Audio Historians - REDD/RCA/Langevin/RFT Lorentz/WSW

[pucho812]

speaking 0f trident studios.

I have heard various stories of the a-range. The all share  designed by Barry Porter which was never disputed that i know of unless a certain person claims that too, he claims everything else trident did.
Anyway all stories include a magical number of 13 ever produced, Cherokee studios in L.A. owning 4 of them at one point,  Cherokee studios making mods to the ones they owned. From talks with Malcom toft, They picked the color because they got it as a surplus sale  for very little money.  But I  also have been told of a number 14 which was in white. It was a very small desk used in trident studios disc cutting room.

 

[pucho812]

Who we talkin' 'bout?

if I mention his name he may show up but his initials start with a J and last name starts with an O.  I have heard him claim every trident circuit I can think of, but I don't know if he also ever claimed the a-range, I couldn't stand to be around him long enough to find out. 

 

[emrr]

Oh, right, RCA.

They did everything at 250Ω for a long time. 

The earliest are mic level mixers before a single program amplifier, for carbon or condenser mics.

Like everything before a certain point in the mid/late 1930's, the earliest are passive mix panels with no amplifiers, those being external.  Balanced H or ladder attenuators with a multistep matching transformer on the output, tap for the number of mix channels, then a master output.  The largest I've seen was 8 channel.    The film version PB-37 (see other post here) also had a bonus HPF. 

The early racks of broadcast amps had a 4 position rack panel mixer with no master, that being the control on the program amp.

The 1937 76-A console used the standalone program (40-C/84) and monitor amp (82/BA-4/14) circuits of the day, many basic RCA designs were tweaked and subtly changed from 1934-1941, with the basic BA-4 monitor amp circuit having a bunch of different part #s from 1937-1956.  The preamp was a 3x1 type that also existed as standalone rack equipment. 

The 1939 76-B changed the preamp to the individual 85-B circuit and continued on with 40 and 82 circuits through the end of that line.  So a 1938 rack of amplifiers with a 78 console surface is really the same as a 1950 76-D for the most part. 

The 1951 BC-2B (never seen any reference to an 'A') had the most patching functionality of any RCA tube console, monitor amp much like the BA-24, a new program circuit that is much like the BA-3/13 but with a 6V6, and a 6072 preamp using the BA-11/12 transformers. 

The 1956 BC-3/4/5/6 moved fully to PCB construction and over to high impedance mixing, and out of necessity reduced the patching options.  Highest amount of negative feedback, all 9-pin tubes except for the monitor amp outputs, and much smaller transformer types.  The least sexy on the inside, and more of a pain to service because of early gen PCB's with lots of hand wiring to/from.  Same external case and footprint as the BC-2B, at least with the BC-3.  Varying widths on the 5/6, and then there's the rarer BC-4 which seems to have a different case style.  The BC-3 is still in the 1967 catalog. 

The Photophone film and recording studio consoles did have basic HP/LP EQ's and some different concepts such as input and output side mixers, one version is documented thoroughly in an RCA Recording Manual that's online.  There are pictures of larger and later variations though no info has really surfaced.  Many of the components in those consoles are the same as the standalone equivalents, in many cases just mounted in a desk with an overall faceplate.  There are some more advanced filter sets and EQ's, some that are sort of 'tilt' shelves (so whoever trademarked 'tilt' recently shouldn't have qualified). 

Film and recording employed some fairly severe HP and LP filters on the program outputs, to tailor for the capture mediums of the time.  If those are removed, bandwidth is excellent.  As example, I just worked on a large number of 1933 RCA pro PA system preamps, and they all measured as full bandwidth as is ever needed for rock and roll, maybe not dog whistles (almost) or pipe organs. 

The pro line broadcast and film stuff until WWII used custom wire wound resistors done on multi chamber bobbins, so noise as good as is possible, essentially the tube noise floors.  Resistors like that don't drift either. 

 

[matriachamplification]

Oh, right, RCA.

They did everything at 250Ω for a long time. 

The earliest are mic level mixers before a single program amplifier, for carbon or condenser mics.

Like everything before a certain point in the mid/late 1930's, the earliest are passive mix panels with no amplifiers, those being external.  Balanced H or ladder attenuators with a multistep matching transformer on the output, tap for the number of mix channels, then a master output.  The largest I've seen was 8 channel.    The film version PB-37 (see other post here) also had a bonus HPF. 

The early racks of broadcast amps had a 4 position rack panel mixer with no master, that being the control on the program amp.

