Matchless HotBox build preparation - PT questions

[RadioComm]

Hello,

I'm considering building a Matchless HotBox based on el34 schematic found at:

https://el34world.com/charts/Schematics/files/Matchless/Matchless_hotbox.pdf

I've found a layout (attached) found on WWW, but it had some issue... And needed correcting.

In DIYLC, I've correct/re-labeled the WWW layout with the following:

* Corrected pinout on V2
* Swapped labels V1 to V2. I like V1 to be closest to input.
* Swapped label A/B of power supply to match schematic
* Modified incorrect and modified V1 pinout values to match schematic.

Any verification of  DIYLC layout would greatly be appreciated. Thanks 

PT questions are:

* What VAC secondary plate voltage do I need to match the A (242VDC) and B (250V) voltage on the output of the power supply. Based on ValveWizards site, I know that post-rectification for voltage is VDC = 1.4 x VAC, but I don't know how to calculate VDC past the filtering ....
* If I do choose to increase the VDC value of the A/B power supply outputs, how would this affect sound?

Thanks so much for the answers. 

ttfn

[scstill]

Is this what you are building?
http://enginerdamps.blogspot.com/2009/01/matchless-hotbox-tube-preamp-pedal.html

Did you see Mercury makes a PT?
https://www.mercurymagnetics.com/model/hotbox/

[RadioComm]

Did you see Mercury makes a PT?
https://www.mercurymagnetics.com/model/hotbox/

I did find Mercury's PT, but yikes... $141.00 USD... And they don't advertise voltage...

I'm considering the Hammond 269EX for *a lot* less, but that would give me 266 VDC post rectifier. Not sure what post filtering would be. May use it at a higher voltage, if I knew what the sound would be. Otherwise would lower voltage with a chassis mounted reverse diode on ground tap.

[RadioComm]

>>>> I don't know how to calculate VDC past the filtering

Not there yet. Still obviously missing a piece... So I figure if using a Hammond 269EX 380Vct (190-0-190). From attached power supply schematic from EL34 hotbox schematic:
* Post full wave rectifier - voltage would be 266 (190*1.4) and the frequency 120Hz (2*60)
* Past the first 22uf capacitor, the voltage wouldn't change...
* So to get to the Label A output, I would use a low pass RC filter formula (attached) where;
   - Capacity Reactance (Xc) is based off of C= 0.000022 and Freq=120
   - Output voltage (label A) is based off of Input V=266 / Resistance = 22000 / and Xc from above.

The math is from the following web site:
https://www.redcrab-software.com/en/Calculator/Electrics/rc-low-pass-filter

Using the web sites calculator, I plug in the values and I get 3.4 V instead of 242 V. Wrong answer. Even broke out my calculator and concurred with web site's voltage.

Will continue to research, but any help or pointers as to what I'm doing wrong would greatly be appreciated. Thanks again.

Headed out on a road trip for the next couple of days to enjoy the weather with the Wife. Take care everyone.

[sluckey]

>>>> I don't know how to calculate VDC past the filtering

Don't overthink this. Use that PT and get a handful of resistors. Shouldn't take over a few minutes to get it right.

[RadioComm]

>>>> I don't know how to calculate VDC past the filtering

Don't overthink this. Use that PT and get a handful of resistors. Shouldn't take over a few minutes to get it right.

Thanks Sluckey. Absolutely. That was the plan all along. My MO has always been Leo Fender's approach: build, measure, listen, tweak, and then listen again. Trying to do the math is just for fun and curiosity. Certainly not a prerequisite to a build.

I will be using the Hammond 269EX (190-0-190) to start. After building, measuring, and listening: to drop the voltage by 5 or 10 volts, I would use a reverse polarity chassis mount zenner diode as described in Dan Torres chapter (attached). For 5V I would use a NTE5243AK and for 10V a NTE5252AK. To increase the voltage, I would tweak the resistors.

Schematic:
https://el34world.com/charts/Schematics/files/Matchless/Matchless_hotbox.pdf

[RadioComm]

I nixed the idea of using a 269EX as a PT. Too much iron for a couple of 12ax7's (power + real estate). I would like to use the same approach as el34 for his tube pre amp project by using a PCB mountable toroid power transformer.

https://el34world.com/projects/tube_box_3.htm

If I can get this to work, then I would update the layout to get rid of all ground to chassis, and redo the filament wiring.

