Jonell Radio. A cheaper version of the Ace 50.

[GeorgeChristofi]

I'm going to start by saying thanks to all the guys who helped me identify this set.

What I have is a Jonell set, which was probably a version of the Ace A50. I have started to dismantle the set prior to actually doing the restoration work and have my first major difference between the two sets. The A50 has a full isolating transformer fitted whereas the Jonell set I have is fitted with a transformer for heaters only. I looked at the ac/dc version of the A50, the U50 and the layouts are fairly similar, with the U50 being closer on the speaker stage.

I am a touch confused though. Now this is something that happens a lot to me but in this case I'm sure something is amiss and not correct in the set.

I have made a drawing of the psu and rectifier valve and just want to confirm my thinking about the operation of the circuit. The ac in to my mind needs to be negative at the top and positive at the bottom so that the 16uf can cap is more positive than the neutral line. Please correct me if I am wrong.

Also, in working that out, I cannot see the reason for the 30 ohm resistor to chassis unless I am being dense and getting neutral and chassis earth confused. In my head, the chassis is floating and not at earth but at either ac live or neutral. I'm just trying to figure out which is the best way of ensuring it is at neutral!

Can anyone sort out my aching brain please before I send myself completely doolally

[marconi_pete]

Originally Posted by GeorgeChristofi

I am a touch confused though. Now this is something that happens a lot to me but in this case I'm sure something is amiss and not correct in the set.

I have made a drawing of the psu and rectifier valve and just want to confirm my thinking about the operation of the circuit. The ac in to my mind needs to be negative at the top and positive at the bottom so that the 16uf can cap is more positive than the neutral line. Please correct me if I am wrong.

Also, in working that out, I cannot see the reason for the 30 ohm resistor to chassis unless I am being dense and getting neutral and chassis earth confused. In my head, the chassis is floating and not at earth but at either ac live or neutral. I'm just trying to figure out which is the best way of ensuring it is at neutral!

Can anyone sort out my aching brain please before I send myself completely doolally

Hi,
I'm guessing the 16uf can is a dual 16uf/16uf can in which case it will have 2 positive connections and a combined neutral which goes to the chassis. The best way to ensure the chassis is neutral is to ensure that the neutral side of the supply is connected directly to the chassis. Be it by the on/off switch or otherwise. if you're lucky enough, the mains lead to the set may have been cut short preserving the connections to the on/off pot making this job straightforward. hope this is of help.

Thanks,
Peter

[GeorgeChristofi]

Unfortunately Peter its not quite that simple. the can on the dual 16uf cap is insulated from the chassis and the only connection from the power supply section goes through the small 30 ohm resistor. The power cord was intact as far as the switch was concerned but both cables inside were black rubber coated, no markings to denote positive or negative.

This set is almost certainly not original so I am tempted to wire the neutral directly to the chassis anyway and reference that.

I may be committing sacrilege but my whole thing with this set is to make it work, safely and look nice on the outside. The inside will be full of new components where needed with no attempt to hide that it has been updated. I will try and keep as many of the original parts where possible but anything that is suspect or out of tolerance will be replaced.

[marconi_pete]

Hi,
would you be able to post a couple of pictures of the chassis out of the cabinet depicting the 16uf can. Seems odd that it's insulated from the chassis as on most ac/dc sets the can neutral is connected directly to chassis. maybe one of the on/off pot too. Had a look at the pictures you posted in the other thread and can just about make out the dual 16/16uf can to the right of the chassis. Looks to be of the conventional type which has a common neutral. sometimes there may not be an obvious neutral connection as the can body itself may be acting as the neutral connection to chassis. Only way to tell is to see the connections to the can itself. You may be able to determine which cable connected to the pot is the neutral by a continuity test with one probe connected to chassis and the other to where the cable is soldered to the pot. Run the test with the on/off pot in the off position.

Thanks
Peter

[GeorgeChristofi]

would you be able to post a couple of pictures of the chassis depicting the 16uf can. Seems odd that it's insulated from the chassis as on most ac/dc sets the can neutral is connected directly to chassis. maybe one of the on/off pot too.

This is why i'm puzzling over it. The set is not capable of running dc as the heaters are all supplied from the transformer and the insulated can has thrown me.

http://www.terminalcomputers.com/radio/DSC_4112.JPG

In the picture you can see the 3 black wires are the mains/ht side of the transformer. The wire that goes to the cap negative comes from the end of the transformer, then you have the resistor and 8uf electrolytic to chassis from the same terminal. The white wire is going to the switch, and so is the black wire from the transformer that is running diagonally to the right. Although not clear, the two wires from the choke go across the cap positive terminals. The other white wire is the ht from the rectifier going to the positive of one of the dual caps. I say white but they look brown in the picture.