The 1937 76-A console used the standalone program (40-C/83) and monitor amp (82/BA-4/14) circuits of the day, many basic RCA designs were tweaked and subtly changed from 1934-1941, with the basic BA-4 monitor amp circuit having a bunch of different part #s from 1937-1956.  The preamp was a 3x1 type that also existed as standalone rack equipment. 

The 1939 76-B changed the preamp to the individual 85-B circuit and continued on with 40 and 82 circuits through the end of that line.  So a 1938 rack of amplifiers with a 78 console surface is really the same as a 1950 76-D for the most part. 

The 1951 BC-2B (never seen any reference to an 'A') had the most patching functionality of any RCA tube console, monitor amp like much the BA-24, a new program circuit that is much like the BA-3/13 but with a 6V6, and a 6072 preamp using the BA-11/12 transformers. 

The 1956 BC-3/4/5/6 moved fully to PCB construction and over to high impedance mixing, and out of necessity reduced the patching options.  Highest amount of negative feedback, all 9-pin tubes except for the monitor amp outputs, and much smaller transformer types.  The least sexy on the inside, and more of a pain to service because of early gen PCB's with lots of hand wiring to/from.  Same external case and footprint as the BC-2B, at least with the BC-3.  Varying widths on the 5/6, and then there's the rarer BC-4 which seems to have a different case style.  The BC-3 is still in the 1967 catalog. 

The Photophone film and recording studio consoles did have basic HP/LP EQ's and some different concepts such as input and output side mixers, one version is documented thoroughly in an RCA Recording Manual that's online.  There are pictures of larger and later variations though no info has really surfaced.  Many of the components in those consoles are the same as the standalone equivalents, in many cases just mounted in a desk with an overall faceplate.  There are some more advanced filter sets and EQ's, some that are sort of 'tilt' shelves (so whoever trademarked 'tilt' recently shouldn't have qualified). 

Film and recording employed some fairly severe HP and LP filters on the program outputs, to tailor for the capture mediums of the time.  If those are removed, bandwidth is excellent.  As example, I just worked on a large number of 1933 RCA pro PA system preamps, and they all measured as full bandwidth as is ever needed for rock and roll, maybe not dog whistles (almost) or pipe organs. 

The pro line broadcast and film stuff until WWII used custom wire wound resistors done on multi chamber bobbins, so noise as good as is possible, essentially the tube noise floors.  Resistors like that don't drift either.

Hey Doug!

was just about to ask about the RCA Compressors that seem to be favoured by many. The wife is gone with the kids so let me think on this for a second as there are a few particualrs I am interested in hearing about.

First is the various RCA Tube Compressors.

Second... let me absorb your post.

More on everything soon. Voice Over demo recordings will be starting on Monday, with a bit of luck

Is it St. Pattys day today?

 

[emrr]

When you talk about the very early stuff that mixed at mic level and changing taps on the mixed output transformer, is that because it was Hybrid Coil mixing?

I think I've always thought about owning an RCA 76-D, simply because it was the mixer that started Rock 'n' Roll as we know it at Sun Records.

Strict impedance matching concepts.  If you expanded or reduced the mix channel count, you changed the series resistors and the tap on the transformer.  Seems to be same mentality of Collins Radio, who early on used input transformers with 30/50/200/250 taps which were patchbay style adjustable on the fly.  Hard to believe those were audible differences. 

On the cheap (maybe, maybe not), get some 85-B preamps and an 84-B program amp, you've got the essence of a 76-B/C/D console. 

There is a rich legacy of available equipment here, for sure.  Still can be quite hard to find, and more recently quite expensive. 

 

[pucho812]

OK.  Roger that.  Message received.  Over. 

Last thing we want is to invite trouble from outside.

8)

He is a bit pompous and fletcher has much to say on that regard. But anyway
I had a non trident question.
what exactly does the RS124 change in the altec 436C?

 

[pucho812]

There's a thread for that, it's all there.  : )

let me search

 

[pucho812]

The last few pages of the RS.124 thread have a few folks who have scratch built etc. and I've chimed in and helped where I can.  The schem.  is  further back so I can have a peek around in the thread and find the page if ya need.  Lemme know.  It's be an easy mod for an experienced old timer such as yourself 

Thanks for the offer but I am not looking to make one. I am curious as what it changed from a user standpoint and what it did to the sonic. I assume part was to match their transmission standards but that is just an assumption.

 

[Walrus]

the Levy brothers were responsible for a few Pultec-Altec clones. 
Audio transformers by R.J Gilson Ltd. of Wimbledom.
Of the units that came across my path, one had an interstage transformer.

