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ID = 13122
United States of America (USA)
Developer: RCA (RCA Victor Co. Inc.); New York (NY) 
Tube type:  Screen-grid Tetrode   RF/IF-Stage   Controlling (mu) 
Identical to UY235 = UY-235_Japan = PH235 = PU035 = 451_deForest = UY35 = T-51 = GY-235 = EY635 = C335 = ER235 = T-35 = RYB235 = C-51 = 235 = 35
Similar Tubes
Normally replaceable-slightly different:
  38035 ; ER551 ; UY-35B
Other class quality (otherwise equal):
Other base:
First year Jun.1931 -- Collector info (Sammler)
Successor Tubes NY235  

Base UY-Base, 5 Pins (USA, April 1927) (Codex=Ha) Top contact with a cap.
Was used by Radio/TV-reception etc.
Filament Vf 2.5 Volts / If 1.75 Ampere / Indirect / Specified voltage AC/DC

In 1929 begins the problem of cross modulation in the USA caused by strong signals of similar frequency and nonlinearities in the first stage. Stuart Ballantyne and Harold A. Snow (Boonton Research Corp.) found a first answer with the tube 551 later called 51 (Arcturus, Majestic, Raytheon May 1931) with "gradual cut-off" (vari-mu, gradual cut-off, GE experimented in 1919 in vain). Probably first publ. IRE paper December 1930. Soon after the 551 RCA came with the same tube called UY235 (235 later 35 and later joined as 35/51, in Japan UY-235). An article, June 1931 in "National Radio News" shows how necessary they were. In short: Trade show in Chicago in 1931 73% pentode and 94.5% variable-mu tubes. In the same year Philips brought the E445 and Cossor the 220VSG. This was a "super control feature for AVC" as Silver-Marshall stated for model 726. The problem: a great negative voltage is necessary and therefore a special AVC tube is involved for the RCA solution. See General Motors model 220 S-10B (1931). Philco used the Wheeler invention (released Oct. 1929) with its model 95 Screen Grid (1929) where a UY-227 triode works as a combination: detector and AVC diode.

Dimensions (WHD)
incl. pins / tip
x 123 x 45 mm / x 4.84 x 1.77 inch
Weight 48 g / 1.69 oz
Information source Taschenbuch zum Röhren-Codex 1948/49   
Tube Lore (II)   p. 27 - tube #35

UY235: Cunningham Radio Tubes Manual, 1932
Tonino Giagnacovo

s_225_g_27.gif UY235: W.Sprick: Austausch-Röhren-Lexikon 1947
Günther Stabe † 19.8.20

Just Qvigstad
UY235: Cunningham Radio Tubes Manual, 1932
Tonino Giagnacovo

Usage in Models 1= 1931?? ; 3= 1931? ; 30= 1931 ; 1= 1932? ; 5= 1932 ; 3= 1933?

Quantity of Models at with this tube (valve, valves, valvola, valvole, válvula, lampe):43

Collection of



Forum contributions about this tube
Threads: 1 | Posts: 1
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UY235 plate characteristics measured with a curve tracer
Tonino Giagnacovo

This is a plot of the plate characteristics of the "super-control" screen grid amplifier tube, measured with a Tektronix 577-177 curve tracer (577 is the display unit, 177 is the standard semiconductors test fixture).

As can be seen, negative-resistance section is clearly visible, when the plate voltage is between 20 and 70 volts, however, less than the 90 volts of the screen-grid voltage. 

This negative-resistance portion of the plate characteristic is used to realize a dynatron oscillator (refer to RCA patent #2067366). 

Graph was annotated with the curve tracer controls settings, as follows:

 - control grid step voltage: 2V per step
 - Y-axis: 2 mA per division
 - X-axis: 20V per division

UY-235 tetrode measured with a TEK177 curve tracer

Two external power supplies have been used to deliver power to the screen grid (90V) and the heater (2,5V).

It very important to adjust the current limiter into the screen grid, as in some conditions during the sweep, and when plate voltage is disabled, it is easy to exceed the maximum permissible power dissipation.

The following image shows the test setup:

The following graph is the same UY-235 connected as a triode, having the screen grid connected to the plate.







End of forum contributions about this tube

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