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Thread ID: 43231 2004-03-07 22:55:00 Off Topic. Valve radio parts Colpol (444) Press F1
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220952 2004-03-08 19:40:00 I have a "Clipper" sitting in my garage. Bought it many (many) years ago on a whim. Was going then, but one of the valves conked out. Have not wanted to get rid of it because how many "old" things do individuals have these days ! Know nothing whatever about its intricacies.
Misty
:) 		Misty (368)
220953 2004-03-08 20:46:00 > Thank you so much guys . Plenty to think about but
> getting a bit techo .
> Anyway here is a bit more info .
>
> "It would be a good idea to cut off the power cord,
> to avoid temptation . It's likely to be rubber
> insulated, and the rubber will be in a state of
> terminal rot . The power cord must be replaced anyway .
> A Megger test of the power transformer is a good idea
> too . They can become leaky, and the high voltages
> (385 volts ac each side of the HT winding was
> standard) can cause smoke . "
>
> The cord fitted at present is strange . It appears to
> be plastic . The neutral ?wire is in the insulation .
> The other two wires are in their own insulated area
> with no indication of Phase or Earth but looking at
> the way it is wired to the present plug tells me
> which is which .
> I am reasonably sure that at some time in the past it
> has been modified as the mounting of the transformer
> shows that a different one was originally fitted . The
> mounting holes are there for a larger one than that
> presently fitted .

It is common for the power cord and transformer to have been replaced . If he radio goes, the transformer is OK at present though it may die during the first 20 or so hours of use . don't leave the radio unattended during that time .

> "The electrolytic capacitors (especially if they are
> in vertical cans ) are probably dead . The others
> should be tested for leakage . "
>
> Reference the vertical cans . The set has two . Turning
> the unit over reveals that they are not conected and
> a number of modern? capaciters have been wired in .

Common practice, should be OK but the replacements could be over 40 years old already . Post the brand names, that helps date them .

>
> The magnet on the rear looks like it is wire wound .
> Two wires go from the Transformer to the base of the
> cone . the other two wires go directly ( via a
> mounting plate) into the main coil and from there
> down to the cone . The area between the point where
> the cone ends,and where it enters the coil appears to
> be wound with a very fine wire .

That is an EM speaker alright, so it cannot be easily replaced . One issue is the loss of humbucking, though that can be retained if you keep the field coil .

> I must add that the speaker still works and the
> output can be understood but the quality is poor

The poor quality may not be the speaker at all . Unless the cone is badly ripped and/or rattling, or the voice coil is audibly rubbing on the magnet pole-piece it is probably OK . Those radios did not produce very high quality sound at all, despite some people's nostalgic memories of "lovely tone . " You can test without replacing by connecting another speaker in parallel on leads long enough to get you away from the original, or if you have the equipment, unsolder one lead frn the speaker to silence it and check the sound on the replacement .

There are many reasons (other than speakers) for poor sound on old valve radios, the most common being gassy or low emission valves, leaky coupling capacitors, RF/IF oveload for older sets or AGC faults for the more modern . Don't leap to conclusions .

> "Pots are usually sealed but with some of the older
> types you could prise the back-cap off and spray the
> inside with contact cleaner . Drilling a small hole
> and spraying cleaner inside was another trick . "
>
> I have tried to take the back off but it doesnt want
> to budge so will try drilling it .

"Sleeve" the drill with tubing so that it can only just break through the back plate . You need only 2-3 mm of drill showing, otherwise you could butcher the internals . Don't trust to manual control, it is all too easy to go too far .

If you don't already have one, buy a cheap analogue meter for testing purposes . I have recently purchased one from Jaycar that is excellent for this work .

Catalogue number is QM-1020, price $39 . 95 . It uses 9 volts at the meter probes for Hi ohms reading which makes it very good for checking capacitors for leakage and it has 5 well spaced ohms ranges for accurate readings on high value resistors & pots etc . Don't bother with a digital meter, they are great for voltage and current but not good on ohms unless measuring resistors . I have about five digital meters but I still need and use an analogue meter regularly . The latest purchase was to replace a 25 year old Hioki AS100D that finally died of old age .

Cheers

Billy 8-{) 		Billy T (70)
220954 2004-03-08 20:59:00 > A humdinger was just a pot across the AC heater
> supply with the wiper connected to earth. It was
> adjusted for minimum hum.

Eh? Say what Terry?

I learn something new every day! I never heard that called a humdinger before so perhaps it was an industry sector/regional thing.

