The tubes are so weightless and the wires are pretty strong... I can't really think of a better option. I'm curious how they were mounted in their original intended application....
Building Power Supplies for 2 X 12ax7 pedals
Moderators: pompeiisneaks, Colossal
Re: Building Power Supplies for 2 X 12ax7 pedals
Re: Building Power Supplies for 2 X 12ax7 pedals
Hmm -
I’ve a handful of NOS sockets but that has to be a rare and expensive “mil spec” option. These are lay-flat with a heat sink that clips in the envelope and has PCB footprint.
No expert, but seen a few methods: soldered vertical on PCB, occasionally with a pad between the tube base and board; flying leads with the tube fastened and supported either directly to PCB or above with with small rail or wire for support; through a chassis hole with a snug grommet at the waist and onto a PCB again. Occasionally I’ve seen a dab of adhesive added.
Commonly applied in portable gear and avionics — “missile tubes” …
I’ve a handful of NOS sockets but that has to be a rare and expensive “mil spec” option. These are lay-flat with a heat sink that clips in the envelope and has PCB footprint.
No expert, but seen a few methods: soldered vertical on PCB, occasionally with a pad between the tube base and board; flying leads with the tube fastened and supported either directly to PCB or above with with small rail or wire for support; through a chassis hole with a snug grommet at the waist and onto a PCB again. Occasionally I’ve seen a dab of adhesive added.
Commonly applied in portable gear and avionics — “missile tubes” …
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Re: Building Power Supplies for 2 X 12ax7 pedals
don't enclose the tubes inside a closed box. You will have thermal issues. Let them protrude through the top side and protect them with drawer handles from your local hardware store. For transport I use a hard case to protect the protruding tubes. Had no issues so far (10+years in use).
Heating with wall wart voltage of 12V worked fine for me. You should use a good regulated / filtering wall wart though to make sure the wart does not introduce issues.
Heating with wall wart voltage of 12V worked fine for me. You should use a good regulated / filtering wall wart though to make sure the wart does not introduce issues.
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Re: Building Power Supplies for 2 X 12ax7 pedals
That's a great idea/ideas!chaccmgr wrote: ↑Tue Jul 28, 2026 7:25 am don't enclose the tubes inside a closed box. You will have thermal issues. Let them protrude through the top side and protect them with drawer handles from your local hardware store. For transport I use a hard case to protect the protruding tubes. Had no issues so far (10+years in use).
Heating with wall wart voltage of 12V worked fine for me. You should use a good regulated / filtering wall wart though to make sure the wart does not introduce issues.
Do you put grommets or anything in the tube holes, or do the tubes just go against the enclosure metal?
Re: Building Power Supplies for 2 X 12ax7 pedals
I finally got home and was able to make the changes to use a 6N21B tube for V2. After also replacing a faulty pot, it's sounding pretty darn good.
I'm going to have to try moving it over to the perf board that will go in the enclosure soon. But first, I think I will try building my own nixie supply on the bread board and see what results I get.
Here's the current Schematic plan to do that:
Here's the current Schematic plan to do that:
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Re: Building Power Supplies for 2 X 12ax7 pedals
no grommets. The holes are big enough to ensure, the glass does not touch the metal. The holes should have a decent size anyway to make sure, the heat of the tube parts that sit inside the box can get out
Re: Building Power Supplies for 2 X 12ax7 pedals
I wanted to see if I could build the power supply myself and make it work. It seems to be working fine and I can get to the target voltages. I'm not sure if I can make it as compact (as the premade $20 one from amazon) when moving it to a perfboard layout.
Here it is with just the home-made supply (and cheap $2 voltage bucking PCB for the heaters):
Well, it's time to try getting this in a format that will fit in the pedal enclosure... but first... I'm not loving this tonestack type. turning up the treble aggressively cuts too much mids and bass... not really useable above noon. So, I guess I'll mess with that while still on the breadboard.
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Re: Building Power Supplies for 2 X 12ax7 pedals
I realized trying to add a mid control was overcomplicating the tone-stack and controls.
I'm currently at this:
I'm currently at this:
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Re: Building Power Supplies for 2 X 12ax7 pedals
Time to start the move of the circuit over to the perf board. I think my schematic is a little more complete now. I wasn't going to do the option that skips the first gain stage and gain control, but it actually seems more useable now. it is about equivalent in gain/output as when the first stage is in with the gain set to about 10 o'clock:
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martin manning
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Re: Building Power Supplies for 2 X 12ax7 pedals
Looking good Matt! Been following along, interesting project.
Re: Building Power Supplies for 2 X 12ax7 pedals
I made some good progress today in the final breadboarding stage. I was able to A/B it against the gain channel of my hotcat with it plugged into the clean channel so that I could see what it was missing. I needed to add back in the potential for more bass resonance. That's why I really increased that first coupling cap after the first stage plate from 1n5 to 22n.
I also found the treble control was rather redundant; I could turn it all the way down and the "edge" control really acted as a full tone control. So, I've replace the tone-stack with just a bass resonance control that going from a modest pretty flat tone to adding some extra low end thump. The full range is totally useable, just depends on the tone I am going for.
I also played with trying to keep the range for the top end all useable. I want it to be able to feel very open without getting into fizziness... thus all the snubbers on all the plate resisters... also the reason for increasing the cap to ground after the edge control from 330p to 1n.
So here we are now... with some new names in the hot sandwich theme. In the current form, I'm also noticing that it cleans up quite nicely from the guitar volume control
I also found the treble control was rather redundant; I could turn it all the way down and the "edge" control really acted as a full tone control. So, I've replace the tone-stack with just a bass resonance control that going from a modest pretty flat tone to adding some extra low end thump. The full range is totally useable, just depends on the tone I am going for.
I also played with trying to keep the range for the top end all useable. I want it to be able to feel very open without getting into fizziness... thus all the snubbers on all the plate resisters... also the reason for increasing the cap to ground after the edge control from 330p to 1n.
So here we are now... with some new names in the hot sandwich theme. In the current form, I'm also noticing that it cleans up quite nicely from the guitar volume control
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Re: Building Power Supplies for 2 X 12ax7 pedals
I don't think the sandwich theme will fit the aesthetic.
I'm painting the enclosure green.
Maybe the Cosmodrome?
Maybe the Cosmodrome?
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Re: Building Power Supplies for 2 X 12ax7 pedals
I haven't even populated the board yet, but I had to build out the whole enclosure layout first because I'm going need to cut chunks out of the board to get it to fit:
Updated the schematic to the new labels... but I'm already tempted to change them again... don't think I will since they are already painted on. Maybe I will try a different theme if I build a second for a friend.
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Re: Building Power Supplies for 2 X 12ax7 pedals
Hey Matt --
That's looking quite fine. Curious to know how much you experimented with various values and voltages through the stages before settling on what's shown in that schematic---particularly plate voltages and plate load resistors, but also coupling and bypass caps.
Best ..
That's looking quite fine. Curious to know how much you experimented with various values and voltages through the stages before settling on what's shown in that schematic---particularly plate voltages and plate load resistors, but also coupling and bypass caps.
Best ..