Bloody hell, haven't seen that unit for a while!
There were two of them at CBS studios London when I joined in 1988. Stacked up unused in a cupboard.
I know that one of them was given as a present (in the late 1990's) to a engineer/producer by the then studio manager. Not sure where the second went.
My understanding was that they were made by the original technical manager George Bala.

 

[matriachamplification]

Speaking of CBS reminds me. There are a couple images of a console we found of a console at Columbia NY. Can anyone identify this or have any details. A stellar classic console I would love to know more about, but a stellar console none the less.

The info here is amazing. We should have a soft promo video ready of RCA and Doug over at ElectroMagnatic Radiation Recorders. With so much ready available info online we are moving through some edits quickly.
REDD has required a bit more tact in nailing down timelines. Thanks Winston for hammer down these details for us.

Lastly I have heard back from Abbey Roads and will be speaking with them about the consoles. I am a beleiver in seeing the full picture and hopefully we can get some of our own film footage of their consoles when/if I can make the trip to the UK.

We would also love to film some old RCA consoles but are awaiting news about a developing studio that may work perfectly. For now we have tons of vintage stock RCA footage that is a blast to watch.

Once I get the audio done I will post it here for everyone to critique for rewrites and clarity. Then onto the website.

 

[pucho812]

Has anyone here seen an RCA 96-A compressor.  I got some photos if you are interested.
It is huge, like around 12 RU for a single mono channel broadcast comp and separate PSU

 

[emrr]

Has anyone here seen an RCA 96-A compressor.  I got some photos if you are interested.
It is huge, like around 12 RU for a single mono channel broadcast comp and separate PSU

I have 2.  There's good pics from a Reverb sale also.

Same as the 86 but a fancier package and separate regulated PSU.  8RU for the amp, 6RU for the PSU.  Works out about the same as the GE BA-5A.

Always good to see another, post!  Maybe in DaveP's thread about building a clone.

 

[Perm0]

I see Geoff Frost got mentioned, to the O.P. check out his youtube channel, you will love the interview;

https://www.youtube.com/user/soundtechniques/videos

Also, for me as a novice the "How to design a mixer" presentation was the clearest I ever heard, got lots of laughs from it  ;D and it really made me understand a lot more on transformers.

I love this guy 

My 32ch mixer comes from the guy that appearantly better be not mentioned  :-X

Love the mixer though !  8)

 

[pucho812]

I have 2.  There's good pics from a Reverb sale also.

Same as the 86 but a fancier package and separate regulated PSU.  8RU for the amp, 6RU for the PSU.  Works out about the same as the GE BA-5A.

Always good to see another, post!  Maybe in DaveP's thread about building a clone.

wow, 2 of them. I bet they sound amazing. I only seem some in pictures.  aside from input and output knobs  what is the row of what looks like push buttons at the bottom on the main unit. what do they do? is that all fixed time constant settings?

 

[matriachamplification]

Has anyone here seen an RCA 96-A compressor.  I got some photos if you are interested.
It is huge, like around 12 RU for a single mono channel broadcast comp and separate PSU

We would very much love pictures. Any "source" images we can currate the better for our mandate of

I have 2.  There's good pics from a Reverb sale also.

Same as the 86 but a fancier package and separate regulated PSU.  8RU for the amp, 6RU for the PSU.  Works out about the same as the GE BA-5A.

Always good to see another, post!  Maybe in DaveP's thread about building a clone.

credible content.

You have 2. Thats fantastic! I will have to check those out in person once the demic is contained.

I will look at DaveP's thread again. Would be a intersting build to take on as we do need a tube compression element to fill out our lesson plan.

 

[emrr]

wow, 2 of them. I bet they sound amazing. I only seem some in pictures.  aside from input and output knobs  what is the row of what looks like push buttons at the bottom on the main unit. what do they do? is that all fixed time constant settings?

tube current test push-buttons.

The time constant is fixed, and there are 3 update versions, plus probably a million hacks done in the field on these and 86's.  1st 2 are single constants, a late '40's note (there's a post about this in an 86 thread) updates it to a dual time constant.  VERY different result. 

 

[Heikki]

...as we do need a tube compression element to fill out our lesson plan.

I think in a mixing console a compressor based on the BBC LIM/2 would work well. It would only need few tweaks and tubes that are more available today would need to be used. The design has some similarities with Fairchild 660. No amplifier stages after the gain reduction stage and side chain amplifier generates the control voltage. Output level is much smaller compared to Fairchild and needs a line amp. 1 + 1 : 1 + 1 output transformer could be used and I believe there's a line amp design that could be used right after it.

