Feeler: Ela M 251 Clone

This is to be true to the Ela M 251e Schematic and for as much of the circuit to be inside the PCB as possible.

Schematic Here: www.jessjackson.com/images/JKSNELAM/m251e.pdf

I am Hoping that Matador will jump on this with me and help to iron out the schematics and board layout. In principle I would love to see this project run parallel with matador and chungers amazing c12 project.

It will utilise the same body as C12 and utilise Chungers double mesh grill, with the hopes he will manufacture one with black mesh on rear side

I have drawn a rough pencil on envelope of the "Alpha" layout, I traced the edges of Matador V1.1A board and extended them down further to accommodate the T14 which can be mounted direct to the back board using small zip ties.

I have utilised the idea of surface mounted relays for pattern switching from Olivers Blackspade 251. This is where I got stuck though (as you can see from my drawing). I am not very familiar with relays and hoping that someone can finalise this layout. I have created an additional drawing with hookup points for you. www.jessjackson.com/images/JKSNELAM/JKSN_ELAM0.1norelay.jpg and here is how Oliver did it www.jessjackson.com/images/JKSNELAM/blackspaderelaywiring.jpg Here is the Relay Datasheet www.jessjackson.com/images/JKSNELAM/relaydatasheet.pdf or maybe now there is a more appropriate relay to use.

An alternate idea would be to place the cathode bias circuit on the back of the Tube PCB instead of the main board to keep runs shorter and to eliminate jumpers across boards.

This circuit could also be used with AC701 Miniature tube with just a few component value changes. (which is most likely the version I will be building first)

PSU: I have not touched this area yet. This is for you guys to brainstorm over. We will not be needing biasing but will be needing remote relay switching.

I am willing to finance the start up if need be.

I am going to throw this in Eagle in the mean time and see if i can get this relay circuit knocked up.



Let me know your thoughts.

J

this could be done with turrets and some bakelite/fr4/lexan, and look much like the blackspade, no real need for pcb...either way it is pretty paint-by-numbers.

you have already done the layout

looks like a good idea!

interested...

J,

I'd love to hear more if/WHEN you figure out this relay switching. I, likewise, am new to relays, and I'm trying to figure out how to incorporate one into a build for getting "true cardioid" and remote pattern switching in the same mic. Thanks

I'm also interested in building an ELA M 251 clone PLEEEEEEEEEEAAAAAAAAASSSSEEEE keep posting as you go!!!

The circuit has been designed in eagle, I brought in my good friend Eric Racy from black box who has partnered with me and has full understanding on relays.

Its been submitted for test PCB. Ordering mouser parts now for test assembly.

Board is in Black and Gold. VERY clean looking.

Cheers

i'm interested too! i'll buy the pcb

Is there enough room for the three relays side by side to fit in the body?
Cool project!

interested

Can't wait ;D

Count me in for a pair!

dmp said:

Is there enough room for the three relays side by side to fit in the body?
Cool project!

Click to expand...

yes. we are also looking into two and three switch relays.

QUESTION:

On the final board would you like to see TURRETS (like in Chunger and Matadors c12 build) or simple through hole to save space.

We can also look at using smaller turrets (maybe teflon pin sized?)

Feedback appreciated on this.

J

Jess, did you specify latching-type relays?  Holding an energized coil right in the midst of the high-impedance section is asking for permanent hum problems.

Also, if you specify only cardioid and omni modes you only need a single SPDT switch.

In for a pair. I like the idea of turrets, with the cutout for PIO output cap etc.

Few questions for clarity... the idea is to do the relay switching from the PSU, not from a switch on the body, correct? Will there be true cardioid? Can this use the existing Matador/Chunger PSU board? (The board that fits with existing tx is nice, but would guess you need 12/24v for the relay. Can this be taken from the heater winding?)

@matador:
if one used latching relays and did not want continuous current draw, wouldn't one also use momentary switches to activate said relays? or would coil current spike at latching and drop--also coil voltage could be filtered, pretty low current no?

interesting concern you raise.

shabtek said:

@matador:
if one used latching relays and did not want continuous current draw, wouldn't one also use momentary switches to activate said relays? or would coil current spike at latching and drop--also coil voltage could be filtered, pretty low current no?

interesting concern you raise.

Click to expand...

Yes, a latching relay utilizes a momentary switch.  Most have two coils (one for each direction).  Non-latching relays require the coil to remain energized in order to hold the switch contants in the "engaged" state.

Since the the backplates of each side of the capsule need to be isolated for the ELA M 251 (as opposed to connected together as in the C12) I don't think that you'll be able to use the metal capsule holder that Tim Campbell supplies.  I believe that it would electrically couple the backplates of the two halves of the capsule. You would instead need a plastic, non-conductive capsule mount.

Just trying to prevent some headaches    …someone please correct me if I'm wrong.

Matador said:

shabtek said:

@matador:
if one used latching relays and did not want continuous current draw, wouldn't one also use momentary switches to activate said relays? or would coil current spike at latching and drop--also coil voltage could be filtered, pretty low current no?

interesting concern you raise.

Click to expand...

Yes, a latching relay utilizes a momentary switch.  Most have two coils (one for each direction).  Non-latching relays require the coil to remain energized in order to hold the switch contants in the "engaged" state.

Click to expand...

it shouldn't interfere due to it being DC voltage