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Old 14th Jul 2019, 9:08 pm   #1
Northyorks1
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Default Sobell 439

Just got this little beauty, I think so anyway. Post is just about how well the chassis has come up using Rustins rust coverter, it's water based goes on so easily full coat on chassis in about 10 min. Put 2 coats on and looks good. It says on the bottle that colour will change to a blue-black colour as it reacts to the rust, but mine has gone a very dark brown and looks well. This stuff goes a long way 250ml bottle will probably last a lifetime. I made the mistake of pouring to much out thinking I would easily use it , but hardly used any. So best to pour out minimal amounts to use as you go, as you can't pour it back into original bottle to use again. Have been looking around house for anything rusty to use it on.

Ian
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Old 15th Jul 2019, 8:49 am   #2
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Default Re: Sobell 439

Nice set, another one on my "to get list."
I've used Rustins rust coverter myself on various things and I agree it's s very good indeed, water based products as with paint are getting better all the time.
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Old 15th Jul 2019, 2:54 pm   #3
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Default Re: Sobell 439

Yes the Sobell Sobellete is a looker but not a performer but it works wll enough

I have a couple of these and it's much rarer sibling (same Chassis) the 430

The larger cabinet and speaker of the 430 does make it sound pretty good.

I am clearing out most of my post war sets except Cossor and the battery sets but I think the 439 the A22 and The Emor Globe will all be staying but not many others

Cheers

Mike T
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Old 15th Jul 2019, 3:45 pm   #4
Northyorks1
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Default Re: Sobell 439

I am in two minds as whether to strip it or not, I really like the pastel green, so if it was stripped it would need to be resprayed. And this case is really in quite good condition compared to most I have seen, with no chips or cracks just minor scratches to the paintwork Which I could possibly live with. I am in no rush at the moment just happy to have it. Quite like your 430 as well Mike.

Ian
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Old 15th Jul 2019, 4:31 pm   #5
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Default Re: Sobell 439

Hi Ian

I think I would leave that alone, its as tidy as you see painted ones except when they are newly painted

I think the colour is called Eu de Nil (Water of the Nile)

When I've seen the Nile its been more brown like

Lovely example.

Cheers

Mike T
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Old 15th Jul 2019, 7:56 pm   #6
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Default Re: Sobell 439

Thanks for comments Mike, I think you are right best left alone. That was a nice little nugget of info, eau de Nil. From now on I am only buying small cased radios
with bakelite cases. I have one large ish wood cased radio that needs a dial glass Ferguson 627U when I find a dial glass it will go, just takes up to much space.

Ian
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Old 15th Jul 2019, 8:20 pm   #7
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Default Re: Sobell 439

I'd vote too for just cleaning case. It's good for 70 yo.

It's a design that's well suited to take advantage of Bakelite.
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Old 18th Jul 2019, 2:19 pm   #8
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Default Re: Sobell 439

Can anyone tell me what type of performance I can expect from this radio. As it is up and running with limited reception, picking up 4 stations on MW which are not great, and nothing on LW. When I opened it I was surprised to see a new smoothing capacitor and volume control. I Have done the usual capacitor replacements and out of spec resistors, replaced broken 12J7GT valve. And there my limited experience ends.

Ian
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Old 18th Jul 2019, 3:00 pm   #9
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Default Re: Sobell 439

Um. It won't be great. It's not even a "short superhet". Grid leak detection.
C23 from V2 anode to L10 in the sole IFT may need adjusted, just before oscillation is best. To much or too little and it's deaf. Re-adjust every time you adjust IFT cores.

It depends where you are, but I'd expect that it ought to get R4 LW with a 30cm loop (can be rectangular on a wooden picture/photo framer 40 turn loop and about 2.5mH or more switched in series for LW, can be sorted for MW).
Local interference will swamp its poor selectivity with any sort of wire aerial unless you are up on the moors or something.
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Old 18th Jul 2019, 3:07 pm   #10
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Default Re: Sobell 439

It's more of a Collector's item than a radio for everyday listening as it has been cost reduced by removal of an IFT and detector / preamp. It's what it is, so I'd not modify it to make it better even though adding an IFT and an 1N34 (1946) or 1N60 (1956) would be simple.

