Infrequent Sound [sex.tex] technology: Philips Philicorda type 22 gm 751/22T Orgue Electronique, 1966-1969, made in Germany

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Introduced around 1966 or '67, the GM751 was the successor to the AG-7500. Early versions of the 751 had tube preamps, and later ones were all-transistor. Has a switch underneath that turns the internal speakers of and on.

The Philicorda 751 (22GM751 with various country specific suffixes such as 22GM751/22 for Germany) was launched in 1967, some of them had both valves (preamp stage) and transistors, followed by the 22GM752, which was fully transistorized. A later model, the 22GM753, launched at the end of 1967, was designed for the stage and was fully transistorized.

Although Philicordas, from the AG7400 to the 22GM753, had slight differences in sound, the Philicorda's typical warm tone, produced using cold cathode tube oscillators, was consistent over the years.

AG7500 (original model released in 1963)

The most completely genuine tube-philicorda, using tube oscillators, preamps and amplification throughout. Neon-bulb dividers. The amp/speakers (AG7600) came in a separate rectangular wooden cabinet with a spring reverb unit contained in a plastic box under the case.

GM751 (released in 1966)

Re-design front panel, slightly larger case. The amp/speakers
are now mounted inside the organ case.
There were at least three different (sub-) versions of this model (though they were identical in appearance).
The first of these utilized tube oscillators, pre-amps & vibrato circuits and a mix of neon dividers and transistors for divide-down.
The biggest change came with the second version which except for the tube pre-amps/vibrato circuits used transistor oscillators and dividers
Finally the third and final version (introduced around 1968/69) was all-transistorized.

GM752 (unsure about the release date)

The GM752 was basically a fully transistorized 751 with 1-piece rocker switches instead of 2-piece push-buttons as used on earlier models.
Provided with an extra outlet for connection to an optional Philips rotating speaker cabinet.

GM 753 "portable" (re-marketed as the "Penncrest" by J.C. Penney in the US and "Porta-Belle" in Sweden), circa 1968.

A sleeker more portable version of the GM751 without the amp/speaker.
Similar tube-preamp as the early 751 (though some units appear to have used transistor amps), case covered in blue tolex.
2-tone control panel and a cover that goes over the keyboard
from the front, tiltable metal stand that looks like 2 upside-down
metal V's.

GM754 (the last version of the portable Philicorda, introduced in 1972/73)

Re-designed front panel (now slanting): 4 horizontal sliders in place of the usual knobs.
Slightly flatter wooden case w/ metal cheekblocks. This model uses IC dividers and therefore does not sound quite as warm and organic as the older models.