UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 23rd Nov 2019, 7:11 pm   #101
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Moreton Cheyney

Hi Allan, if you get stuck for the mains tranny PM me as I may have soimething used that would be suitable.

Ed
Ed_Dinning is offline  
Old 24th Nov 2019, 11:12 am   #102
allan
Pentode
 
allan's Avatar
 
Join Date: Oct 2005
Location: South coast near Ringwood/Christchurch, Dorset, UK.
Posts: 230
Default Re: Moreton Cheyney

Thanks Ed
I'll bear that in mind.
I must see if there's anything written about driving push pull audio valves with differently processed signals.
Allan
allan is offline  
Old 24th Nov 2019, 8:44 pm   #103
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Moreton Cheyney

Hi Allen, try Langford -Smith, or Terman, most likely in there if it exists

Ed
Ed_Dinning is offline  
Old 26th Nov 2019, 11:05 am   #104
allan
Pentode
 
allan's Avatar
 
Join Date: Oct 2005
Location: South coast near Ringwood/Christchurch, Dorset, UK.
Posts: 230
Default Re: Moreton Cheyney

My Terman hasn't got anything like the MC circuit Ed.
Thinking about it though. The asymmetry will produce harmonics across the spectrum if one driver has top control plus bass control and the other has no top/bass control.
Allan
allan is offline  
Old 30th Nov 2019, 12:20 am   #105
allan
Pentode
 
allan's Avatar
 
Join Date: Oct 2005
Location: South coast near Ringwood/Christchurch, Dorset, UK.
Posts: 230
Default Re: Moreton Cheyney

I've now managed to hear a test signal through the RF and IF stages of the MC receiver. Also, I identified the coils as Wearite types. I've made a chart giving some basic information but I wonder if anyone knows the tuning condenser values and oscillator padder values for the PO series of coils? Scroll to the end of the page
Ref.. http://www.radiomuseum.co.uk/Moreton%20circuits.html

Allan
allan is offline  
Old 30th Nov 2019, 7:09 pm   #106
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Moreton Cheyney

Hi Alan, some pretty comprehensive notes there and a well packed chassis.
From memory the tuning caps for the lower frequency ranges were 500pF. There should be a thread somewhere that gave the datasheet for Wearite coils with padder data etc.
I may have some of the detector diodes if you need them.

Ed
Ed_Dinning is offline  
Old 1st Dec 2019, 1:16 pm   #107
regenfreak
Heptode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
Default Re: Moreton Cheyney

Your patience is epic

Quote:
The local oscillator fails to run on any other waveband and looking at the padder for the MW oscillator it looks very odd because it's made up from a small (unmarked but low value) condenser in series with three others in parallel. Either someone has attempted to alter the coverage or attempted to replace the original. My best bet is to remove these and measure the value. Wearite oscillator coils data is listed below assuming an IF of 465KHz. Something is clearly wrong, but then again.. what value tuning condenser and what value padders were assumed when Wearite made the coils?
In your Wearite table, PO2 has very low inductance 35 microHenries for MW with an IF of 465kHz. Usually it is around 70-130 microH for IF at 455KHz depending the inductance of the RF coil.

I only have Denco Maxi Q datasheets. Now the annoying thing is that different generation of those MaxiQ local oscillator coils use different padder values. I have a few of those Maxi Q but I never used them. But I ended up winding my own oscillator coil to match the exact value based the tracking calculations of Terman, Langford Smith or Henney etc. The difficulties are that those tracking solutions do not always match the values in a real working set because the tracking solutions are sensible to the stray capacitance of components on the chassis and wirings.

It looks like someone did a hatch job of matching the exact value of the padder to minimise the tracking error. Since they are silver mica caps, they don't really go bad often.

The air variable gang usually goes from 370pF up to 500pF. I would desolder the air gang, RF coil and padder to get measurements.

Last edited by regenfreak; 1st Dec 2019 at 1:21 pm.
regenfreak is offline  
Old 1st Dec 2019, 1:25 pm   #108
allan
Pentode
 
allan's Avatar
 
Join Date: Oct 2005
Location: South coast near Ringwood/Christchurch, Dorset, UK.
Posts: 230
Default Re: Moreton Cheyney

Thanks for the offer Ed but I have a vast collection of parts.
I've added a couple of tables on my MC web page for the Wearite coils based on a rather blurry document I discovered. I think my tuning capacitor for 3 bands is probably 500pF but that for the 2 highest bands looks about 250pF so I imagine the designers had to fiddle around getting the padders and RF tuning right.
I think it's time to dig out my grid dip meter to investigate the coil pack because the local oscillator refuses to work on 4 of 5 ranges and only partly on MW and none of the RF amp coils seems to peak up.
The good news is I actually heard a medium wave station and the AVC/QAVC voltages look good so the Westectors must be in fairly good shape.
Allan
allan is offline  
Old 3rd Dec 2019, 4:05 pm   #109
allan
Pentode
 
allan's Avatar
 
Join Date: Oct 2005
Location: South coast near Ringwood/Christchurch, Dorset, UK.
Posts: 230
Default Re: Moreton Cheyney