[marconi_pete]

Ok what you have mentioned makes sense. Looks like an autotransformer is in use which means the set is an ac only set with an earthed chassis, in which case ignore my previous comment about the live chassis thing as this doesn't apply here. The can is most probably isolated from the chassis to stop the sets chassis ever becoming live under fault conditions. Hope this helps. the 8uf electrolytic should be polarised with a positive and neutral connection with the neutral going to ground or in this case the chassis. Just zoomed in on that photo and can see one of the positive terminals is marked with a red dot. The other connection with a yellow cable attached. Where does that go to? The connection from the can to the electrolytic on the left doesn't look like the neutral connection to me.

Thanks,
Peter

Thanks,
Peter

[GeorgeChristofi]

I put the link in as it will give you an ultra high res image. If I attached it you wouldn't get near the size it is in the link..

I'll see if I can get it to shrink on this PC, I'm not at my normal PC.

[GeorgeChristofi]

It also doesn't look like an autotransformer, it's just connected from the mains to the input of the rectifier at the same time as the input to the transformer for the heater filaments.

[marconi_pete]

Yes does seem odd. That yellow lead from the 16/16uf can, where does it go to?

Thanks,
Peter

[GeorgeChristofi]

The yellow lead goes to one side of the output transformer. That's the side on the output of the choke.

[ms660]

The voltage dropped across the 30 ohm resistor might be supplying a fixed minimum bias voltage for the IF amp and Mixer valves, see black wire from neutral out on the on off switch:

http://www.terminalcomputers.com/rad...s/DSC_4113.jpg

If that's correct then that would tally up with the fact that there appears to be a cathode bias resistor (330 ohm) for the 6Q7 for biasing to suit Gram/PU:

http://www.terminalcomputers.com/rad...s/DSC_4115.jpg
http://www.terminalcomputers.com/rad...s/DSC_4112.jpg

Lawrence.

[marconi_pete]

Originally Posted by GeorgeChristofi

the yellow lead goes to one side of the output transformer. Thats the side on the output of the choke.

Just had another look at that image and there is clearly a cable going from the on/off pot straight to the 16/16uf can. Can you do a continuity test with the on/off pot in the off position. One probe on one of the two cables going into the set (mains lead) and the other on the connection to the pot with the red lead attached as that goes directly to the 16/16uf smoothing can. If you get no reading or open circuit with the pot in the off position then thats likely to be the live connection with the other being the neutral. Double check by repeating the test with the pot turned to the on position. If you now get a reading that will confirm which cable is the live one. The yellow lead from the smoothing can to the output transformer, is it connected to the primary or secondary of the transformer. i.e is it connected directly to the speaker leads?

EDIT
The electrolytic can on the left connected between the smoothing can and the chassis is most probably connected between neutral and earth. The neutral being the smoothing can terminal and earth being the chassis. if the yellow lead is connected to the primary of the output transformer that would confirm my theory.

Thanks,
Peter

[GeorgeChristofi]

Originally Posted by marconi_pete

Just had another look at that image and there is clearly a cable going from the on/off pot straight to the 16/16uf can. Can you do a continuity test with the on/off pot in the off position. One probe on one of the two cables going into the set (mains lead) and the other on the connection to the pot with the red lead attached as that goes directly to the 16/16uf smoothing can. If you get no reading or open circuit with the pot in the off position then thats likely to be the live connection with the other being the neutral. Double check by repeating the test with the pot turned to the on position. If you now get a reading that will confirm which cable is the live one. The yellow lead from the smoothing can to the output transformer, is it connected to the primary or secondary of the transformer. i.e is it connected directly to the speaker leads.

I tried that initially. There is no continuity as it seems that the on off switch is broken! If I measure between the cap negative and the chassis I get no continuity either.

[marconi_pete]

I tried that initially. There is no continuity as it seems that the on off switch is broken! If I measure between the cap negative and the chassis I get no continuity either.

The yellow lead from the smoothing can to the output transformer, is it connected to the primary or secondary of the output transformer?

