Reela Baroud

[condense]

Hello
Sorry I am still a relative beginner - this is my 4th repair. I am fortunate to have got my hands on this set but am struggling to match it to the schematic. I have only got a schematic for a Bernaud 54 and I suspect mine may be slightly earlier. That said they appear very similar (same valve lineup).

I am confused as the set appears to have more electrolytics than it should (assuming I have identified them correctly )

Does anyone know if electrolytics were used instead of non electrolytics and whether that makes a difference in terms of replacements.
In the photo the large red capacitor (in the blue circle) has a value of 5000 cm (by my maths equivalent to 5000 pF) has positive and negative markings at each end. It is these markings which have made me think it must be an electrolytic. There are 4 further caps with the same markings so if they are all electrolytic it would mean I had 8 in the set altogether.
The schematic I have indicates that there should only be 5.

Anyone have any ideas? I would be very grateful for any input

[condense]

Sorry this should say Reela Baroud

(It does now - Mod.)

[Mr 1936]

Hi Condense

As you say, about 5000 pF. Anything under about 1 microfarad is unlikely to be an electrolytic, and 5000 pF extremely unlikely. Sometimes non-electrolytics have a polarity marking, where the negative end or a marking of "OF" indicates the outside foil. By making this the grounded side the screening is (slightly) enhanced. This is rarely critical.

You should be able to trace where the capacitor fits in the circuit and deduce its function from that.

[condense]

Thank you
I have attached a schematic which I think was done by an enthusiast. The blue circled ones are clearly electrolytic but the symbols on the 2 red circled ones indicate they are electrolytics too. This seems unlikely given the values.
I really appreciate the help as a beginner to this and would appreciate it if anyone could advise if an electrolytic is needed in these positions?
Thank you for any help you can give me

[ms660]

The ones circled in red won't be electrolyitcs, the 50nF triode anode de-coupler is, I suspect, an error, would expect something much much less, 500pF maybe.

Lawrence.

[condense]

Thank you
I really appreciate your help

[Herald1360]

Attached clearer circuit.

It's an "interesting" design- it seems to be live chassis almost for the hell of it! Mains transformer with auto primary and heater secondary, half wave rectification, HT- resistor for output stage bias enables ECL80 cathode to be grounded and contact potential bias for ECL80 triode.

The 2.2M decoupled by the suspect 50nF looks like negative feedback of a sort, maybe it's a drawing error or perhaps it's an empirical solution to ECL80 instability?

[Mr 1936]

Hi again condense

That is a rather strangely drawn schematic and hard to read. I think there might be some errors, so don't rely on it completely. Getting values wrong by a factor of ten, or decimal points in the wrong place can happen all too easily. The electrolytic symbol has been used wrongly for non-electrolytics.

Why not trace out your own circuit ? It's not too difficult. The valveholder pins are numbered 1 to 9 clockwise, looking from underneath and starting after the gap. Resistor colours are read in the sequence body, tip, spot.

The ECL80 is a combined audio amplifier triode and output pentode. It's slightly unusual in that although the two parts are separate entities within a common envelope (the triode is the smaller upper bit when you look at it) the two cathodes are connected together internally to Pin 3. This has a bearing on the rest of the circuit design.

It looks like the designer has chosen to connect the cathode to the chassis, which means they then needed to generate a source of negative bias for the grid 1 of the pentode. This is done by the decoupled resistor at bottom left. All the HT current drawn by the radio flows from the chassis back to mains neutral upwards through this resistor, so the voltage at its upper end is negative relative to chassis. This negative bias (something like -8 volts) is fed to the pentode grid 1 of the ECL80 (Pin 9) via the high value resistor at bottom right. The audio from the triode anode of the ECL80 (Pin 1) is also coupled to this grid by a capacitor which is drawn so small that it's hard to see. I can't read the value but I would expect something around 10 nF (0.01 uF). This capacitor must have low leakage, so it's best to replace it with a modern one.

The pentode anode of the ECL80 (Pin 6) is fed back to its grid by a high value resistor, decoupled to chassis by the 50 nF capacitor circled in red I can only think that this is tone correcting feedback or to damp out instability The value of 50 nF is far too high to be believed, as it will shunt nearly all audio frequencies to ground.

The pentode anode of the ECL80 (Pin 6) goes to the output transformer primary, and is decoupled to chassis by the 5000 pF capacitor also circled in red. This is probably a "tone corrector" which reduces excessive treble. 5000 pF is a believable value for this. The peak voltage here is quite high, so if you replace it, ideally use something rated at 1000 volts.

Considering that the ECL80 was introduced in 1950, some of the passive components look like ones from a much earlier era. Maybe they were using up surplus stock ?

Hope this helps you. Mr 1936.

[condense]

Thank you for your comprehensive replies. It is an odd set up and I think there are some errors on the schematic. Fortunately there aren’t many caps in the set. Generally the values are on the caps too so I am going based on what I can see rather than the schematic.
I was perplexed by the chassis arrangement and so wanted to double check about the electrolytics so feel reassured now - thank you.

I will post an update once I’ve recapped it. There’s a lot of work to do on the outside too but I think it will look lovely when done

[condense]

I have now replaced all of the usual suspect capacitors and the set is working nicely. I thought it may be helpful (should anyone get the same set) to add a list of the ones that I replaced and the conversion from "CM" to farads - it seemed to make sense to go slightly lower on most which I wouldn't usually do. I didn't get as far as drawing the circuit out although it probably would have been a good one to do it on as it was fairly simple. There's no tone control but the radio sounds pretty good - I was pleasantly surprised given the small size.
CM Quantity Conversion
5,000 2 0.0047uF
50,000 2 0.047uF
500 3 470pF
Electrolytic (50uF x2) 2 47uF
Electrolytic 25uF 1 25uF
20,000 1 0.02uF

I also touched up the paintwork rather than giving it a full respray - it has a gold paint effect over a cream colour and I decided on reflection to maintain its original.