670 Complete

[cjenrick]

Latest:
Original input for the 670 might have been a UTC A26 tranny. Lucky me, I scored 2 on evilbay, hoping to sub them for A24 LA2A!

Might have located Mr. Neim Narma, engineer for the 670. If so, will try to get interview.


If anybody has the dimensions for the power transformer, I would be very interested. ADL also sells the 600 ohm attenuators and wafer switch. They are using pretty much the exact same circuit as original, comlete with the old school neg. bias supply.

[cjenrick]

Check this out!!!

Hello Chris,

I just received word back that, yes, Rein Narma designed the "Fairchild 670"
in 1952. He is one of the founders of "xxx", and has since semi-retired.
Mr. Narma is still on the Board of Directors, and stops in from time to
time. He stated that you may reach him at his AOL address as follows:

And this!!!

Hello Chris,

the Fairchild is the American development of the U13 captured by American
troops during WWII same time when they got some K4 tape machines....
I rewound some x-formers over the years, but have no replacement x-formers.
I have the U73 x-formers that s all...

Best

Oliver

[img]graemlins/beerchug.gif[/img]

[cjenrick]

If you have any questions you want me to ask Mr. Narma, please post them so I can ask a bunch at once. This way I don't have to bug him over and over.
Thanks,
CJ

[Learner]

Yes, I have a question or 2 if it is not too much to ask. [img]smile.gif[/img] [img]graemlins/wave.gif[/img]

Please ask Highness Narma, what is his thought on the factors/components/circuit design concept that contributes to the MAGIC sound of the infamous 670?

Also, if he was asked to design another tube compressor with the most contemporary/available parts what would be his approach and circuit layout be? ;) :D [img]smile.gif[/img]

[img]graemlins/peace.gif[/img]

[thermionic]

Be interested to know if the original 670 trafos have mu-cores??? Recently found out that "Gavs" Sowter was experimenting with mu-metal as far back as the late '20s..

Also; CJ, not sure if I've any more 670 info than you, but if you like I can send over the pages I have anyway in case there is a page or two you haven't seen.

[cjenrick]

Thermionic, I faxed PRR the users manual and he graciously scanned it and put it here:


See if you have any additional data, be glad to see it!
Will ask about mu-metal cores.

CJ Fairchild

[thermionic]

CJ, just checked the link, looks like there's not much I can send you in terms of the operating instructions / curves etc. I do have several schematics for the 670 though, original and redrawn, so if that's useful I'll send it over, but I imagine you probably have what you need schem-wise, say if you're missing a schematic block and I'll see if I have it.

[kpeek1]

I was looking at the schematics for the 670. I am lost about the number of 6386 tubes it uses.

Looking at a picture of the back of the 670 it has
eight 6386. Yet the schemtic shows eight triodes (four tubes).

Am I wrong in thinking the 6386 is a DUAL triode?

What am I missing?

Thanks

KEvin

[thermionic]

Kevin, go to this link:

http://www.recording.org/cgi-local/u...c;f=6;t=001221

The 6386 is a dual-triode and the 670 has four per channel, the above link will give you more info on the 6386 than is healthy to know! :D

[cjenrick]

I just got a ton of Fairchild stuff from RF. Thanks RF! 660, 666, 670. The 666 (watch out for that one!) apparently uses transistors in the control amp. Semi PRR like?