American octal steel tubes in LDC microphones?

[rock soderstrom]

1620 is 0.3 amps @6.3v (1.89 watts) same as 12ay7, only slightly higher than ef800 (.275 A). Black steel would dissipate heat out better; higher radiation than glass

Somehow I had the lasting impression that the steel tubes get hotter with the same heating current, which admittedly sounds strange.

 

[dmp]

Also EF800 is a higher mu tube (50) than the EF86/804/806 (38)...
Nice info here from the old days
I think a try-it-and-see is what's needed, not going to figure it out with datasheets
But most mic tubes seem to have higher mu than the 1620 (from datasheets)

Somehow I had the lasting impression that the steel tubes get hotter with the same heating current, which admittedly sounds strange.

They are only called the 'laws' of thermodynamics because they've never yet been observed to be wrong... Maybe steel tubes are the black swans of energy conservation

 

[emrr]

Also EF800 is a higher mu tube (50) than the EF86/804/806 (38)...
Nice info here from the old days
I think a try-it-and-see is what's needed, not going to figure it out with datasheets
But most mic tubes seem to have higher mu than the 1620 (from datasheets)

Nice PRR find there.

Remember mu is misleading, those numbers are always much closer together in the real world and they don't translate to enormous dB differences in that context. Nothing a decent preamp can't deal with, we're always higher than ribbon output.

 

[dmp]

Remember mu is misleading, those numbers are always much closer together in the real world and they don't translate to enormous dB differences in that context. Nothing a decent preamp can't deal with, we're always higher than ribbon output.

Thinking of signal-to-noise, SNR, not too low an output.
This may be a totally incorrect thought process, but if you have a high mu (50) and low mu (20) tube, with the same EIN, the SNR would be 50 vs 20.

 

[rock soderstrom]

Yeah, good info! We all miss PRR.
The underheating and the small anode current of the VF14 make the differences in terms of mu relatively small.

I used these measurements as a guide:

http://www.moxtone.com/mU47_U47_part3.html

 

[emrr]

Thinking of signal-to-noise, SNR, not too low an output.
This may be a totally incorrect thought process, but if you have a high mu (50) and low mu (20) tube, with the same EIN, the SNR would be 50 vs 20.

But mu is NEVER 50 or 20. That's ideal, and is virtually always degraded by real world component values. It doesn't take a lot to turn an ideal 50 into a real world 20. A 20 into a 10.

 

[dmp]

But mu is NEVER 50 or 20. That's ideal, and is virtually always degraded by real world component values. It doesn't take a lot to turn an ideal 50 into a real world 20. A 20 into a 10.

but doesn't that still give you a 2x improvement in snr between the high and low mu tube? (50/20 -> 20/10)

 

[emrr]

I don't know that it matters in the real world. My 1932 Carrier with 2 stage 864's is plenty quiet, and the capsule is severely band-limited too. I'm not bothered by hiss.

Which is paradoxical when you consider that layout, resistor noise, and cleanliness can all contribute far more noise than the tube. The resistors in the Carrier are original, several are bored into a block of wood and look like screw terminals for mounting wires.

The first MK-47 project here, generally regarded as a mic with higher hiss. Some have improved it somewhat with very slight layout changes. Given the tubes, if it were just the tubes, this should be a relatively quiet mic, maybe quieter than a VF14.

 

[k brown]

I used to have a couple of these (and variations) - I used as mic pres; sounded pretty good, actually.
https://www.preservationsound.com/2016/05/the-fisher-pr6-phono-preamp-circa-55/
They were my first dips into the thermionic world.

Here's a PRR post on diyAudio:

 

[k brown]

Here's a nice metal tube project:
https://groupdiy.com/threads/little-tube-mixer.42522/

 

[Recording Engineer]

To spin this just a bit, but still in the spirit of using “different tubes” in microphones, what’s everyone’s thought on the 7788 / E810F? I’m thinking possibly in a cathode-follower circuit. I’ve seen a few have used them for a phono preamp; y’all’s phono preamp talk made me think of it again.

 

[rock soderstrom]

To spin this just a bit, but still in the spirit of using “different tubes” in microphones, what’s everyone’s thought on the 7788 / E810F? I’m thinking possibly in a cathode-follower circuit.

This is an impressive tube, but would not be my first choice for a microphone, as from my point of view it is more of a driver tube with ample current capacities.(Ia as a triode=16,5mA!) Do you need that much in a microphone? Also high transconductance which can lead to a pronounced oscillation tendency, you will probably need a grid stopper.

Edit: really nice tube for a SE Headphone amp project with an output transformer
Edit2: similar "super tubes" are the C3g and D3a

http://vinylsavor.blogspot.com/2018/05/tube-of-month-e810f.html

 

[Recording Engineer]

Overkill, for sure, but that still doesn’t stop me! My next mic over the next few months will be a Church 47 -inspired, with a Vintage Windings HS-52!

Yes, definitely some oscillation concerns there though.

 

[rock soderstrom]

Overkill, for sure, but that still doesn’t stop me! My next mic over the next few months will be a Church 47 -inspired, with a Vintage Windings HS-52!

Ok, you like it big! Very interesting, keep us posted.

 

[k brown]

I think a close clone of the Church 47 would be an awesome project!
https://funkwerkes.com/web/wp-content/techdocs/MixedProAudio/Church-Tube-Microphone.pdfhttps://tapeop.com/interviews/107/church-mic-bonus/



Humorous caption describing it as a dynamic (from a Command Records sleeve pic):

 

[Recording Engineer]

Edit2: similar "super tubes" are the C3g and D3a

I’ve an excellent Valvo C3g to eventually put a Ronin Applied Sciences Pegasus -inspired mic. Have the original Samar transformer for it too, but hopefully, eventually Mark will find the time to build a choke for it for me.

Kick myself for not buying an original when they were first available; I say that because I got to track with one a few times at a studio in town.

 

[rock soderstrom]

I think a close clone of the Church 47 would be an awesome project!
https://funkwerkes.com/web/wp-content/techdocs/MixedProAudio/Church-Tube-Microphone.pdf

Humorous caption describing it as a dynamic (from a Command Records sleeve pic):

I have to confess, I didn't know the Church 47 microphone story at all, I had to google it first.

B+ 275V! Here is the schematic and some info:

Edit: k brown has edited/extended his original post, so now some info are doubled ;-)

 

[k brown]

I have to confess, I didn't know the Church 47 microphone story at all, I had to google it first.

B+ 275V! Here is the schematic and some info:

So interesting that the shock mount had no provision for tilting the mic.
I've long thought about making a shock mount like that; using silicone bands in place of rubber.

 

[Recording Engineer]

So interesting that the shock mount had no provision for tilting the mic.

I don’t think they had a need really, being designed for massive boom movie sound; from my understanding.

 

[k brown]

I don’t think they had a need really, being designed for massive boom movie sound; from my understanding.

Yes, built by Stanley Church, engineer at MGM Studios.