tested measurements and I'm not sure I trust the accuracy and/or validity of the results from that calculator! :rolleyes: I think I'm good, as long as I can get the voltage up to where I want it!

And @Wally I totally get where you're coming and appreciate you noticing that I wasn't really looking for opinions of why I shouldn't do what I was bound and determined to do anyway! :p I fully respect your experience, knowledge and expertise and also value your opinions. I realize what I'm doing is somewhat unorthodox and hope you realize I was just bustin' balls a bit! :D

First off, here's the organ/chassis donor, before being stripped:






IMG_2065.JPG
IMG_2060.JPG
IMG_2064.JPG


It was a 10 watt, 6AQ5 powered JCM800/2204 style amp that I just never bonded with, even though it functioned very well. I've removed the 7-pin socket adapter plate and move the octal sockets one hole closer to the rectumfryer, to make room for the fourth noval socket and moved the dual 16/16 can inside on the wall near the PT.

More pics when all is tidied up and ready for building.

Thanks For Playin'
Gene
 
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Nickfl

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@jsnwhite619
Yeah, I'm already planning on using the 8K primary in my OT. And that calculator does funny things when you actual put in the R value for load. When you leave that blank, the Calculated current ends up more in line with what tube data sheets and math tell us it should be, around 91mA. Also, that calculator shows much higher voltages than measured in the real world! I've plugged in the numbers from several amps with know/tested measurements and I'm not sure I trust the accuracy and/or validity of the results from that calculator! :rolleyes: I think I'm good, as long as I can get the voltage up to where I want it!

And @Wally I totally get where you're coming and appreciate you noticing that I wasn't really looking for opinions of why I shouldn't do what I was bound and determined to do anyway! :p I fully respect your experience, knowledge and expertise and also value your opinions. I realize what I'm doing is somewhat unorthodox and hope you realize I was just bustin' balls a bit! :D

First off, here's the organ/chassis donor, before being stripped:






View attachment 831858 View attachment 831859 View attachment 831860

It was a 10 watt, 6AQ5 powered JCM800/2204 style amp that I just never bonded with, even though it functioned very well. I've removed the 7-pin socket adapter plate and move the octal sockets one hole closer to the rectumfryer, to make room for the fourth noval socket and moved the dual 16/16 can inside on the wall near the PT.

More pics when all is tidied up and ready for building.

Thanks For Playin'
Gene

So, that calculator seems screwy because it is giving you current draw at full output power, if you click on the show formulas button you'll see that it is using a rule of thumb calculation to determine class A output power and then using that power to work backwards with the voltage to give you current draw.

That's why if you don't enter a plate load number it gives you the correct idle current because its default assuming everything is in class A and idle current will not increase at full power but if you enter your load, which is going to run the amp in class AB, then it's showing higher current at full power.

For the purposes of transformer ratings you want to think in terms of idle current because that is the rating manufacturers are providing you with.

Also note that this calculator is using an assumption of 3.6 milliamps of current draw per preamp triode, which is in my experience about three times higher than what you'll see in most guitar amp preamp tubes.

So, with all of that taken into consideration I think you are comfortably well within the limits of that power transformers HT current rating.

As @jsnwhite619 said, I'd be more worried about heater current because you are right there at the full rating with your tube complement leaving only 0.05 amps to spare.
 
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The Ballzz

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@Nickfl
Thanks for that! Yeah, the filament current draw is just about maxed out, but on the plus side, that current draw doesn't/shouldn't fluctuate much during use. Also, if we can assume a 10% tolerance/fudge factor, which is not at all unreasonable for a well reputed and well tested manufacturer like Magnetic Components/ClassicTone, the 10% "safety factor" of that calculator AND your real world observations/impressions, I should be well in the ball park on the filaments.

Funny thing about that calculator though, is that when I plug in the numbers from my, bone stock, well tested and measured 5E3 clone, I get this:

Selected transformer voltage: 355-0-355

Calculated voltage at first capacitor (B+): 443.75V. Subtract 6V, if using choke.

Calculated filament current (typically the 6.3v secondary): 1.56A

Calculated current: 68.63mA at 16410R calculated load (10% plus factored in). Preamp valves current draw is estimated at typical 12AX7 max dissipation of 1.2W at 330V, i.e. 3.6mA per triode
Actual measured voltage (calibrated Fluke 179, with good leads) at the first filter cap with a JJ 5Y3 is 377vdc, bumps up to 385-390vdc with various NOS/UOS 5Y3s and of course a SOVTEK 5Y3 jumps it to nearly 415 vdc, but nowhere near what that calculator shows! If I manually enter the 14 watt and 0.45mA filament specs of the JJ 6V6 S, instead of choosing just a generic 6V6, the current goes up a little bit to 77.43mA, while all other calculations remains the same. All this still leaves me fairly well in the ballpark, and just a curiosity about the assumptions made by that calculator! It seems the calculator can give a reasonable reference, but if any of the calculations are gnat's a$$ close to any limits, it's time to get out the pencil/calculator, spec sheets, observed real world measurements and do the math for yourself! :D Of course when we remember that these are cathode bias amps and factor in the voltage drop across the cathode resistor, it all comes closer to being in line!

