Langevin Progar

Does anyone have any experience of one of these?
Anyone heard one?
Its a 4 stage broadcast Limiter circa 1940, the manual is 19Meg so can't post but can be found here:-
http://schematic.danrudin.com/index.php?dir=Langevin/
Thanks
DaveP

They didn't show up until post-war as far as advertising history shows, and there's a date on the schematic.  There's a story that hasn't been substantiated about it being a pre-war design. 

So there is.....
Originally drawn in 46/47
thanks Doug

DaveP

That Progar is an interesting circuit.  For years, I always wondered if anyone had ever used a "pentagrid converter" tube (or as Sylvania called it in their tube manuals, a heptode) for a variable mu element in an audio compressor/limiter.  This Langevin is the first one I've seen...using 6L7 bottles.  Newer miniature versions would be the 6BA7 and 6/12BE6.  Other octals would be the 6SA7 and 6SB7, and I'm sure some others.

Besides this Langevin, did anyone else ever use a pentagrid/heptode for a compressor/limiter?

Sidebar:  My 1950 RCA manual (RC-16) indicates the 6L7 was being made for "renewal" purposes, apparently rather than for new designs.  Also interesting, that same manual has a circuit for an audio **expander** using a 6L7 along with a 6J5 and a 6H6.

Bri

Brian,
The 6L7 is also used in the W.E.1126-A/C, the Altec A-322C, the Presto 41-A and the Gates SA-39A/B.
I've just made a SA-39B and I'm very impressed with the tube.

I've not done a comparison yet, but I think there are advantages in having the CV on a separate grid from the audio input.

If you put "Ken-Rad 6L7" in Google you get a pdf of the Engineering report on the 6L7.

Most of those old expander circuits can be modified to be compressors by generating -ve CV instead of +ve and adjusting the bias of the control tube to suit.
best
DaveP

Dave (or anyone else), have you ever run into a compressor or limiter which used pentagrid/heptode tubes other than the 6L7?  There were a number of them in octal, loctal, and miniature versions, since they were very widely used in broadcast radio receivers.

Just curious....

Bri

The federal AM 864/U used 6sk7...

6SK7 is a "remote cutoff" pentode, so only 3 grids vs. the 5 grid 6L7 and others.....

Bri

gotcha. I was too lazy to look it up, so I rolled the dice when I posted that...

I recall RDH4 says pentagrid types can handle higher signal input than remote cutoff types.  Don't have it with me to confirm. 

RDH4 Chapter 16.3 page 685

See attachment.

This is the beast:-
http://www.vintageaudio.net/members/view.php?item=116

It appears to be two compressors in one, hence the complexity.
Not sure its worth $5000 though.
best
DaveP

Brian Roth said:

Besides this Langevin, did anyone else ever use a pentagrid/heptode for a compressor/limiter?

Click to expand...

I just started a thread about a 1940's Wilcox M57D1 Tube Limiter that uses 6SA7's:
https://groupdiy.com/index.php?topic=77133.0