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| | Triode
Valves - Fewest Electrodes For Purest Sound.
The Triodes described on
this page are PX4, PP3/250, ACO44, 4XP, AC/P1, PX25, PP5/400, PA20, 2XP, ACO42,
2P.
Right from the first radiogram manufactured in
1929, to the last radiogram in 1952, triode valves were utilised by R.G.D.
There were exceptions, televisions did not feature triodes after WWII, and in
1939 the top of the range radiogram utilised tetrodes (though some lower in
the range still used triodes). But generally the triode valve was the output stage
of choice. Why? - the purest sound results from the least interference to
the signal being amplified, and the device that performs this function
beautifully is the triode valve.
R.G.D. usually incorporated triodes supplied
by Mazda, namely AC/P1, PA20, PP3/250, PP5/400. Other manufacturers
produced similar equivalent products that may be interchangeable, for example
PP3/250 may be substituted by PX4. Some triodes that may possibly be found
in an R.G.D. receiver are shown below.
![Image of early Osram PX4 balloon](rgd_t_px4earlyosr.jpg) ![Image of early PX4 showing logo and type number](rgd_t_px4earlylogo.jpg) ![Image of early PX4 showing sloping electrode structure](rgd_t_px4slopelect.jpg) ![Image of early Marconi PX4 balloon](rgd_t_px4earlymar.jpg)
Early Marconi PX4 original 1929 shape |
PX4 logo clearly visible rectangular
box |
Sloping electrode structure of early
PX4 |
Marconi branded early PX4 about 1929 |
![Image of shouldered PX4 chrome anode](rgd_t_px4shochrome.jpg) ![Image of shouldered PX4 dull anode and cooling fins](rgd_t_px4shofins.jpg) ![Image of straight sided PX4 dull ladder](rgd_t_px4strladder.jpg) ![Image of straight sided PX4 and cooling fins](rgd_t_px4strfins.jpg)
Shouldered PX4 from 1930s chrome anode |
Shouldered PX4 & fins to aid anode
cooling |
Straight sided PX4 with dull ladder
anode |
Straight sided PX4 & fins to aid
anode cool |
![Image of PP3/250 balloon](rgd_t_pp3250balloon.jpg) ![Image of PP3/250 1930s shape](rgd_t_pp3250should.jpg) ![Image of ACO44 1930s shape](rgd_t_aco44.jpg) ![Image of ACO44 Mullard branded but MOV](rgd_t_aco44mov.jpg)
Mazda PP3/250 early
balloon (PX4 equiv) |
Mazda PP3/250 later 1930s shape |
Mullard ACO44 from 1930s (PX4 equiv) |
Mullard ACO44 but made by MOV |
![Image of 4XP](rgd_t_4xp.jpg) ![Image of AC/P1](rgd_t_acp1.jpg) ![Image of PX25 balloon](rgd_t_px25balloon.jpg) ![Image of PX25 straight sided](rgd_t_px25straight.jpg)
Cossor 4XP from 1930s (PX4 equiv) |
Mazda AC/P1 triode from late 1920s |
PX25 balloon shape high power by MOV |
Later PX25 shape, £ coin as size
comparison |
![Image of PA20](rgd_t_pa20.jpg) ![Image of 2XP with paper label](rgd_t_2xp.jpg) ![Image of ACO42](rgd_t_aco42.jpg) ![Image of 2P](rgd_t_2p.jpg)
Mazda PA20 balloon shape 2v
heater |
Cossor 2XP early paper label 2v heater |
Mullard ACO42 1930s 2v heater |
Cossor 2P, lower power output 2v
heater |
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SITE.
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