My New Project?? - Collins Limiter

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cannikin

Well-known member
Joined
Feb 8, 2005
Messages
1,009
Location
Seattle Washington
Hey Guys
I had so much fun with the Gates Sta that I'm thinking of building this Collins Limiting Amplifier. How do I figure out the rating of the Power transformer for this puppy?

Collins356.jpg


Of Coarse if you guys have any suggestions for a different point to point project I should try first.. let me know. (the RCA BA6a is out of the questions Sowter Trannies are too expensive).
 
datasheets, but voltages really help in determining that. 40 or 50mA for each 6v6, 10 or so mA for the 6386, and I would not expect much at all for the 6al5 but I am not sure in an application like this, I would probably say 10mA. Then heaters, 0.3A for the 6al5, 0.35 for the 6386 and 0.45 for the 6V6s. So if I was doing this I would get something in the 150mA range with 2A on the heater and then build it and see how I did when it is all built and I can measure the current. Worst case is you are wrong and you have a power transformer to us for something else.

I would say build a SE amp first if this is your first point to point project, They really seem to pickup alot of noise from bad layout. My pushpull amp has been really forgiving in layout in comparison. Or maybe I have just gotten alot better at layout then I relise.

That new avatar is massive.

adam
 
why not a federal AM864?
the collins looks very much to the stalevel schematics.
the am864 is 2 6sk7gty 6sn7 6sq7 based input and output traffos are the same (600-10K) choke 15H (300ohms) .....
do a search for am864 on the forum...
keep us in touch
audioforge
 
i have a 356e that runs fine on a hammond 369ax. also found an old choke out of a 26u that works well along w the hammond. the 356e is very much like a 26u (but w/o the interstage trafo) so the psu on the 26u works w a 356e, and the 26u's psu is well documented . also, the manuals for the 356e or 212 console clearly state how to implement different release times. the 212 console manual is like a textbook of universal information such as summing, pads, stuff like that. very nice. copies of those docs are available online if you look around. i'd scan them for you but they are too big for my scanner. the console manual pages fold out to nearly 4' wide. in fact i've always wanted to have a hall runner rug embriodered w it's schematic. beautiful.
 
The Federal is a good choice if you're concerned about tube costs. It uses all cheap, easy-to-find tubes.

Frankly, from looking at the schematic, I thought it was kind of a mediocre circuit--until I paid Soundguy a visit one day and heard his AM864/U. I only listened to it on a full mix, but I liked what I heard. To date, I've never built a direct clone of anything, but I am considering doing one of these someday...
 
Dave,
I am still just in the collecting parts phase of the federal limiter, but I have decided using the Sowter 600/10K input transfromer and the Edcor 10K/600 for the output. Lacking a good vintage transformer that can take DC for the output I was thinking of turning the output into capacitor coupled instead of txn loaded. 6SN7 tubes can be had cheap and are plenty so adding a WCF to each output phase, after the voltage amp, might be a more economical alternative to expensive output transformers. It might help low end response as well. What do you think?
Tnx,
Tamas
 
The output is push-pull, the DC in the primary is balanced. There's no need for a gapped output transformer. The XSM10K/600 (which I believe you were going to use originally) would be fine. That particular transformer can tolerate a couple of mA of imbalance.
 
Could anyone help determining what sort of taper R8 (1K 1W) should be on the federal limiter? My guess is that it should be a rev log to increase limiting as one turns the current control pot clockwise, but I am likely to be wrong.

Thanks,
Tamas
 
here some more infos about the am 864 .seems also know as bc 730 before called am 864. adrianh began to scan the manual in april but no news from this date....

Amplifier, BC-730
JAN Type: BC-730
Nomenclature: Amplifier
NSN: 2C330
Weight: 25 Lbs
Power Input: 110/220 VAC 60 Hz 80 W
Power Output: 60 mW
Description: The BC-730, a Federal Telegraph model CA-421, is a cmpressor amplifier with a constant output. The frequency response is within 1 db from 100 to 4000 Hz. Inputs from -40 to -25 db at a noise level of 0 db are allowed a distortion of 10 average value at full gain - 40 db; for inputs of -60 to -35 db the gain is between 35 and 38 db. The gain varies inversely for inputs between -35 and -25 with the input level, giving an output level of 0 db constant within 1 db. The compression time is about 0.05 seconds and the release time is about 2 seconds.
Source: TM 11-487A, 20 Aug 50
Manufacturer: Federal telegraph
audioforge
 
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