Bill Putnam's first compressor design — the all-tube 175B that paved the way for the LA-2A and 1176. A limiter built on a 6386 tube and the foundation of the Universal Audio sound. Rare, coveted, and historically essential.
The Universal Audio 175B was Bill Putnam's first commercially produced limiter. Designed in 1961 at his United Recording facility, the 175B used a 6386 dual-triode tube for gain reduction and an all-tube signal path. It became the standard vocal limiter at United Western and was the direct ancestor of the Teletronix LA-2A — Putnam licensed the LA-2A design after acquiring Teletronix in 1965. Today the 175B is one of the rarest Putnam designs, with surviving units trading hands at $8,000 to $15,000.
The 6386 dual-triode is the heart of the 175B. Variable-gain triode topology — slow, smooth, musical compression with built-in tube harmonic content.
Input transformer, tube gain stage, tube gain reduction, tube output. No solid-state in the audio chain.
Direct ancestor of the LA-2A. Bill Putnam's design philosophy of 'musical compression that you do not hear' starts here.
Universal Audio 175B — Bill Putnam's original tube compressor. The grandfather of every UA compressor since.
From the original release through current production. Each version has its own character.
First production run. Two-rack-unit chassis. Now extremely rare — fewer than 200 estimated to survive.
Updated revision with circuit refinements. Most common surviving variant. Still very rare.
Universal Audio's UAD plugin emulation of the 175B. Closest you can get to the original sound without owning the hardware.
A short list of rooms and records that put the UA 175B on the map.
Bill Putnam's original room. The 175B was the standard vocal limiter on Sinatra, Nat King Cole, and Beach Boys sessions.
Allen Sides preserved the United Western philosophy at Ocean Way. Original 175B units still in regular rotation.
Capitol's mastering and tracking rooms used 175B units on vocals throughout the 1960s. A few originals remain in service.
Vintage King has placed the UA 175B in more rooms than nearly any dealer in the world. Here is what we tell engineers when they call.
Buying decisions get easier when you can hear the difference yourself. Talk to a consultant before you commit.
The 175B is one of those design pieces — you can feel Bill Putnam working out the ideas that became the LA-2A. Slow, gentle, musical compression that flatters anything you put through it.
Use case · price range · what we recommend.
Vintage 175B, professionally restored by the Tech Shop. Tube replacement, recap, transformer service. Best for collectors and historic-sound rooms.
Universal Audio's official emulation. The closest you can get to the original sound at a working-engineer price.
If you cannot find a 175B, the LA-2A is the design that grew out of it. More common, more affordable, similar philosophy.
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