• 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.

Low Voltage Aikido questions

Elkaid

Member
2003-01-14 1:06 am
Canada
Hi gentlemen,

After an 8+ years pause, I've decided to resume my low voltage aikido hpa project based on Mr. Broskie Aikido 24Volts pcb. (I chose 48V B+, 12BH7 route)

However, I have two questions for you guys:
First one: In the manual it is stated
Internal Shields If the triode’s pin 9 attaches to an internal shield, as it does with the 6CG7, 6DJ8, 6GM8/ECC86, and 6H30, then capacitors, C5 and C6 can be replaced with a jumper wire, which will directly ground the shield. However, using capacitors will also ground the shield (in AC terms) and allow using triodes whose pin-9 attaches to the center tap of its heater, such as the 12BH7

Since I'm using 12BH7 valves, I'm guessing I should use capacitor in C5&C6 position right ? However, can someone could explain me why those capacitors have been removed from the part list for the 12BH7 build ? A mistake ? Should I use them or not ?

My other question is about the headphone output. Mr. Broskie is suggesting LM317/LM350/LT1085. Will I run into problems using those parts since they're limited to 30-35V differential ? (I'm using 48v B+) Would LM317HV be more suitable ?

Here's the shematic on which my pcb is based on:
24V Aikido Line Stage and Headphone Amplifier

Thanks a lot for your help
 

Koonw

Member
2013-04-09 9:37 pm
Hi gentlemen,

After an 8+ years pause, I've decided to resume my low voltage aikido hpa project based on Mr. Broskie Aikido 24Volts pcb. (I chose 48V B+, 12BH7 route)

However, I have two questions for you guys:
First one: In the manual it is stated


Since I'm using 12BH7 valves, I'm guessing I should use capacitor in C5&C6 position right ? However, can someone could explain me why those capacitors have been removed from the part list for the 12BH7 build ? A mistake ? Should I use them or not ?

My other question is about the headphone output. Mr. Broskie is suggesting LM317/LM350/LT1085. Will I run into problems using those parts since they're limited to 30-35V differential ? (I'm using 48v B+) Would LM317HV be more suitable ?

Here's the shematic on which my pcb is based on:
24V Aikido Line Stage and Headphone Amplifier

Thanks a lot for your help

Hi.
I think it's ok to ground pin 9 of 12bh7 if you're using 12.6V (series 2*6.3V) heater, as grounding the CT would reduce hum, however there shouldn't have another ground for heater as this would create a ground loop causing hum.

For the other question, my sim analysis (not full sch) shows that the bias for upper regulator R12 has too low current to make U1 to regulate properly so during cold start, almost entire 48V is applied on top of U2 causing it to exceed the specifications, see attached. After the tubes has warmed up and running it's ok. So you may need to reduce 48V somewhat to 40V or find another way for this problem.
 

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Last edited:
I tried it and couldn't get it to work

I tried the circuit with 6GM8s and the solid state output driver and couldn't get it to work. Some people have gotten it to work though.

If you are driving high Z phones skip the silicon and build an Aikido push-pull as Broskie describes in one of his blogs using a big cap (30uF) from the cathode follower.

Cheers, Steve
 

Elkaid

Member
2003-01-14 1:06 am
Canada
I tried the circuit with 6GM8s and the solid state output driver and couldn't get it to work. Some people have gotten it to work though.
Cheers, Steve

I'm beginning to wonder if I should go on with this project as its main use would be an headphone amplifier.

This, added to the countless comments about how the Aikido topology is almost a joke doesn't help.

Thanks for your comment, I'll evaluate other options and see if it worth it.
 
Build it and see

It's about experimenting after all.
I wonder about those who dismiss it, have they actually heard it?
I like the Aikido HPA (all tube version) and have 2 friends that have built it and like it as well.
I have not listened to it in isolation but compared it to commercial products. It compares favourably. I think the Aikido is a fairly high res. design. Tube rolling is a must to get the best out of it.

See kinks below to my posts.

http://www.diyaudio.com/forums/tubes-valves/268390-experimenting-aikido-12vac-kit.html

http://www.diyaudio.com/forums/tubes-valves/268193-adventures-aikido.html

I also built an all 6CG7 line stage but the bass was a little too tubey (slow and slightly indistinct) but this was compared to a mega bucks ARC REF 3. I've changed it over to 6CG7 input tubes and 6DJ8 outputs but haven't had a chance to really listen to it yet.

Cheers, Steve