The next project on the bench is this 1967 SA-39B Limiter.
The SA -39B Limiting Amplifier is the trusted guardian of the
audio signal in thousands of broadcast stations around the
world. The unique circuitry developed by Gates engineers
years ago and continually upgraded has been accepted as
the world standard. By positive and smooth prevention of
overmodulation with consistently louder audio signals, the
SA -39B provides better station coverage, (a 3 decibel in- crease in over-all average audio signal is equivalent to doubling power). Usually installed near the transmitter it is
an ideal replacement for older, slow acting limiters.
The very fast attack time, essentially instantaneous, is associated with six switch selectable release times. In this manner the engineer may adopt the mode of operation best suited
for him.
Although action is extremely fast, distortion remains low at
compression levels as high as 25 dB.
The SA -39B design provides separate input and output level
controls and wide scale 4" meter, calibrated in decibels of
compression, for direct reading.
SPECIFICATIONS
MODE: Monaural.
CONTROLS: Input and output level controls on front panel.
METER: Reads directly in decibels of limiting.
IMPEDANCES AND LEVELS: Input: 500/600, 150/250, 30/50 ohms.
Input Level: -20 dBm to +20 dBm, (adjustable).
Output: 500/600 ohms.
Output Level: +18 dBm, maximum (adjustable).
GAIN: Maximum 50 dB.
RESPONSE: -±11/2% or less 30-15,000 Hz up to 15 dB compression.
Only slightly higher up to 25 dB of compression.
NOISE: 65 dB or better below any adjustable output level.
LIMITER ACTION: Attack time, essentially instantaneous. Release time: six positions from 0.2 to 1.2 seconds.
SERVICING: Front panel drops down. Tubes in rear.
POWER: 117 volts, 50/60 Hz, 90 watts.
MECHANICAL: Size, 19" x 14" x 91/2" deep. Weight packed: 74 lbs. Domestic. 96 lbs., Export. Cubage 9 cu. ft. Finish: Two-tone beige gray
with escutcheons in black.
TUBES: Total eleven, seven types.
At this point it looks like a Recap and possible tube change...I see a burnt resistor but it does pass audio...
Comments
Nice!
Nice!
They had some much space in those years it seems.. What is it a
They had some much space in those years it seems.. What is it a 6U ? Could have been done in 2 (unless there's risk of overheating..) :)
Nice job ahead tho ! Curious of how it sounds (transparent or colored ? )
pcrecord, post: 464033, member: 46460 wrote: They had some much
Its 6 u, I actually have two in right now. Both units are slightly different. They are in for a overhaul and a few mods (Attack, threshold added and release moved to the front of the panel).
I am pretty sure you could do this in a 3 u without heat issues.
The sound so far is very coloured :). With the repairs it will likely still be coloured....
Thanks for the details.. sad that I'm the other side of Canada ;
Thanks for the details.. sad that I'm the other side of Canada ;)
You are just slightly more than half way ;)
You are just slightly more than half way ;)
Very cool!!!
Very cool!!!
Recapping is done in the first unit...waiting for tubes...
Recapping is done in the first unit...waiting for tubes...
Attached files

Are you using NOS tubes? (Not sure if thats even a relavant ques
Are you using NOS tubes? (Not sure if thats even a relavant question)
kmetal, post: 464049, member: 37533 wrote: Are you using NOS tub
many of those tubes aren't available new. 6X5, 6JS7's and the pair of 1612's for example.
Kurt is right, some are hard to find but I got some new and nos.
Kurt is right, some are hard to find but I got some new and nos. there is pretty good selection these days. I had to buy them from three different sources this time though...
Trying the new Caps...needs new tubes but starting to have some
Trying the new Caps...needs new tubes but starting to have some Mojo
Testing a new Threshold Control
Testing a new Threshold Control
Cool! Love the simplified control set. Rode sticker not so much
Cool! Love the simplified control set. Rode sticker not so much. This thing can generate some serious grit! Would have loved it for my old blues rock band.
Looking forward to hearing the final product.
I am not too happy about the sticker either, but it's not my uni
I am not too happy about the sticker either, but it's not my unit. The owner can do what he wants. Although it might have to disappear when I paint it.
Still waiting for the preamp tubes... but I have added the thres
Ready to go... added threshold, attack, release in the front...T
Ready to go... added threshold, attack, release in the front...TRS input and ot connections and three pronged grounded power cord....