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Old 29th Apr 2022, 11:57 am   #1
Osvaldo LW1DSE
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Default Becker Brescia autoradio with seeking station.

I am in process of re-restoring this vintage autorradio made in Germany about 1960. It performs 9 pin tubes of the E series but one, the RF amplifier EC92: ECH81 mixer & oscillator, EBF89 IF & detector, EABC80 audio and carrier detector, ECC85 relay driver and EL84 audio output.
The rectifier is a Greatz bridge with selenium diodes in a block.

It has permeability tuning mechanism and a spring driven brass gear made to search stations according to 3 selectable strenght field in the front by a switch. Also 3 fixed tone settings: normal, bassy and trebbly.

Only MW AM, no SW or FM.

The power unit uses a 115Hz vibrator that hadto be opened and cleaned, the contacts was good.

This set has several years with me: it was gifted to me by Félix LU5DBX and was used few time.

It is 12V by nature. Several capacitors was replaced by newer units using Siemens pieces trying to maintan german parts as I can. Also some brazilian parts as substitute.

The gear was cleaned with solvent and oiled as it was solidified and dirty.
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Old 29th Apr 2022, 12:24 pm   #2
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Default Re: Becker Brescia autoradio with seeking station.

The seeking function is called pressing the bar under the dial.
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Old 29th Apr 2022, 8:55 pm   #3
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Default Re: Becker Brescia autoradio with seeking station.

I am surprised that the audio output valve is an EL84.

Car radio designers often used low current (heater and anode) pentodes to reduce the load on the vibrator and battery.
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Old 30th Apr 2022, 11:57 am   #4
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Default Re: Becker Brescia autoradio with seeking station.

Yeah. I have a 45 sec video of the pet doing its job but I don't know how to upload it here, if possible.

Googling for it I found a guy selling a sister of mine close to one thousand dollars.

Yesterday I replace 'lytics with newer units and the EC92 triode is now a EF94 RF pentode.
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Old 30th Apr 2022, 12:08 pm   #5
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Default Re: Becker Brescia autoradio with seeking station.

Note the newer 10mF @ 50V Siemens cap close to the vibrator, giving more clearace from it for better ventilation and aspect.
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Old 30th Apr 2022, 7:36 pm   #6
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Default Re: Becker Brescia autoradio with seeking station.

I have a Blaupunkt 'Koln' car radio in my collection. It has a somewhat similar valve line-up, including an EL84 for the audio output (this is in a seprate box along with the vibrator power supply).

This set also has seek tuning, the difference being it is activated by pressing the tuning knob. And it has one other facility, it covers the FM band from 87 to 100 MHz.
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Old 1st May 2022, 4:50 pm   #7
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Default Re: Becker Brescia autoradio with seeking station.

Ok. Yes, in my pet the output stage is inside the vibrator power supply: EL84, matching transformer and coulpling network to EABC80's triode plate. The cathode biasing net of the EL84 doesn't return to ground directly but though secondary of the OT giving some few dB of negative feedback. The secondary has a tap, perhaps to accept 4 or 8 ohms speakers. The entire secondary is used to perform NFB. As a comment, there are two unused holes of the size of two new absent sockets. So, I suppose that it can accept another EL84 and (perhaps) a phase splitter to make a pushpull stage.

Can anyone say me how to upload a video of say, 30 sec showing my pet performing?

Many thanks in advance.
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Last edited by Osvaldo LW1DSE; 1st May 2022 at 4:58 pm.
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Old 7th May 2022, 1:11 pm   #8
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Default Re: Becker Brescia autoradio with seeking station.

I completed and finished the restoration. I added another 10mF @50V cap to form a pi filter with the internal inductor (original) and cooperates to reduce ripple in the vibrator circuit. Also, the cathode bypass is replaced by a newer unit 4.7mF @ 25V all from the Siemens trade to maintain german heritage.
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Old 7th May 2022, 1:21 pm   #9
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Default Re: Becker Brescia autoradio with seeking station.

Here it is depicted the addition of an extensible antenna and the vibrator waveform viewed in the primary side. It appears good as I could learn reading the Mallory manual and an OAK page: https://www.cool386.com/msp/msp.html.
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Old 11th May 2022, 8:54 pm   #10
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Default Re: Becker Brescia autoradio with seeking station.

The restoring lavour is finished and the pet now has its new and own site at home.
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Old 13th May 2022, 5:23 am   #11
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Default Re: Becker Brescia autoradio with seeking station.

Hi all!
My experience with these radios, my brother had a Becker-Mexico is that they much better perform, if the vibrator will be swapped by 2 Darlington-transistors.
Old vibrators are not only noisy.....

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Old 15th May 2022, 6:42 pm   #12
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Default Re: Becker Brescia autoradio with seeking station.

I shall never do such a sacrilege. Mechanical vibrator is performing very well and I have another one to replace in case of catastrophic failure. I read some articles in the web who says that a properly designed trafo and with wright value of buffer capacitor, a vibrator can perform over 30 years with no fault.
A clean contact may have some milliohms of resistance whilst a bjt loss a volt across its emiter collector joint, much higher than a vibrator. So I wonder which advantage are you talking about.
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Old 15th May 2022, 9:46 pm   #13
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Default Re: Becker Brescia autoradio with seeking station.

A CMOS oscillator, divider to give an equal mark space ratio (important to avoid transformer saturation) and a couple of low Rds power FETs is the way to go.

Mechanical vibrators are not reliable or quiet, but it's easy enough to make plug in alternatives.

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Old 16th May 2022, 11:57 am   #14
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Default Re: Becker Brescia autoradio with seeking station.

May be. But keep in mind that I don't want nor need to replace the mechanic vibrator as it is performing ok. And I have one more forvreplacement.
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