RCA High Fidelity SP 20 PPP 6V6 circa 1954 Live Test

RCA SP-20 Push-Pull Parallel 6V6 Mono Amplifier — Circa 1954 — Olson-Era Ultra-High Fidelity
Tested via direct iPad DAC streaming, Yamaha NS-10 Monitor
Ribbon Mic via Zoom H6

A single RCA SP-20 tube amplifier, one of the true early heavyweights of the high-fidelity era. Designed and released around 1954, this model represented RCA’s short but focused leap into home audio excellence. It was the high-powered sibling to the SP-10, building on its parafeed architecture but adding an extra pair of output tubes for more muscle. And it still carries that creamy industrial RCA blue finish that’s since become iconic — a visual echo of its broadcast pedigree.

The SP-20 was engineered at a pivotal moment, when RCA, fresh off its leadership in broadcast and recording technology, turned its attention briefly to the home audio frontier. As RCA took over the reins of audio development after Western Electric’s divestiture, this was their Chrysler HEMI moment — engineered for dominance, but not for luxury’s sake. Under the guidance of Harry Olson, this wasn’t a glamorized consumer product — it was designed to do a job, and do it really well.

The SP-20 was built to pair with RCA’s best available loudspeakers, including the LC-1A full-range coaxial and the 8”, 10”, and 12” SL series drivers -- so this amp is of that calibre and above! With nearly 20 watts of real-world output from its push-pull parallel 6V6 layout, it likely has enough headroom to drive both vintage and modern speakers — especially if you’re chasing that elusive combination of refined flatness, warmth and clean articulate midrange. It includes a simple adjustable input level control and an input sensitivity well suited for direct source or preamp use, depending on your setup (may need tweaking!).

And unlike later EL34 or 6550-based designs, the SP-20 leans into the clarity and control of the 6V6 — not brite, but not too soft, very refined and disciplined, with enough musicality to keep things engaging. It’s an amp that keeps your speakers in line and speaking the truth — flat, faithful, but also with enough tube lover's dynamics.



Condition:

This SP-20 is a nicely surviving example, and was in regular use by a careful audiophile friend before arriving here. The smooth RCA blue finish is largely intact, with a few minor oxidation spots in the crevices and two larger nicks at the rear top-right corner. Transformers show minor surface oxidation. The front RCA badge is in excellent shape.

The amp does not include a bottom cover, so plan accordingly. Output is via a vintage 4-pin socket — banana plugs fit temporarily for testing, but you’ll likely want to adapt or install proper binding posts. Input is handled by a standard RCA phono jack.

When tested with an NS-10 monitor, the amp fired right up and produced clean, tonally balanced sound. It performed beautifully straight off an iPad with direct signal, though when using a preamp, I found that input level adjustment was critical — easy to overdrive if not matched properly.

Several poly film coupling capacitors were installed by the prior owner, along with replacement of out-of-spec resistors. The tubes include:



(4) Matched vintage smoky glass 6V6
(1) Sylvania 12AU7
(2) Sylvania 6AU6
(1) Raytheon 5U4GB rectifier


Also included is a full photocopy of the original RCA manual and schematic, published in 1954.

In short, this amp appears to be plug-and-play for the experienced at this time — but as with all vintage gear, you should expect to provide ongoing attention, if not immediate repairs or adjustments, to suit your system and preferences.

Additional Notes:

I only have a single SP-20. If you already own one, this is your lucky break — a chance to build a matched pair. Otherwise, enjoy it in a dedicated mono system, where it will truly shine. I’ll be uploading a video soon — and if you like what you hear there, just imagine how good it will sound once it’s installed and singing in your system.


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