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bagudan 2nd June 2012 09:02 PM

Matchless Hotbox Layout problems
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Ive allways wanted to build the matchless hotbox high voltage tube preamp pedal, but have been hesitating because the projects on genrealguitargadgets are a bit tricky to read/understand.

Ive tried redrawing the layout using software found on the internet, But I still have doubts. I think there are some components in the schematic, not showing in the layout?
The third resistor from the right side of the board (maybe a 2,8k??) I cant read what it says in the original layout? And unfortunately still a bit of a beginner when it comes to reading schematics.

What about the three places on the upper side of the board that says "point B"... Where is point B? Maybe it is obvious? But Im unsure.
The original layout has the pin numbering on the tubes in revers order on V2. i have tried to turn it around in my layout?

So tell me what you thinK. Does this redrawn layout get me closer to a succesful build, or should I let it go.
Have built several tubeamps from verified layouts succesfully, and I know how to discharge caps and work safe around highvoltage... but Im still a paintbynumbers kindaguy....

Link to original ggg layout:

Link to ggg schem:

Link to ggg Bill of materials:

kevinkr 2nd June 2012 11:08 PM

:cop: This belongs in Instruments & Amplifiers forum per forum policy.


Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

bagudan 2nd June 2012 11:37 PM

Sorry... I Will correct my mistake:)

Loudthud 3rd June 2012 12:06 AM

If you look at the schematic you will see the B+ power supply voltages marked A and B. Simply connect all the points marked A together and all the points marked B together.

bagudan 3rd June 2012 06:38 AM

Ahh, I see;)

Tubed 7th June 2012 01:10 PM

Hotbox Layout Problems
I've built 2 of these and am about to start a third. It is a challenging build. The first one is huge and ugly, the second one my friend borrowed and won't give back so I am building a third.
The resistor is 2200 or 2.2k.
The B+ voltages A and B are labeled reversed on the layout from the schematic but the voltages are correct'
On the layout the "Clean Vol" and "VOL CH2" pots are shown wired from the front or backwards.
I'm not sure about the layout of the tone stack wiring. It caused me grief on the first one. I fixed it by trial and error and used a 3 way FMV tone stack on the second build
On the layout, tubes V1 and V2 are labeled opposite the schematic.
On the layout the pins of V2 is labeled and wired incorrect. Renumber V2 clockwise.
Change the lead going to the pin labeled 7 to 2, 8-3,6-1,1-6,2-7,3-8 and 9 is unused.
I built 3 "Real McTube II"s before trying the Hotbox. They all sound great and are an excellent first project. It's designed by the late Fred Nachbauer and a step by step build and theory guide comes with it. It's on
The power supply from the "Real McTube II" can be modified for the "Hotbox" and is a huge upgrade in AC hum reduction and a huge cost savings in transformer and capacitors prices.

bagudan 21st June 2012 07:45 AM

Hi. Thanks for the excellent and very helpful reply! I didnt see it until today, infortunately.
Ive also built the Real Mctube, and I like it, and Im also going to try the back to back transformer powersupply in this build, to save some money. Ill correct the mistakes in my layout, and upload it later, so others can use it, if they are interested.

bagudan 21st June 2012 08:03 AM

1 Attachment(s)
Here it goes...

Niquel 17th July 2012 06:19 PM


Originally Posted by Tubed (
The power supply from the "Real McTube II" can be modified for the "Hotbox" and is a huge upgrade in AC hum reduction and a huge cost savings in transformer and capacitors prices.

I'm trying to build my own Hotbox and i have taken a look to the Real McTube but have some questions.

I don't understand the ground connections from the Real McTube between the second and first rectifier bridge, I thought that both negative pins had to be connected and the pin 9 from each tube not used as it is suposed to be 12V. What values did you use for filter Caps and R in the power supply?

Thank you,

Loudthud 17th July 2012 06:56 PM

Since the first bridge is floating, pin 9 just provides a center tap to give a ground reference. This balances any ripple noise between pins 4 and 5. If you twist those wires together, the noise will tend to cancel when it trys to bleed into the signal.

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