Thanks Again Sir! :cool:
Gene
 

The Ballzz

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Load lines and what they actually mean and represent are like a foreign language to me. I've tried to read, study and understand, but some little clue just isn't clicking on the light bulb in my brain! Maybe someday the switch will flip?
Thanks For Sharon Though,
Gene
 

Nickfl

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@Nickfl
Thanks for that! Yeah, the filament current draw is just about maxed out, but on the plus side, that current draw doesn't/shouldn't fluctuate much during use. Also, if we can assume a 10% tolerance/fudge factor, which is not at all unreasonable for a well reputed and well tested manufacturer like Magnetic Components/ClassicTone, the 10% "safety factor" of that calculator AND your real world observations/impressions, I should be well in the ball park on the filaments.

Funny thing about that calculator though, is that when I plug in the numbers from my, bone stock, well tested and measured 5E3 clone, I get this:

Selected transformer voltage: 355-0-355

Calculated voltage at first capacitor (B+): 443.75V. Subtract 6V, if using choke.

Calculated filament current (typically the 6.3v secondary): 1.56A

Calculated current: 68.63mA at 16410R calculated load (10% plus factored in). Preamp valves current draw is estimated at typical 12AX7 max dissipation of 1.2W at 330V, i.e. 3.6mA per triode
Actual measured voltage (calibrated Fluke 179, with good leads) at the first filter cap with a JJ 5Y3 is 377vdc, bumps up to 385-390vdc with various NOS/UOS 5Y3s and of course a SOVTEK 5Y3 jumps it to nearly 415 vdc, but nowhere near what that calculator shows! If I manually enter the 14 watt and 0.45mA filament specs of the JJ 6V6 S, instead of choosing just a generic 6V6, the current goes up a little bit to 77.43mA, while all other calculations remains the same. All this still leaves me fairly well in the ballpark, and just a curiosity about the assumptions made by that calculator! It seems the calculator can give a reasonable reference, but if any of the calculations are gnat's a$$ close to any limits, it's time to get out the pencil/calculator, spec sheets, observed real world measurements and do the math for yourself! :D Of course when we remember that these are cathode bias amps and factor in the voltage drop across the cathode resistor, it all comes closer to being in line!

Thanks Again Sir! :cool:
Gene

yeah, that calculator makes some pretty broad assumptions and uses pretty basic formulas it's a good ballpark tool but it's definitely not any more accurate than that. In particular the formula its using to give your voltage is very simplistic. It doesn't account for transformer sag in any manner and it's just multiplying the transformer voltage by a rectifier coefficient number which it seems to have sort of pulled out of its butt... It uses a 1.25 multiplier for the 5y3 and in my experience 1.15 is more common but in certain circuits with certain transformers it can be as low as 1.0 or even sometimes lower so B+ is very much a rough guess when calculated using that website.

Current draw calculation seems more accurate though. As I mentioned before, if you don't enter the primary impedance it gives you a pretty reasonable guess of idle current and if you do enter primary impedance it's giving you something along the lines of current draw at full power, though it should be noted that you will probably draw more current and output quite a bit more power when the amp is overdriven.
 

The Ballzz

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Well here's the 5E3 Deluxe and my planned build, respectively with the 8K OT figured in, just for comparison. Both with 100mA PTs JJ 6V6 specs, but different HT values. Given that the full draw current overages are pretty similar and given both PTs are from the same manufacturer and that the 5E3 is fantastic in all ways, I'm now fairly confident going forward! I think even using my "on hand" 100mA choke will be fairly safe in the pre-OT/CT location.

The 5E3 Deluxe:
Selected transformer voltage: 355-0-355

Calculated voltage at first capacitor (B+): 443.75V. Subtract 6V, if using choke.

Calculated filament current (typically the 6.3v secondary): 1.56A

Calculated current: 124.12mA at 8000R load (10% plus factored in). Preamp valves current draw is estimated at typical 12AX7 max dissipation of 1.2W at 330V, i.e. 3.6mA per triode
And the Proposed Twi-Luxe:
Selected transformer voltage: 315-0-315

Calculated voltage at first capacitor (B+): 393.75V. Subtract 6V, if using choke.

