I forgot all about it, probably because I quickly gave-up on finding dual 250k/500k pots. PS do com reader Alekos Gavriilidis from Thessaloniki Greece went ahead and built it anyway, using separate pots instead of dual-gang pots , and found this to yield useful results. Alekos writes:
“… i’ve just finished the project (EQ TUBES 6SL7). Im sending you photos of this project. I used 4 tubes 2 in parallel for every channel. Now the sound is incredible!!!!!!! P.S. I had a little noise from the filaments so i changed the voltage from AC to DC volt. Soon it will be in a studio”
Here’s his notes on the schematic:
Here’s a quick diary of his build:
…and here’s the layout that Alekos used for the panel:
He also provided plots of the action of the various controls:
Thanks very much for sharing this with us Alekos! If you’ve had success building one of the circuits that I’ve posted here over the years, please let us know about it… your success might encourage others to do the same.
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View Comments
Thats a nice build. Think i will put this on the "to do" list.
Are dual pots no longer produced at all?
I have a buch of them from machines i gutted troughout the years. Prob not the right values as always.
Great to see you posting again Chris!
Hi Pief. Dual pots are made, but i couldn't find one this body size with these values AND the long shaft.
I wish I had more time to post but life has gotten hectic and I waste too much time on instagram! I'm posting there most days, check it out if you haven't already... same name...
Hi all
Thanks for building and testing this, fascinating
I have a Neutrik bode plotter, I will build this, and post the plots. Then we can see the various frequencies and the action of the Q controls!
When you say you used 2 tubes in parallel, is that just as it sounds, connect them pin for pin in parallel to lower the noise!
I'll post plots as soon as it's finished
Paul
Hey Chris. This is great.
If you can find old CTS dual gang pots, you can exchange the resistive element with the single ones in current production. I believe it has the exact same shape.
Congratulations to Alekos, that is a very neat build.
It's funny timing, but I just did this last month for the first time - I needed a certain dual-gang alpha (no longer made) and I cannibalized a new alpha for one of the decks and it worked out great!
That´s good. I have done it a few times also.
Another less useful tip: 16mm Alpha pots with pull switch only come in "guitar" values. You can also exchange those resistive elements with almost any other brand.
BTW, if I search the "schematics" tag, the latest post is about those Argentinian magazines I sent you... 3 years ago.
I have some more stuff. Do you want some scans?
hi Nicolás, sure, please send them... CR
Hola Nicolas : Soy Pablo de Argentina . Podrías enviarme esos escaneos de revistas ? .. Me interesa !...Mi correo es pablitosax@yahoo.com
Saludos !
Great build! Curious... Are there no input and output transformers?
Fantastic and inspiring! Can we hear it?
Correct me if I'm wrong but to me it seems that if you turn treble Q fully to ground side then gate is grounded and there is no signal at all in output. Should there be a resistor from wiper to gate like in bass side.