With the back off, I can see where the "Telefon" socket connects.
It sits directly across the speaker, soldered to the output transformer, which is
of B&O's own production, fitted to the bottom of the cabinet right behind
the speaker.
As mentioned above, this output transformer does not correspond to the
service manual, that suggests a Peerless CL4 but it will probably work fine.
So this connection allows for something like transmitting radio through the phone
or, maybe more likely, using the radios speaker as external monitor for phone
calls (hands-free ?).

Martin

Martin,

I doubt if the same dial lamp was used in the Master 39K and the Master deluxe 39K.

Not according to the following document.

I have no idea if Philips or Osram have a replacement.

I agree. It looks more like the Beolit 39 lamp.

Martin

Martin,

The speaker is plugged in behing the CY1 valve.

I asume the output transformer is located underneeth the plug.

I can see a small black object what looks line a transformer but to be a 100% sure,  I have to take out the chassis.

Rudy

Nice photo again.

Yes, there's exactly room for it right below decks under the plug/socket.
No need to dismount any further, I'm sure it's down there.
But thanks anyways, greatly appreciated !

Martin

Sockets are found in many other sets, even cheaper ones, but here the
leads are just soldered to the output transformer. As mentioned earlier, this set
does does not correspond to the service manual but bears no traces of being modified
so it may have been produced like this.
Well, that is, the socket is on the chassis, but it is not connected and of course
there's no plug either.
The connection from the radio "heart" pushbuttons mounted on the front panel consists
of a dial-lamp socket type connector on the side of the chassis (red arrow).

Martin

One more service sticker is found, taped to the IF can. Well, the tape seems to be
holding on merely out of old habit but it did its job nicely for 50 years and the
sticker is preserved.
It's again from the same repairshop and dated 18/8-1958
That's 52 years ago and I feel tempted to add a similar sticker of my own when done,
simply to add my 5 cents to the sets story.

Martin

Apparently, the pushbutton frame is also marked according to the model (see "Kø").

(I want to make some observations too )

Several valves in this set has a label near their socket, telling in handwriting
when (and by who) the valve was replaced.
Dates in 1956 and 1958 match the stickers at the back.
You don't find repairshops leaving info for the next repairer like this anymore.

Martin

The Master 39K came in two different chassis versions. They are very similar with
only a few components difference, mainly related to the fitting of a new output
valve, CL6 instead of CL4.
This set has the "late" chassis with a CL6 and other components corresponding to
what is referred to in the service manual as "Version II".

Martin

The chassis looks to be in superb condition.
There's not a lot obviously bad and most components look fine.

The majority of resistors used in this set are of the Vitrohm brand and they
are all cast in black plastic or bakelite with printed values.
One resistor, however, looks newer than the rest and is of a later type with the
well-known color-bands.
Its position, directly connected to the output valve, suggests that this resistor
was replaced along with the valve in the late 1950s as also suggested by the label on
the valves base. This corresponds nicely to the age of this resistor which would
have been a new component then.
Nothing to worry about and if it's still doing fine, I think, I will leave it here.
If not, I will try to find a correct old type to fit instead.

Martin

I'm as technical as a bag of crisps, but this thread is fascinating!

A beautiful radio and a glimpse back into the past.  Was the repairer in 1958 a distant relative Martin - he seems ultra-thorough too !!

Thanks for a brilliant thread.

Lee

Always great, these threads :)

To add to the 'confusion': mind the order of the pushbuttons on mine...

Martin, where your's has the telefon socket mine just has an empty hole (which seems to be original) and of course no transformer (seems to be fitted under the chassis).

The socket of the dial lamp seems also to be a voltage selector.

Unfortunately, the mains capacitor in mine seems to be replaced at some point in time...

Thanks guys. Your feedback is greatly appreciated !

Yes, the dial lamp doubles as a means of setting the working voltage. Or at least
switching between 110V and 220V.
Running on other voltages would require a lamp with different specs, which could
be ordered from B&O.
The missing filter/smoothing cap in ipauls Master 39K is of course a shame but
not a catastrophe. I suppose we can see this as part of this particular sets history,
defective components become replaced and it'll be alright.
Given a situation of complete restoration to original appearance, also inside, a
search for an original capacitor would have to be initiated. The old capacitor
was probably dead, just as it is in the set I have on the bench, but this type
of capacitor can usually be "re-stuffed" - more about that later.

Martin

A green capacitor near the rectifier valve looks a bit new as well. So does a
blue plastic sleeved electrolytic one mounted nearby.
I will let them both stay if they work and, judging by its type, at least the
green one will probably be fine.
Unfortunately, the same cannot be said about a capacitor right behind it, the one
wrapped in blue paper, a Janco component.
At one end the hard black wax or tar-like substance has been pressed outwards, forming a
huge blob. This is not good.

