Philips high-impedance speakers.

[telstar]

Hi. I have a Philips B2G25U radio, which was made when Philips made a decision to eliminate speaker transformers, and to use 800 ohm speaker coils. I do not think that these loudspeakers would last very long, and it would be a hard job obtaining replacements. I was thinking about converting it back to a conventional 3 ohm speaker & o/p transformer (or is it lack of chassis space/Philips design problems that would make this difficult or impractical ?
Does anyone else have one of these sets, and have thought about converting their B2G25U radio ?
Regards
Mike

[radiogammon]

Hi Mike,
This is certainly possible, but if the original speaker is working OK, why replace it? I have several Philips sets with high impedance speakers and they are all working fine. I have only ever had to replace one because of failure of the speech coil. As well as saving money, Philips also reckoned that eliminating the output transformer also gave better quality sound as this also eliminatated losses due to the transformer. It probably makes little difference to a set of this size and quality, but is more noticeable in their upmarket sets with large speakers.

[Paul Stenning]

I agree with John - if it's working don't worry about it. All the Philips high impedance speakers I have come across worked fine.

Make sure the output valve is not being over-run (by that cap being leaky) as the anode current goes through the speaker coil.

[telstar]

Hi Paul & John. Many thanks for your replies. I will try the Philips out and see if it functions at all.
Regards
Mike

[stephanie]

So, in case these speakers are burned out, or otherwise damaged beyond repair; has anyone subbed a normal op tranny plus standard speaker in one of these radios?

Would it just be a case of simply connecting the tranny primary across the original speaker connections and then connecting the speaker across the secondary? Or do you have to do circuit mods also?

[Steve_P]

What you need to do is convert it to a standard system. I've never done it, but I think it will go something like this:

1: Remove and discard 800 Ohm speaker.
2: Remove R1.
3: Remove 50uF cap, and fit a 32/32.
4 Link the output of the UY85 to the first of the two caps.
5.Link the Transformer Primary here.
6. Connect R1 between the two capacitors.
7. Link the rest of the set to the second capacitor.
8. Put your 8 Ohm speaker on the secondary of the output transformer.
9. CHECK YOUR WORK.

Then switch on and hope!

Cheers,

Steve P

[stephanie]

*jaw drops*

Ooohhh boy. Let's hope it's not fried.

[Studio263]

I've fitted an output transformer to these sets before with no difficulty, one from a hybrid TV suited fine and there was plenty of space to mount it. In my case the original loudspeaker was open circuit, which of course made the screen grid of the output valve glow orange!

I'd say the Philips design was a poor one. The standing anode current of the output valve will flow through the loudspeaker, heavily damping it's response, and de-polling the magnet if you get the connections reversed.

The loudspeaker voice coil also has to be wound with unusually fine wire, perhaps that's why mine failed. I've seen a Cossor version of this set with a conventional loudspeaker and and a transformer fitted from new, they must have got wise.

[Tim]

If your set is the one I think it is, it will employ a UCL82. I have found these valves(particularly in these small Philips sets) to go grid leak and pass excess anode current. The cathode resistor sometimes goes LOW in value too, or might have been replaced (indicating past problems--PCB leakage??) with a lower/different value. I find a 470 ohm works well.
(If it isn't the set I think it is, and consequently doesn't use a UCL82, ignore above)

[paulsherwin]

These are small platicky sets so it makes sense to underrun the output valve - nobody is ever going to listen above a few hundred mW. UCL82s are cheap and easy to find of course, but reducing the current drawn would protect the speaker too.

Paul

[Tim]

but reducing the current drawn would protect the speaker too.

Yes Paul,hence the 470 ohm, which is higher than the original value resistor, and will reduce the anode current of the valve, a point I didn't make clear in my previous reply.

[Paul Stenning]

Originally Posted by Studio263

The loudspeaker voice coil also has to be wound with unusually fine wire, perhaps that's why mine failed. I've seen a Cossor version of this set with a conventional loudspeaker and and a transformer fitted from new, they must have got wise.

Actually from the dates on the service info the ones with transformers came first and the ones with high impedance speakers directly as the anode load followed.

Comparing the two side by side, the high impedance speaker sets do sound better. Though that's probably because the transformers were made down to a price.