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Author Topic: powering tube mics in the field?  (Read 18385 times)

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Offline H₂O

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Re: powering tube mics in the field?
« Reply #15 on: August 28, 2009, 02:53:01 PM »
Some tube's can use both, but I do know for a fact the AC701k in the power supply schematic's I have seen use DC power - (i.e. Neumann KM5x, Schoeps m221, etc)

Looking to the mic body schematic I provided before (which is VERY similar to m221b) It appears that Pins 3 and 6 are a common ground.

The from some of the links I provided before the EF732 does appear to support both AC and DC current types.
http://www.radiomuseum.org/tubes/tube_ef732.html


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Offline Jhurlbs81

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Re: powering tube mics in the field?
« Reply #16 on: August 28, 2009, 04:42:06 PM »
I spoke with Alan over at the Telefunken USA.  He is going to provide all the required specs to help make this happen.  Probably won't have them till next week sometime. 

Quote
Looking to the mic body schematic I provided before (which is VERY similar to m221b) It appears that Pins 3 and 6 are a common ground.
Since this is a redesign of the original, not a replica, won't the schematics vary?


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Re: powering tube mics in the field?
« Reply #17 on: August 28, 2009, 04:52:14 PM »
Since this is a redesign of the original, not a replica, won't the schematics vary?



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Re: powering tube mics in the field?
« Reply #18 on: August 28, 2009, 05:43:42 PM »
Someone around here uses something like this:

http://www.tonnocover.com/Batteries_Chargers/RoadPro_12_Volt_Battery_Jump_Starter_Air_Compressor_T451061.html#

Its a roadside car battery charger and emergency kit...  But it uses a 12v battery and has a built in inverter for 120vAC... 

Just found one with AC Inverter:

http://www.tonnocover.com/Batteries_Chargers/RoadPro_12_Volt_Portable_5_in_1_Power_System_T451464.html


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Offline Walstib62

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Re: powering tube mics in the field?
« Reply #19 on: August 28, 2009, 07:13:44 PM »
The answer to the original question lies in the layout of the power supply module. Without that, I cannot advise on the best powering option for this unit. If you can get that schematic, I would be interested in seeing it. My guess is that there is a filament regulator circiut there. What it needs for an input I can only guess without a schematic. One thing for sure is that it would certainly need a constant current output. If the filament current is excessively low, then the cathode will be starved, thus decreasing the tube current. If the current is too high, then there is risk of damaging the filament or at least decreasing filament life.
And yes, the plate voltage is  higher than the capsule voltage since there is a 500K res. in series with the cap and 200K in series with the plate.

As to the ac vs. dc issue, isn't the filament electrically isolated from the cathode-therefor not in the signal path?
I deal with tubes every day, but they are much bigger, have 150 KV across them and emit X-ray.

Thanks!

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Re: powering tube mics in the field?
« Reply #20 on: August 29, 2009, 12:36:51 PM »
Is sound quality affected when powering the caps though a dc-dc convertor (assuming the quality is good)?  Would there be any sonic benefit to running these off a bank of batteries instead of converting the voltage?

Thanks
Jesse 

Offline H₂O

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Re: powering tube mics in the field?
« Reply #21 on: August 29, 2009, 12:56:06 PM »
Is sound quality affected when powering the caps though a dc-dc convertor (assuming the quality is good)?  Would there be any sonic benefit to running these off a bank of batteries instead of converting the voltage?

Sound quality should not be affected as long as correct filtering and shielding is applied to the design.  DC-DC converters typically use a switching component which can add noise but this can be managed.

Most modern recorders, pre-amps, etc have dc-dc converters in them already (to take your battery power and convert it into the various required voltages to operate the various components).

Example is that the Oade m148 uses a battery bank of 4 12v SLA's to get the 48v for phantom power and the E.A.A. PSP-2 uses a custom DC-DC converter to convert 5-9V to the required 48V.  Both sound amazing and similar - but the PSP-2 is 1/4 the size and probably a quarter or an eighth the weight.






« Last Edit: August 29, 2009, 01:01:33 PM by H20 »
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Offline Jhurlbs81

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Re: powering tube mics in the field?
« Reply #22 on: August 29, 2009, 02:19:17 PM »
Quote
The biggest load is the filament, so it's best to run that directly from the appropriate batteries (probably 4x C or D) to avoid conversion losses.  The higher plate voltage could be generated with a DC converter or simply a stack of batteries.  Since the current required for the high voltage supply is small that should be economical.

Yeah, the current battery box I've been using uses 4 C batteries and 4 30v cells. 

Offline Walstib62

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Re: powering tube mics in the field?
« Reply #23 on: August 30, 2009, 01:26:40 PM »
Thanks for the clarification. Certainly I can see where an induced ac component of even several milivolts could cause problems. I haven't dealt with basic vacuum tube theory in years, so I am pretty rusty.
 

Offline dactylus

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Re: powering tube mics in the field?
« Reply #24 on: August 31, 2009, 10:51:13 AM »


Very interesting reading.

I have a pair of Neumann Gefell M582 tube mics that were refurbished by Peter Drefahl that I'd love to be able to run in the field. 

I currently have an ac power supply built by Peter Drefahl to power these mics.  When I inquired about the possibility of using dc power in the field I didn't receive a very encouraging response as to the possibility of finding a practical solution. 

The m582 mics use "Telefunken" EC92 tubes and will accept a wide variety of the Neumann and Gefell sd caps that I have, as well as the multipattern, large diameter, Gefell UM70.  It would be GREAT to come up with a practical, workable solution to run these remotely...

 ;D




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Offline Walstib62

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Re: powering tube mics in the field?
« Reply #25 on: August 31, 2009, 11:32:14 AM »
Can you get the schematics?

Offline Teen Wolf Blitzer

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Re: powering tube mics in the field?
« Reply #26 on: August 31, 2009, 12:18:10 PM »
I'll hit up Busman for schematics to his toobes.   ;D

Offline H₂O

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Re: powering tube mics in the field?
« Reply #27 on: August 31, 2009, 03:08:44 PM »
What you really need is schematics of the power supplies showing output voltages and maximum currents by pin.
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Offline Teen Wolf Blitzer

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Re: powering tube mics in the field?
« Reply #28 on: August 31, 2009, 08:11:54 PM »
That's what I meant.  The supplies not the mics.  I sent Chris an email but have yet to hear back.  I would guess he can provide or get that answer ???

Offline dactylus

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Re: powering tube mics in the field?
« Reply #29 on: August 31, 2009, 08:39:48 PM »


Very interesting reading.

I have a pair of Neumann Gefell M582 tube mics that were refurbished by Peter Drefahl that I'd love to be able to run in the field. 

I currently have an ac power supply built by Peter Drefahl to power these mics.  When I inquired about the possibility of using dc power in the field I didn't receive a very encouraging response as to the possibility of finding a practical solution. 

The m582 mics use "Telefunken" EC92 tubes and will accept a wide variety of the Neumann and Gefell sd caps that I have, as well as the multipattern, large diameter, Gefell UM70.  It would be GREAT to come up with a practical, workable solution to run these remotely...

 ;D

^^

It looks like my Telefunken ec92 tubes will support ac or dc too.

http://www.radiomuseum.org/tubes/tube_ec92.html


« Last Edit: August 31, 2009, 08:44:59 PM by dactylus »
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