I'm trying to bread board the voltage plate half of the power supply to eventually get the two output VDC voltages (250VDC and 242V) from the HotBox schematic (link post above) post tweaking the resistors. But those two output point (row 27 & row 40) voltages are not dropping post filter...
 
* Wall wart is 12VAC/1A spec
* Reading 14.3VAC on the output of the wall wart
* xfrm input is set for the two 12VAC inputs in parallele
* Output of the xfrm is 211.8 VAC
* Post rectifier is 280.1 VDC
* Post filter 22K ohms (row 40) ~280.1 VDC. The picture makes it look like the resistor is plugged into row 41, but it's not...
* Post filter 4.7K ohms (row 27) ~280.1 VDC. The picture makes it look like the resistor is plugged into row 26, but it's not...

What am I doing wrong?
 
 Thanks for the help.

[sluckey]

In order for those droppers to drop any voltage, there must be some current flowing through them. In order to make the current flow you must have a load on each node. IOW, put an appropriate size resistor from each node to ground. You can roughly figure about 2mA for each 12AX7. Do a little math and use that as a starting point. Then get a handful of resistors for any fine tuning.

[sluckey]

Look at the design example at the bottom of this page. Should give you the big picture.

     http://www.valvewizard.co.uk/smoothing.html

[RadioComm]

In order for those droppers to drop any voltage, there must be some current flowing through them. In order to make the current flow you must have a load on each node. IOW, put an appropriate size resistor from each node to ground. You can roughly figure about 2mA for each 12AX7. Do a little math and use that as a starting point. Then get a handful of resistors for any fine tuning.

Understood. Thanks. At least the part for needing a load to drop the voltage and simulating the 12ax7 loads with a resistor for each node.
 
As far as "You can roughly figure about 2mA for each 12AX7. Do a little math and use that as a starting point.", maybe easier said than done. For now anyway  I'm going to read valvewizard's page, and maybe it will become clearer.

Thanks so much again sluckey. Will proceed down that route.

[sluckey]

The Matchless parallel filter nodes makes this very easy! You have 280v at the left side of a dropper and you want 242v at the right side of the dropper. So, the voltage ***ACROSS*** the resistor will be 280-242=38V. So, the dropper resistor value needs to be 38V/.002A=19K. I would use 18K or 20K, whichever is in stock. See how easy. I bet you can do the other one.

Extra points if you get it right tonight! 

[RadioComm]

The Matchless parallel filter nodes makes this very easy! You have 280v at the left side of a dropper and you want 242v at the right side of the dropper. So, the voltage ***ACROSS*** the resistor will be 280-242=38V. So, the dropper resistor value needs to be 38V/.002A=19K. I would use 18K or 20K, whichever is in stock. See how easy. I bet you can do the other one.

Extra points if you get it right tonight! 

You are so totally awesome  Thanks a million  Love getting the answer first and then figuring it out 

Won't get the extra points thought... Movie night with the Wife  Snuke the peak in while microwaving dinner...  Most definitely will get back to it tomorrow.

Thanks again

[sluckey]

You could have done the calculation faster that the microwave!  Deal is good until midnight.   

[RadioComm]

You could have done the calculation faster that the microwave!  Deal is good until midnight.   

Well before midnight EST. But my usual MO... Fell asleep during the movie... Wife stopped movie. Will resume tomorrow as long as I can stay awake  I'm the early to be bed, early to rise type. So off to bed I go. But before:

280-250=30V ---- 30V/.002A=15K. So awesome! I have my two resistor values and extra points!

Will test the values tomorrow,  update the layout, share it, and start the build.

Once again thanks a millions sluckey 

[RadioComm]

Good morning,

Haven't gone down to the basement yet, but have updated the layout to reflect the 'new' power supply. In the layout, I used pin 2 of the LM7812 for ground. This is based off of www diagrams and el34 build picture (pictures can be deceiving). I'm sure the swapping of pin 2 & 3 in el34's schematic is a typo.

Thanks again sluckey for all your help.

[RadioComm]

Here's the update layout from this morning. Thanks again.

[PRR]

Don't overthink this.

[RadioComm]

Don't overthink this.

  Thinking is most definitely over rated  But... I enjoy it sometimes for recreational purposes 

The thinking part is over, started slowly but surely the building part.