Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Sat 24, 2020 5:10 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 8 posts ] 
Author Message
 Post subject: Loewe Bella Opta 3710W
PostPosted: Jan Sat 04, 2020 3:51 pm 
Member

Joined: Nov Tue 12, 2019 3:24 am
Posts: 31
I recently bought a Loewe Bella Opta 3710W tube radio.

The dial tuner cord was bad, but with some good advice from posts in this forum and on YouTube I managed to replace and rewire that.

Then it turned out that the variable air capacitor was totally stuck. After soaking the axis with WD40 for several days, and finally warning up the axis with my soldering iron, the gunk loosened. It is now working smoothly.

The FM band (UW) is working very, very well. Nice clear signal across the wave lengths. However, on the MW and LW bands there is only static and hum. (some occasional "crackle spike" noise at some frequencies, but no channel reception)

I have a schematic, but I am new to this, so I need some help on where to start looking for the problem. Any help is appreciated


Attachments:
File comment: Schematic
Loewe-Opta_Bella_3710W.pdf [381.77 KiB]
Downloaded 36 times
Top
 Profile  
 
 Post subject: Re: Loewe Bella Opta 3710W
PostPosted: Jan Sun 05, 2020 12:53 am 
Member
User avatar

Joined: Nov Fri 10, 2006 12:24 am
Posts: 2799
Location: Thornhill, Ontario, Canada
Raspberry wrote:
I recently bought a Loewe Bella Opta 3710W tube radio... The FM band (UW) is working very, very well... However, on the MW and LW bands there is only static and hum. (some occasional "crackle spike" noise at some frequencies, but no channel reception)... Any help is appreciated
I don't know the model, but if it has piano key switches they may be the problem. Another possibility is that the AM oscillator has stopped working, e.g. AM tuning cap plates shorting, failed component around the ECH81. Of course, another component in the AM RF section may have failed, although that is shared by the FM (If amplifier), so should be OK. My bet is switches or the ECH81 circuit.
Hope this helps...
Cheers,
Roger
PS Just remembered... I repaired a Loewe-Opta "Kobald 5700" a few years ago... a small AM-FM tabletop. Problem was the piano key on/off switch (not coil switching.) I could not repair the switch, so I by-passed it and added an in-line on/off switch to the mains cable. Of course, not your problem!

_________________
Roger Jones,
Thornhill, Ontario
Ontario Vintage Radio Assoc. http://www.ovra.ca


Top
 Profile  
 
 Post subject: Re: Loewe Bella Opta 3710W
PostPosted: Jan Sun 05, 2020 2:15 am 
Member
User avatar

Joined: Jan Tue 31, 2012 1:55 am
Posts: 14309
Location: Mountains of Mourne. Ireland.
Image
Replace all the Electrolytic capacitors as a first step.
Some of the old μF (microfard) values are no longer common... so choose the next nearest capacitance value, up or down.

Examples: 47μF and 33μF are some of today's common values.

The Voltage rating of an electrolytic capacitor is how much juice it can handle.
This can be increased.

Electrolytics are polarized - with negative and positive leads. Mark the negative side in/on the chassis or circuit-board with a Sharpie before removing.

Replace components, one at a time. lol

A handy capacitor conversion chart, can be found via this link...
http://www.antiqueradios.com/forums/vie ... 9#p2920449

------------

Your filter/smoothing capacitor C65 and C66 is a dual (multi-section) Electrolytic capacitor (can - canister)...
containing Two 50μF rated at 350V ←Working Voltage.
Disregard the second (test or forming voltage) rating - - it's not too common for it to be mentioned!

You can gut it and restuff it with regular Electrolytics, or you can connect the new ones underneath (inside the chassis). After disconnecting the leads to the old one.

See... Removing and restuffing/rebuilding capacitor cans...
viewtopic.php?p=3108287#p3108287

------------

Other Electrolytics that I can see are...
C63 50μF
C53 50μF
there may be more, you will have to eyeball them.

