RCA 96-A from scratch

[DaveP]

About 10.6mA flows down the divider from B+, then 2.4mA goes off to the screen grids.

Originally, 3.3mA  came back into the string from the 6R7 (later mod upped that to 6.3mA).  All that current stabilises the operating points in a simple manner.  The timing bias of -3.9V is stabilised by the entire 70mA of the compressor as it is returned to the transformer CT.  In this way,  when the screens try to turn off, they are unable to change their voltage as they  they are overwhelmed by the much greater current passing down the string.  The process was useful in the 1930's as electricity networks were not so stable as they are today.

The threshold voltage is also stabilised at 42V by the same string.

Many of the V series mic pre's used voltage dividers to stabilise the g2 voltage, albeit with much less current.

DaveP

 

[5v333]

thanks!
i looked at the 6R7 in the wrong way.

 

[rackmonkey]

It will not have the same round VU meter (never seen one for sale) but it will have a vintage 4.5" meter, they always look good.

DaveP

How large is the original meter? I have dozens from around the period in various sizes if you’re interested. Also have many of the 4.5 rectangles if you just prefer that. Happy to donate to this cause for the cost of shipping from USA to France (just because it’s a cool project).

 

[DaveP]

That's very kind of you to offer but we have already bought the meter now.

Best
DaveP

 

[rackmonkey]

You approach projects in a much more organized way than I do. 

 

[DaveP]

It's the Asperger's

DaveP

 

[DaveP]

You approach projects in a much more organized way than I do.

I don't post after a successful project, I post as it happens, so the potential for looking like a ******** keeps me very focussed.

DaveP

 

[rackmonkey]

I don't post after a successful project, I post as it happens, so the potential for looking like a ******** keeps me very focussed.

DaveP

Very savvy!

 

[emrr]

The round meter is the standard Weston size most commonly seen.  The bezel is custom.    500 microA I believe.  The 96-AX used the standard Weston rectangle size VU type once that standard came around. 

 

[rackmonkey]

From the picture at the top of the post, I couldn’t really tell if the round meter had a raised, gable-like part at the bottom or if it was just the normal embossed Bakelite. But looking at others on the web it’s clear just how custom the bezel was. Stamped metal with a Van Dyke beard at the bottom. Really cool and unusual.

I have several exactly like the rectangle versions. Needless to say, none like the round one. Thanks for the info.

 

[emrr]

Good time to post this again.  Left is a 96-A, middle is an 86 meter, right is NOT one I've ever seen on a 96-AX, maybe a remote meter for an 86 or 96 from a transmitter control console. 

------EDIT-----
1945 catalog, page 20, Transmitter Control Console, accessory 43504, extension meter for 86-A1

 

[DaveP]

Thanks Doug,

Very useful to see those meters and where the check-points are.

Best
DaveP

 

[rackmonkey]

I originally did a search on “RCA 96-A” and pictures of units with the round meter and the larger rectangle meter on the right come up. I have several like the one on the right. Maybe the ones I saw with the big meters were from transmitter control consoles like you said.

A search on “RCA-96AX” brings up no pictures of said units, unfortunately.

Good info though. Thanks for posting.

 

[Ricardus]

It's the Asperger's

DaveP

Same here.

 

[DaveP]

It comes in handy for GroupDIY, but I often get the wrong end of the stick, according to my wife. :-[

But then women do expect us to have telepathic skills at their level :

DaveP

 

[emrr]

I originally did a search on “RCA 96-A” and pictures of units with the round meter and the larger rectangle meter on the right come up. I have several like the one on the right. Maybe the ones I saw with the big meters were from transmitter control consoles like you said.

A search on “RCA-96AX” brings up no pictures of said units, unfortunately.

Good info though. Thanks for posting.

Pretty much no one mentions the 'X' and it doesn't seem to be on the tags either, but looking at the catalogs any unit that was available in a 'VI' or an updated 'VU' version, the update got 'X' tagged on the ID. 

 

[DaveP]

I'm still working on the front plate as it takes a lot of working through in 3D, but this is the general arrangement.

Everything is just laid on at the moment.  The front will be sprayed black when its complete.

Big Rollins Smith meter dominates and the chrome vents add a touch of 1930's Art Deco.



The attack, release and threshold are along the base with all the balance and switching controls.

DaveP

 

[emrr]

Cool, where did you source the chrome?

 

[DaveP]

They are thin bow handles and cut down cup handles, from Amazon Uk and morehandles.co.uk.

I needed to solve that before giving the project a green light.

Best
DaveP

 

[rackmonkey]

Pretty resourceful!