After much deliberation, this project is the one that got me motivated...
This is my first DIY amp,
I purchased all of the Iron from Thermionic labs figuring if there OPT is as good as its suggested, there may be a benefit by going all in...
One thing worth mentioning right off, the 5H choke is considerably (and alarmingly) smaller than the 193H Hammond...
I emailed TLabs (the name is a bear to spit out never mind spell) and was assured, that the itsy bitsy choke was in fact every bit what was needed....
So, laying out the Iron (on my own, and before the Sun rose this am...) I have came up with the following...
This evening, and still feeling accomplished, I compare to Stephe's layout and notice the choke 90 to the PT in the rear,
with the OPT 90 to the choke...
I thought I read where in these pages today that the coupling between the PS and Choke was not as important as the say the choke or PS with the OPT...
I feel silly asking, but honestly thought my layout had much less chance of cross talk because the lines of flux had not interfered with the OPT in any way.
Anyway, this next image is more similar to what Stephe had done...
Are they both equal, is one clearly better than the other and if so, which one ?
This is my first DIY amp,
I purchased all of the Iron from Thermionic labs figuring if there OPT is as good as its suggested, there may be a benefit by going all in...
One thing worth mentioning right off, the 5H choke is considerably (and alarmingly) smaller than the 193H Hammond...
I emailed TLabs (the name is a bear to spit out never mind spell) and was assured, that the itsy bitsy choke was in fact every bit what was needed....
So, laying out the Iron (on my own, and before the Sun rose this am...) I have came up with the following...
This evening, and still feeling accomplished, I compare to Stephe's layout and notice the choke 90 to the PT in the rear,
with the OPT 90 to the choke...
I thought I read where in these pages today that the coupling between the PS and Choke was not as important as the say the choke or PS with the OPT...
I feel silly asking, but honestly thought my layout had much less chance of cross talk because the lines of flux had not interfered with the OPT in any way.
Anyway, this next image is more similar to what Stephe had done...
Are they both equal, is one clearly better than the other and if so, which one ?
Stick with Skunky design. She is very meticulous about her layout decisions. Best to keep them at 90°. Also, she uses the bolts for mounting other devices internally, you may run into some spacing issues inside. If you go with your design, you would want to rotate the output transformer 90°. You never want adjacent cores parallel to each other if it can be avoided. Chokes can put out a fair amount of noise and the power transformer is further away and not side-by-side with the output transformer…there should be little or no coupling between the two.
Last edited:
Got it...
Though parallel cores would mostly have an issue if they were in line so to speak...
a ways back i hooked up my signal generator to my x-over chokes and and ear phone to the other chokes and actually found the null zones by ear... was surprisingly fun with immediate results...
Was contemplating what it would take to do the same in this circumstance..
Im guessing 1v 60hz into the PS primary, putting a properly sized resistor across b+ and my scope across the leads of the choke.. then the choke with 1v, 60 hz and scope to opt secondary...
Though parallel cores would mostly have an issue if they were in line so to speak...
a ways back i hooked up my signal generator to my x-over chokes and and ear phone to the other chokes and actually found the null zones by ear... was surprisingly fun with immediate results...
Was contemplating what it would take to do the same in this circumstance..
Im guessing 1v 60hz into the PS primary, putting a properly sized resistor across b+ and my scope across the leads of the choke.. then the choke with 1v, 60 hz and scope to opt secondary...
Don't get lost in conjectures, the only valid method is assembly on a breadboard to validate in reality before moving on to final assembly.
This is tried and tested. Can’t hurt to do a little testing on positions as you stated. Might be fun. However, Best to ask the person who designed and built it. Possibly ask her if she has any ear to speaker hum, or if any AC ripple shows up at the speaker terminals with the volume all the way down. If not, best bet would be to stay with the known design. Skunky is very particular about AC wiring layout. Follow her lead closely! Most of all, have fun!
Last edited:
The 2nd one was harder, and easier than the 1st one... in many ways. Have to say again, Feel like I just finished a Triathlon...
You folks who have been doing this for years, and on number 8, 15 or more have my utmost respect...
So much more than meets the eye but 100% doable if committed..
Truth be told, the 2nd one showed me a tiny mistake I made on the first one, will correct before 1st listening ...
That said 99.9% done, sad and glad at the same time....Sorry for the lousy staging, Had to share!
Will get better pics soon!
You folks who have been doing this for years, and on number 8, 15 or more have my utmost respect...
So much more than meets the eye but 100% doable if committed..
Truth be told, the 2nd one showed me a tiny mistake I made on the first one, will correct before 1st listening ...
That said 99.9% done, sad and glad at the same time....Sorry for the lousy staging, Had to share!
Will get better pics soon!
Attachments
I really like the styling. It's both Modernist and International. Much thanks.
All good fortune,
Chris
All good fortune,
Chris
Last edited:
Amazon,
https://www.amazon.com/gp/product/B06XXM74SC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Modified the internals, as sold as a V meter, changed the resistor and trim pot, now a mA meter... made a new face plate too ;-)
Stephe just sent me a Skunkie pic so now have another background...
Will swap out if I need to go into them for any reason..
Attachments
Used an adjustable power supply to cause a full deflection of 15 volts while the trim adjustment was centered.
I found 1mA was required for full deflection.
