1950's Philips-NEFA program amps/preamplifiers. Racking tips?

[Conviction]

Hi everyone,

I finally dug up some 600 ohm/60k CT input transformers for these Philips-NEFA differential program amps/preamplifiers from the mid 1950's. The original input transformers were long gone and eBay gives a hint on why. The amps come from a broadcast console consisting of 8 modules, 4 in and 2 out, used by SR at several local stations back then. 2 EF86's on the input, 2 EL84's in PP out. 600 ohms in/600 ohms out. B+ 250V, should draw around 30mA according to the original test/meter panel I found.

They work like a charm, sounds great… But I need some racking tips/ideas.

They fit sideways on a 19” frame. I could drill two holes in the panel and make use of the original mounting, although I feel it would be a little ugly if I don’t cover the holes up with another panel.

I also consider a PSU in-the-box * Perhaps I should start looking at some 3RU chassis with room for two + a PSU.

Would be sweet to make something a little more aesthetically pleasing.
So, hit me up with ideas if you have some spare time.

Here’s the schematic of a close relative, the Ha16:

* Being differential, push-pull, they reject dirt very effectively. They don't even mind a power transformer relatively close (tried on the bench).

 

[5v333]

el84?
sounds like power amps of some kind?
do you have shematic for theese?

 

[Conviction]

el84?
sounds like power amps of some kind?
do you have shematic for theese?

Well, a lot of Philips-NEFA/Televerket/SR microphone (pre)amp designs from then actually made use of pentodes in push-pull: EL84, E81L, EL91 etc. Or DL94 as in my 2891A preamplifiers (although max output level, running at 90VDC B+, is in the range of 500-600mW).
I wouldn't call these power amps per se, but sure, they're able to push quite the level.

The close relative (or perhaps sibling), the Ha16 (see schematic in the first post), has two E81L in PP. The Ha16 was the standard module at SR during the mid-to-late 1950's. They built every console/system around it. It's all about the surroundings, I guess.

The modules above comes from a console designed for local stations, able to send program material back to the closest central (RRC, Rundradiocentralen). So, power amp, program amp, preamp... In this particular console every section made use of these modules: mike input, line input, listening amp (with another OT), program amp...

 

[emrr]

el84?
sounds like power amps of some kind?
do you have shematic for theese?

No different than all the program amps and compressors using 6V6's. 

 

[Conviction]

One sold for 10k (SEK) yesterday, complete with patchbay and a hefty PSU. Imagine the heater amperage.

 

[5v333]

ive taken alot of interest in the old american broadcast gear with high voltage and amperage capabilities.
most europeean stuff ive looked at have much lower signal capabilities.
so when old stuff like this that was used in little Sweden comes up, i get curious.

i have seen the 6v6 in alot of compressors but nothing else. what program amps are you refering to EmRR?

Im about to put together a preamp for my NYD EQ, with 6v6 output tubes,

 

[emrr]

i have seen the 6v6 in alot of compressors but nothing else. what program amps are you refering to EmRR?

Collins 356B
Langevin 117A
Langevin 5117
Altec 429 (PP 6AQ5)

Those are all either Program or Monitor depending on power strapping or feedback strapping. 

Keep in mind in many cases the use of a compressor replaced the program amp.  Collins 356B replaced by 356E.  Both PP 6V6. 

Lots of RCA's with PP 6F6's.  Also two with SE 6L6, and another with SE 6V6.  One RCA Photophone line amp that's just a single PP 6V6 stage between input and output transformers. 

All the GE stuff in one era is essentially same as RCA, in later era it's same as Collins. 

 

[5v333]

Thanks!

 

[PRR]

> 2 EL84's in PP out

Where do you see 84s??

The EL81 is a low-Mu high current type for TV sweep or pass-tube.

 

[Conviction]

> 2 EL84's in PP out

Where do you see 84s??

In my units  I posted, quote, "the schematic of a close relative, the Ha16:"

I haven't confirmed exactly how similar they are, but that's a job for tonight.

 

[Conviction]

most europeean stuff ive looked at have much lower signal capabilities.
so when old stuff like this that was used in little Sweden comes up, i get curious

"Little Sweden" had great EE's at the time! Fröberg (remind me to at least try to remember his first name), the brain behind several designs, must have (Doug made me aware years ago - déjà-vu) been fed some D.T.N. Williamson (THE topology of the time) during his education.

... But for really understanding the philosophy behind the choice of having all these capable units do all kinds of work we need a time machine. Some we can figure out, like reliability (the nature of differential amplifiers), versability, low distortion... Plus the fact that every program material from the Swedish Radio passed the closest RRC before hitting the transmitters.

 

[Conviction]

E81L is not to be confused with EL81. Fooled me too some years back.

E81L:

 

[Conviction]

After some thinking I've come to the conclusion that I'll just buy a couple of 19" 3RU panels and mount them individually. The mains transformers will be housed in Mu-metal enclosures I've salvaged. XLR's on the fronts. Perhaps I'll lash up a simple faceplate. Originally I had the idea of mounting a 1mA DC meter and a switch to make use of the measurement sockets.

I have a second pair with Unitran input transformers. Same ratio, but a lot bigger. Unitran was the go-to before JS took over completely.