Perhaps it will get 8 or 10 MW and 1 or 2 LW with a loop aerial and better alignment.
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Old 18th Jul 2019, 6:26 pm   #11
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Default Re: Sobell 439

Thanks for information Mike. I am not planning to use it much at all, its just dissapointing how poor the perfomance is. And with my very limited knowledge I did not know the capabilities of this radio. The tweaks you mention are beyond my knowledge, But I am not planning to change anything other than try a loop aerial with it. I bought it for its looks originally, so it will just sit there looking pretty.

Ian
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Old 18th Jul 2019, 6:51 pm   #12
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Default Re: Sobell 439

Can you identify the adjustable C23 between the IFT can and the second valve anode?

It *IS* pretty. At least it does "go".
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Old 18th Jul 2019, 9:07 pm   #13
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Default Re: Sobell 439

Yes can see C23.
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Old 19th Jul 2019, 8:43 am   #14
Mike. Watterson
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Default Re: Sobell 439

Try adjusting it with a plastic tool with small blade tip.
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Old 19th Jul 2019, 9:56 am   #15
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Default Re: Sobell 439

May sound a silly question, but should it be adjusted with radio on or off.
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Old 19th Jul 2019, 10:27 am   #16
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Default Re: Sobell 439

You can only adjust it with the radio on. Choose weakest station. The adjustment will increase or decrease the apparent sensitivity, but it will suddenly go deaf or whistle if you go past the loudest point, then back off.

You can then see if BBC R4 LW works.

You'll need a loop, even 20 turns bell or speaker wire or thin coax (short all cores) around a box will work. Mount loop vertically. LW would need about 50 or 60 turns, it's simpler to put a 2.5mH approx choke/coil in series.

The L3 and L4 are a little more affected by a loop than an aerial and earth. Likely C18 means no external earth is needed (ideally on neutral side of mains, especially in Ireland as that is bonded to earth and an earth spike at each meter box here).

L3 (MW, affects LW) and L4 (LW) are to peak the RF at the 500m /600kHz and approximately 1800m/175kHZ low frequency ends of bands.
L5 and L6 set the lowest tuning frequency (assuming scale pointer is aligned to maximum closed point on tuning). C20 is RF peak and C22 is higher frequency tracking alignment (200m / 1500kHz usually, though some sets use 1400kHz). There is no tracking alignment for LW.
All values from Trader 939.

Do make sure L5, L3, C22, C20 are correct (MW) and L4, L6 are correct (LW).
Looking at CIRCUIT (not Chassis):
The parts on the right of V1 set the low and high frequencies to match scale if pointer is correct when capacitor fully closed. The parts on the left peak the low frequency and high frequency signals for a particular aerial (though hardly affected by a long wire) when the set is correctly tuned.
You can either use two loops wound at right angles and switched, or one with a series coil/choke switched in series. Or a 6" long ferrite rod with MW & LW coils (switched and ignore taps for transistor base).

Even a 3m / 10ft wire draped on the curtain rail ought to work. I have a 1935 TRF that picks up MW at night and R4LW during the day 9km west of Limerick city with 3m wire on curtain rail (inc feed). So your Sobell ought to get BBC R4 LW. I can't say if French language station or RTE1 LW are possible on it.
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Old 19th Jul 2019, 10:31 am   #17
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Default Re: Sobell 439

Actually the Trader 939 does give alignment instructions.

Note the "Repeat" as the adjustments interact!

IF should be rechecked AFTER RF/LO is done.
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Old 19th Jul 2019, 10:32 am   #18
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Default Re: Sobell 439

Do you get distorted sound at low setting of the volume control?
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Old 19th Jul 2019, 12:44 pm   #19
Northyorks1
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Default Re: Sobell 439

No sound is not distorted. Thanks for advice Mike just trying to get my head round it, dont have much experience with aerials other than the fact there is one on my roof. My son has just made up a loop aerial that we are trying at the moment.

Ian
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