[ARC5] OT - the BC-221-D, tube types.

[Kenneth G. Gordon]

On 17 Dec 2016 at 21:03, Leslie Smith wrote:

> Hello Ken:
> I see the point you made from the diagram in the manual TM-11-300. 
> I must say "thank you", because I believe I got the manual from your
> web-site. 

It doesn't matter: I put everything that is up on that website for anyone to use who needs it.
 
I'm glad you found it useful.

> To Jim:  I set out to follow your suggestion and trace the circuit; in a
> few moments I discovered that the layout demands careful thought to get
> to the socket of the 77 tube.  The 77 is built on a sub-assembly, and a
> sub assembly sits over the pins of the tube socket.  
> I'm uncertain how much I must unbolt to see the socket.   So I'll defer
> that line of investigation for a moment.  

I am curious, Les. Why is it that you feel the need to dig into the BC-221? Is something 
wrong with it, or is it simply your inate curiousity?

> It seems that Ken may be right - the VT-77 is a kinda-weird pentode.  
> Perhaps it was made so that the oscillator grid was shielded from the
> cathode (etc) in an attempt to get better stability?
> I'm quite confident these fellows knew exactly what they were doing.  
> It seems that it took only 20 years to develop a sophisticated
> understanding of how "it" all worked.   (Say 1915 to 1935)  Rather like
> the sudden spurt in computing from the 60's to the 90's.

Yes. The OT (Old Timers) were no dummies...and they didn't have computers to help them 
either.

> The LM series of meters are to be quite different in design from the
> BC-221 sets.  Earlier, but not necessarily more primitive.  Although
> these only contain 3 tubes they are "clever".   Clever = designed with
> great insight.  Astonishingly precise at a time when Mega-cycles were
> hard to measure.   According to the manual, the 1000kHz crystal is
> accurate (or was accurate) to within 50Hz, uncompensated.  This at a
> time when frequency measurement was a black art.  

I agree. I still find uses for my two BC-221s.

> 73 de Les Smith
>    vk2bcu at operamail.com
> 
> Note:  I profoundly dislike this modern (and completely incorrect) habit
> of denoting Mega-Hertz as mHz.

I most heartily agree!!!!! That is VERY annoying to me!

> Correctly understood, mHz (with the
> lower case "m") denotes a scaling factor of one one-thousandth.

Or "milliHertz".

>  Thus
> 1mH is on 0.001Hz.   The upper case "M" denotes Mega - a scaling factor
> of one-million.  This the change, from upper-case "M" to lower case "m",
> represents an error of ten to the ninth power!  

Correct...

Ken W7EKB

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