Quote:
Originally Posted by regenfreak View Post
In your Wearite table, PO2 has very low inductance 35 microHenries for MW with an IF of 465kHz. Usually it is around 70-130 microH for IF at 455KHz depending the inductance of the RF coil.
The original sheet isn't clear but in retrospect I think it should read 85uH not 35uH as that value does seem to fit the calcs.
I'm hunting for my GDO at present.. I have 3 different types which I remember putting in the same box about 2 years ago....
I do have a Peak LCR meter.
Allan
allan is offline  
Old 7th Dec 2019, 10:29 am   #110
allan
Pentode
 
allan's Avatar
 
Join Date: Oct 2005
Location: South coast near Ringwood/Christchurch, Dorset, UK.
Posts: 230
Default Re: Moreton Cheyney

Just a quick note for anyone following this thread.
The RF/IF sections of the Moreton Cheyney are now mostly working.
Open circuit oscillator coils fixed. The IF amplifier mostly OK since wrapping bacofoil around 6K7 valves. Amplified AVC still causing grief when aligning.. Westectors due to be changed. Audio stages providing attenuation rather than gain but I can now hear lots of LW & MW broadcasts on headphones connected to the anode of the first AF amplifier but only at the strength of a crystal set despite 9 valves all working hard.
Allan G3PIY
allan is offline  
Old 7th Dec 2019, 4:02 pm   #111
regenfreak
Heptode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
Default Re: Moreton Cheyney

Quote:
Before I refitted the long wave coil I checked the medium wave coil. Now this of course works over part of the band so must be basically OK. Wrong! the medium wave coil also had an open circuit feedback coil. This one however is rather odd. Instead of measuring its inductance once I'd resoldered the broken wire (again close to the solder tag so was easy to fix) I found the tuning coil measured 88uH and 4.2 ohms, but the repaired feedback coil measured 66 ohms which was too high for my LCR meter to check its inductance. I have heard of
From your schematic, it is a Hartley topology. From the top of my head, I vaguely remember the inductance ratio between oscillator tank coil and feedback coil is roughly 4:1 to 5:1.
66 ohms is way too high. It does not add up.

Last edited by regenfreak; 7th Dec 2019 at 4:20 pm.
regenfreak is offline  
Old 7th Dec 2019, 4:33 pm   #112
allan
Pentode
 
allan's Avatar
 
Join Date: Oct 2005
Location: South coast near Ringwood/Christchurch, Dorset, UK.
Posts: 230
Default Re: Moreton Cheyney

I did double check this high resistance coil and it was OK. I believe Wearite used a solderable cotton-covered resistance wire so that the medium wave feedback was controllable. I have read somewhere about damping a medium wave coil. Presumably the combination of coil and its capacitors were so ideal for the 6K8 type of mixer that the resistance wire was used.
This tends to be proven because the medium wave oscillator worked over more than half the dial with the feedback coil open and just the stray capacity in place.
http://www.radiomuseum.co.uk/Moreton...tml#anchor4703
Allan
allan is offline  
Old 8th Dec 2019, 3:09 pm   #113
regenfreak
Heptode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
Default Re: Moreton Cheyney

I have not been able to find any info this quirky high resistance feedback coil in a MW Wearite you mentioned. If your RCL meter cannot measure its inductance, then it must be very high over 10H etc.


The Wearite datasheet states that if the oscillator voltage is too high," a 50-500 ohms resistor " shoud be in series with the feedback coil.

For the oscillator triode section of a hexode-triode, two anti-parasitic and over-excitation damping resistors are sometimes in series between the grid blocking capacitor to stop parasitics and instability. Ideally the oscillator heterodyn voltage should remains the same across the whole wave band

The American seems to use the heptode-tride changer 6K8 in a different manner from the British. For the Pentagrid convertor, if the oscillation voltage is too high, it can be reduced by lowering the number of feedback turns, oscillator plate voltage or the coupling coefficient between the feedback windings and the oscillator tank coil.

I have seen british radios use the 6K8 with inductively coupling feedback on SW, and capaciive coupling for MW and LW which I find the idea odd as I am mostly familar wih Pentagrid convertors.
regenfreak is offline  
Old 8th Dec 2019, 4:57 pm   #114
allan
Pentode
 
allan's Avatar
 
Join Date: Oct 2005
Location: South coast near Ringwood/Christchurch, Dorset, UK.
Posts: 230
Default Re: Moreton Cheyney

Wearite must have introduced a feedback winding of constantan for their MW coil PO2 ?
The wire is something like 40SWG and constantan has a resistance of 40 ohms per meter at this gauge which sounds right to me. I fitted a new coupling winding to the PA2 coil a week or so ago and that used about 1.5m of circa 40 SWG wire.
The PO2 now works perfectly so the feedback is working as it should.
I've now put the RF/IF stages on hold to look at the audio side.
There are several dodgy capacitors I need to swap, some resistors gone high and the volume control pair are both open circuit... just for starters.
Then there are a few weird circuit changes made by the last owner (perhaps to circumnavigate an untraceable fault?) so I'll need to figure out the original circuitry and make that work.
The area is very congested but by using physically smaller components I should be able to see better.
First step is to figure out whether the old pots (2M and 25K) are linear or log.
Then work out if the circuit at the 2M pot is wired incorrectly.
Currently the pot is wired so the input is direct to grid and the grid leak going from zero ohms to 2Mohms as the volume is increased which feels wrong.
Allan G3PIY
allan is offline  
Old 8th Dec 2019, 8:39 pm   #115
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Moreton Cheyney

Hi Alan, there was an article about Wearite coils in either Radiophile or RB many years back where the use of a resistance winding was mentioned; I believe it also come up on the Forum as a thread at about the same time. I believe it was only on some of the coils, not the full range or applications.

