Hi,

just found on last Friday in Te-laviv flea market, (wow, it's a rare item I think...) for about $60

a  Grand Prix 609 K Moderne radio.

Cosmeticaly it looks  good, one small knob is missing, and no speakers included...

All the tubes inside are original with  a B&O date sign: APR. 1963, and one ECL86 is BY Haltron

    Problems (for now)

1. The FM tuner not works - the local ocsilator not works, (it's not a tube problem)

has someone have an idea why not?

2. the IF stage was tested with 10.7MHZ signal generator, connected directly to the FM tuner out.

what is strange is that the FM gain of the IF chain looks very low, as the total FM noise is very low, and the audio tone

vary it's amplitude as the RF signal is increased , just like AM IF amplifier, I know that an IF stage for FM works at maximum gain so the

noise and audio must have apprx. the same amplitude, in FM receivers. I replaeced the IF tubes, no change.

any idea?

thanks... Aaron

Welcome to Beoworld !

What a nice find, congratulations !

Most FM problems are usually related to the ECC85 frontend tube which is
fairly short-lived compared to most other tubes.
It's not uncommon to see the original IF tubes still in good condition after 50+ years
whereas the frontend tube will have been replaced a couple of times.
A voltage check on the anodes will almost always reveal any problems in that area.
Apprx 200 Volts would be normal for both anodes.
Have you tried with a new tube ?

Martin

Martin,

Thanks for the fast reply, please note that I'm Ham radio too, and strated my hobby at the same date as the tubes in the B&o radio....I have very good experience with tubes,

note that the moment i saw the radio for sale I knew i'ts something good...

when i looked on the back I saw the tubes list, wow, it has 2 push pull amplifiers...

I was looking a long time to find good FM tube radio to put it in the living room...

you suggest that the ECC85 is suspect, I replaced the tube with E88CC that i have

a lot here. its still not works. I even tryed to see the local oscillator with my spectrum analyzer, with small antenna.  not working yet.

I see that you have the same radio, so when you rotate the dial knob on FM, do you hear the regular FM sound between stations? or the noise volume is very  quiet?

BTW, all the voltages are looks ok in the tuner unit.

The Grand Prix 609K from my restoration thread is now in Japan, entertaining customers
in a shop selling contemporary scandinavian design (mainly teak) furniture so
I'm afraid, I cannot just go and test things like that but I do seem to remember that it
was pretty quiet when tuning between stations. Actually, I would expect that from
a B&O top of the line receiver like this, not to put out loud noise if technically avoidable.

I never saw an E88CC in place of a ECC85 so I cannot advice on the replacement
but if the local oscillator does not run, you will normally hear some kind of noise
that alters in "pitch" or "content" as the dial is travelled but the Grand Prix will probably
suppress this noise, at least to a certain level so maybe that won't help the diagnosing.

I suppose, after the ECC85, the culprits could be bad contacts in the switch bank, a broken
coil wire somewhere in the local oscillator, cracked solder joint, bad tube socket contact or
a dead capacitor.
The ceramic capacitors, as used in tuner frontends like here, are generally very reliable but I
have seen some shorted or strong ohmic ones recently (ref. my other resto threads) so worth checking.

Is the -3.2 Volts on the second grid (osc. grid) OK ?
How about the AGC line ?

Martin

The E88CC was replaced  in my Balupunkt Sultan FM radio, that i restored few weeks ago.

I remember that the sensitivity of the radio was increased after changeing the original ECC85.

as noted , I didn't noticed any suspected  components yet.

I see that I need the manual...(any help?)

i will try later this evening to continue my work.

Regarding the FM noise, please note that low signal level station will be heard with low volume... if this is normal working of the FM radio.

Today, all FM radio's works with Hi gain IF with limiter, on the IF chain, that give constant audio level, not dependent on the level of the 

antenna signal, more or less...

Aarong:

Regarding the FM noise, please note that low signal level station will be heard with low volume... if this is normal working of the FM radio.

Does this mean, that you actually have a station albeit weak ?
If that is the case, check the AGC line and voltages around the IF amplifiers.

Martin

No the FM tuner is not working yet. the test was done by injecting 10.7MHz FM signal from RF generator to the output of the tuner.,

so all the IF link can be checked and calibrated again. this is my general work with old FM radio's.

OK, we're back at the local osc. then.
It's merely a handful of components or two, the ECC85 tube being the only
active part.

Martin

Thanks!!!  i opened the tuner cover. i'm testing the voltage on the tube, all looks ok.

this tuner is very very uncommon in it's circuit. the oscillator/mixer is the right tube and the left tube is the RF amp. (correct?)

few caps, around L102 and may be the Varicap of the AFC are suspects IMO.  (i will continue on th enext day)

Aarong:

this tuner is very very uncommon in it's circuit. the oscillator/mixer is the right tube and the left tube is the RF amp. (correct?)

