Aristona SA2025A

1953

Condition and performance:

	Cabinet:	80%
	Reception AM:	90%
	Reception FM:	80%
	Sound Quality AM:	60%
	Sound Quality FM:	60%
	Sound Quality P.U.:	60%

Features:

	P.U. Entrance:	Yes
	Tape Recorder Entrance:	No
	Extra Loudspeaker Output:	Yes, 5 Ohms
	Loudness:	Yes, only on bass
	Treble Control:	Yes
	Bass Control:	Yes, switchable
	Tone Register Switches:	No
	AM Bandwidth Switch or Control:	No
	Tuning Indicator:	Yes, EM80
	Build-in Antenna:	Yes, FM and SW
	Build in Ferrite or Window Antenna:	Yes, LW and MW
	Separate AM/FM tuning:	Yes

Technical Specifications (Partially measured):

	Tubes:	ECC85, ECH81, EBF80, EF85, EABC80, EL84, EM80, EZ80.
	Wave Bands:	LW, MW, SW from 25 - 50 meters, FM from 87.5 - 100.5 MHz
	Intermediate Frequencies (IF):	452 kHz, 10.7 MHz
	Loudspeaker:	9768M
	Resonance Frequency Fs:	?
	Frequency Range Power Amplifier:	45 - 23,000 Hz (After modification).
	RMS Output Power at 5 Ohms:	3 Watts
	Cabinet:	Bake-lite, dark brown.
	Dimensions:	46 x 28 x 20.5 cm
	Mains Power Voltages:	110, 127, 145, 220, 245 Volts~
	Mains Power Consumption	65 Watts
	Retail Price	?

Description:

The Aristona is in fact a brother of the Philips BX433A. The main difference is the cabinet itself, dial scale and the addition of the EM80 tuning indicator.
It it is a mid class radio.

Repairs:

Because almost all the black paper/tar capacitors have leakage and/or are increased in value, they are all replaced by polyester film capacitors.
Most amplifiers have a limited frequency reange, especally at the highest frequencies, so the power amplifier is rebuild from scratch, as show as in the schematic diagram below.

The power amplifier is a universal type. The tone control is a passive high frequency tone control. (Treble).
The negative voltage feedback is done by R10 and R36. The extra C5 capacitor adds a bit in the Bass, which can be defeated by the Bass switch. Negative voltage feedback usually reduces the distortion and improves the amplifiers stability.
To improve the amplifiers stability more, a networks of R1, R2 and C64 is added to make the impedance load to the EL84 tube more flat. The highest frequencies sounds also better, more Hi-fi alike.
The decoupling capacitor at the cathode of the EL84 has left out to get current feedback and further improvement of the power amplifier stability.

After building up the power amplifier section, further repairs are also done.

Screen resistor R20 of 56K is replaced by 56K 3 Watts.
Reason: This resistor was increased in value, which lead in less reception sensitivity of the FM band.
Screen resistor R15 of 82K is replaced by 82K 3 Watts.
Reason: This resistor was also increased in value, which lead in less reception sensitivity of the AM and FM band.
Resistor R22 of 47K and capacitor C52 of 1000 pF are replaced.
Reason: Both components are increased in value, which lead then in lost of the high frequencies on FM audio.
AM IF, FM IF, AM HF and FM HF are re-aligned. regarding to the service manual.
Reason: Optimal reception sensitivity of the broadcast stations.

Performance after repair:

After repair, the reception of the broadcast station is good, but the sound quality is still too poor. Main reason is the loudspeaker itself, which gives distortion at the bass frequencies. Later I have to find out the resonance frequency and the stiffness of the spider or cone material.

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