USA home build 1

1935

Condition and performance:

	Cabinet	90%
	Reception AM	90%
	Sound Quality AM	70%

Features:

	P.U. Entrance:	Yes
	Tape Recorder Entrance:	No
	Extra Loudspeaker Output:	No
	Loudness:	No
	Treble Control:	No
	Bass Control:	No
	Tone Register Switches:	No
	AM Bandwidth Switch or Control:	No
	Tuning Indicator:	No
	Build-in Antenna:	No
	Build in Ferrite or Window Antenna:	No

Technical Specifications (Partially measured):

	Tubes:	6A7, 78, 77, 43, 25Z5.
	Wave Bands:	LW, MW.
	Intermediate Frequency (IF):	135 kHz
	Loudspeaker:	Philips AD 2500 (Not original).
	Resonance Frequency Fs:	?
	Frequency Range Power Amplifier:	?
	RMS Output Power at 5 Ohms:	?
	Cabinet:	Massive wood, brown lacquered.
	Dimensions:	37 x 22 x 16.5 cm
	Mains Power Voltages:	115 Volts~
	Mains Power Consumption	?
	Retail Price	?

Description:

This radio is one of the first super hetero-dyne receiver. The main difference with the current receivers is, there is no Automatic Gain Control, but the gain has to be adjusted by had. The manual gain control act also as a volume control. Now you can easily notice the differences of the strength of the broadcast signals.
The AM detection is the grid detection which is common in the early thirties. One of the dis-advantages of grid detection is the audio distortion when setting the audio to a low value.
The LW/MW switch is placed at the back side.

Repairs:

The power cable is also a resistance cable and is rotten. It makes also a short cut. The internal 150 resistance wire is also open.
Solution: Power cable is renewed and a resistor of 150 Ohms 17 Watt is placed under the chassis for the heater supply.
Several resistors and capacitors are renewed.
Reason: Resistors are increased in value and capacitors measured electrical leakage.
Output transformer is defective. An output transformer with a primary impedance of 5600 Ohms is placed.

The electronic circuits around the 77 and 43 tubes are rebuild, regarding to the datasheets of the 77 and 43 tubes.
For safety reasons and to prevent to plug in the curent 230V~ main power, an US power plug is fitted.

Performance:

After repairing, the performance of this very old radio is very good. The AM reception is very well and the sound quality is also quite well, due to the high Q-load of the AD 2500 loudspeaker, which results in a pretty full type of sound.

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