Dale capsule mount issue

I have a pair of Dale capsules in my U-47 builds, mounted in the brass 3 set screw holder / mounts that were sold in a group buy for use with them.
I am only getting one  side of the capsule, I think it is an issue with the holder. I can turn the capsule around and the other side will work, but only one side at a time. I tried to center the capsule center line over the set screws (almost impossible) but can't get both sides to work at once.
My theory is that the holder is only contacting one side of back-plate...
Has anyone else had this issue or had success using this combination?

nielsk said:

I have a pair of Dale capsules in my U-47 builds, mounted in the brass 3 set screw holder / mounts that were sold in a group buy for use with them.
I am only getting one  side of the capsule, I think it is an issue with the holder. I can turn the capsule around and the other side will work, but only one side at a time. I tried to center the capsule center line over the set screws (almost impossible) but can't get both sides to work at once.
My theory is that the holder is only contacting one side of back-plate...
Has anyone else had this issue or had success using this combination?

Click to expand...

The M7 has a common backplate for both side ,  so it is unlikley to be the cause of the problem , you should measure 0 Ohm from the backplate to the mount , Are you swapping the wiring connection when you flip it ?, or are they connected to the same wiring to the mic when they do work,
Best
Dan,

Which U47 build is it and which method is implemented to get the signal from the rear diaphragm to the grid in omni mode? If it's the relay it could be that the relay isn't engaging or some other wiring issue involved with those nodes.

Thx!
jb

While I am using a relay to "add" the back diaphragm for omni, I have disconnected the lead from the front and connected the lead from the back individually (bypassing the relay) to test. Signal is fine from the front and nothing from the back, the results are the same when I remove the capsule from the mount and turn it around (so both sides are confirmed working).
I am used to M7 capsules having only one back-plate connection,  but looking at this one it appears to be a "sandwich"... of course there is no back-plate connection, it relies on the mount set screws to contact.

Can you measure continuity between the two sides of the backplate-sandwich?

If not that would be the reason but M7's have one backplate unless you have found a dual backplate M7 which might be nice for certain setup's...

Do you have some photo's of the capsule, hole patterns, backplate-sides, etc?

Thx,
jb

Are you sure the capsule is being polarised in both cases?

nielsk said:

I have a pair of Dale capsules in my U-47 builds, mounted in the brass 3 set screw holder / mounts that were sold in a group buy for use with them.
I am only getting one  side of the capsule, I think it is an issue with the holder. I can turn the capsule around and the other side will work, but only one side at a time. I tried to center the capsule center line over the set screws (almost impossible) but can't get both sides to work at once.
My theory is that the holder is only contacting one side of back-plate...
Has anyone else had this issue or had success using this combination?

Click to expand...

I own both a Dale Ulan and Cathedral Pipes M7 and yes they are a single backplate in both cases. So it does sound like you have a polarization problem or airgap issue. Photos are always helpful with these questions.  It probably is a minor issue just back track.

Here you can see the side of the capsule, there is a thin ring of exposed brass that is the contact for the back-plate, but does not line up with the set screws if the capsule is fully seated in the holder.
This appears to be of a "sandwich" construction...
I am able to align the ring with the set screws (VERY carefully and difficultly) and get perfect contact from the solder contact to the back-plate ring

Front view...

Side view, mounted.
As I mentioned, I can connect the front side only, good signal, back side only, not good.
Remove capsule and turn around in holder, exact same results.
How can I measure the polarazation voltage? The prospect of trying to put a probe on the center of the capsule sounds like getting a hole in the capsule!

That's very odd behaviour.  Do you have a capacitance meter and can you measure the value between front / back and the backplate ring?

Seems like if you rotate it and you're using the same backplate ring-to-set-screw and you get signal then the BP is making the proper connection.

Are you actually soldering the front/back directly to the grid to test this or going through the relay/switch for the rear diaphragm connection?

Thx,
jb

Also, maybe something is shorting the rear facing diaphragm to the holder-ring when it's positioned like that? Can you measure continuity between the rear-lead and ring when installed like that?

