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Old 23rd Apr 2018, 5:26 pm   #21
G6Tanuki
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

Quote:
Originally Posted by GeorgeChristofi View Post
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.
There were a number of the cheap 1950s/1960s TRF "kit" sets [Premier Radio etc] which used a 6.3V heater-transformer but fed the mains straight to a half-wave rectifier to provide the HT (along with a live chassis).

I wonder if - given your description of the set apparently having been 'got at' - perhaps it once had a proper HT-secondary winding on the transformer but this has gone open-circuit and someone's decided to keep it going by kludging together a 'live chassis' approach for the HT, wiring the mains straight to the rectifier as would have been the case for an AC/DC set?

I can easily see how, being told by an early-1960s repairman "It's going to be at least 5 for a new transformer, assumimg I can find one to fit" a customer could have said 'is there no cheaper way to fix it?', the repair man drawing on his inevitable Capstan Full-Strength and saying "Well...."
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Old 23rd Apr 2018, 6:07 pm   #22
GeorgeChristofi
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

Unlike the ace A50 and A51 which both had a full lay down transformer with centre tap ht windings this has the tiny little transformer. There are no spare holes in the chassis so unless the small transformer was a direct fit for another one it is unlikely. I can see the cost saving being made as it is an own brand department store set so the buyer would have shaved the price as low as possible, making the supplier look for any way to cut costs. The dial is obviously A50 derived, the speaker and grill is certainly A51. The cabinet is a standard slope front box, nothing remarkable about it.

All in, it is actually a plain, boring looking 3 band set. However, plain and boring sometimes fit in better than elegant and gaudy. I would describe the whole thing as functional.
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Old 23rd Apr 2018, 8:24 pm   #23
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

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Originally Posted by ms660 View Post
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.
Yes it was quite common for KB to use auto transformers in their small cheaper models, like the FB10 KR20 HR10 OB10 QB20. The single autotransformer was also used to supply the HT, this way the HT voltage could be kept correct, as well as the heater voltage, by use of the the voltage adjustment taps for the different mains voltages. I believe the winding had a thicker wire for the heater tap, and thinner wire for the rest of the winding.
These were still classed as a "live" chassis though.
STC who owned KB, bought Ace radio but that was not until about 1961, well after this radio was made.

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Old 23rd Apr 2018, 8:26 pm   #24
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

The Roberts P5A was similar too. At 16 16s + P.T. in 1946, it was hardly a particularly cheap set.

https://www.vintage-radio.net/forum/...4&d=1481033427
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Old 24th Apr 2018, 7:46 pm   #25
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

That Roberts is a different way of doing it to the KB ones I mentioned. In the KB radios it was only an autotransformer, there were no isolated windings.
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Old 24th Apr 2018, 10:49 pm   #26
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

Those of you who helped me identify the set will remember the strange serial number plate on the back of the chassis.

It bugged me so much that while I was doing some other work to the chassis I decided to remove it and see what was written on the back...


A sort of surprise. but a pleasant one.
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Old 24th Apr 2018, 10:54 pm   #27
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

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Originally Posted by crackle View Post
That Roberts is a different way of doing it to the KB ones I mentioned. In the KB radios it was only an autotransformer, there were no isolated windings.
That to me is almost identical to this set, bar the fact that the heater is tapped there but actually on a separate winding on mine.
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Old 25th Apr 2018, 7:50 am   #28
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

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Originally Posted by GeorgeChristofi View Post
those of you who helped me identify the set will remember the strange serial number plate on the back of the chassis.
It bugged me so much that while I was doing some other work to the chassis I decided to remove it and see what was written on the back...
A sort of surprise. but a pleasant one.
That's great proof, well found. I would add that to your model page on the Radio Museum when you are ready.

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Old 28th Apr 2018, 2:26 pm   #29
GeorgeChristofi
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

Ok... running through the set, the first thing I have found is the volume pot/on off switch is .... fubar. also, the tone switch is having contacts falling apart. The contacts thing I can sort because there is a multipole switch so I can use a spare set of contacts.

What I haven't got in stock or as salvage is a half meg log pot with a spdt switch on the back. Ebay has been sparse, China haven't got any and neither have RS, Farnell and Rapid. Can someone point me in the direction of a supplier of NOS or salvaged components please? If I didn't want to keep the originality I could put a mains switch on the rear panel and put a standard pot on the front (mind you, finding a long D shaft pot is hard as well) but I would like to keep it as original as possible so need some pointers please.

I have looked at my usual guitar amp suppliers too... nothing with a switch or wrong shaft... I'm a bit stuck

Last edited by GeorgeChristofi; 28th Apr 2018 at 2:27 pm. Reason: adding text
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Old 28th Apr 2018, 2:29 pm   #30
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

Possibility? (select value):

https://www.bowood-electronics.co.uk...1166f5392216c0

Lawrence.
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Old 28th Apr 2018, 7:54 pm   #31
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

Many thanks for that Lawrence.
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Old 14th May 2018, 1:36 am   #32
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

Right...here is a question that should easily be explained here.....

I have a replacement mains transformer which has no centre tap. My thinking is such that this transformer (which fits the original mounting holes perfectly) would be a safer option than just soldering the neutral line to chassis.

According to the trader sheet, the original a50 was full wave rectified but this set is half wave rectified, using both diodes in the 6x5gt as a parallel pair. Now, If I made it full wave by adding a couple of silicon diodes to complete the bridge configuration would that result in a better (more stable, less noise) power supply than just leaving it in half wave mode as is?

