24v aikido distortion

[poolorpond]

you know when you shut off a tube pre while the music is still playing and the music starts to died down and distort? Well, that is what my 24v aikido is doing all the time. I was barely getting anything out of it until I recalculated the voltage divider at 115k instead of the recommended 130k on broskie's site. Now I hear some music behind this scratchy noise. It sounded like it is just running out of steam.

I am running 2 6922 and 2 7DJ8 . The tubes work fine in a buffer that I use on my dac. I don't know much about the 78j8 other than it can take a higher heater voltage.

power supply is per schematic on the sitewith a 24v, 50VA toroidal tranny, 60mh choke, regulated to 24.9v. Originally it was down a few volts until i dialed in the regulator. It plays better with the extra couple of volts.

any thoughts

[ilimzn]

I am sorry but the problem is really obvious:
For starters, why did you 'wishful think' instead of actually read the 24V aikido documents?
12V across cathode-plate is really too low for a 6922 type tube. The 7Dj8 is a 300mA series chain version of the 6DJ8, which means if you connected all the heaters in series, you likely have the 6922 underheated, which just adds to the problem. Brosikie clearly says you need to use 6GM8/6N27P/ECC86, designed for the job, and you are not - it's as simple as that.

[audiorasp]

The 24v Aikido pcb user guide lists resistor values on pg. 10 for use with the 6DJ8/6922 at 24v. Also read "Heater Issues" on pg. 8.

[woodturner-fran]

mmm, I'll have to check my aikido stuff, but I think you can do a 6DJ8 in a 24V aikido.

Have a look at the booklet and see. I can say I am running a 24V one with 6GM8 and it sounds bloody great (despite a small bit of hum left).


Check the heaters at the pins of the sockets and do a few measurements is all I can suggest and post back here with them. JB himself is helpful but can be slow in replying - I'm sure he gets huge volumes of mail.

Fran

[2wo]

You are only getting 12v across each tube…John

[poolorpond]

cherhit, thanks, I had been looking at the design posted in may of last May when he first posted the 24v project and didn't see this.

ilimzn, yes, I didn't really look too carefully at the specs for the 7dj8 and just assumed they were compatible in this set up. The voltage drop across across each of the heaters in series is as specified in the old write up, but the heaters heat up at considerably different speeds. This should have been a tip off that something was off with one of the pairs. I guess I need another pair of 6922s- 6GM8s are out of my price range. Thanks.

[poolorpond]

You know, I keep reading that the 7dj8 is a direct replacement. Let me try changing out the resistor values first and see what happens. thanks again for the suggestion to look at the manual.

[dsavitsk]

Originally posted by poolorpond
6GM8s are out of my price range. Thanks.

They are $5 at Radio Electronic Supply: http://www.vacuumtubes.net/prices.htm

[Shoog]

It seems that the ECC88 can be used down at 12V plate to cathode per valve, but it seems a totally stupid idea. The 24V Aikido was mean't to use the ECC86 and thats what I would use and nothing else. These are not an expensive valve and should be cheaper than any ECC88.

Shoog

[woodturner-fran]

I think I paid $2-3 apiece from either tubedepot or AES recently. As cheap as you can get.


Fran