I'll take a peek at my Dale M7's tonight to compare. I purchased those on his last production run.

Thx,
jb

With the capsule leads disconnected, I see 90 pF on each side between capsule lead and back-plate lead

It sounds like the capsule is ok. Especially if there is no DC continuity between the leads.

I would measure ohms and capacitance between the leads in and out of the holder... Just to confirm that something isn't shorting or causing a fault....

Are you experiencing this fault in  omni mode only or are you connecting each diaphragm to the tube grid independently and testing then doing the same with the capsule uninstalled and reversed?

Can you confirm that the relay is working properly and measure continuity through it when in omni mode?

The 60V bias voltage goes to the backplate only so each diaphragm sits @ 0V. You can measure that at the divider node (2M/3M). Front diaphragm only feeds the grid in cardioid and both front and rear feed the grid in omni. Rear is switched into the grid via the relay circuit which uses another conductor on the cable to control it ON or OFF.


Thx,
jb

Did you try fully seating it and tightening the set screws in front of the ring?

Banzi, do you mean the set screws are supposed to seat into the "front" ring and not the "middle" ring?
The first way I tried this was to fully seat the capsule into the holder, this way the set screws do not center over the "middle" ring, but the do not entirely clear it either. They do contact the "front" (covered by blue tape) ring.
This resulted in the same problem as described in my first post.
I then tried placing the capsule into the ring so that the set screws centered on the "middle" ring, no difference.

Is it possible the set screws are supposed to seat into the blue taped over "front" ring and pierce the tape, and I may have not sufficiently pierced the tape? ?

Just to clarify, although I am using a relay to add the backside for omni, I have been testing with the relay completely out of circuit.
I am connecting the capsule lead directly to the node of tube pin 6 and the 60m resistor.
I get good continuity from the "middle" ring to the node of the 100m resistor and the 0.01 cap.
Connecting one at a time, the front side works perfectly, the back side makes practically no output, and both connected makes for a very low level, "hollow" sounding output.
I turn the capsule around in the holder and get the same result.
This is a homebrew VF14 build with a Cenimag CM-2461NiCo output using the "Oliver" adapted original circuit, I have built several of these with different capsules, never a problem.
I have also built most of the "authentic" U-47 kits, never a problem. and have restored original U-47s, so while I am no expert I do have some practical experience with these...

This is a real mystery.

In summary:

If you mount the capsule one way round, the front diaphragm works but the rear does not work.
If you mount the capsule the other way around, the (new) front diaphragm (which was the rear last time) works but the (new) rear (which was the front last time) does not work.
You measure decent capacitance from each diaphragm to backplate whether the capsule is mounted or not?
You measure no continuity from either diaphragm to backplate with the capsule mounted?
You measure no continuity from diaphragm to diaphragm?

What if you short each diaphragm in turn to the backplate? What is the capacitance of the other diaphragm to backplate in this situation?

Absolutely. The capsule has to be fully seated, with the electrical contact made between the holder and the brass ring, and the set screws tightened in front of the brass ring to keep it in place. With the set screws on top of the brass ring, a relatively big shock to the microphone would easily displace the capsule out of the holder, and probably do some damage.

If it doesn't work when fully seated either, my bet would be to look elsewhere for the problem: the capsule and mount are probably ok.

nielsk said:

Banzi, do you mean the set screws are supposed to seat into the "front" ring and not the "middle" ring?

Click to expand...

Thanks for the reply.
The set screws are pointed, so if they are to be screwed down in front of the middle ring, should the points cut through the blue tape and bite into the front ring?

BTW, did a little test, took out the Dale capsule set up and installed a chineese capsule, works perfectly...

It's a tolerance thing; with some holders you'll pierce through, with others you'll tighten up  before reaching the blue top. All electrical contact is made between the capsule and the holder itself, so as long as the capsule is tight and can't be damaged, you're good.

Otherwise, good thing I'm not  a betting man! 

nielsk said:

Thanks for the reply.
The set screws are pointed, so if they are to be screwed down in front of the middle ring, should the points cut through the blue tape and bite into the front ring?

Click to expand...