When my grandmother died I got the grundig rf150.
It's a Bookshelf radio from I think the 1960's. My grandmother used it as long as I can remember (the new sony mini set was never used haha).
I replaced some lightbulbs and repaird the buttons (you could only set it to FM with a bit of tape haha). And well it looks nice.
The only thing is that when I play it I think the bass is cracky and sloppy, the only way of solving this is putting the tone potentionmeter at 75 Procent or higher to ''high''.
It plays like this for at least 10 years (as long as I can remember), so I was asking if it is just the nowadays music on this little thing or is there something wrong?
Playing music from the 60's gives way better results..
What I've done:
-used an external speaker, works for a little bit, but bass still is a bit sloppy/cracking
-Used an aternative source than FM radio
-Made a video (you can't hear it very well but i think you can hear what I mean, it's recorded from a radio station.
https://www.youtube.com/watch?v=-G_xL9ZW-aQ
-Dc offset on speaker terminal with grundig on tape: around the 60mV
What i've Noticed
-If i put it off it is really suddenly of, it's not playing for a second or 2(bad caps?)
-If bass kicks in you can see it a bit in the lights..
-If you set the tone pot to ''75 procent high or higher it's gone and playing old music is also good.
It's a Bookshelf radio from I think the 1960's. My grandmother used it as long as I can remember (the new sony mini set was never used haha).
I replaced some lightbulbs and repaird the buttons (you could only set it to FM with a bit of tape haha). And well it looks nice.
The only thing is that when I play it I think the bass is cracky and sloppy, the only way of solving this is putting the tone potentionmeter at 75 Procent or higher to ''high''.
It plays like this for at least 10 years (as long as I can remember), so I was asking if it is just the nowadays music on this little thing or is there something wrong?
Playing music from the 60's gives way better results..
What I've done:
-used an external speaker, works for a little bit, but bass still is a bit sloppy/cracking
-Used an aternative source than FM radio
-Made a video (you can't hear it very well but i think you can hear what I mean, it's recorded from a radio station.
https://www.youtube.com/watch?v=-G_xL9ZW-aQ
-Dc offset on speaker terminal with grundig on tape: around the 60mV
What i've Noticed
-If i put it off it is really suddenly of, it's not playing for a second or 2(bad caps?)
-If bass kicks in you can see it a bit in the lights..
-If you set the tone pot to ''75 procent high or higher it's gone and playing old music is also good.
With a radio of that age I would certainly change all the electrolytic caps and possibly the PIO caps too. (They are the ones that look like they are made out of waxed paper.)
clean all contacts (switches,potentiometers,fuses,.......).
the electrolytic caps probably are dried out/weak.......substitute theese step by step.
have a look at the speaker,because there could be some dust on it inside.
i have a few old radios (telefunken,loewe,...) - now in a working condition.
the electrolytic caps probably are dried out/weak.......substitute theese step by step.
have a look at the speaker,because there could be some dust on it inside.
i have a few old radios (telefunken,loewe,...) - now in a working condition.
It is a nice radio for what it is!
Here is a service manual for the radio: Grundig RF150 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
The audio amp output is AC coupled, so DC offset measurement is meaningless.
The audio output is not especially powerful, it uses AC187/188 transistors, those are Ge complementer transistors used in portable radios in the '60s. Interestingly, all the other transistors are Si.
Just enjoy it!
Peter
Here is a service manual for the radio: Grundig RF150 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
The audio amp output is AC coupled, so DC offset measurement is meaningless.
The audio output is not especially powerful, it uses AC187/188 transistors, those are Ge complementer transistors used in portable radios in the '60s. Interestingly, all the other transistors are Si.
Just enjoy it!
Peter
The DC offset is likely due to the driving stage
being bootstraped using the output capacitor ,
hence the driver DC current run through the speaker.
This to save the cost of a resistor and a capacitor.
being bootstraped using the output capacitor ,
hence the driver DC current run through the speaker.
This to save the cost of a resistor and a capacitor.
Yeah, ~15 mA into maybe 4 ohms at DC gives ~60 mV.
Anyway...
These old Grundig sets tend to be quite reliable, but obviously this one is about 45 years old now and may appreciate a complete overhaul.
