Champion 832 - 4 valve set

http://www.radiomuseum.org/r/champion_minuet_832_2.html

I wonder if it's that easy?
It's a TRF, so looks simple, no L.O. or I.F., 1955 very late for a TRF

R&TVS: Later version of 784 (1954), so Vol III p 48 of 1958 edition

"Volume control" is 1930s style gain control on RF stage, "Throw out" aerial for local reception, an external aerial may upset alignment. Original used a Line cord Dropper. Later 784 versions used internal Dropper. There are two versions of 832, one with US valves (line cord dropper as on early 784 always suggests an imported US design) and one UK/European types.

I don't see any reaction on it. The 300pF on V2 anode and 10nF to V3 grid suggests V2 is anode bend detector as there is no grid resistor but there is substantial cathode resistor. Schematic of UK /European U series type valves of 832 appears to be the 784 type M

No Trader sheet for Minuet 832 or earlier 784.

Basically a SG Det Pen 1932 TRF using all 1950s Rimlock Pentodes. UF41 UF42 UL41 UY41

I predict all the Brown Hunts and the Waxed paper caps are bad. The cardboard covered Electrolytics may be bad too.

You need a 300V leakage tester. You can use a uA meter (or a neon with a 10nF 400V cap), 2 x 1M resistors and the set's own HT supply.

Is that 10k pot on feeding V1 cathode the volume control?
Looks like the main dropper has been replaced already to some extent.
Looks like the sort of circuit that Sinclair would have used if he designed valve radios.

Mike

Looks like the sort of circuit that Sinclair would have used if he designed valve radios.

Mike

My thoughts too.. A bit messy, but essentially a polo and two WW's seem to bridge the original dropper.. I was more bothered about that other, rather rusty looking WW that looks to have been overheated at sometime.

Marion

PS
Reggie... Give us a clue, was it Rufforth, Wigginton, or Murton? Or was it somewhere else?

It's not a true volume control, just RF gain by changing RF amp cathode resistor instead of negative voltage via AGC.

Very typical for 1930s (or Sinclair in 1960s). Strange on 1950s model.

Marion - Knavesmire. Gotta love the house clearance boys.

The issue of the dropper - yes, it does appear to have been 'bridged' by some hefty resistors and that 'polo' and the other one is underneath. I am confident that the 'work' was not done by the phantom but by the old guy that also owned the radio manuals. There was a huge heap of other stuff too about industrial electrical engineering and it was all in the same box - so my (best guess) is that the owner knew what he was doing. Ha.

Still, what's the best step with this one? Michael, you were bamboozling me with science in your first reply a bit. Still learning here. It's clear that on no accounts should this one have any power yet until I can be sure what those droppers are or are not doing and the lack of decent trader sheet makes it slightly difficult. I have the schematic pdf but still just getting my head around how to read them.

Marion - Knavesmire. Gotta love the house clearance boys.

Of course!... I'd forgotten that one

Marion

i cant find the circuit so sorry cant help with this one.
but it looks like the top dropper is for the heaters so maybe better to change it for a capactive dropper.
rob t

I'm sure Chris can put it in the Tech library. It's in R&TVS as 784
The CAPACITORS are the issue, The dropper either go high, open of fall off. Just don't poke them!

Never power up without checking leakage on the grid coupling capacitors and any snubber/"tone correction capacitors"

Assuming UF41, UF42, UL41 and UY41 and not the other version:
It's essentially a 110V set! HT V4 UY41 fed via 150 Ohms (5W) from same point as series chain
12.5
21
45
31
----
119.5V

A 1150 Ohm resistor 15W or more, feeds all this direct from mains.

So peak HT on main 32uF HT is about 140V I think. This only feed the o/p transformer. All other HT inc. UL41 Screen Grid is on 2nd 32uF (probably a dual section can) fed by 2k2 (listed as 2.2 1.5W, the "k" is missing!) maybe 15V drop on that to about 125V for rest of HT rail.

I could be up to 20% out on the voltages.

It's an updated version of a 1930s US 110V design! This is why the earliest 784 had a "line cord" dropper. A favourite way to convert 110V sets.

