• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

aikido heater

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I have finished my breadboarded Aikido headphone amp (6CG7 and 6H30) so far that today I tested the heater part of the psu. It consists of a 9V 50VA toroid and a regulator that delivers 6.15V (thread about the regulator somewhere here on diyaudio).
After checking all connections and inserting the tubes I flipped the switch and happily saw the heaters of one board starting to generate the homely orange....

The other side...nada...nichts...nothing.
I checked all connections again and checked voltages, and I do have 6.15V on pin5 of all four tubes, measured on the soldering joint to the sockets.

Do I have a case of shxxxy sockets on one of my boards? Never had that happen but can't think of another cause...

Btw: I also tried some EL84 in that board, but no heaters coming on...
My problem is continuing...

This is my fourth tube amp (all being headphone amps) and I hate to ask silly questions, but after trying a bunch of different things the tube heaters on one board are not working...

Just to rule out the most obvious things:

- heater wires are connected identically
- the psu (regulator) is grounded
- I have switched sides --> all tubes are good, heaters have continuity
- I do have 6.15V on all pins 5 on the boards
- boards are populated identically, jumpers are in
- my regulator has been tested with a load od 2.2 ohm = ~2.9A

This is driving me crazy...

To illustrate things two images of my breadborad attached...

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

Anybody has an idea what could keep the left side of working properly...??

Thank you!
Do continuity check on the wire going to pin 4. You said you have 6v at pin 5. Is this measured to ground or from pin 5 to pin 4. I've seen where the conductor was broken inside the jacket. Maybe you have a bad solder joint on pin 4. Resolder everything at the filament power supply, you never can tell.
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woodturner-fran said:
I think Janez has it - looks very like one board is upside down - the one on the left in the pic.

That would mean your heaters are connected to pins 5 and 6 on those tubes rather than 4 and 5.


Looks like the case to me too.. Definitely mirror imaged. Just pull the tube sockets and turn the board over and solder them on the other side. If you are really motivated you can carefully remove and relocate the other components to the other side if you want them to look the same - that's not necessary to get it to work however.
Janez (and Kevin and Fran),

you are absolutely right...very much to my disgust though :apathic:
Being the visual guy that I am my main focus was to build a mirrored amplifier without rotating the boards...it absolutely escaped me to pay attention to the pinout of the sockets.

Duh, beginners mistake...but another good one that I will remember...:)

Flipping one board will not be a problem since I will have a top lid to cover the internals... but a nice mirror layout is not possible.

Thanks guys,
hvala mnogo (the closest to slovenian that I know :))


Would you mind sharing your LV regulator topology? I've got a 9-pin stereo Aikido under construction, and have gone the route of running each set of 6.3V heaters in series (to take advantage of the 12.6V transformer I have and the lower current requirements at that voltage).

In any case, your setup looks much more robust than my (admittedly amateurish) LM317T-based effort, which pales in comparison.


running your heaters in series is fine (depending on the tubes used though), but you cannot run a regulator from your 12.6V transformer and get 12.6V for the heaters...? You sure know that you will need some voltage to be dropped across the regulator to make it work properly. You can of course wire the heaters in parallel and run the regulator from the 12.6V, just use a dropping resistor before the regulator so that there are about 3V dropped across it.

My regulator is basically very simple and uses the LM1084 that can take 5A, just pay attention to heat dissipation since this thing can get mighty hot!

schematic attached...

An externally hosted image should be here but it was not working when we last tested it.


Yep, I did the math properly (I hope):

12.6*sqrt(2) = 17.81 DC volts after rectification, minus about 1.4V in diode drops gets you to 16.41VDC, leaving you ~4.11V to burn in the regulator. I admit it's quite tight and probably would not respond well to changes in line voltage.

Thanks for the schematic - I'm more than willing to consider a supply similar to the one you've got (9VAC 5A input), I'm just using what I have around, which was a cheap 12.6VCT 3A transformer and an LM317T.

Where'd you source your heater transformer?


I think it also depends on the tube combo you are planning to use and the current demand. My 6CG7/6H30 are drawing around 2.8A so I choose the LM1084. When you are running 6DJ8's for example your transformer and the LM317T might be just fine...

My heater transformer is a Talema/Nuvotem unit I sourced from RS Germany.


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