Calculated filament current (typically the 6.3v secondary): 2.22A

Calculated current: 126.21mA at 8000R load (10% plus factored in). Preamp valves current draw is estimated at typical 12AX7 max dissipation of 1.2W at 330V, i.e. 3.6mA per triode
You see, I'm just endeavoring to do as much homework, studying and planning as possible to avoid getting to surprises that cause me to have to back up and do it over again! And while I realize that during a project like this, those kinds of occurrences are nearly inevitable, minimizing them is always advantageous and increases the enjoyment factor. FWIW, three of my first four builds fired up without a hitch and have only been apart for wellness checks and slight mod on one of them. The one with a snafu, my first build, ended up being attributable to a rather janky and questionable VRM/VVR design provided by the kit purveyor. A fairly simple fix!

Thanks For Your Thought & Comments!
Gene
 

The Ballzz

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Well folks, I just got lambasted by downloading DIYLC! While making my first layout, it really helped figure out and find some tricky details. No worthwhile pics yet, but heaters and PT is wired in and I'll get a pic up tomorrow, after a bit of house cleaning. If anyone has the time and/or inclination, I'd sincerely appreciate comparing my layout to the schematic. Please discount the input part of the schematic, as I've worked that out in the layout. I'm at the point where I need to make a few judgement calls on fusing and standby switching, before the final push. My quandaries concern:
A> As can be seen, I only have a fuse on the AC Mains Hot. The chassis already has another fuse holder installed (from a previous build) and I'm trying to decide what the best use of it is, or if I should just remove it and put a plug in the hole? I've considered fusing the B+ between the rectifier and choke, but am endeavoring to avoid extra wire length? Some folks recommend fusing the HT center tap. Again, is the extra wire length an issue, or other problems?
B> I read repeatedly that the use of "standby" switches is useless at best and even harmful to amps/tubes/etc, especially if not designed properly. On the other hand, I've been using, playing and owning amps with standby switches for more that 50 years and find their use very convenient and there's already a hole and label on the faceplate for it! What is the least harmful and/or detrimental way to put a standby function in this amp I'm building? Could it be as easy as a "mute" switch that simply grounds the guitar input?
Here's the layout and schematic for easy comparison. There is a link to download a pdf of the layout that is much clearer than the jpeg I was able to upload I am brand new to DIYLC and don't know yet the best ways to share!


TWI-LUXE #1.pdf
TWI-LUXE #1.jpg




Twi-Luxe-5E3-A-Schematic copy.jpg



Thanks 2 All 4 Looking & The Help Yet To Come!
Gene
 

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The Ballzz

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I've updated the layout in the previous post with a re-worked input jack scheme and the addition of fusing the HT Center tap. Also the uploaded layout is a little bit more clear, but if you want to see it really clearly, click on the pdf.

Thanks For Looking!
Gene
 

Nickfl

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The general consensus seems to be that a mute switch is better than a B+ interrupting standby if you want that functionality. Just grounding the signal somewhere should work fine. I'd probably do it at the grid of your phase inverter triode, that seems like it would be easier than dealing with switching all the inputs plus it's closer to you switch location.
 

The Ballzz

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Now that my layout is finalized, it's time to get started. While it won't be the prettiest amp on the block, I'm hoping for the best sonically. Remember, this chassis is being converted from something else, but all the sockets, switches, jacks and pots are new!

Heaters and off board power supply are wired and tested! Turret board is fully staked and I'll begin population tonight!

IMG_0559.jpeg
IMG_0564.jpeg


Thanx 4 Lookin'
Gene
 

The Ballzz

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Hey Folks,
I was torn about resurrecting this 8-9 month old thread or starting a new one for the actual final build? I made the executive decision (I'm President of me!) to simply continue with all the great comments, info, etc, that has already been shared here!

The circuit board has been fully prepped and leads attached, along with a revised "0" volt ground scheme. My current plan is to fully wire in the board to the prepped chassis and then populate all the on-board components. This should help avoid any/all soldering iron "nicks" on caps, etc. Remember, I'm an assembler, not a real tech, repairman or amp designer! Also, please understand this is my first "scratch" build, with a design that is a marriage of two different amps and I've left myself lots of "wiggle" room, extra space, turrets, etc, for changing things, if all doesn't work as expected! Worst case will be to simply turn it into a cathode bias version of a 5E4 Super! This needs to get finished and off my bench, so that I can tackle the Modulus JTM45 kit I have just ordered!
Thanks 4 Playin' Along,
Gene

IMG_0615.jpeg
 

The Ballzz

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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! :cool: 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

TWI-LUXE VOLTS.jpg
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The Ballzz

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TWI-LUXE in its current, temporary home:

IMG_0621.jpeg
IMG_0622.jpeg
IMG_0623.jpeg


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
 




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