Any thoughts on the hybrid bridge rectifier? good, bad, makes no difference except you don't need a centre tap?

Even in half wave mode, the set should be within the ratings of the single tube rectifier, having a rating of 70mA where the set consumption (as specified) is only 55ma. I could if I wanted to just put in a silicon bridge rectifier, but that seems to be defeating the original design.

Last edited by GeorgeChristofi; 14th May 2018 at 1:37 am. Reason: spelling error... didoes isn't correct....
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Old 14th May 2018, 8:33 am   #33
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

Wasn't the transformer originally only supplying 6.3v for the valve heaters.
It is likely to be a smaller transformer (mounting holes) than one which can supply the HT and LT voltages on an isolated winding from the mains.
In other words is the replacement transformer you have able to supply the additional power for the HT as well as the LT without over heating.

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Old 14th May 2018, 9:54 am   #34
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

A hybid circuit is good, it takes out any DC component from the transformer so less likely to put the core into saturation. This would cause less primary heating.
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Old 14th May 2018, 12:23 pm   #35
GeorgeChristofi
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

Quote:
Originally Posted by crackle View Post
Wasn't the transformer originally only supplying 6.3v for the valve heaters.
It is likely to be a smaller transformer (mounting holes) than one which can supply the HT and LT voltages on an isolated winding from the mains.
In other words is the replacement transformer you have able to supply the additional power for the HT as well as the LT without over heating.
Yes, the only thing the original was supplying was 6.3v for the heaters with the incoming mains tied to the chassis on one side and direct to the two diodes on the 6x5 on the other through a 50 ohm resistor.

I have a replacement transformer that is taller and has an ht winding on it as well as the 6.3v for the heaters but it is 250-0 rather than a centre tapped 250-0-250. This certainly seems to be man enough for supplying the required HT (70mA ) as well as the heater current from the other valves (2A).

Quote:
Originally Posted by TrevorG3VLF View Post
A hybid circuit is good, it takes out any DC component from the transformer so less likely to put the core into saturation. This would cause less primary heating.
That is good to know, hadn't thought of the dc feedback into the transformer from the use of the chassis as a dc ground. I think I shall go with the hybrid bridge then. I have enough 1n5408's in stock to do the job of finishing the bridge configuration.
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Old 13th Jun 2018, 7:43 pm   #36
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

Ok.... long time no update but several things have happened. First, I have rebuilt most of the set but have come across a real oddity with regards to the tuning coils. Still working that one out but it is looking less and less like an Ace 50 but more like an Ace Mayfair radiogram chassis in a tabletop case.

Second thing to happen... I managed to buy a second one! This also has a non standard valve in position 2 and the rectifier is missing. Although I have taken lots of photos of the inside, I have yet to actually do anything other than look. The second one looks much cleaner and more factory standard.

Where things have come apart is the aerial coil and tuning coils. The Ace 50 shows two coils for each. The radio itself only has a single coil for the tuning except for short wave where there is another coil on the same former. I'm assuming that this coil is commoned up with the other 3 wavebands to get the signal to the grid of the hexode of v1. the other set of three coils match up with the oscillator anode coils for IF so that part is straight forward.

I'm going to keep looking. For those wanting to keep up with the progress, you can watch things so far on youtube, search term, jonell 1949 tabletop radio.
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Old 13th Jun 2018, 7:56 pm   #37
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

I wonder if your tuning-coils could be similar to the Barker-88: basically on MW/LW the aerial is fed [through the primary of a SW coil - L1] to a capacitor (C2) between the bottom-end of the MW/LW coil and earth. It works as a sort-of- "Pi-network" with a fixed input capacitor (C2) and a variable output-capacitor to tune it.

On shortwave it's more traditional.

This only works because the inductance of the SW-coil's primary winding is (L1) very low at MW/LW frequencies, and conversely the fixed-capacitor in the MW/LW circuit (C2) has a low impedance on short waves.
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Old 13th Jun 2018, 9:40 pm   #38
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

It could be. The schematic for the ace 50 shows this layoutClick image for larger version

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and the mayfair has this sort of layout.Click image for larger version

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The coils themselves are what threw me off. I have spent almost 3 days now drawing the switch, measuring capacitors, coil resistances and just been going round in circles. I have replaced almost all the capacitors in the coil assembly because they were nowhere near the values written on the capacitors. Rather than follow any schematic, I replaced old for new, based on the markings. I also was measuring continuity with af as well as rf just to try and figure this little bit of fun out.

The other issue this then raises is the if frequency. At the moment, I'd like to just get it going prior to an alignment but I will have to consider what the IF should be. Ace seemed to have a preference for 645Khz and 472Khz. Both are not far enough apart to worry about at this stage and can be measured later but it would be good to find out which I'm meant to hunting for when I do get to power on stages.
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Old 13th Jun 2018, 10:48 pm   #39
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

When you measured the values, did you remove the capacitors from the coil pack?
If they were mica capacitors it is unusual for them to wander off.
Replacing them will almost certainly require the set to have a full realignment.

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Old 14th Jun 2018, 7:29 pm   #40
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Default Re: Jonell Radio. A cheaper version of the Ace 50.

I did remove them... they were wax coated. Only two were within what was written on the capacitor, let alone any circuit diagram. Yes, I know I'm in for a full alignment.... That fun is yet to happen!
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