Invicta model 60 - Oscillator Not working. - UK Vintage Radio Repair and Restoration Discussion Forum

'LIVEWIRE?' · 13th Dec 2019, 10:46 am

To me, the F.C. circuit of the model 60 is a conventional valve-era superhet in which, as far as I can see, the only parts liable to prevent the osc. from working are the bandswitches, capacitors C18, C20 & 21, and maybe a couple of resistors, but the radio's owner (not a forum member) is having problems. He tells me he's tried a (known good) substitute Frequency changer valve, has checked the osc. coils, etc, but not found the fault. Does anyone know what the most likely cause of this fault is?

Skywave · 13th Dec 2019, 8:56 pm

Cause could be due to many things: a few diagnostic measurements are necessary. For a start, I would see if the control grid of the osc. valve has a -ve potential on it.

Al.

'LIVEWIRE?' · 13th Dec 2019, 9:38 pm

Having earlier heard from the set's owner, he reports that the HT is onl150v, which, to me seems a bit low, although I'm not familiar with the Invicta model 60. As the HT is supplied by a l-c Pi Filter from the Rectifier cathode, I'd expect at least 200vDC, maybe more. Anyway I'll remind him to check if there is a negative voltage on the triode's control grid.

'LIVEWIRE?' · 19th Dec 2019, 11:43 pm

Further to the above, I've just been informed that the o/p valve is drawing about 11mAmore than it should so I;ve advised checking the obvious things like cathode bypass capacitor and resistor. I don't have the circuit in front of me but presume that it includes these components. I'm also told that the F.C. is still not oscillating, but don't know what else to suggest checking. It's a straightforward valve-era F.C. circuit so in theory not much to go wrong. Anyone have any ideas?

cathoderay57 · 20th Dec 2019, 9:22 am

Is the osc valve heater lit? Have the valve pins and sockets been cleaned? What are the voltages on anode, grids and cathode? Have the wavechange switch contacts been cleaned? Have the decoupling capacitors on the Osc HT supply been checked; ditto any AGC line decouplers? Cheers, Jerry

'LIVEWIRE?' · 20th Dec 2019, 10:04 am

Thanks for the suggestions, Jerry. As I don't have the radio here, I'll pass on your comments to the owner. As he has been repairing.restoring radios for some years I'd have thought he'd have checked all of those, but no harm in a reminder to do so.

Silicon · 20th Dec 2019, 10:26 am

I assume you are quoting from the the RTVS service sheet.
It mentions two alternative mixer valves, a CCH35 or an ECH35.
The radio has a typical AC/DC power supply.
The ECH35 heater is not wired into the normal heater chain.

The AF output valve has two alternatives, a CBL31 or a Pen DD4020.

The Trader service sheet states that the CBL31 has an anode current 10mA greater than the alternative Pen DD4020.

Voltages and currents could vary significantly depending on which valves are installed.
Which ones are fitted to the radio?

'LIVEWIRE?' · 5th Jan 2020, 12:44 pm

I haven't yet seen the radio-it's owner is bringing it to me tomorrow, but the FC Valve is a CCH35, and the o/p one, afaik, is a CBL31. I've now been told that a length of wire applied to the grid cap of the FC results in a strong signal from 5 Live, but only a very weak one at the aerial socket, but why this is the case puzzles me, unless the low impedance of the coupling winding on the aerial coil is shunting it.

cathoderay57 · 5th Jan 2020, 1:40 pm

Sounds like it would benefit from an RF alignment. There are trimmers across the LW, MW and SW aerial coils (on Trader Sheet #811 these are marked as C27, C28, C29 whereas on the RTVS or manufacturer's data sheet the numbering might well be different). Not trying to teach you to suck eggs, but take care as this is a live chassis set. Also if not done already then a squirt of switch cleaner on the wavechange switch contacts might help. Cheers, Jerry

'LIVEWIRE?' · 5th Jan 2020, 3:14 pm

I did think a realignment would be in order, Jerry. I know now that this is a 'live chassis' radio, having seen the circuit diagram. Perhaps what I'll do first, having made a few basic checks, is a realignment. Before anyone assumes that I'm a compulsive 'twiddler', please be assured that I'm not, but if the sensitivity is down for no obvious reason, in this case, some adjustments may be required.

PJL · 5th Jan 2020, 3:52 pm

Trimmers can also be a source of losses.

