Philips B2G04U

I’m having an ongoing struggle with this set not helped by the fact that the only Service Sheet available seems to be for the B2G81U although they look very similar?

My current question relates to the Output Transformer as the Service Sheet shows the Primary as being 41 Ohms? Surely this is far too low for a set of this type and I’m assuming (hoping) that this is a misprint?

Ik heb een voortdurende strijd met deze set, wat niet wordt geholpen door het feit dat het enige beschikbare serviceblad voor de B2G81U lijkt te zijn, hoewel ze erg op elkaar lijken?

Mijn huidige vraag heeft betrekking op de uitgangstransformator, aangezien het serviceblad aangeeft dat de primaire 41 ohm is? Dit is toch veel te laag voor een set van dit type en ik ga ervan uit (hopend) dat dit een drukfout is?

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Hello to you too, Donald; Welcome to this forum,

The first service document I found states: 'Apart from presentation, the B2G04U is similar to the B2G81U'. So there's problem one solved.

As for the output transformer. In none of the service documents I found on line, I saw any mention of the primary impedance. Could you upload [see right when replying] a screenshot of the service document you have or possibly a photo [smaller than 1MB]?

Regards,

hans

--
raaf apenstaart multiweb punt nl

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Hi Donald,
41 Ohms is not the impedance but the dc resistance.
Philips often indicated the dc resistance of coils on their schematics.

--
Vriendelijke groeten,
Onno

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The 41 ohms measured on the primary of the output transformer is a dc measurement with a ohmmeter and not the impedance of the primary coil.

--
Cees PA1DBA

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Hello Donald,

Links to Service Information for the B2G04U and the B2G81U.

Philips B2G04U

Philips B2G81U

Unfortunately, the dc-resistance of the primary is not stated in them.

But looking at the voltage drop over the primary (215 - 205 = 10 V), the 41 Ohm in the information you have, cannot be correct. The current needed to drop 10 V over 41 Ohm would have to be: I = V / R = 10 / 41 = 244 mA, which is way too high.

I cannot read what the cathode voltage of the UCL82 in the schematic is. But when looking at the Philips datasheets for the UCL82 and the ECL82 I think it should be 16.5 V, giving a cathode current of 42 mA. The anode current will then be around 35 mA. The dc-resistance of the primary would then be around: R = V / I = 10 / 0.035 = 350 Ohm.

I noted on the UK Vintage Radio Forum that you measured the dc-resistance of the primary to be 320 Ohm. To me that seems close enough.

--
Groet,
Robert

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Correction:

10 / 0.035 = 286 Ohm (so my earlier 350 Ohm was wrong).

Still seems close enough to the measured 320 Ohm.

--
Groet,
Robert

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Thanks Robert - very helpful.

The schematic for the B2G81U that I have shows the Output Transformer Primary DC resistance as 41 Ohms and the Secondary as <1 Ohm.

[image]

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Checking my own set again I note that I have a UCL82 anode current of 26.4mA and a voltage drop across the Primary of 8.7V.

So with R = V / I = 8.7 / 0.0264 = 329.5 Ohms - what I am actually measuring as the DC Resistance across the Primary is 331 Ohms!

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Hi Donald

So with R = V / I = 8.7 / 0.0264 = 329.5 Ohms - what I am actually measuring as the DC Resistance across the Primary is 331 Ohms!

That's less then half a per cent and falls well within the margin of error of a good multi meter. So to all intents and purposes your measurement of the DC-resistance and your prediction are equal.

Succes, kind regards, EJ

--
We hebben allemaal twee levens. Het tweede begint als we ons realiseren dat we er maar één hebben.

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Given the voltages noted in the schematic on which I based my prior posts, the anode current you measured (26.4 mA) seems low to me.

That with Ohm's Law you derived the dc-resistance of the primary to be very close to your measured 331 Ohm by measuring the anode current, is not surprising.

What voltage do you measure on the "top side" of the primary (which according to the schematic I bases my earlier posts on is the same as the screen grid voltage of the UCL82)?

What is the cathode voltage of the UCL82? And is the value of the cathode resistor in your radio 390 Ohm, like in the schematic I based my prior posts on?

But probably more to the point: What problem are you trying to solve in your B2G04U?

--
Groet,
Robert

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Thanks Robert for your ongoing help and support.

On the UCL82 the grid screen voltage is 213V, the anode voltage is 204V while the cathode voltage is 16V.

I increased the value of the cathode resistor to 500 Ohms thinking that it would be kinder to the UCL82.

I had an O/C section on the Dropper (now bridged), a scorched cathode bias resistor (R20 390 Ohms) which fell apart (now replaced) and UY85 a cathode/heater short (valve replaced). Working my way systematically through this set but my main problem was that the radio seemed to operate ok through my Lamp limiter BUT when I switched to the Direct setting the audio faded quickly and I was getting a loud fizzy, buzzy noise as if the set is over-running in some way! I looked again at the circuit diagram at the way in which the valve heaters were wired up and noted that V1 (UCH81) was next in line. I checked all the valve pins of the UCH81 for shorts but nothing showed up but in the absence of a valve tester and on a hunch (sorry!) I replaced V1 and this has resolved the problem.

I still have issues with a very noisy volume control (may need disassembled) and a scratchy variable capacitor.

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If anyone has access to the schematic, I'm a bit confused as to why C28 spans the entire width of the set from point 27 just to terminate on the chassis? What would be wrong with simply connecting this cap with point 19 which is unused and on the negative rail, same as R21?

[image]

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