 

[ruffrecords]

what's interesting with Sweetenham is the following. Sweetenham, Neve, porter, the holy trio of early British solid state consoles of Sound techniques, Neve LTD, and Trident all read the same trade magazine called wireless world and in one issue, they did an article on transistors and the 3 transistor amplifier. They published a generic circuit in the magazine.  They all read that article and all studied the circuit. It became the backbone of their work for a long time. They all applied the concept and circuit to an extent in that article and all came out with very different sounding results.

Although I already commented that I think this story is more myth than reality, it intrigues me so I did some research. I have looked though every issue of Wireless world from 1955 to 1965 and I cannot find any article that matches this description. The dc coupled pair, of which the three transistor versions are variants, is featured several times but there is no article on 'the three transistor amplifier'. I also looked at Tape Recorder Magazine, which morphed into Studio Sound over the same time period. The reason I looked at it is because I rememeber in the mid 60s it ran a series of articles on building a home studio mixer. The reason I looked there is because I actually built my very first mixer based on the PCBs supplied by the author David Robinson. The mic pre used a dc coupled pair and there was a single transistor stage following it. Not a triple as used by Neve and Swetenham but three transistors total. I discovered the article I had used to build my own mixer was an update of an earlier one at the beginning of the 60s. I checked this out and sure enough the circuit was almost identical but used germanium transistors instead of silicon. But what was most interesting was it said the mic pre was based on a BBC design. So my next port of call was BBC tech pubs and I found a BBC Monograph 26 entitled 'Transistor Amplifiers for Sound Broadcasting' published in 1959 and sure enough on page 13 there is the same three transistor mic pre used by David Robinson.

http://downloads.bbc.co.uk/rd/pubs/archive/pdffiles/monographs/bbc_monograph_26.pdf

Cheers

Ian

 

[ruffrecords]

Nice detective work and research Ian, thanks.

On a slight tangent but related to your flow: Do you know if those wonderful BBC technical docs which we have access too now were actually available to the general public at the time of publishing?

It being a public funded corporation seems that they ought to have been but some do have an air of "for internal use only" about them.

Well is does say Price 5/- on the front so I guess there were readily available. Also the BBC R&D dept was well known and respected and they had pretty decent audio facilities - just look at all the 'recorded at the BBC' music by very famous bands. Rupert was definitely into broadcasting.  Missionary radio was his big thing in the late 70s after he left Neve and I suspect he was into it a long time before that. The BBC circuits certainly 'escaped' into more general circulation because David Robinson credits the BBC for his mic pre circuit in 1961 (IIRC) and the monograph was published only 2 years earlier in 59.

Cheers

Ian

 

[matriachamplification]

Although I already commented that I think this story is more myth than reality, it intrigues me so I did some research. I have looked though every issue of Wireless world from 1955 to 1965 and I cannot find any article that matches this description. The dc coupled pair, of which the three transistor versions are variants, is featured several times but there is no article on 'the three transistor amplifier'. I also looked at Tape Recorder Magazine, which morphed into Studio Sound over the same time period. The reason I looked at it is because I rememeber in the mid 60s it ran a series of articles on building a home studio mixer. The reason I looked there is because I actually built my very first mixer based on the PCBs supplied by the author David Robinson. The mic pre used a dc coupled pair and there was a single transistor stage following it. Not a triple as used by Neve and Swetenham but three transistors total. I discovered the article I had used to build my own mixer was an update of an earlier one at the beginning of the 60s. I checked this out and sure enough the circuit was almost identical but used germanium transistors instead of silicon. But what was most interesting was it said the mic pre was based on a BBC design. So my next port of call was BBC tech pubs and I found a BBC Monograph 26 entitled 'Transistor Amplifiers for Sound Broadcasting' published in 1959 and sure enough on page 13 there is the same three transistor mic pre used by David Robinson.

http://downloads.bbc.co.uk/rd/pubs/archive/pdffiles/monographs/bbc_monograph_26.pdf

Cheers

Ian

Amazing connections. This is perfect for our story arc.

I think in a mixing console a compressor based on the BBC LIM/2 would work well. It would only need few tweaks and tubes that are more available today would need to be used. The design has some similarities with Fairchild 660. No amplifier stages after the gain reduction stage and side chain amplifier generates the control voltage. Output level is much smaller compared to Fairchild and needs a line amp. 1 + 1 : 1 + 1 output transformer could be used and I believe there's a line amp design that could be used right after it.

Thanks! I really like the BBC connection as well.