Thanks,
Peter

[GeorgeChristofi]

Originally Posted by ms660

The voltage dropped across the 30 ohm resistor might be supplying a fixed minimum bias voltage for the IF amp and Mixer valves, see black wire from neutral out on the on off switch:

http://www.terminalcomputers.com/rad...s/DSC_4113.jpg

If that's correct then that would tally up with the fact that there appears to be a cathode bias resistor (330 ohm) for the 6Q7 for biasing to suit Gram/PU:

http://www.terminalcomputers.com/rad...s/DSC_4115.jpg
http://www.terminalcomputers.com/rad...s/DSC_4112.jpg

Lawrence.

The black wire from the switch goes to a 220k resistor, then into the 1M resistor which ends up on pin 4 of the 6Q7, one of the diodes. It is strange though how there seems to be no direct connection to the chassis from any part of the psu when everything else is connected to it. Granted, the chassis on the schematic for both the A50 and the U50 are isolated from earth by a capacitor at the E terminal of the antenna so the chassis could be floating but then it seems a very small resistor to carry the entire current back to the ac connection, even if it were a fusible link

[ms660]

The black wire from the switch goes to a 220k resistor, then into the 1M resistor which ends up on pin 4 of the 6q7, one of the diodes. It is strange though how there seems to be no direct connection to the chassis from any part of the psu when everything else is connected to it. Granted, the chassis on the schematic for both the A50 and the U50 are isolated from earth by a capacitor at the E terminal of the antenna so the chassis could be floating but then it seems a very small resistor to carry the entire current back to the ac connection, even if it were a fusible link

That confirms that the 30 ohm resistor is supplying a bias voltage to the IF/Mixer.

The 30 ohm resistor will only be passing the DC current taken by the valves (not the heater/transormer current) plus a bit of ripple, so it won't be dissipating a lot, well under 1/2 watt for a typical receivers DC load current.

Lawrence.

[GeorgeChristofi]

Originally Posted by ms660

That confirms that the 30 ohm resistor is supplying a bias voltage to the IF/Mixer.

The 30 ohm resistor will only be passing the DC current taken by the valves (not the heater/transormer current) plus a bit of ripple, so it won't be dissipating a lot, well under 1/2 watt for a typical receivers DC load current.

Lawrence.

I understand what you are saying but I can't equate that to any of the schematics for either the A50 or U50 but I can see it on the diagram for the A51 set. So, it looks like I'm going to be the guinea pig and draw the schematic of the set and compare notes between 3 or 4 different sets to get an accurate diagram.

[ms660]

I don't have access to the Ace schematics so it was just guesswork from me going on the photo's you've posted, normally with that type of bias arrangement the resistance value would be a lot higher so as to produce sufficient voltage across it to bias the output valve, the output valve's cathode being connected direct to chassis, that higher value resistance would be made up of at least two resistors in series forming a potential divider, the voltage across the whole being large enough to bias the output valve and the voltage at the divider tap being used to bias the IF/Mixer valves.

It's possible that the original receiver circuit has been altered at some time?

Lawrence.

[GeorgeChristofi]

Originally Posted by ms660

I don't have access to the Ace schematics so it was just guesswork from me going on the photo's you've posted, normally with that type of bias arrangement the resistance value would be a lot higher so as to produce sufficient voltage across it to bias the output valve, the output valve's cathode being connected direct to chassis, that higher value resistance would be made up of at least two resistors in series forming a potential divider, the voltage across the whole being large enough to bias the output valve and the voltage at the divider tap being used to bias the IF/Mixer valves.

It's possible that the original receiver circuit has been altered at some time?

Lawrence.

The honest answer Lawrence is somewhere between 'a little bit' and 'who bodged this together?' I fount the dial lights wire pushed into the tag strip by the band select switch and secured with bits of round wood... no solder, just friction fit in the eyelet. I'm pretty sure this is a sign of 'got at' as well as the way some of the components have been wired. some are twisted round pins, some are soldered with the barest of lead and others have got more lead than wire terminal.

I think my approach from here on is going to be one of leave the rf section intact except for wax caps which will be like for like changed and the rest of it will follow the A51 diagram power supply wise unless one of the others is more of a match to what is in the set. I think though that I will redraw the diagram in stages, as I work on it, so as to know what was connected to where. I think that is going to be the safest way to go about the job, unless I decide to change the transformer completely but that would ruin the back of the set and detract from the originality.

Can you think of any other set that had the mains connected directly to the rectifier? I may look at a diagram for that just to see if it was common practice to just have a filament transformer with the rest of the set direct to the wall.

[ms660]

Yes there were other receivers that had a filament transformers and mains live feed to the rectifier but I don't know off hand what the models were, someone else on here is bound to know.

EDIT: Just remembered one, Pilot Little Maestro 10 AC.

Lawrence.