Altec Birdcage (639A) microphone dynamic capsule replacement

[dmp]

I have this Altec Birdcage mic that had no sound from the dynamic capsule (ribbon is working great).
The thin wires from the capsule had lost connection - trying to repair it they just kept breaking and it is shot.
I'm wondering if anyone has ideas on a replacement for the dynamic capsule?

It needs to be omni to work (the mic puts the dynamic in combination with the ribbon to get cardiod)
And the dimensions are about 34mm diameter with an allowed depth of about 20mm

 

[mjrippe]

I think it is the same element as the 633 "Saltshaker", please correct me if I am wrong, so maybe find one of those?

 

[dmp]

Good to know, but those sell for quite a bit now. $400+! I would love to find a beat up 633 or 639 to use for parts but I think I might be waiting a long time.
I was just looking at a EV 635A and I might be able to get that capsule to fit.
I wish I knew of a new production mic with a decent large diaphragm capsule.

 

[mjrippe]

Someone might be asking $400+ but they *sell* for considerably less.
Actually I have an Altec 660 which might work as well. It is on loan to a friend, but I don't think they use it much. If you're interested I can get it back and measure it.

 

[dmp]

Actually I have an Altec 660 which might work as well. It is on loan to a friend, but I don't think they use it much. If you're interested I can get it back and measure it.

I would be interested - let me know. I never heard of the 660 but they do look similar.
I did see somewhere that the older versions (western electric) had aluminum diaphragms while the Altec labelled mics had mylar. The 639 had mylar.

 

[dmp]

Here's a few pics as I started taking it apart. A transformer, an inductor, a resistor (620 ohm), a capacitor (0.12 microF)
I'm working on tracing a schematic as I've been unable to find one.
The only sketch I've seen does not show all these components. It does look original.
Piston style ribbon.

 

[mjrippe]

Interesting, looking at your earlier photo the diaphragm is silver while I recall my birdcages having the metallic blue diaphragm. Perhaps they changed over time. Anyhow, I'll see about getting that 660 back and let you know.

 

[dmp]

I recall my birdcages having the metallic blue diaphragm

Interesting. This is the only one I've looked at. Now that I really look at it, I think it is metallic, not mylar.

 

[dmp]

I traced out a schematic. Haven't seen one anywhere online. The 4 wires for transformer taps come up through the base metal that seals off the dynamic chamber and were connected, then sealed in goop. Probably to connect on assembly to get the right ribbon/dynamic mix. The switching doesn't make sense to me for 'D' and 'C'?

 

[mjrippe]

Is it possible that you have R and D backwards? The three settings should be C (Combined or Cardioid) with both elements attached, D (Dynamic) only, and R (Ribbon) only.

I got my 660A back and pulled it apart. The dynamic element is bluish-silver and measures 17.5mm deep and 36mm in diameter. As mentioned by Preservation Sound (altec – Page 2 – Preservation Sound), the output is very treble-heavy. Perhaps this blends well with the darker ribbon?

In any case, it is not a special mic on it's own and mine is cosmetically rough so I would be willing to sell you the capsule to get your birdcage up and running again.

 

[dmp]

That would be great. The element I pulled out measures the same so I think that is the right element. I'll send send you a PM

You might be right about the labeling.

 

[mjrippe]

Here is a photo of the 660 taken apart. I re-assembled it for shipping

 

[amageddian]

I'm troubleshooting my Western Electric 639A mic, which sounds unusually thin when on ribbon-only mode (I'd expect it to sound very boomy, especially when talking a few millimetres from the mic). I opened it up to inspect the ribbon, which looks fine, but after peeling back some of that ancient putty, I found that some of the wiring seems to be disconnected.

I have tried to compare against the hand-drawn schematic posted above, but the wire colours indicated don't seem to correspond to those in my microphone. Where should these loose wires connect?

 

[dmp]

Those wires come up from the lower section and allow different connections of the transformer taps. I think they should be like that (insulated and coiled up in the putty) - unless you got the mic with problems and somebody messed with it before.
But if the putty was undisturbed and you pulled them out like that, then I think it was correct. You might just want to reflow the solder since they are exposed, put heat shrink on them, and coil them back up.
If the mic was previously healthy, I would first look at the switch. Clean the contacts and make sure they are tensioned. It's a pain to get in to the switch though. I never removed the switch, I bent out the tabs and disassembled it in place. Be very careful of the fragile dynamic element.
The ribbon alone on mine is very full with a ton of low end and good sensitivity. The dynamic has much less low end, but when combined into cardiod, the mic has a nice sound and a reasonably good unidirectional pattern.
If your 'C' pattern has pretty good sound and directionality, it would also imply the switch was making a poor contact in 'R'

 

[dmp]

What does the connection at the top look like where the two wires connect for the ribbon? Still painted black?

 

[amageddian]

What does the connection at the top look like where the two wires connect for the ribbon? Still painted black?

Yes.

 

[amageddian]

Those wires come up from the lower section and allow different connections of the transformer taps. I think they should be like that (insulated and coiled up in the putty) - unless you got the mic with problems and somebody messed with it before.
But if the putty was undisturbed and you pulled them out like that, then I think it was correct. You might just want to reflow the solder since they are exposed, put heat shrink on them, and coil them back up.
If the mic was previously healthy, I would first look at the switch. Clean the contacts and make sure they are tensioned. It's a pain to get in to the switch though. I never removed the switch, I bent out the tabs and disassembled it in place. Be very careful of the fragile dynamic element.
The ribbon alone on mine is very full with a ton of low end and good sensitivity. The dynamic has much less low end, but when combined into cardiod, the mic has a nice sound and a reasonably good unidirectional pattern.
If your 'C' pattern has pretty good sound and directionality, it would also imply the switch was making a poor contact in 'R'

Thanks for the tips @dmp . It did work well previously, even after a re-build of the body following a nasty fall. So I'm not sure when it lost its low-end. It currently doesn't sound so good in Cardioid either, honestly, although the pickup pattern is correct (much higher response at the front compared to the back). Could that suggest another component having failed, or some ribbon problem that I can't detect visually?

 

[dmp]

It's possible it needs a new ribbon but in that picture the ribbon looks awfully good.