Filament current is 100mA.
But assuming 240V = 119V on filament, then the 1150 Ohms has 250-119 = 131V and current is 114mA approx (131/ 1150). So HT current is 14mA max.

V3 cathode bias is 220 Ohms
So from curve of UL41 with about 120V g2 we can see what current output takes and what the rest of HT current in 2k2 Resistor is,

This on UL41
http://www.radiomuseum.org/tubes/tube_ul41.html

shows with HT 170 is Ig2 = 10, Ia= 53, with 165 Ohms Cathode.
shows with HT 100 is Ig2 = 5.5, Ia= 29, with 165 Ohms cathode.

So under 20mA for Ia is possible for 220 Cathode, still, I expect the filament voltage is somewhat lower than 119.5V and thus filament current less than 100mA. I can't see the HT current being as low as 14mA.

Certainly not only does a single RF amp TRF mean "local stations" only, but the 220 Ohms cathode resistor AND lower HT means the UL41 can't go as loud as the UL41 in the DAC10 (150 Ohms Cathode, 190V Anode and 27.5mA Anode current). If the change of cathode resistor and lower screen / g2 was linear on UL41, I'd expect about 15mA UL41 Anode current and about 7 mA for the rest of the circuit.

I'm sure Chris can put it in the Tech library. It's in R&TVS as 784

I didn't bother scanning it as Reggie said he has the schematic

lack of decent trader sheet makes it slightly difficult. I have the schematic pdf but still just getting my head around how to read them.

Trader sheet does not exist for this model and I suspect the pdf Reggie already has, is the 784 schematic from R&TS.

hi chris what vol of r+tvs is it in?
rob t

Ah now there's a thing, Radio & Television servicing volumes. I've seen so many groupings and sets they are so many and many people have many differences.

My suite its in vol V (1953-1954) page 60 with schematics on page 62

many thanks found it vol V
rob t

Ah now there's a thing, Radio & Television servicing volumes. I've seen so many groupings and sets they are so many and many people have many differences.

Indeed.
And my pair of R&TVS 1951 Edition (one book is Radio 1945 to 1951 and one is TV 194? to 1951) have models missing from the 1951 volumes of my six volume set (I to VI) that ends 1957-58 with a single index. Mysteriously I have a Vol VII (1958/1959) with its own index then after that the books I have don't have volume numbers, just years and their own indexes.

I believe there is a 1953 set, with some models not in the 1957-58 ending 6 vol set.

How does 1953 to 1954 get to be "V"? Have you a version with better pre 1951 coverage? Mine that's III

Also it's amazing how many UK models (not export) that seem to turn up not in ERT/Trader/R&TS at all (I have several). It's reasonable that Export ONLY models are not covered I suppose.

Assuming UF41, UF42, UL41 and UY41 and not the other version:
It's essentially a 110V set!

It is indeed this set.

Additionally, the 'polo' on the dropper (fed by two resistors from top to bottom) is marked as -
160ohm 0.3amp 5% ZE
which reads 1.16 on a meter when set to 20k ohms top contact to bottom.

Just about all the caps are split or oozing so (except the smoother which is visually in good condition. It's an RS double-32uf) , I can replace those first - then what?

Id be tempted to replace those capacitors, and throw it on a lamp limiter or Variac and see what happens. But that's just me..

Id be tempted to replace those capacitors, and throw it on a lamp limiter or Variac and see what happens. But that's just me..

So would I .. except I'd just remove the mains filter cap (if there is one) and change the audio coupling cap and then power up via the lamp limiter and with one finger on the mains switch watch and smell for while that way you can start to fault find and see what difference it makes when changing/cleaning things one at a t time .... but thats just me as I think fault finding is the best bit.

I have the 1957 860 "New Minuet" three valve TRF version, nice and easy to work on and a surprisingly good performer.

John

I think that's the plan. I'll make it safe then see what happens.

If nothing else, I was thinking of rigging up a simple battery transistor circuit and wiring that in there. The case is so wonderfully 'art-deco', white loveliness. It would be shame for it to just be a shelf-hanger
.

If nothing else, I was thinking of rigging up a simple battery transistor circuit and wiring that in there.

Marion