The model number has been erased but it uses 57, 58, 47 and 80 valves and an autodyne frequency converter. I have got the set going quite well except it won't tune above about 1200 kHz. I have tried everything like rf and if alignment, replaced all relevant components, torn my hair out but no dice. I am hoping there are some in the club who have struck this problem

The last Autodyne I worked on with that front end was an EMMCO. Did you purchance score a circuit? I reverse engineered the one I had.

The dial probably finishes at 1500 kHz.. Do make sure the valves 57 & 58 are in the right holes. They are pin interchangeable but the sharp cut off pentode (57) is normally the converter.

Some times the coils wander. There is also the risk of coils changing value, or the valve being weak. Low voltage is not to be overlooked.

We can only speculate without a circuit.. Did you check the cathode resistor of the converter (If fitted).

I would be looking at the oscillator circuit. The EMMCO Oscillator coil is in the cathode & plate circuit..

Marc

Does the circuit look similar to this:
Image Link

The 12AU6 is a sharp cutoff tube, and there's no AVC applied to it. And uses an IF transformer with a tap on the primary, not sure why they needed that. Usually this circuit gets used in radios without an IF amp section, and they assume the user justs tunes in one strong local station and then adjusts the volume. Often found on cheap clock radios.

The circuit for the EMMCO as I drew it ,and I think I managed to get the errors out of, as it was wired wrong when I got it.: Appears in Silicon Chip page 91August 2009.

It may be similar up front? Most sets followed roughly the same plot with minor deviations.

We had not established that it was an EMMCO AC5 at the time of writing.

Marc

Sorry for my late reply. Its definitely an Airzone. A circuit I have found in Silicon Chip 20/7/2002 covering Airzone
models 500/505/515 is pretty close to what I've got.
I have pretty well checked every component including the cathode resistor. I would like to measure the actual autodyne frequency but my counter is not up to it in this circuit. Btw, the dial is a vertical drum with no frequency calibration, just horizontal lines

The major hassle that can happen with equipment of the modern era is its likely inability to withstand the B+ of a valve radio.

This however, does not stop its use as HV blocking capacitors can be used. Due to the impedance an capacitive effects the counter would throw the oscillator off frequency.

Many of the drums were 0 - 100. at that age, the highest frequency would likey be 1500 kHz. and the IF frequency could be below 455 kHz.

The frequency counter will not calibrate or read correctly if Modulated frequncy is inputted.

Marc

Ok Marc. My counter (home built) has an internal fault in that readout leds are not lit - I will attend to it at some future time. I tried using the counter function in a couple of DMMs I have but results were inconclusive. I have a No of 455kHz osc. coils and I intend to experiment with these in the autodyne ckt.
I think I have posted in the wrong category and I apologise for that.
Almer

Almer, don't worry about the incorrect forum. Sometimes general discussion ends up turning into tech talk.

The beauty about these forums is that some of the rules aren't as rigidly enforced as on other websites. The thread can be moved at a later stage though this elderly forum software doesn't allow me to do it from the site - I'll have to manipulate the database at some stage.

In the meantime the conversation can continue here.

I think using 455kHz coils may be unwise. you need to establish what the IF coil frequency is.

With Airzone in 1937 area, they were using 175 kHz with most of the battery sets and 456kHz with the rest.

Secondly the coil must match the tuning gang or you will not get correct bandspread or frequency.

The same rule applies to the DMM. Its manual may tell you its frequency range 40Hz to 40kHz is often possible. It is also not likely to be happy with modulated RFeither.

I would expect all paper caps to be replaced and resistors checked, is this so? Were any Mica caps touched?

It would be relavent to know what trimmers & slugs (if any) are available to make adjustments?

"Shotgunning" & changing things willy nilly have the potential to cause more problems, rather than sort out what may be something simple.

Marc

I do not make it clear I was talkiing about Osc. coils designed to work with a 455 kHz IF. After trying about 3 coils I found one, after getting the polarity of the feedback right, that works like a charm, giving full bc band coverage.
I don't have much idea what was wrong with the original osc coil but I don't really care. The customer will be happy though.

Why I was looking to see what was changed in the oscillator circuit, was to get an idea what was there that could upset things.

It has been reported by a few of the more technical people in our Radio Club and I have seen it; that due to the construction methods of some coils and the materials used to maintain their structural integrity failing. The coils can change physically, sufficiently to alter their characteristics substantially.

This may in this case be "due cause" and the customer satisfied, in the knowledge that it has all been put right.

Marc