Is the Philips Type 310A IF filter superfluous?

[pentoad]

S26
Is this there to just to stop the IF signal reaching the aerial?

[AdrianH]

I would suggest the other way around to stop a 470KHz or 628 meters signal from the antenna getting directly to the IF stages.

Adrian

[ms660]

To stop signals at or near to the receivers IF frequency from getting through to the IF stage.

EDIT: Post crossed.

Lawrence

[pentoad]

Other radio designs do not seem to incorporate this feature

[ms660]

Originally Posted by pentoad

Other radio designs do not seem to incorporate this feature

Plenty of models did but some manufactures weren't so fussy.

Lawrence.

[Sideband]

I think it also depends on IF frequency. There is an IF filter fitted to my 1938 Philips 470A. The IF on that is very low at 120Khz and the filter is to prevent 2nd channel images on SW.

[mister valve]

I have heard that before the "Copenhagen Plan" of 1950, there were some CW & other transmissions that operated at various frequencies between the LW & MW broadcast bands, which included the 450kHz - 480kHz, which is where most later AM radio's have their I.F. frequencies. Any powerful broadcast within that range of frequencies would go straight through the the I.F. stages and to the 2nd detector. It could also desensitise the set due to the A.V.C. action. So an "I.F. Trap" was often incorporated in the Aerial circuit, and tuned to the frequency of the receiver's I.F. amp. to reject any frequency at or near the receivers I.F. frequency. Fortunately, it isn't necessary for I.F. Traps nowadays, but check that its resonant frequency hasn't drifted into the L.F. end of the Medium Wave Band (or the H.F. end of the Longwave Band).

There are generally two types of I.F. Traps used, a series tuned trap (an inductor and capacitor in series) which presents a low impedance at resonance, they are usually placed between the aerial input circuit and earth (chassis). Or a parallel tuned trap (with inductor and capacitor in parallel) which presents a high impedance at resonance, these would normally be put in series with the aerial input circuit.

[G6Tanuki]

There were indeed transmitters operating between the top end of LW and the bottom end of MW: they were generally navigation-beacons sending CW, intended for use by ships and aircraft.

It was not unusual, if using a really goos, high wire antenna, to hear morse-code in the background of the signals you wanted,

Probably the silliest choice of IF was the WWII-era R1155 aircraft receiver. It had an IF of 560KHz, and that was close enough to a Radio Telefis Eireann broadcasting transmitter on 566KHz from Athlone. When you're flying at 25,000 feet over England you were essentially line-of-sight to this rather powerfukl transmitter. "Athlone filters" had to be fitted o many R1155 receivers as a result.

[pentoad]

I have a problem adjusting the core: it slipped downwards. When I extracted it from the other side I noticed the tiny brass thread was covered in pink wax and quiet smooth. I removed the wax with a soldering iron but the brass thread does not engage with the inside of the coil former so it is free to move.
Not sure what to do about that.
I'm wondering if there wasn't any thread there in the first place and that the core is held in position by wax alone, it's the only coil adjusted from the underside.
The plastic tube it sits in appears to be smooth and unthreaded.

[mister valve]

Originally Posted by pentoad

I have a problem adjusting the core: it slipped downwards. When I extracted it from the other side I noticed the tiny brass thread was covered in pink wax and quiet smooth. I removed the wax with a soldering iron but the brass thread does not engage with the inside of the coil former so it is free to move.
Not sure what to do about that.
I'm wondering if there wasn't any thread there in the first place and that the core is held in position by wax alone, it's the only coil adjusted from the underside.
The plastic tube it sits in appears to be smooth and unthreaded.

If you cannot get the 'I.F. Trap' to tune to, and stay on the I.F. frequency, it may be simpler to just take it electrically out of circuit whilst physically leaving it in place for 'originality' reasons. I don't think there are any transmissions around 470kHz nowadays, so they are superfluous really.

[pentoad]

I did manage it, but it was a bit tricky as there is very little margin for error
I secured it with a little gob of candle wax and used a soldering iron on the threaded portion, it soaked inwards by capillary action so it is reasonably secure.