EQP1A trouble (turret design) please help!

[Deepdark]

Hi all. I need help with my turret build of a Pultec EQP1A. It has been done with cinemag transformers. Main issue is with the output transformer.

When I power up the unit, it make a kind of vibration sound, very loud, like if there was two metal plates vibrating on each other. I checked all voltages and they looks ok, exepted 2, which are a little low, according to the schematic, I retrace all wire and everything looks good, all resistors values looks good, too. I used the linked modified schematic I received, which is made to accommodate the Cinemag CM9600. I'm a little at a loss with that issue, i dont know what can cause the transformer to make such a noise and I'm afraid the trouble is behond my knowledge.

I tried it on my computer to hear what appened. I sended a white noise through it and back to my interface and it's all noise. No matter what i tweak in the eq sections, it seems to not work. Maybe it works and the noise cover it all, i dont no. I dont have Any scope to Check it. If you could provide some help i would be gratefull.

You can check the linked layout with the voltages in blue (schematic values) and in red (my values). My understand is that the trouble sits around the 12AX7 section. But I can't sorting out the noise coming from the output transformer. I noticed that when I touched the turret mark with a star on the layout, the noise coming from the OPT attenuated a little. What could that means?

Thank you

 

[Deepdark]

Modified schematic

 

[Deepdark]

little update about the eq. I reversed the feedback wires and the motorboating sound dissappeared. I got trouble at first trying to equal the original voltages by increasing cathode resistors from 470r to 2k2 and the feedback from 150 to 880r. So, at the end, becuase of instability and oscillations, I came back to the values on the linked schematic, I just strapped 0.05uf caps across the feedback resistors,  increased the 830pf cathode caps to 2200pf.

I had to replaced the 12ax7 for a 12au7 and the 12au7 for a 12bh7 by the time I worked with the increased cathode resistors to get it useable.  The only really annoying issue was that when I boosted the lows, there was a kind of pumping oscillation around 8k.

From the moment I get back to the original resistors values (and reversing the interstage wiring), strapped the caps, etc. I got a really nice and working unit. I tried it with the 12au7/12bh7 combination. Tonight I'll try it with the original tubes.

I have a very litttttle bump around 80hz and 5k. Low pass is around 20hz and high pass around 18-19k.

I'll post the final test result with the original tubes tonight. If someone want to argument about the past issues, give their opinions, etc. Go for it  I'd like to expand my knowledge and it could help someone else who wish to build a EQP1A entirely with Cinemag transformers.

 

[Deepdark]

Hi

So I tried the original tubes but 12au7 in output squeal. 12bh7 fixed it and sound awesome. 12ax7 in input in a little instable (little oscillation around 8k) and 12au7 fixed the trouble. This combination is really the best. No oscillation at all, sound really nice, but of course, a little less gain than with the 12ax7. I have to came to the conclusion that the CM9600 isn't ideal in the circuit. It sound reallly good, though.