In a fit of nostalgia, I started bidding on eBay for a Philips 115B, and also put out a request for a schematic of same. GTC advised he had one for the 115, noting that the power amp was a 6V6GT. My bid was successful for the 115B, which arrived with an EL33 as the power amp. 115 schematic shows bias resistors as CT-200+25-Earth. My 115B has CT-75+25-Earth. I've followed a debate about 6V6GT being a direct replacement for EL33 (not evidently without changing grid bias). All valves in 115 schematic other than 5Y3GT show cathodes to Earth. I had a look at the schematic for a Philips 119 which has an EL33A as power amp, with CT-150+35-Earth. 115B power trannie (no secondary leads connected) is pushing out 257v AC per side of CT to plates of 5Y3GT.
Do I assume 115B had EL33 as original power amp, or was that a swap for the 6V6GT at some stage? Work has been done beforehand - badly - under the chassis.

I think you may have a Mullard 1107 chassis, which has the EL33 and also the 75+25 ohm bias resistors.

There were A, B and C variants. According to the notes, B differed from A as regards dial glass and tuning gang, and C differed from B as regards on/off switch separated from tone control.

I'll email you the 1107A/B/C schematic and notes.

GTC
How did you work that out? I am impressed. Where do you get knowledge like that. A lifetime in the industry?

Once you mentioned EL33 and 5Y3 I trawled my schematic indexes. Mullard and Philips were partners and it often pays to check both brands in these situations.

Given enough clues I can usually find things but when it comes to knowledge, what I don't know would fill a sizeable library.

When looking at the valves the absence of cathode resistors often indicates that th set is back biased. The Centre tap of the HT secondary will not go directly to earth.

EL33 requires -6V grid bias on a 250V rail, whearas 6V6 requires -12.5V. So while they are pin interchangeable, the bias on the control grid, will be wrong, as you suspected.

Marc

Marcc
Thanks for your input. Yes the Mullard 1107 schematic GTC provided to me shows -5.4 volts of bias on the EL33A listed for the power amp., and as GTC makes clear the Philips and Mullard companies were partners. GTC - That is valuable knowledge to a neophyte like me. I am now more confident to go ahead with restoring my 115B, which by the way was in shocking condition as the under chassis wiring was all perished rubber leads, which I am now replacing.
Another couple of questions - R18 on the schematic shows 10k ohms, but my multimeter shows it at 8500. I noticed one end looks a little "melted". I think I should replace it - your thoughts gentlemen. Last question - I am never going to use the pickup function, so is there a way to bypass a lot of the shielded connecting wires, and still have a working radio. Okay it's not kosher restoration, but I'm not in the selling game here.

Re R18, if you devalue 10K by 15% you get 8.5K. If you can see the tolerance band on R18 it may be 20%, so you'd still be within spec, however if it's 10% you're outside spec.

The melted bit probably indicates overheating. Given that it's shown in the schematic as a 1/2 watt resistor, it's not expecting to have to do a lot of work, so something's probably not right upstream or downstream of it, and shorting capacitors would be my first guess.

Alternatively, 1/2 watt may have been too small for the job and a 1 watt resistor may be more appropriate. But look for shorted/low resistance caps first.

Re the shielded wiring, I wouldn't bother touching it unless I found it shorting out internally. I had to make a similar pick-up wiring decision with my Airzone where the rubber insulation was falling off. The Airzone's shielded stuff has very heavy duty outer shield, which I suspect you have too, so it doesn't move easily.

However, if you want to "decommission" the pick-up, simply unsolder the inner wire at one or both both ends and then either cut it or insulate it.

My Airzone switched 240 volts to an octal socket for the turntable. I removed that feature completely for safety's sake.