Murphy A40

[John10b]

Just for clarification was there a Murphy A40? The reason I ask I can only find information on the A40C and A40RG?
I’m reading the circuit of A40C and looking at the tone control circuit in the af stage, what are the actual marking for the switch s2 i.e. bass-treble etc? The picture of the Radio doesn’t show it. Many thanks.
Cheers
John

[Cobaltblue]

I think you would struggle to get those massive Chassis and Speaker into a table top set there's not a lot of spare room in the A40C.

My A40C is not easily accessible but it would probably be marked M N B or similar for Mellow Normal and Brilliant (or Bright)

Cheers

Mike T

[John10b]

Sorry chaps don’t know what you're on about?
I was asking for info, please see post#1.
Cheers
John

[Nickthedentist]

I think they mean that there was only a Console and RadioGram version of the set, and never a standard tabletop set (which I suppose would have simply been called the A40).

And hasn't Mike answered your Q re. the markings of the tone control?

Nick

[John10b]

Thanks Nick for the clarification and yes you're right, sorry Mike you did explain, need to get brain into gear.
Cheers
John

[Paul_RK]

The A40C doesn't have a tone control, just a bandwidth, i.e. selectivity, switch, with four settings from maximum selectivity to best audio quality. The knob is unmarked on my set, as are all the others except wavechange.

Paul

[John10b]

That’s interesting Paul, I was looking at the audio circuit and noted an elaborate “tone” circuit, I’m just curious.
I’ve not heard this set working but I’m sure it sounds excellent.
Cheers
John

[Cobaltblue]

Originally Posted by Paul_RK

The A40C doesn't have a tone control, just a bandwidth, i.e. selectivity, switch, with four settings from maximum selectivity to best audio quality. The knob is unmarked on my set, as are all the others except wavechange.

Just goes to show just how long ago it was since I saw my A40C
Probably the late 1990's

Cheers

Mike T

[John10b]

Paul thank you for the info. Just so I get it clear in my head, what I call a “tone” controle circuit in the audio stage, Murphy are calling it “selectivity” and they did not have it marked? If that is so isn’t that unusual?
Mike the sound quality must have been superb.
Cheers
John

[HamishBoxer]

They do sound stunning to say the least. Mine is in need of o/haul this year to restore it to a former glory.

[Synchrodyne]

From the schematic, it looks as if different gangs of the same switch (S2) controlled both the IF selectivity and AF “tone”.

At the AF end, it could be that different frequency response trimming circuits were switched in to modify or correct the response curves produced by the corresponding selectivity positions. Also, there appears to be an adjacent channel notch filter (LC circuit) that was switched out at the widest selectivity position.

Combining the selectivity and treble tone controls was not unknown. For example, Dynatron did it on its T69, T99 and T139 models.

Similarly, switched AF adjustments synchronized with selectivity positions was not unknown. The Quad AMII tuner had an LC circuit with steep upward tilt to extend the frequency response from the “natural” 3.5 kHz to 5 kHz in the narrow position, using the same L as was used for the adjacent channel notch filter in the “filter” position. (The following AM3 did not have this upward tilt facility.) And the Carver TX11a tuner of the 1980s had an AF mild upward tilt circuit (RC) to ensure that the response did get to 15 kHz in the wide position.


Cheers,

[John10b]

Thank you for the explanation, I did notice in the circuit diagram the action of switch S2. I can see it makes sense to couple the af stage to the front end.
I never came across this model during my time working for a Murphy dealership.
Cheers
John