------------

Moving forward...
the wax and paper capacitors should also be replaced.
Also, check resistors by measuring in circuit - - if you get a strange reading, lift/unsolder one leg and measure again. Close enough, is good enough.

German/European capacitors...
Question: which ones to replace?
viewtopic.php?p=3123758#p3123758

------------

Ask more questions... :)
and... post some photos if you are unsure about anything.

Posting photos to a forum thread.
viewtopic.php?f=2&t=365653


Greg.
oh... 8) good video tutorials...
viewtopic.php?p=3128591#p3128591


Top
 Profile  
 
 Post subject: Re: Loewe Bella Opta 3710W
PostPosted: Jan Sun 05, 2020 3:42 am 
Member
User avatar

Joined: Jan Tue 31, 2012 1:55 am
Posts: 14309
Location: Mountains of Mourne. Ireland.
Find the pinouts for your tubes on-line, and... transfer their pin numbers onto your schematic.

You will now be able to identify/follow their pathways into the circuit, and the components that are connected to them.
Image
Bottom view of sockets - - when viewed from below.

Grid numbers and pin numbers are different.

Other abbreviations for tube radio diagrams/schematics.
F filament
H heater
P plate (anode)
K cathode
G grid
S shell (metal)

NC no connection (iV and IC on European diagrams)
Hct heater, center tap

Greg.


Top
 Profile  
 
 Post subject: Re: Loewe Bella Opta 3710W
PostPosted: Jan Sat 25, 2020 2:13 am 
Member

Joined: Nov Tue 12, 2019 3:24 am
Posts: 31
Thanks for the advice!

By eyeballing the paper capacitors, I think I might have found at least one bad one. I am attaching a picture. It looks as the marking is 0.05/250. Do I need to find a perfect match, or what are my options here?

Also, I found the pin out of EF89. But when I look at where the capacitor is located, it looks as it is not on the schematic? I attached a sketch of what i think it looks like. Could it be that this is a repair patch? The wires are read, and seem out of place. Any ideas? I can send more pics if needed.


Attachments:
Cap.JPG
Cap.JPG [ 84.49 KiB | Viewed 783 times ]
Opta.jpg
Opta.jpg [ 343.13 KiB | Viewed 783 times ]
Top
 Profile  
 
 Post subject: Re: Loewe Bella Opta 3710W
PostPosted: Jan Sun 26, 2020 5:41 am 
Member

Joined: Nov Tue 12, 2019 3:24 am
Posts: 31
I guess the capacitor I marked is really C44?


Top
 Profile  
 
 Post subject: Re: Loewe Bella Opta 3710W
PostPosted: Jan Sun 26, 2020 7:13 pm 
Member
User avatar

Joined: Nov Fri 10, 2006 12:24 am
Posts: 2799
Location: Thornhill, Ontario, Canada
Raspberry wrote:
I guess the capacitor I marked is really C44?
I may be missing something, but how did that cathode get negative to ground?
Cheers,
Roger

_________________
Roger Jones,
Thornhill, Ontario
Ontario Vintage Radio Assoc. http://www.ovra.ca


Top
 Profile  
 
 Post subject: Re: Loewe Bella Opta 3710W
PostPosted: Jan Mon 27, 2020 4:52 am 
Member

Joined: Nov Tue 12, 2019 3:24 am
Posts: 31
I found the attached pin out online. The capacitor in the photo seems to be connected to pins 3 and 1.


Attachments:
EF89.JPG
EF89.JPG [ 59.92 KiB | Viewed 657 times ]
Top
 Profile  
 
Post New Topic Post Reply  [ 8 posts ]  Moderator: sofaslug

All times are UTC [ DST ]


Who is online

Users browsing this forum: Google [Bot] and 27 guests



Search for:
Jump to:  


































-->


Privacy Policy :: Powered by phpBB