Alctron T190 to P2P/Turret ELA M 251E conversion

[ottosteer]

Hello all,

I’ve been wanting to do this project for a while but I haven’t found a suitable body. At least not one that’s available for purchase so I went for the next best thing. I bought an Alctron T190 ($400 with PSU) gutted the insides and replaced the capsule with a reskinned original CK12 and I designed and laser cut acrylic for the turrets as well as the output strapping PCB for 200 and 50 ohms. There were a few challenges while designing this project, namely the smaller size of the T190 compared to an original ELA M 251E. The other part was to convert the output of the PSU from 150V B+ and 6.4V heater down to 120V and 6.2V by simply increasing the value of a couple resistors (100k and 57k) in the filter section and added 1R for the heater.

Tube used is a GE 5 Star 6072 and transformer used is an AMI T14. I have two T14/1 from stuck in US customs. Once I receive those, it will go in for proper 200 ohm strapping.

 

[Tahoebrian5]

Very nice

 

[shabtek]

that's gorgeous! do you have any spare acrylic parts?

 

[ottosteer]

that's gorgeous! do you have any spare acrylic parts?

Thank you. Then only spare I have is pictured here and was part of the prototyping process. (Holes are not quite lined up on it.) I can make more if needed.

 

[benqbasic]

Very nice work. Love the attention to detail.

 

[RuudNL]

The inside certainly looks nice, it must have been a lot of work to create this.
But I doubt if this will make the microphone sound different...

 

[ottosteer]

The inside certainly looks nice, it must have been a lot of work to create this.
But I doubt if this will make the microphone sound different...

I certainly didn’t do it for sound. However, the other options are PCB builds which have footprints that determine certain component size. Not to mention, tube dampening on those pcb builds are non existent. So I guess all those things i mentioned does affect sound. I will say it does sound better than the stock T190. As far as work, it took about 4 iterations and about 2 hours worth of computer design which I enjoy. About a half days worth of work. I’d also be a little disappointed if I bought a real ELAM 251 that’s all PCB and not turret/P2P. P2P and turret builds are much easier to maintain and fix.

 

[freshtapescent]

Looks beautiful!! How did you handle capsule polarization? Like a C12 with a cap to grid or?

 

[ottosteer]

Looks beautiful!! How did you handle capsule polarization? Like a C12 with a cap to grid or?

thank you. I Just followed the schematic. Backplate straight to grid with a 100M grid resistor (upped from 30M). The diaphragm is polarized through an 8M series resistor and .01uF cap to ground.

 

[freshtapescent]

Any schematic for a 251 I’ve ever seen has pattern switching via switches on the mic. Backplates aren’t tied together. IIRC, the front capsule and front backplate are always in-circuit and only the rear cap/backplate gets adjusted with pattern select switches. As you’re remote pattern switching, I’m still not sure exactly what you’ve got hooked up. Sorry if I’m missing something obvious or being obtuse.

 

[ottosteer]

Any schematic for a 251 I’ve ever seen has pattern switching via switches on the mic. Backplates aren’t tied together. IIRC, the front capsule and front backplate are always in-circuit and only the rear cap/backplate gets adjusted with pattern select switches. As you’re remote pattern switching, I’m still not sure exactly what you’ve got hooked up. Sorry if I’m missing something obvious or being obtuse.

I understand your question now. It’s set up as cardioid only at the moment as I have no room for switching with relays. I might use a small switch inside eventually to go between patterns but it will require removing the the outer sleeve to switch.

 

[Delta Sigma]

I understand your question now. It’s set up as cardioid only at the moment as I have no room for switching with relays. I might use a small switch inside eventually to go between patterns but it will require removing the the outer sleeve to switch.

If you can squeeze it in, you could do a reed relay to connect/disconnect the rear diaphragm. Then use remote polarization via power supply. Throw a little switch in the power supply the relay. I did this with my M49 and it works well.

 

[ottosteer]

If you can squeeze it in, you could do a reed relay to connect/disconnect the rear diaphragm. Then use remote polarization via power supply. Throw a little switch in the power supply the relay. I did this with my M49 and it works well.

That sounds like a good solution. Will have to try it.

 

[Biffel]

Hello all,

I’ve been wanting to do this project for a while but I haven’t found a suitable body. At least not one that’s available for purchase so I went for the next best thing. I bought an Alctron T190 ($400 with PSU) gutted the insides and replaced the capsule with a reskinned original CK12 and I designed and laser cut acrylic for the turrets as well as the output strapping PCB for 200 and 50 ohms. There were a few challenges while designing this project, namely the smaller size of the T190 compared to an original ELA M 251E. The other part was to convert the output of the PSU from 150V B+ and 6.4V heater down to 120V and 6.2V by simply increasing the value of a couple resistors (100k and 57k) in the filter section and added 1R for the heater.

Tube used is a GE 5 Star 6072 and transformer used is an AMI T14. I have two T14/1 from stuck in US customs. Once I receive those, it will go in for proper 200 ohm strapping.

Hi!
I actually have the exact same plan - Have Mic, Capsule, Transformer and Tune already here (see pictures).
Would you by any chance sell the spare Acrylic plates or give me the 3D-Data?
Then I could laser-cut or 3D-print it and finally do the build (which I didn‘t have time for yet).
I btw. also found an acrylic tube on Amazon with the right dimensions - so my longtime-goal would be to also rebuild the outer housing to original, but thats out of scope for now.

I will also do detailed electric and acoustic measurements before and after the mod and will share with the community

Thanks in advance!