990 inductors

[theoverstayer]

I am having trouble finding the 20mH inductors used in the 990. I think of seen some diy pics here of 990s with them - anybody know where I can get them?

Thanks, Jefff

 

[NewYorkDave]

Try looking for 20uH and you might have better luck :wink:

 

[CJ]

20 uh, which is 30 turns of #30 enamel around a bic medium point.

:razz:

which will keep your 70's technology 990 happy.

:grin:

 

[soundguy]

70's technology rules.

battlestar gallactica included.

dave

 

[CJ]

Too modern.

1940's UTC/WeCo for me.

Hemingway and Bogart rule.

Now where's the pinout on that Quad Eight?

 

[soundguy]

pm me if you need it, I'll dig it up.

dave

 

[NewYorkDave]

...or just a few turns through a ferrite bead.

Really, though, small ready-made 20uH chokes should be easy to find.

 

[theoverstayer]

For the help

 

[Larrchild]

A month or so ago, I attempted to intervene in a post on GS that was batting around the question of "Does the emitter inductor serve mainly for stability or to reduce high frequency noise component?" with some of my famous tech-humor to defuse the flames.
By the way, what does it do?

 

[bcarso]

Very funny captioned picture of Bardeen, Brattain, and Shockley!!

(Shockley would be unhappy with my order of names there) :razz:

The emitter inductors allow the input series noise to be low in the audio band while shaping the open loop gain at higher frequencies to achieve a decent stability margin, and in concert with the very careful compensation networks elsewhere allows high loop gain at audio frequencies and decent slew rate. It is Deane's basic innovation and covered by a patent. There's a fairly thorough discussion of it in a Jensen white paper---perhaps someone will post a link.

 

[Larrchild]

Thanks for the concise answer! No doubt someone will be around soon to contradict you. But it's the best answer I've heard. I believe it.

off topic, but still fun: http://www.bellsystemmemorial.com/pdf/brattain_lab_notebook.pdf
Brittains Lab notes from the day the "Crystal Triode" first made A.C. Gain.

About a quarter-way down, read : "We attained the following A.C. values at 1000 cycles
Eg=.015 R.M.S. volts Ep= 1.5 R.M.S. volts"

They must have shat themselves.

 

[Winston OBoogie]

...

 

[bcarso]

[quote author="Larrchild"]Thanks for the concise answer! No doubt someone will be around soon to contradict you. But it's the best answer I've heard. I believe it.

off topic, but still fun: http://www.bellsystemmemorial.com/pdf/brattain_lab_notebook.pdf
Brittains Lab notes from the day the "Crystal Triode" first made A.C. Gain.

About a quarter-way down, read : "We attained the following A.C. values at 1000 cycles
Eg=.015 R.M.S. volts Ep= 1.5 R.M.S. volts"

They must have shat themselves.[/quote]

This forum is far less contentious than some. I remember a debate in another forum that raged for a zillion posts about adding a current source to a voltage regulator circuit, that had various famous heavyweights all trying to get the last word. We generally peter out around here after a bit, with a few acrimonious exceptions, including one I was regrettably party to when I should have had a lie-down before clicking on submit.

I am surprised that the inductor question in the other forum wasn't settled by referencing a Jensen white paper on the 990 though---but I guess that would have spoiled the fun.

Re getting gain out of the crystal triode---yes, those were the days to bring a change or two of underwear to work at Bell Labs.

It's funny that some still think they got their ideas from Roswell debris---as if there had been no solid-state physics before 1947.

 

[Larrchild]

thats a defining moment in history.
thats for sure.
making it possible to type on my PC about how i hate IC's.
hehe

 

[bcarso]

A great sci-fi story exploiting ironies like that: Forgetfulness, by "Don Stuart", nom de plume of John Campbell.