Ed
Ed_Dinning is offline  
Old 10th Dec 2019, 12:20 pm   #116
allan
Pentode
 
allan's Avatar
 
Join Date: Oct 2005
Location: South coast near Ringwood/Christchurch, Dorset, UK.
Posts: 230
Default Re: Moreton Cheyney

Thanks Ed. Now that the RF side is much improved I'm tackling some instability which I suspect is from the AVC circuitry. Because there seems to be a few wiring errors in the set, perhaps made by the last owner looking for a fault I'm trying to work out how QAVC and AVC are supposed to work. I've made notes at the end of this page. Comments welcomed.
http://www.radiomuseum.co.uk/Moreton%20circuits.html

I'm also looking at the audio section which I think has been butchered.
I removed the ganged volume controls. Not easy to extract these but I fixed the 2M pot which responded to switch cleaner and replaced the 50K pot which had loose terminals.
http://www.radiomuseum.co.uk/moreton2.html

I also removed the two Westectors and I suspect both are open circuit.
I fitted a couple of 1N4148 diodes but may swap these for germanium types or maybe Schottky diodes.
Allan
allan is offline  
Old 11th Dec 2019, 1:31 am   #117
regenfreak
Heptode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
Default Re: Moreton Cheyney

Quote:
This tends to be proven because the medium wave oscillator worked over more than half the dial with the feedback coil open and just the stray capacity in place.
http://www.radiomuseum.co.uk/Moreton...tml#anchor4703
In the following attached schematic of RCA Victor 1AX MW AA5, it looks like the feedback coil is an open winding but in fact it is wounded on top of the oscillator tank windings acting like a gimmick capacitor. The feedback is capacitively coupled. This is not uncommon. The rationale of using this gimmick cap is thought to be that the manufcaturer was a cheapskate, savng the cost of a silver mica coupling cap. But I could not figure out the obvious advantage of using high resistant wire for the feedback winding in Wearite oscillator coils.
Attached Files
File Type: pdf RCA Victor 1AX.pdf (236.2 KB, 78 views)

Last edited by regenfreak; 11th Dec 2019 at 1:41 am.
regenfreak is offline  
Old 11th Dec 2019, 10:24 am   #118
allan
Pentode
 
allan's Avatar
 
Join Date: Oct 2005
Location: South coast near Ringwood/Christchurch, Dorset, UK.
Posts: 230
Default Re: Moreton Cheyney

That US circuit is interesting om. I seem to recall other instances of this sort of practice which look very odd when tracing a circuit. One was for BFO injection and another was a TV chassis that used two wires twisted together to make small capacitors.

The Wearite leaflet mentions the fact that the oscillator voltage may exceed the rating for the valve and they recommend adding a resistor of 50-500 ohms in series with the reaction winding.
http://www.radiomuseum.co.uk/New/wearite.pdf
Presumably their designers decided to use resistance wire, around the minimum value of their suggestion, to tame the the PO2 oscillator coil to about the amplitude of their other coils because of complaints from manufacturers. Perhaps just to save a few pence for a resistor...we'll probably never know...
Maybe the PO2, used in a battery portable using say the DK91, was too energetic and could damage the valve?

I can actually hear broadcasts in long and medium waves now but extremely weakly as I'm listening at the diode detector. The first AF amplifier is only giving me a voltage gain of 3 so clearly has a problem. It's wiring disappears into a jungle of resistors etc. What I can hear sounds like a crystal set with broad tuning and clear speech. I was tweaking the IF stages on what I thought was Radio 4 but turned out to be the Irish station on 252KHz. I'd removed the dial so it wouldn't get damaged.
The oscillator on two highest shortwave bands can't be encouraged to start up so once I've got decent audio I'll look at those.
Allan
allan is offline  
Old 11th Dec 2019, 2:57 pm   #119
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
Default Re: Moreton Cheyney

Resistance wire is normally used to damp resonance within the coil caused by capacitive coupling between turns/layers.
PJL is offline  
Old 11th Dec 2019, 5:09 pm   #120
stevehertz
Dekatron
 
stevehertz's Avatar
 
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,809
Default Re: Moreton Cheyney

The epic continues. Out of interest, to what extent are you planning or hoping to restore this receiver? a working chassis or to build a cabinet etc.
__________________
A digital radio is the latest thing, but a vintage wireless is forever..
stevehertz is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 3:32 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.