I wanted the 15 to equal 150 mA so
Im Lucky, the KT120 Monoblock had a 10 Ohm sense resistor already planned for the test tip jacks...
150mA across the tube would equal a 1.5volt drop across the cathode resistor of 10 ohms)
I figured I probably will never need a tube biased at 150mA but thought the headroom would be good...
So, 1.5v / 0.001 = 1.5K ohms total required (in the meter and meter resistor) for full deflection.
The meters movement itself measured 150 ohms. If I had a 1.5k-150 = 1350 ohm resistor I would have tried that.
Since I have a trim pot kit I did a 1k resistor and a 25 turn 500ohm trim pot in series...
I drilled a small hole in the back of the plastic meter and used a hot glue gun to affix the trim pot in place...
Which was tricky...
I found that a short sleeve of wiring insulation on my bench just happened to fit the adjustment screw snugly, and was long enough to guide the trim pot into the correct place
Added a dose of molten glue and whamo....
I found 1mA was required for full deflection.
I wanted the 15 to equal 150 mA so
Im Lucky, the KT120 Monoblock had a 10 Ohm sense resistor already planned for the test tip jacks...
150mA across the tube would equal a 1.5volt drop across the cathode resistor of 10 ohms)
I figured I probably will never need a tube biased at 150mA but thought the headroom would be good...
So, 1.5v / 0.001 = 1.5K ohms total required (in the meter and meter resistor) for full deflection.
The meters movement itself measured 150 ohms. If I had a 1.5k-150 = 1350 ohm resistor I would have tried that.
Since I have a trim pot kit I did a 1k resistor and a 25 turn 500ohm trim pot in series...
I drilled a small hole in the back of the plastic meter and used a hot glue gun to affix the trim pot in place...
Which was tricky...
I found that a short sleeve of wiring insulation on my bench just happened to fit the adjustment screw snugly, and was long enough to guide the trim pot into the correct place
Added a dose of molten glue and whamo....
Yes a few little things,
The lighted power switches are available in a 120v version, no rectifier for the led needed...
i added a ul/Pentode switch to each, since then i have removed as one was giving me a problem, i should have bought something a little more skooem (aVe'ism) may revisit this...
all iron from thermionic labs,
had some ringing on the 1k square wave, upped the schade fb resistor from 150k to 220k and added a 50pF cap across.. tamed it down quite a bit but will be doing more work on that. I don't mind a little distortion and right now they put out about 14w at less than 2%, at typical listening they are 0.5%..
if you goto the valve wizzard site you can see where the negative bias circuit came from.. the next step up from skunkies schematic was adding another capacitor and diode before the last 100 uF cap.. this slows down how fast the neg bias circuit bleeds off..
After i tame the square wave i plan on trying a few types of coupling caps.. I was lucky, before the war I stocked up on russian paper in oil caps, i also have a few different types from my Elsinores speaker build..
The lighted power switches are available in a 120v version, no rectifier for the led needed...
i added a ul/Pentode switch to each, since then i have removed as one was giving me a problem, i should have bought something a little more skooem (aVe'ism) may revisit this...
all iron from thermionic labs,
had some ringing on the 1k square wave, upped the schade fb resistor from 150k to 220k and added a 50pF cap across.. tamed it down quite a bit but will be doing more work on that. I don't mind a little distortion and right now they put out about 14w at less than 2%, at typical listening they are 0.5%..
if you goto the valve wizzard site you can see where the negative bias circuit came from.. the next step up from skunkies schematic was adding another capacitor and diode before the last 100 uF cap.. this slows down how fast the neg bias circuit bleeds off..
After i tame the square wave i plan on trying a few types of coupling caps.. I was lucky, before the war I stocked up on russian paper in oil caps, i also have a few different types from my Elsinores speaker build..
Yes, i tried only the 220k and still had ringing, then tried a 100pf cap across that resistor but it affected the leading edge into a radius of sorts.. two 100pf caps in series reduced the ringing enough to make me happy for now...
Since then (and a few hours after putting it all together again) i stumbled across a post at stephes site where she mentioned that depending on the amp she has tried many sized schade fb resistors and gone up to 1meg depending on the amp...
Disconnecting the schade FB cranked up the gain tremendously (wish i actually measured it) and completely removed any ringing on the plate of the input tube... next time in i will be swapping in many different size resistors and also be looking at the 8-10k square wave ..
A year ago i had only considered building my first amps, but only considered it. Something about the KT120 monoblocks lit my fuse... many things I have been trying to understand for a year or two suddenly came into focus. That's not to say i consider myself anything but a novice, still much more to learn. i find this entire journey thrilling 🙂
Since then (and a few hours after putting it all together again) i stumbled across a post at stephes site where she mentioned that depending on the amp she has tried many sized schade fb resistors and gone up to 1meg depending on the amp...
Disconnecting the schade FB cranked up the gain tremendously (wish i actually measured it) and completely removed any ringing on the plate of the input tube... next time in i will be swapping in many different size resistors and also be looking at the 8-10k square wave ..
A year ago i had only considered building my first amps, but only considered it. Something about the KT120 monoblocks lit my fuse... many things I have been trying to understand for a year or two suddenly came into focus. That's not to say i consider myself anything but a novice, still much more to learn. i find this entire journey thrilling 🙂