Grundig KS 715GB Radiogram

[Tedzed1]

Well time to make a start.

It works to a fashion, but with a slight mains hum that does not vary with the volume, the record deck controls stick so needs the old grease removing and new reapplying, but the cartridge seems ok.

No lock on stereo on FM, it tries to break in as you tune towards a station, but only for a split second, not even long enough to light the stereo indicator, I may struggle with this problem, unless someone knows the fix.

The old rectifier is an AEG B30 C350/250, could someone please tell me if this is a suitable replacement if required as I have one in stock?

http://uk.rs-online.com/web/p/bridge-rec...s/2278508/

The schematic is included below.

All advice or suggestions will be gratefully received.

[tiv48]

one of these should do for a replacment bridge rec
http://www.ebay.co.uk/itm/Diode-Bridge-R...upplies_ET&hash=item43b37fd920
for the hum check c47/c46.
clean all swiches can cause allsorts of problems.
for the decoder i have found problems with the small disk caps.
for good stereo realy need a good external aerial.
sound very nice so well worth the effort
rob t

[Tedzed1]

Thanks for the advice Rob, would it be worth changing C43 while I am at it.
I take it the replacement rectifier will work, just that it is a bit of overkill?

[Yorkie]

Thanks for the advice Rob, would it be worth changing C43 while I am at it.
I take it the replacement rectifier will work, just that it is a bit of overkill?

If it's a simple task to replace C43, why not? Like C46 & 47, it will have 100Hz on it from the bridge rectifier. However, it might be worth cheking the ESR and capacitance to see if they seem to be problematical or it's just random replacement based on supposition rather than diagnosis. That said, we know that electrolytic caps in transistoried equipment are physically small and over the years will dry out and develop a high ESR. That will often degrade the performance, but not necessarily stop equipment from working. If you do replace C43/46/47 and the hum persists, at least they're no longer suspect and the hum problem lies elsewhere.

As to the bridge rectifier, yes, it will work, but as you say Paul, it's overkill, as its rating is more than twenty times the WV and twenty times the current (given that the fuse rating is 315 mA).

Generally, the markings on high current bridge rectifiers show the current and voltage ratings, so for example, a 1502 is 15 Amps at 200 Voits, 2502 is 25A at 200V, 2506 is 25A at 600V and so on. Markings are a bit more obscure for lower volatge and current ratings.

If you've got a Maplin nearby, a KBPC1005 (60V 2A) Stock No AQ98G will only set you back 69p and might be a better bet. (But if it 'aint broke, don't fix it!).

Good luck with the restoration. (Very high component count, and lots of 'three-legged fuses'!)

[tiv48]

it is over kill but cheaper than maplins and you will have 19 spare ones.
i doubt the original is faulty .
i would lift one end of the 315ma fuse and see if the hum is still there.
if so the fault (hum) will be c46/c47 or high quasent current in one of the output stage
check, change the caps first i bet you will find blisters on the connection end .
rob t

[Tedzed1]

Thanks all for the suggestions so far, I will lift the fuse first rob, and see what happens, I actually went to Maplins yesterday
and brought replacements for C39, C43, C44, C45, C46, and C47, so I will try replacing a couple tomorrow.
There are only two makes between the six caps, three are FRAKO, and the other three are the dreaded WIMA.

[Tedzed1]

Well, all the above mentioned caps have been changed, which has eliminated the hum, and the record deck has be re-greased and is working as it should.

The problems that still remain is no stereo on FM, and the sound on the right channel is very distorted, until I change the voltage selector from 240V to 220V, which improves matters slightly, but still does not quite sound right, it seems to me there is a voltage drop somewhere, but not to sure where to look first?

[Steve_P]

I think there's a separate module on these for Stereo. There is, I think, a stereo light on the front, if there is, follow the wiring back.

If it's OK on AM and obviously the record deck, then if the rectifier isn't starting to go, then check the IF alignment on FM and if the module (Module 8 it's called I think) plugs in, remove and see if it works OK on Mono. Then clean the socket and pins carefully and put it back.

Never had this before. I'd look at mine, marked up Mandello, but it's in storage.

Cheers,

Steve P.

[Rolf Zetterberg]

Sorry,but it seems as if there is no stereo decoder in this set.It should normally be a 7-pin PCB in the middle below those three IF cans.Instead there's a small dummy PCB with only two components-a resistor and a capacitor.
Rolf