Martin

What's even worse is that this blue cap is the suppression capacitor. Sitting right
across the AC mains, it is in a very stressed position and the tiniest leakage
here will cause a heat build-up in the component which probably explains why
one end has started to bulge outwards. Its not uncommon to find the suppression
cap blown to pieces due to it's own failure. In most cases the set will
still work, just without the noise suppression but if the cap shorts hard, the fuse
will blow or something will start to burn.
A Class X or X2 component is called for here, this will also be in thread with
modern safety regulations which most of the set isn't anyways.
Being a safety component, this is a capacitor that I will not try to hide but merely
leave it visible to any future repairer.
This photo show the old and the new capacitor.

Martin

A couple of wax-paper type capacitors are leaking wax. This is typical for this type
of component and in a set like this, these "waxies" are usually all leaky or all OK.
Almost never the latter.
Fitting wax-filled paper components in a set with high voltages and high temperatures
doesn't make much sense today and I like to replace them on sight.
One of them seems to have let go of one of its end caps. This cannot be good either.

Martin

Another oozing "waxy", at the lower right in this photo.
Easily a couple of hours work here. Wonderful !

Martin

Yes, this one has definitely passed its sell-by date.
Components like this makes visual fault-finding easy. 

Martin

Old and new.
For this set, I chose to use some of the best capacitors available.
The LCR polypropylene capacitors are a bit expensive but they are very reliable
and will practically last forever.
They come in a very suitable voltage range for valve sets and they are axial (one
lead out each end) so they will make "tidy" repairs when replacing the old axial ones.
They have nice long leads and are even yellow in color.
Unfortunately, they are not easily available in Denmark but Chris in the UK (Medogsfat),
as always, didn't hesitate to jump in and lend a helping hand.
Thanks Chris, your help is greatly appreciated ! 

Martin

Capacitors, capacitors - always capacitors...

I spend many hours of my life replacing capacitors, I've replaced thousands and
this set will definitely add a good handful or two to that count.

The first ones that normally spring to mind are the filter and reservoir capacitors.
These are high voltage components, very often found leaky and a faulty
filter and/or reservoir capacitor can physically explode, causing a
huge mess (and provide for an unpleasant surprise).

In this set, as in many others, the filter and reservoir capacitors are built
together as one combined component. Later sets use electrolytic capacitors, that is
capacitors with fluid content, but this set uses dry capacitors. That is capacitors
with non-fluid contents and for insulation between layers of metal foil the most
likely materials used are paper or wax or both.
Fluid dries out and the paper absorbs moisture. Hard to say which is best, they are
usually all bad after 50+ years and these are 70+ years old.
A quick ohm-meter test across the two caps showed apprx 100Kohm, slowly climbing,
on one cap section, which would be acceptable for a start, but no more than 13Kohm on
the other section, not climbing, which is definitely a no-go.

Good thing that the owner didn't just plug it in.
It could have caused havoc in there, taking out the rectifier valve and possibly
the filter resistors as a minimum.
The lack of a mains fuse doesn't help much (!).

The capacitance and ESR meters can stay in the drawer, this is simple fault-finding
and given ohm-readings like these there's no reason to spend more time measuring.
There's no way around it, these caps will have to be replaced.

A.H.Hunts Capacitors in England will be a well-known brand among vintage radio restorers
and most of their production were good quality components when new. The problem with
most of their caps, however, is that they typically don't seem to age very well.
Their cast plastic types (Mouldseal) tend to physically crack, even if left factory new
and unused in the drawer and their paper capacitors tend to leak and turn resistive.

The filter and reservoir capacitor(s) in the Master 39K is a Hunts dry type, physically
one large cardboard (or carton) box with a metal jacket, fitted to the top of the chassis.
The red arrow points to it here:

Martin

And a closer look from the side.
Note that it says "Dry electrolytic..." which actually is a contradiction.
Note also that the capacitor sits on a dark piece of fiber material to add
insulation between the capacitor and the grounded chassis.

Martin

Now, where do I buy a new capacitor like this ?
The short answer is: I don't.
I will have to empty the box of its old contents and fit new capacitors
inside to preserve the original chassis look.
This can be a huge task and is something I will normally only do if I can
allocate time for it and usually only in special sets.
I think this set deserves it so out with the box and let's see what we can do.

Two screws hold the large component to the chassis and three leads connect to the
filter resistors and chassis ground respectively.
The leads are of the cloth covered type, red color for the two positive leads that
go below decks and a short black one connects to a grounding tag just beside
the capacitor on top of the chassis.
The red leads are in surprisingly good condition so I will try to preserve these but
the black one is hard and makes a crumbling noise when touched so will have to
be replaced.

Martin

The metal bracket (or jacket) slides right off.

Martin