The rectifier is a B30C300, for example, which is likely to be one of those pesky selenium types known for their unreliability. A modern silicon one in DIL/DIP package can replace it (e.g. Fairchild DFxxM).
Electrolytic caps were not exactly generously-sized at the time. C35, for example, is a 25V type seeing 20.5 V nominal, which with a less lossy silicon rectifier and today's higher mains voltage is likely to be even higher. If you can fit a nice new 680µ-1000µ 35 V, use that. Actually you could/should probably replace all the electrolytics (step by step, as suggested). Use quality ones, and they should last another 45 years.
Paper caps were no longer used at that time. This unit uses film (polyester), ceramic disc and styrofoam caps, all of which tend to be quite stable.
BTW, there is a ceramic disc cap in the loudness circuit, C29 (1n2). Maybe they could not find a film cap with this value at the time (it still isn't easy today), and who knows, maybe it even uses an X class dielectric at least.
Check all those old carbon film resistors for correct value, especially in the power amp and power supply sections. They tend to creep up as they age, large values and those that get warm more severely so. You can use nice new metal film resistors, 1/4 W and 1/2 W, the blue cheapies will do fine.
I would swap all the noise-relevant resistors in the power amp, which would be the input series resistor R38, emitter resistor R44 and those in the feedback in particular (R45-R53, especially R46/47/51). R39/41 and R56 should be checked.
The switch array may appreciate a good cleaning.
Finally, touching up the alignment on the radio section would probably be worthwile, but unfortunately this tends to require special tools (e.g. for adjusting the cores) and equipment (like a sweep generator).
hmm, thanks for all the reactions, I will see and think about it.
The only thing I am asking myself for a long time. There are more typs of capacitors (electrolyte,PIO) etc
Do you Always need to replace them for the same type, or just for the same value (so it doesn't matter if electroylite or Film?)
and are there types that you can't buy new anymore?
The only thing I am asking myself for a long time. There are more typs of capacitors (electrolyte,PIO) etc
Do you Always need to replace them for the same type, or just for the same value (so it doesn't matter if electroylite or Film?)
and are there types that you can't buy new anymore?
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Basically, before replacing any cap, you need to know about its function in the circuit and the resulting requirements. Often the capacity and voltage handling required (along with available space) will also narrow down choices considerably. You just aren't going to see a 1000 µF 35 V cap as anything else than an electrolytic.
You do not have to replace all the caps anyway. Film capacitors, for example, tend to be quite stable unless mistreated. They very rarely fail in signal-related tasks or as power supply bypass. Same goes for ceramics.
In a restoration job, you can generally focus on the kind of things that commonly need attention: Electrolytics (best replaced by quality new ones), selenium rectifiers, switch contacts and varicap contact brushes, scratchy pots, suspect-looking solder joints, previous botched repair jobs (if any), burnt-out lamps, cosmetics. Trimpots may also be oxidized and should be checked for correct function. Also inspect fuseholders for corrosion. If the mains cable still is a thin single-insulated job with two distinctly visible cores, replace it by a modern double-insulated one (you can buy these with a Europlug molded on).
Grundig generally used speakers with paper surrounds, which are quite durable. The speaker would need inspection if it still sounds bad after the electronics have been worked on.
You do not have to replace all the caps anyway. Film capacitors, for example, tend to be quite stable unless mistreated. They very rarely fail in signal-related tasks or as power supply bypass. Same goes for ceramics.
In a restoration job, you can generally focus on the kind of things that commonly need attention: Electrolytics (best replaced by quality new ones), selenium rectifiers, switch contacts and varicap contact brushes, scratchy pots, suspect-looking solder joints, previous botched repair jobs (if any), burnt-out lamps, cosmetics. Trimpots may also be oxidized and should be checked for correct function. Also inspect fuseholders for corrosion. If the mains cable still is a thin single-insulated job with two distinctly visible cores, replace it by a modern double-insulated one (you can buy these with a Europlug molded on).
Grundig generally used speakers with paper surrounds, which are quite durable. The speaker would need inspection if it still sounds bad after the electronics have been worked on.
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