HMV 441 - Columbia 357 clone help, please with tuning.

[Scotorvm]

Was hoping someone would know which areas to check on this set Labelled as a Columbia 357.

I can't pick anything up on LW, but on MW there are two stations coming in loud, only issue is I can't separate the stations. Turning the tuning dial I cannot tune in 1 station. I can hear that 1 is Real Radio, not sure about the other.

The set checks out OK with the key tests mentioned in the HMV 441 service sheet.

All pitch block caps have been bypassed / replaced, all out of value resistors replaced, valves purchased as working.

The aerial I am using is a wire leaving the shed, running along the top of a fence - 15m then into the house then 8m in the attic. Strangely the MLA-30 loop aerial i have installed doesn't seem to do anything.


Thanks for looking.

[mister valve]

Do the two station get stronger if you tune the set towards the 550 meter end of the dial ? if so it may be that the signal strength is strong enough to get straight through the RF & IF stages to the (2nd) detector stage then amplified in the AF stages so you can hear it from the speaker.

It sounds to me like the Local Oscillator has stopped working. Have you checked the voltages around the frequency-changer valve MX40 ? Check you have 120 volts on the Osc. Anode (pin 1). If not, check Resistor R3 (50k ohms) for going high or open circuit, and check Capacitor (Condenser) C5 for short circuit.
If you touch the top cap of the MX40 valve (Tuning condenser fully meshed), do you get a lot of 'noise' plus maybe strong local stations superimposed ? If so then yes I would suspect the local Oscillator is not working.
P.S. DO NOT TOUCH THE TOP CAP OF THE I.F. AMPLIFIER VALVE (VMS4B) it is the Anode on this Valve, and has high voltage on it.

[Scotorvm]

Originally Posted by mister valve

Do the two station get stronger if you tune the set towards the 550 meter end of the dial ? if so it may be that the signal strength is strong enough to get straight through the RF & IF stages to the (2nd) detector stage then amplified in the AF stages so you can hear it from the speaker.

It sounds to me like the Local Oscillator has stopped working. Have you checked the voltages around the frequency-changer valve MX40 ? Check you have 120 volts on the Osc. Anode (pin 1). If not, check Resistor R3 (50k ohms) for going high or open circuit, and check Capacitor (Condenser) C5 for short circuit.
If you touch the top cap of the MX40 valve (Tuning condenser fully meshed), do you get a lot of 'noise' plus maybe strong local stations superimposed ? If so then yes I would suspect the local Oscillator is not working.
P.S. DO NOT TOUCH THE TOP CAP OF THE I.F. AMPLIFIER VALVE (VMS4B) it is the Anode on this Valve, and has high voltage on it.

Thanks Mister Valve, going to check this tomorrow

[Scotorvm]

Originally Posted by mister valve

Do the two station get stronger if you tune the set towards the 550 meter end of the dial ? if so it may be that the signal strength is strong enough to get straight through the RF & IF stages to the (2nd) detector stage then amplified in the AF stages so you can hear it from the speaker.

It sounds to me like the Local Oscillator has stopped working. Have you checked the voltages around the frequency-changer valve MX40 ? Check you have 120 volts on the Osc. Anode (pin 1). If not, check Resistor R3 (50k ohms) for going high or open circuit, and check Capacitor (Condenser) C5 for short circuit.
If you touch the top cap of the MX40 valve (Tuning condenser fully meshed), do you get a lot of 'noise' plus maybe strong local stations superimposed ? If so then yes I would suspect the local Oscillator is not working.
P.S. DO NOT TOUCH THE TOP CAP OF THE I.F. AMPLIFIER VALVE (VMS4B) it is the Anode on this Valve, and has high voltage on it.

Mister Valve, you know your stuff
I'm an idiot , I replaced all the caps That were hidden in the pitch block, all other waxies. The only cap I did not replace was C5, because it was never there to begin with (since I acquired the set). Checked the circuit diagram, soldered a 470nF polyester between R3 (measuring 48.5K) and ground. All working well now Thank you..

By the way, everything you mentioned, the set was doing, stronger towards 550, touching the top of MX40, noisy with local stations superimposed.

[mister valve]

Originally Posted by Scotorvm

Mister Valve, you know your stuff
I'm an idiot , I replaced all the caps That were hidden in the pitch block, all other waxies. The only cap I did not replace was C5, because it was never there to begin with (since I acquired the set). Checked the circuit diagram, soldered a 470nF polyester between R3 (measuring 48.5K) and ground. All working well now Thank you..

By the way, everything you mentioned, the set was doing, stronger towards 550, touching the top of MX40, noisy with local stations superimposed.

Delighted you have found the fault. These sets when working properly, are capable of giving really good quality sound - partly due to the stagger tuned IFT's, but also the tonal correction circuits, output transformer, and loudspeaker that EMI (The Gramophone Company) used in their sets.

I.F. alignment is difficult with those sets, because you do need a Wobbulator & Oscilloscope to get the correct shaped passband. So if it hasn't been touched in the past and the set's sensitivity/selectivity are OK, I would leave well alone.
Kind regards, Kevin (mister valve)

[Scotorvm]

Thanks Kevin, I have been tinkering with this set for a year now, so pleased to put it all back together and give it a wee polish

Cheers
Lee