Quite common circuits for a B&O, really.
The "tubes" in the schematics is actually one tube. The ECC85 is a double-triode and to ease the reading of the schematics,
it has been divided into its two parts, indicated by the incomplete circle "glass envelope".
But yes, the left part in the schematics is the tuned RF amp, the right part is the mixer/osc.
It's a hard working tube.

Martin

Hi Martin.

Some good news here...

I found the problem in the FM tuner.  it's a long story...

any way, I decided do disassemble the tuner from the radio, to make it easy to track the problem.

First,  please note that the schematic you sent me is not as my tuner ! there is some  variations.

Second, i found that one part of the variable capacitor have apprx. 47 ohm resistance to ground !!!

so when i looked with lupe inside the capacitor, I saw a very starnge fenommen inside the capacitor, that looks like a grass of metal hairs

that grew inside for about 50 years...

 this metal "grass" was grew inside the frame of the capacitor, and made a short to ground,

 that show 47 ohm between the ground and one stator of the capacitor, ! ! !

after a good cleaning with alcohool the variable capacitor is OK now !

I assemble back the capacitor, connected power to the tuner, and now It's WORKING !

later i will assemble back the tuner in the radio, I took a picture of the "short" in the capacitor before cleaning.

Well done !

I know the phenomenon, it's called tin whiskers. Never saw it in a tuning capacitor myself though, but
I can't see why it wouldn't happen.
Ultra thin hairs grow from tinned surfaces, sometimes seen as a single strand or two, other times as a close
woven carpet made of conducting metal strands.
The UK vintage radio forum did a larger research together with NASA on the subject and
NASA confirmed that it was indeed tin. It happens with silver, zinc and cadmium too in certain alloys.
It's a huge problem in certain germanium transistors (AF116/117 in particular) where the whiskers
grow from the inside surface of the metal housing, which is grounded in HF circuits, and eventually reaches
one or more junctions or leads inside the transistor, thereby disabling or even completely shorting the transistor.
The same thing happens regardless of the transistor being used or not. Even unused, old stock, devices can
have the fault. Tapping the transistor with a pencil or similar will sometimes see it burst into life but it won't last long.
In the Beomaster 900 models, a bracket holding an electrolytic capacitor is usually found completely
covered with tin whiskers.

More info and photos etc. on the subject
http://nepp.nasa.gov/whisker/photos/index.html

And of course, we would also like to see photos of your set.

Martin

Dillen:

I know the phenomenon, it's called tin whiskers. Never saw it in a tuning capacitor myself though, but
I can't see why it wouldn't happen.

In retrospect, I think that was the fault in my Dirigent!

Funny that it would appear all the sudden, but I believe the receiver sat on a shelf for at least a decade right before I got it, so perhaps moving it around finally collapsed the whiskers and caused the short...

Yes, of course, that would have been the cause !
Notes taken.

Martin

Hi Martin,

very intersting! see the picturs below...

btw,the pictures in nasa site are of the same type of capacitor as mine...

Exactly ! A school example of tin whiskers.
Not hard to imagine how wrong this can go electrically.

Worth cleaning off the whole capacitor, I think.
A vacuum cleaner and a brush, I suppose, could do it.

Nice photos BTW.

Martin

Great forum this! Great people.

I just spent yesterday evening with Aaron - a 2-hour drive from my place, and we had a great time at his workbench, doing some calibration together on vintage B&O equipment.

One meets the nicest people here, and it's great to have another very-capable fellow vintage B&O tech in Israel.

Menahem

After the visit of Menahem at my home i'd the opportunity to see inside the 3400.

I helped to do the  final tuning of the FM tuner.

Now let's go back to my 609K.

After recalibarting the FM tuner it's look very good. I replaced the ECC85 to E88CC and now i have 6db more gain.

The EF89 was changed to EF183. Now the FM receiver works very good.

Now the bad news...  the 2 pushpull audio output transformers of the ECL86 are one anode side disconnected inside...so only one tube

is working in each amplifier.... (why?)

I replaced one of the xfmrs with one from my junk box that was inside not working Sansui 220 receiver.

So, at last the 609K is working, one channel only. i decided to live it as is for now, as i don't need stereo amplifier for this radio.

70 ohm 10W resistor inserted in the main line, to reduce the voltage inside. our main is 235Vac, and this radio is 220Vac.

for the last 3 days I enjoy very much to listen to this old FM radio, the AFC works great! and the sound is very good! (with external speaker).

I'l post in the future  picturs and more data of the 609K.

Aaron

Aaron

Very strange that my BM3400 transformer also failed the same day!

Anyway, here is a link to Hammond who make output driver transformers for tube equipment (among many other types)

http://www.hammondmfg.com/5caud.htm

Perhaps there is a problem upstream of the transformers, which overstressed the windings....

Menahem