I managed to pick this radio up and wandering if anyone could assist with a schematic?

http://www.ebay.com.au/itm/280943583509ssPageName=STRK:MEWNX:IT&_trksid.

I have seen it in John Stokes's book (More Golden Age of Radio) as model 715 so may be very similar.

Regards
Angelo

Is it an Aussie or Kiwi Philips?

Not sure Monochrome. I think it may be Kiwi. Is there a site for kiwi philips radio schematics?

Kevinchant's site doesn't list it.

If it is a Kiwi Philips it may have NZ stations marked on the dial: 1YA, 2YA, 3YA, 1ZB etc. I have never had much luck obtaining Kiwi circuits in the past. You could try contacting the New Zealand Vintage Radio Society, http://www.nzvrs.pl.net/ Or perhaps a Kiwi member of this forum may be able to help you.

I am not able to 'blow up' the image on Ebay enough to maintain enough clarity to see the dial markings. What I do know is that seller has been offloading a lot of Atwater Kents and Philcos, which at the time were very common in New Zealand.

On the dial it looks like the inner circle says New Zealand, the middle circle, Australia and the outer circle Kilocycles. Though it is a bit hard to see. There is an ARTS&P sticker on one of the I.F. cans with the letter D ( I cant offhand recall which year D represents) New Zealand radios also had ARTS&P stickers on them and some did have Australian stations marked on the dial. One givaway that suggests it could be from New Zealand is the 8μF filter can cap. It is a TCC brand which are made in England. I'm sure an Aussie set from that era would of had a locally made filter can cap. Please correct if I'm wrong.

D = 1937.

Australia made lots of condensers at the time and for many years thereafter. Brands included Wetless, Chanex, AWA and Ducon. None are probably made here now though Atco and Plessey were still making them here in the 1990's mainly for industrial applications.

Steve Savell emailed me to say that it will be based on the 6500, 6501 series of Aussie Philips Radioplayers. I will see when I pick it up.

I think some of those tubes will be very difficult to locate if they are problematic. Always have difficulties trying to locate those European tubes.

If it like the 6500 schematic then the tube line up is EZ3, AK2, AF3, ABC1 and AL2.

Not many of those easily found on Ebay.

Also had a quick look at the schematic for the 6500 on Kevinchant:

http://www.kevinchant.com/uploads/7/1/0/8/7108231/6500.pdf.

it has a wierd voltage divider which I haven't seen before. Seriously large wirewound resistor that looks like it has a couple of taps in it - the material on it says that "all biasing voltages are obtained from a resistor (R10) wired in series with the negative high-tension return lead. This resistor is wound as part of te main voltage divider (R2) and is provided with a clip for adjustment of the mixer, I.F. and A.F. bias..." Looking at the photo, that is one big wirewound resistor.

Anyone have any experience with that sort of set up before? Any tips will be appreciated.

Regards
Angelo

Tonight I've been doing a bit of research on Philips NZ. There was this link from the NZVRS website: http://www.radio-restoration.com/Philips.html.

And I'm with Steve Savell - that Angelos 716 P is based on the 6500/6501.

Those wire wound voltage dividers were common in 1930's radios. Fingers crossed that yours is still intact.

That wierd resistor is the "Back bias", which sets the bias on the grids and 'yes' they do fail. If it is intact measure it's resistances for future reference.

Being back biased the chassis is positive relative to the centre tap. Make sure that the filter caps are not connected directly to chassis or it will "hum". The CT is the most negative point of the HT.

Marc

Thanks guys. If the voltage divider is open can you replace with individual wirewound resistors in series?

From my research, wirewound resistors 'tend to be' more stable and sturdy than carbon comp resistors.

What sort of power rating would those resistors be? They look massive? Must be a fair bit of current running through them.

If it does follow the 6500/6500 that looks like the trickiest part of the circuit.

I agree Marc, the notes to the 6500 circuit remind people to ensure that the two filter caps are insulated.

Never understood why some use that sort of configuration and others attach the negative end of the filter cap to the chassis. Is one method considered to give better performance over the other?

Regards
Angelo

One really needs to see the circuit. It might just list the resistances.

The Backbias carries all of the current from the valves and the bias voltage is developed, in acordance with V= IR. The wattage is the square of the current multiplied by resistance (Catch 22... you have to know them)

Beware: There may be two resistors not interconnected on the same former. That is a trap.
One may be the screen divider the other back bias, or the earthy end of the screen divider is one & the connection to CT is somewhere towards one end and not the end: It will got to chassis.

Summary: Look very carefully here, one slip up can cause major hair pulling.

One of the rough methods I have used in the absence of proper information, is to measure the length of a non open section (the longer the better... they can open at the clamp from corrosion) then measure the resistance of the length of good wire. That will give you ohms per millimetre & you can guestimate the resistance between pins.

Do clear all other items & mark (photo) from the resistor before measuring. Sometimes you can be lucky & get the resistances either side of the break. Zip ties & shrink tube hold wire groups together.

I have also stripped one of those of wire & used its terminals like a telephone pole.

Marc

Wirewound resistors are usually available in 5, 10 and 20 watt ratings from Jaycar or Altronics. If using them remember that they can throw off a fair bit of heat.

One must, as a generalisation, be careful with back bias resistors. "Heavying them up" can have dire concequences. If they are of a marginal value, and there is an overload such as a heater cathode short. They become fusistors and self destruct.

Far better them doing that than frying a transformer, or rectifier.

Fortunately if this is the same circuit as 6500? 6500 has voltages on tube elements listed. Note this is with a meter of 1000 opv and a digital may read higher.

The back bias section of the resitor (R10) is in toto 300 ohms. The grid of the output tube is on the CT which is -24V from the chassis which means 80mA is going through R10 when the set is working properly. That is 1.92 Watts call 2W.

From that, to get 3V the tapping would be 37.5 ohm from the earth (chassis) end.

240 + 22 = 262 for one half then perhaps a 39R would get you close. EVATCO have some 2 & 3 watt resitors which would keep the physical size down, if they have those values? Some one else might also. 5 watt should be easy (Jaycar)

Use this as a guide & see what values you can extrapolate from the resistor

Marc