• 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.

Question about Aikido

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hello!
My friend and I built our Aikido 6SN7 linestage based on the attached circuit.

However, the official Aikido octal manual do not listed following positions with 1M resistors:

R5, 6, 7 and 12

How come?

Assume the B+ voltage is 300vdc, can I use 243R for R2, 4, 8 and 11??

Thanks!
 

Attachments

  • Aikido 6SN7.GIF
    Aikido 6SN7.GIF
    38.5 KB · Views: 607
Did you buy the PCB from aikido? You can ask any question from them. I would recommend to buy the PCB to support aikido, you won't be disappointed the quality of the PCB. Since there are many Rev. A to E, that's the reason there are many value of resistors.

I believed the first pic is Rev. C and the Recommend values are correct. I guess the R2,4 are greater than R8,11 based on recommend so play around, assume R2,4 is 30 ohm greater ...lol...I guess it should work for anything in that ranges.

R2,4 = 270 - 1k
R8, R11 = 240
 
The 243R should be fine for the positions you mentioned. The 1M are fine for the other positions. Regarding the 12SN7 circuit, it's an earlier version. Broskie regularly tweaks resistor values.

The nice thing an amateur such as myself likes is that the cathode resistor pairs, R2 and R4, in your first post can be changed to alter current draw and therefore power dissipation. No calculation required. Just use the same R value. E.G. change them both to say, 330 ohms. The same thing for resistors 8 and 11.

More recent Broskie designs often use a higher R value for the first tube (lower current) and a lower R value (higher current) for the second tube .

If you want to measure the dissipated power first measure the voltage drop across R2 (or R11) and knowing the resistor value calculate the current. Next measure the voltage from cathode to plate of the "lower" triode, calculate the dissipated power and compare it to the tube's spec. You can also measure the voltage from cathode to plate of the "upper" triode. Ideally it will be the same as was measured across the "lower" triode. This will indicate how well the two triodes in any given tube match. A difference of 10% or less is pretty good.


Steve
 
No, go with the 243 ohm resistors in your original post. I was just giving you an example.

Don't get bent out of shape between say, and I'm just giving an example here, a 330 vs a 332 ohm resistor. As long as you use the same for R2 and R4 on the input tubes you're fine. You can, if you wish, use a resistor value different from the R2 and 4 for R8 and R11. As long as R8 and R11 are the same.

So, go with the 243 ohms for R2, 4, 8 and 11 you first proposed. Measure then calculate the dissipated power then get back to us.

I'm working on a Broskie creation right now and the good thing/bad thing is that the boards are really thick. This makes them rugged but hard to experiment on.

See picture. You might use some thick cut-off cap leads through the board as shown then connect R2, 4, 8, 11 resistors to them so they may be changed more easily. You would of course solder them up. I haven't in the picture, it's just for demonstration of the concept.

Regards, Steve
 

Attachments

  • P1040120.JPG
    P1040120.JPG
    669.2 KB · Views: 275
No, go with the 243 ohm resistors in your original post. I was just giving you an example.

Don't get bent out of shape between say, and I'm just giving an example here, a 330 vs a 332 ohm resistor. As long as you use the same for R2 and R4 on the input tubes you're fine. You can, if you wish, use a resistor value different from the R2 and 4 for R8 and R11. As long as R8 and R11 are the same.

So, go with the 243 ohms for R2, 4, 8 and 11 you first proposed. Measure then calculate the dissipated power then get back to us.

I'm working on a Broskie creation right now and the good thing/bad thing is that the boards are really thick. This makes them rugged but hard to experiment on.

See picture. You might use some thick cut-off cap leads through the board as shown then connect R2, 4, 8, 11 resistors to them so they may be changed more easily. You would of course solder them up. I haven't in the picture, it's just for demonstration of the concept.

Regards, Steve

Sure I understand, so I stick with 243 for all 4 positions. I'm really appreciate.

Would it be much easier make it hard-wiring with terminal board? PCB has another problem is that it restricted the usage of big resistors, especially wirewound resistor for cathode.
 
R8, R11 = 240- I would keep this value the same


R2,4 = 270 - 1k - Only play around with these value.


R3, 9, 10 = 300 ohm for 300V


Good idea Steve with the solder, that's an easy way to swap out. I was thinking to buy 3 positions switch or some kind of a adapter socket to solder many value of Rs ...lol....
 
Tubenstein,
I've built on terminal boards, they'll take up much more room than the PCB. You don't need big-watt wire wound resistors, 1/2 or 1 watt that came with your kit are all you need. For R3, 9, 10 use whatever came with your kit, not super critical. Not trying to be snarky or patronising, but don't over think it. Just build it, play with it, have fun with it.

Different kit but see: Battle of the Cheap Line Stages – Part 1 | Wall of Sound | Audio and Music Reviews

Steve
 
Thanks for the link Steve. I am excited and looked forward to finish the preamp.

I have been ordered parts and the latest version of aikido octal PCB. Edcor takes 2 months to arrive so I probably won't be complete after new year.

By the way, what is the value of your coupling caps? John told me start at 1kuF. What if I try .33uF, .47uF, .66uF? Does that mean less bass?
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.