Champion TRF

[Neil Purling]

These Champion TRF's all seem very similar. There's the 784, 832 and 860.
The 784 and 832 look similar. Specifically the 784 M and 832 US valve version.
It just seems to be different valve choices & the basic circuit is the same. Actually this is also very similar to the kit radios of that era. Apart from that the kit radios had a heater transformer.

Anyway I have a 832 Minuet. Money has changed hands, but it has not yet arrived.
Valves are original. The dropper has been changed for a Radiospares replacement for a Marconi T18DA. What value was OEM fit?
They do seem to be in a rather poor state if the dropper is original, so I suspect the component was only just adequate on power rating or was not very well coated over the windings.
Not sure what to do yet. It depends on whether that replacement dropper was a good match and hasn't over-run the valves.
There's no knobs, no dial or backplate, so this thing is never going to be a pristine restoration.

[Neil Purling]

I looked for service data on the Champion 832 Minuet with US valves. Is the circuit exactly the same as 784 B variant? The Newnes page on the Champion 784 B does not mention the dropper value.
I calculated the value to be 1050 ohms, 25W.
The non-original dropper is slightly under-running the heater chain as the sections in use total 1100 ohms.
If I had a resistor mounted on an aluminium plate sprayed matt black would that be a better heat radiator?
Just wondering about where the heat was being concentrated.

[FERNSEH]

Hi Neil,
Why not consider a capacitive dropper for the heater chain? My calcs come out with 4.14 microfarads for a receiver with 0.15amp valves.
Champion 784B with 6BJ6, 6BH6, 50L6 and 35Z4. (Some sets use 35L6 in lieu of 50L6) Need to drop 140 volts. 21 watts
Capacitor value worked out by this means. 240 X 240 = 57600 minus 140 X 140 = 19600. = 38000. Square root = 195
6.28 X fc works out to approx. 4.14mfd.

DFWB.

[Neil Purling]

I have been evicting life-expired waxies from this Champion 832. All were leaky of course. The sole Mouldseal was the o/p valve grid-coupler. As is typical of it's kind it crumbled as soon as I touched it.

To re-form electrolytic capacitors I use the power supply of my Mullard 3-3 with only the rectifier in place. This is good enough. The 3-3 has a 300 volt HT rail, which is the highest voltage I can get. That passes through a neon indicator. This has a internal resistor for across the mains usage. It strikes at as low as 51uA, albeit at a level that is barely visible in daylight.
The OE 32/32 Dubilier Drilitic is in a aluminium can encased in a card sleeve, date code LL. No matter how long I leave it on my patent re-former I still have a 633uA current flow.
This capacitor is a long 22mm dia tube & I only have a CCL 40+40+20uf of anything like the same diameter.
It is supposed to lurk under the chassis. The CCL electrolytic is on the re-former rig now.
The only other capacitors I have at 32uf are the short, fat cans that are approx 35mm diameter that won't fit the clamp.

[Graham G3ZVT]

Originally Posted by Neil Purling

The OE 32/32 Dubilier Drilitic is in a aluminium can encased in a card sleeve, date code LL. No matter how long I leave it on my patent re-former I still have a 633uA current flow.
This capacitor is a long 22mm dia tube & I only have a CCL 40+40+20uf of anything like the same diameter.
It is supposed to lurk under the chassis. The CCL electrolytic is on the re-former rig now.
The only other capacitors I have at 32uf are the short, fat cans that are approx 35mm diameter that won't fit the clamp.

I would re-stuff the original can with normal axial or radial electrolytics.

[Neil Purling]

The CCL Can has re-formed. I have stripped the card sleeve off the Dubilier can. Underneath was one word 'Champion'. The card sleeve was also marked 'Not for re-sale'. As if they were only supplied to equipment makers and they were marked in case they were sold on.
Are there reliable pages for Dubilier capacitor dates?
The Dubilier waxies are: LKLM, LNDM and LABC.
There are also two Hunts 25uf electrolytics as cathode bypasses on V2 and V3.
I can't see dates on these. Are these to be trusted?
I know that they are low voltage components without a massive voltage on the + plate.
I am suspicious of them just because of the maker. They are well-beyond their intended lifespan.

I reckon a set like this was not supposed to last very long.

To make this work I have just been throwing in bits from my boxes of accumulated re-cycled parts. Russian stuff & re-cycled stuff incl a mustard type. Only one new 0.1uf 630V Polypropylene by t.s.e. . Who are they?
Even the mains lead is from something else. BTW it is the neutral lead that is switched.