I spent my apprenticeship a small factory/service shop where we made heaps of custom equipment for commercial clients (andthe boss's golf course buddies). We used to call that a hum-cancelling pot and we only installed them in hi fi gear where the filaments were fed from an isolated 6.3v winding. The pot was used to provide a "tunable" virtual-earth to cancel out heater-cathode leakage and induced voltages. Filament wiring was wound up to a tight twist with a hand drill to minimise radiated fields!

It was varied and very enjoyable work.

Cheers

Billy 8-{) 		Billy T (70)
220955 2004-03-08 22:33:00 That's right Billy. With many older sets, at least the UK ones, the humdinger was a wirewound pre-set straight pot of about 100 ohms.
Humdingers were also used fairly recently too on some valve amplifiers for hum reduction, instead of centre tapping the 6.3v secondary to earth.

Another common fault with old sets is the poorer quality enamel used on the transformer windings, leading to open circuits. Very easy for 48/50swg wire to oxidise right through, especially in intervalve transformers.

I forget now how many thousands of turns of 48swg I calculated to fill the bobbins on the old EKCO, good job I had the use of a coil winder :), else I'd still be winding by hand 15 years later.

(EKCO not echo, was short for E.K. Cole, but I forget what the E K stood for, they were one of the first radio manufacturers to use the new wonder plastic material "Bakelite" for the cases. 		Terry Porritt (14)
220956 2004-03-08 22:39:00 Ah-Ha, just found my notes on the intervalve tranny. 14,000 turns 46swg on the primary, and the secondary was 2 separate windings each of 14,000 turns 46swg.

So the intervalve transformer had a 2:1 step-up ratio :D 		Terry Porritt (14)
220957 2004-03-08 23:43:00 Just musing here Terry, but wouldn't that be a 1:2 step up ratio?

Coil winding was my least loved job. Winding RF & IF coil sets out of Litz wire for marine RTs was an awful job and if you counted the turns wrong the boss would pull the offending coil out and throw it at you! On one memorable Monday a set built from scratch over the weekend by a team of two (suffering from a Friday night hangover) for an urgent sale was found to have coils that were somewhat outside the required specs. The Boss swore & cursed for a while, then there was an almighty crash as it hit the floor, then he dragged it out to the workshop by the Mic cord and told us that jobs were on the line if it wasn't fixed by the next morning.

Nostalgia.

Cheers

Billy 8-{) :8}
Coil drying oven was a ZC1 valve case with a 75W lightbulb
in the bottom and a coil rack across the middle. Meths lamp
to burn off the fabric cover and the varnish (no easy-soldering
polyeurethane varnishes then) and sealing wax to secure the
windings. After termination and drying they were dipped in hot
wax to keep moisture out. 		Billy T (70)
220958 2004-03-09 00:55:00 Of course, a 1:2 ratio.

I tried to buy some litz wire some 12 years ago or so to wind a high Q frame aerial for medium wave, but couldnt find a supplier. There was some mention of heavy duty litz wire for , I think, switch mode power supplies, or was it inverters? Anyway at exhorbitant cost. 		Terry Porritt (14)
220959 2004-03-09 02:19:00 Isn't that 1:1:1 ? A single ended driver to push-pull output? ;-)

I let Beacon Radio wind mine.:D 		Graham L (2)
220960 2004-03-09 02:35:00 Whilst in rambling mode, I always get confused wth transformer ratios, it's all in the words and symbols, eg a one to two step up ratio, or symbolically 2:1 as 1:2 really means 1/2. So maybe I was right when I said a 2:1 ratio??

The secondary winding was in a divided bobbin, and the original was continuously wound, I had to make new bobbins as the original was distorted, and made a tapping so that I could either have 1:1 ratio or a 2:1 ratio, or is that 1:2 ?:|

Anyway 14,000 primary and 28,000 turns total secondary.

The valves were MS4B screen grid HF valve, 41MHL detector and af amp, and PM24M output pentode.
These numbers dont mean much to the southern hemisphere colonists who used ungodly American types :D 		Terry Porritt (14)
220961 2004-03-09 02:57:00 Col: That mains cord seems to be a bit naughtily wired . The earth wire should be the one in the middle . Phase and neutral are usually insulated as well as embedded in the sheath .

The vertical can electrolytics have obviously been terminated with extreme prejudice . If the modern tubulars haven't exploded they may have reformed and be OK . :D

All the connections on the speaker plug are at high voltages . The wire going to the field could could have well over 400V DC . The input of the speaker transfomer will be fed from 300-350V . You can get a "good" belt from that . :_|

It might be simplest to replace the volume control . It will probably be marked 500k, or 250k . The "modern" 470k or 270k values would be perfectly OK . If DSE or Jaycar haven't got a suitable physical size (shaft, mounting ferrule) a television serviceman would almost certainly have some in the junk box . :D 		Graham L (2)
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