13th Dec 2019, 10:46 am	#1
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Invicta model 60 - Oscillator Not working. To me, the F.C. circuit of the model 60 is a conventional valve-era superhet in which, as far as I can see, the only parts liable to prevent the osc. from working are the bandswitches, capacitors C18, C20 & 21, and maybe a couple of resistors, but the radio's owner (not a forum member) is having problems. He tells me he's tried a (known good) substitute Frequency changer valve, has checked the osc. coils, etc, but not found the fault. Does anyone know what the most likely cause of this fault is?

13th Dec 2019, 8:56 pm	#2
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Invicta model 60 - Oscillator Not working. Cause could be due to many things: a few diagnostic measurements are necessary. For a start, I would see if the control grid of the osc. valve has a -ve potential on it. Al.

13th Dec 2019, 9:38 pm	#3
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Invicta model 60 - Oscillator Not working. Having earlier heard from the set's owner, he reports that the HT is onl150v, which, to me seems a bit low, although I'm not familiar with the Invicta model 60. As the HT is supplied by a l-c Pi Filter from the Rectifier cathode, I'd expect at least 200vDC, maybe more. Anyway I'll remind him to check if there is a negative voltage on the triode's control grid.

19th Dec 2019, 11:43 pm	#4
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Invicta model 60 - Oscillator Not working. Further to the above, I've just been informed that the o/p valve is drawing about 11mAmore than it should so I;ve advised checking the obvious things like cathode bypass capacitor and resistor. I don't have the circuit in front of me but presume that it includes these components. I'm also told that the F.C. is still not oscillating, but don't know what else to suggest checking. It's a straightforward valve-era F.C. circuit so in theory not much to go wrong. Anyone have any ideas?

20th Dec 2019, 9:22 am	#5
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,382	Re: Invicta model 60 - Oscillator Not working. Is the osc valve heater lit? Have the valve pins and sockets been cleaned? What are the voltages on anode, grids and cathode? Have the wavechange switch contacts been cleaned? Have the decoupling capacitors on the Osc HT supply been checked; ditto any AGC line decouplers? Cheers, Jerry

20th Dec 2019, 10:04 am	#6
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Invicta model 60 - Oscillator Not working. Thanks for the suggestions, Jerry. As I don't have the radio here, I'll pass on your comments to the owner. As he has been repairing.restoring radios for some years I'd have thought he'd have checked all of those, but no harm in a reminder to do so.

20th Dec 2019, 10:26 am	#7
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,162	Re: Invicta model 60 - Oscillator Not working. I assume you are quoting from the the RTVS service sheet. It mentions two alternative mixer valves, a CCH35 or an ECH35. The radio has a typical AC/DC power supply. The ECH35 heater is not wired into the normal heater chain. The AF output valve has two alternatives, a CBL31 or a Pen DD4020. The Trader service sheet states that the CBL31 has an anode current 10mA greater than the alternative Pen DD4020. Voltages and currents could vary significantly depending on which valves are installed. Which ones are fitted to the radio?

5th Jan 2020, 12:44 pm	#8
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Invicta model 60 - Oscillator Not working. I haven't yet seen the radio-it's owner is bringing it to me tomorrow, but the FC Valve is a CCH35, and the o/p one, afaik, is a CBL31. I've now been told that a length of wire applied to the grid cap of the FC results in a strong signal from 5 Live, but only a very weak one at the aerial socket, but why this is the case puzzles me, unless the low impedance of the coupling winding on the aerial coil is shunting it.

5th Jan 2020, 1:40 pm	#9
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,382	Re: Invicta model 60 - Oscillator Not working. Sounds like it would benefit from an RF alignment. There are trimmers across the LW, MW and SW aerial coils (on Trader Sheet #811 these are marked as C27, C28, C29 whereas on the RTVS or manufacturer's data sheet the numbering might well be different). Not trying to teach you to suck eggs, but take care as this is a live chassis set. Also if not done already then a squirt of switch cleaner on the wavechange switch contacts might help. Cheers, Jerry Last edited by cathoderay57; 5th Jan 2020 at 1:52 pm.

5th Jan 2020, 3:14 pm	#10
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Invicta model 60 - Oscillator Not working. I did think a realignment would be in order, Jerry. I know now that this is a 'live chassis' radio, having seen the circuit diagram. Perhaps what I'll do first, having made a few basic checks, is a realignment. Before anyone assumes that I'm a compulsive 'twiddler', please be assured that I'm not, but if the sensitivity is down for no obvious reason, in this case, some adjustments may be required.

5th Jan 2020, 3:52 pm	#11
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Invicta model 60 - Oscillator Not working. Trimmers can also be a source of losses.