There are two strips of the plastic/bakelite applied to the top of the set that look original. They are not moulded into the case.
One of them hides a heat-crack that has had some sort of tape applied on the inside. The slab of hardboard has to be replaced. I can find somethng in a skip somewhere.

[Neil Purling]

Has anyone else got one of these? I need a photocopy of the dial.
I don't have chassis retaining screws either, which are rather more important.
Just tell me what thread, *BA for whatever. Assuming they are regular machine screws.

[Chris55000]

Hi!

If the set was British designed & made the chassis screws will be most likely 2BA at ¾" long cheese–head slot type!

I suspect you'll have to get a "parts mule" for the dial, knobs, etc!

Chris Williams

[Neil Purling]

As the Champion 832 looks like a slightly revised 748 is the dial the same? A photocopied 748 dial would do.
I have made an enquiry to Ed Dinning in case a small autotransformer for the heaters, (82.6V) is possible.

[Ed_Dinning]

Hi Neil, a rough calculation shows that about 2.2uF should work nicely and will be smaller than a transformer for this somewhat cramped set

Ed

[Neil Purling]

Referring to the 1954 Champion range 784B that has the same valves. My 832 has the heater chain as: V3,V4,V1,V2. Newnes has the rectifier (V4) first.
The HT dropper or anti-surge resistor is that huge Marconi part of which only the 160 ohm section is used. looking at Newnes suggest OEM was probably 150 ohms.
What is unsettling is that the heater dropper is 317 ohms. I measured it. So how's that dropping 147 volts?
has anyone got an un-molested Champion 832 or a 784 B with the same valves?

[FERNSEH]

"What is unsettling is that the heater dropper is 317 ohms. I measured it. So how's that dropping 147 volts?"
Simple Ohms law I = V/R gives 0.463amp. And it's a 0.15amp heater chain.

DFWB.

[Herald1360]

Yes, but the heaters are in series (0.15A not 0.463 (0.45?)A).

That would need 980R for 147V drop.

317R is suspiciously close to the 300R line cord used on the 0.3A chain 784.

[PJL]

Seems to be some confusion. Post 2 says the heater dropper measured 1100 ohms but that is contradicted in post 11.

The 18DA had a 0.1A heater chain (UL41) and used a sectional 1250 ohm dropper with voltage adjustment settings. The minuet also uses a 0.1A heater chain (UL41) although the early 784 used octal valves with a 0.3A heater chain.

[FERNSEH]

Information from the 1953/54 R & T servicing book.
Early production sets employ 0.3amp valves: 6BA6, 6AM6, 25L6 and 25Z4.

DFWB.

[Neil Purling]

Yesterday I had 1st sound. However the set was very insensitive & I know that they can be far better. The glow of the heaters appears pink because the camera is over sensitive to infra-red

My interpretation of the diagram from the 1953-54 Newnes Radio & TV Servicing is that in the Champion 784B the 240 Volt input was at the junction of R5 and R6.
R5 goes to the rectifier anode. The Heater ballast is R6 & it should be 1K, or therabouts.
I have altered the wiring to be exactly as it says in Newnes. The heater ballast is the gold coloured 'contact-cooled' 1K 25 watt resistor.
R5 is the green resistor that is 317 ohms.

[Neil Purling]

During the day it gets the local Kingstown Radio. It is the local hospital radio & the transmitter is atop the hospital building itself. All of 45W ERP. Noisy of course, especially after dark. The interesting thing is that it is only 18Khz apart from the Manx Radio frequency.

[Ed_Dinning]

Hi Neil, I wondered if it had been a 120v set.
With 82v of heaters and 0.15A a 317 R would bring it up to about 130v
Quite within the range of approximations used in those days !

I believe you did it right by using the 1K as it is what is required, not what is fitted that stops things going BANG.
Look for any resistors that have gone high in value or an output transformer that has shorted turns . I would think primary resistance should be at least 500R

Ed

[Neil Purling]

Hard to say what it was meant to be as the mains cable had been cut at the back of the set.
I don't know if Champion exported this model with it being a 'second-set'. I think that The Phantom, whoever they were made some mistakes when substituting the dropper section.

I need to find some hardboard or plywood to make the heat-deflector & get some mains cable of the proper length.

[PJL]

The Marconi had the same line up so the dropper should have worked OK, it should have had a total resistance of 1250.