radiomuseum.org
Please click your language flag. Bitte Sprachflagge klicken.

SABA 446 WLK - Repair Help

Moderators:
Martin Renz Ernst Erb Vincent de Franco Martin Bösch Mark Hippenstiel Bernhard Nagel Otmar Jung Heribert Jung Eilert Menke 
 
Please click the blue info button to read more about this page.
Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » SABA 446 WLK - Repair Help
           
Roee Sulimarski
 
 
IL  Articles: 6
Schem.: 4
Pict.: 0
08.Aug.08 16:06

Count of Thanks: 14
Reply  |  You aren't logged in. (Guest)   1 Hi,
I am a new member at "Radio Museum" , and I need help repairing my new old Radio - SABA 446 WLK.
I downloaded the schematics from the web and checked the radio . the problem I have is that I am not able to receive any AM (Middle range) station which transmits at my area.
from the examination I did to the radio, it seems like the amplifier circuit which services the TT input works well,
but the receiver first stage doesn't respond at all. when I checked the voltages on one of the grids of the AK2 tube
I was measuring -12Volts (does it make any sense? where can such voltage come from?).

I would appreciate any help someone could give!!!

Thanks in advance,
Roee.
 
I attached the relevant schematics.

Attachments:

Martin Renz
Martin Renz
Officer
D  Articles: 694
Schem.: 262
Pict.: 349
12.Aug.08 08:12

Count of Thanks: 5
Reply  |  You aren't logged in. (Guest)   2
 
Hello Roee,
your question was about the -12 V at the Grid of AK2. Measure the Voltage at the 250 ohm resistance. You will find it there, caused of a current of 5mA. That is not the problem of your receiver.

In case your oscillator is running, it might be detuned. Its frequency will be far away from the 468/492 kHz .This can be caused by bad capacitors. Saba used silver micas during these years, that often are destroyed by corrosion of the silver plate. They look like this one:



You will find them here (the 220p ones):




If their capacity is to low or zero, you must change them with new silver micas of low tolerance. There might be more problems, like bad coil cores, which are difficult to repair.

Resistors like these are sometimes broken, you should check them.


Without equipment like a AM signal generator it will be difficult to repair this radio. You should check every part of the circuitry from the back.

Please note that I am no expert in this kind of repair. I repaired a Saba 452WK with success and I describe here my experience with this model.

Any other experts are welcome to help.

Martin Renz
Roee Sulimarski
 
 
IL  Articles: 6
Schem.: 4
Pict.: 0
14.Oct.08 20:33

Count of Thanks: 5
Reply  |  You aren't logged in. (Guest)   3

First of all THANK YOU VERY MUCH Martin!!!!
you helped me alot - thanks to your detailed answer I managed to fix the Radio Receiver.

Second - in the WLK 446 there is a mono phono input at the back of the radio.
I tried to connect one channel (L\R) of my Dual 1249 Turn-Table in order to listen to a vinyl record,
but the volume level at the speaker was very poor (almost hear nothing), although the volume control
switch  was at the highest level...
does someone can help me to solve it?

P.S.
when I hear A.M. Radio the volume at the speaker output is high enough.

Hans M. Knoll
Hans M. Knoll
Editor
D  Articles: 2127
Schem.: 159
Pict.: 102
14.Oct.08 21:31

Count of Thanks: 3
Reply  |  You aren't logged in. (Guest)   4
 

 

Hello Roee.
 
You need for this Radio, a  RIAA- Equalizer- Preamplifier like this or this
 
She must have a gain from  34 to 40 db  ( 50x to 100x amplification )
 
Or, a high level cartridge  "ceramic" like DUAL CDS 650 (Keramiksystem CDS650)
 
 
Regards Hans
 
 

This article was edited 15.Oct.08 11:00 by Hans M. Knoll .

Roee Sulimarski
 
 
IL  Articles: 6
Schem.: 4
Pict.: 0
18.Oct.08 20:05

Count of Thanks: 5
Reply  |  You aren't logged in. (Guest)   5
 

Thank you very much  Hans ,
I see that the one you recommanded on is an inside installation especially for dual,
http://dual.pytalhost.eu/tvv47/TVV47_08.jpg

thanks agagin,
Best Regards,
Roee.

Lars-G. Lundelin
 
 
FIN  Articles: 136
Schem.: 27
Pict.: 102
13.Feb.09 17:38

Count of Thanks: 4
Reply  |  You aren't logged in. (Guest)   6

Hi!

Regarding the SABA 446 WLK, I must tell my experiences after refurbishing the set.
 

When all apparent faults were out of the way, there were still problems, like Roees question about lack of , as he said, AM (MW) reception. Although it's not coming out wether he could receive HF (SW) or not. In my case the MW and LW was dead while the HF(SW) worked excellent. Measured the osc at the AK2 with no readings, meaning that its not running. One of my specialities (maybe it's someone else's too) is tapping on variable caps and this time it worked again, I found the culprit.
The two varicaps in the osc, one 250, the other 550 µF didn't work very well. You can reach them in front of the chassis, two modest looking screws. When I touched one of them with my finger, I heard a heavy crackling and then a hissing sound. The next touch silenced the set again (like Onslow's TV-set).
Did not dare open this capacitor, instead I sprayed KONTAKT PRF 6-68 into the cap while turning it back and forth several times with a screw driver.
Switched on the set after 10 minutes and I could hear the sweet hiss from the LS. 
When I looked at the schematics, I was a little bit confused about the different IF-frequencies (ZF).
There are: CH=ZF=485 kHz and ZF= 468 bzw. 492 kHz.
Found out that in this set the IF is 485 kHz, so I tuned it to the appropriate scale readings.
Next step was the antenna circuit (Vorkreis) and came to a reasonable sensitivity.
Must say that this SABA 446 WLK is one of the best homeradios I've ever heard. Especially the selectivity and the working bandwith facility is admirable.

Happy Valentine's day to All

Lars-G.  

 

  
rmXorg