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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.

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...

Attached files


Link555 Fri, 05/01/2020 - 07:30

pcrecord, post: 464033, member: 46460 wrote: 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 ? )

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....


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