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Old 6th Jan 2022, 3:53 pm   #1
Biggles1998
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Default BC5639 on the bench

Hi

just joined the forum for it vast knowledge and advice, and hopefully feedback also.

so i've dipped my toe into restoring a GEC BC5639, and seen some others have attempted these radio's also, looks like a good starter for me as it seems to be simple enough to get around.

although saying that i went around in circles looking at the Cap values the other day, then realised that two circuit diagrams i had referred to the CAPs with different ref numbers LOL. (and a typo on the circuit diagram in regards to the dual 16/32 cap)

So anyway i picked up the radio with the intention of a refurb, and at least it was in a working state, but now on the bench and parts ordered for the CAP replacements.

I read a comment about the tone pot sparking, which i think i have on this, so have taken it apart,cleaned and maybe look to do the circuit amendment i found.

as it's my first attempt, i think ill stick to replacements rather than trying to hide new inside old (unless i feel brave).

wish me luck.. photos to follow..

mike
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Old 6th Jan 2022, 9:31 pm   #2
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Default Re: BC5639 on the bench

Seems the easiest first step after the breakdown out of the cabinet is the dual 16/32uF tin cap. Why do they hook the leads through connectors? Bit awkward to unsolder!
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Old 7th Jan 2022, 1:28 pm   #3
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Default Re: BC5639 on the bench

Hello Mike

Firstly solder is not glue you shouldn't rely on a solder connection it is always better to have some form of mechanical connection as the joint will be much stronger and less likely to fail. My other Idea is a guess in that it was done for production in that they had someone building up the components and wiring that was then soldered as a later stage in production. I do also wish you every success with your first restoration. You will get a lot of help and support from people on this forum. I do sometimes choose to cut the wires rather than try and unsolder them it depends on the situation

Regards Chris
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Old 7th Jan 2022, 2:30 pm   #4
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Default Re: BC5639 on the bench

Hi Mile, welcome to the forum.
It's not clear which, and how many capacitors you intend to change, we all have are own ideas on that, perhaps you are just targeting the electrolytics, which is fine, but you should still change C18 (Trader sheet no 1005) as a matter of priority.
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Old 7th Jan 2022, 4:53 pm   #5
Biggles1998
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Default Re: BC5639 on the bench

Thanks guys, Yes I've started to cut and remove and then look at tidying up the connectors afterwards at the moment and yep C18/C23 is now already out, and had a deformation on the base when I looked, new part to go back in, and the plan is to replace all the caps.

I'm tempted to try and place the replacement inside the can, but as it's the first attempt it might not come out as planned.

LOL.
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Old 8th Jan 2022, 7:34 am   #6
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Default Re: BC5639 on the bench

If you really mean all the capacitors then that rings alarm bells!

Most of us would say that a thorough job would involve the electrolytics and all the paper dialectric caps (typically wax covered), but leave the small-value mica caps in the RF and IF stages alone. Sometimes these are also wax covered, but they rarely give trouble unless disturbed.

The images in this post show how I re-stuff a smoothing can.

https://www.vintage-radio.net/forum/...62&postcount=4
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Old 8th Jan 2022, 3:30 pm   #7
Biggles1998
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Default Re: BC5639 on the bench

Hi - thanks for the tip, and yes it was in the back of my mind about changing all caps, and the effect on the tuning (if that's the right expression).

i do have a number of caps that look like mica ( waxed and non ), so will take your advice and try and leave these alone and concentrate on the larger paper wax caps instead, of which i've removed "C11" (on my sheet no'132 service bulletin i'm using as reference).

will look at trying my hand at dissecting this as a test to see what happens, along with the Dual Cap.

thanks for the link for the repack..
Mike - G1KOT
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Old 9th Jan 2022, 2:37 pm   #8
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Default Re: BC5639 on the bench

Well that's the Main 16uf/32uf cap removed and cleaned out.. bit if a hack job, but at least the can is in good shape..
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Old 9th Jan 2022, 3:03 pm   #9
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Default Re: BC5639 on the bench

Hi

The subject of cap replacement has been discussed several times on this forum, and opinions vary. I can see the point of doing all the electrolytics and papers if you want to do it once and for all, e.g. if its a set for someone else or access is difficult. It's not the wax on the outside that's the problem, it's the wax on the inside. Wax dipped mica dielectric types don't suffer the same problems as wax impregnated paper. That's not to say they can't fail, but it's rare.

The downside of major replacement in one hit is not that it will affect tuning (the above types aren't used in tuned circuits) but that you can possibly make an error or inadvertently disturb something. Even worse would be two errors, making fault finding very hard.

Personally, I use an intermediate approach which involves changing electrolytics and only those paper capacitors in circuit positions where leakage might cause mischief i.e. any high impedance circuits like grid couplers or the AGC line, or anything to do with mains filtering or isolation. The changes are made progressively, checking for operation after each change.

On another topic, although I realign sets that I restore (because I like to and have the test gear) many of them would have worked fine without it unless someone has already been in there twiddling. Plenty of sets will have failed in the past and then been put in the loft because they cost a lot of money and the owners couldn't bear to throw them away. These original faults vary, but misalignment is rarely one of them.
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Old 10th Jan 2022, 8:34 am   #10
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Default Re: BC5639 on the bench

Thanks for the advice,
its the start of my learning curve where i was expecting to replace all the caps, but as you say some are rarely needed to be replaced, and indeed i'm in no rush to get this done, so as you mention change test and continue after each element changed.


along with making up some other kit, such as a poor mans varicap (bulb style) are on the cards.

thanks
Mike
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Old 22nd Jan 2022, 8:17 pm   #11
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Default Re: BC5639 on the bench

So after the 16/32uf tin replacement and 1x paper cap first test seems to good , picking up smooth radio and now onto a few other paper caps..
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Old 22nd Jan 2022, 8:33 pm   #12
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Default Re: BC5639 on the bench

Yes it's always worth trying-it-to-see-if-it-still-works after replacing each component; that way, if it doesn't work you have a very good idea on where to focus your attentions!

I once replaced several parts at the same time on a radio and re-wired the new parts one-pin-further-round on the valve-socket; that one took some finding!
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Old 24th Jan 2022, 10:37 pm   #13
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Default Re: BC5639 on the bench

All caps replaced and getting signals across the bands which is good, hard to tell on the strength as i've not really got anything to guide me on.. but signals heard on LW, MW and SW with just the internal loop antenna, which means im still on track .. now the question around resistors, i've just taken measurements with the multimeter and most seem to be over 10%, but in taking readings while they are in situ, can it throw the readings of? do you need to remove the resistor in total to measure, or measure as close to the body as possible?
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Old 25th Jan 2022, 12:11 am   #14
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Default Re: BC5639 on the bench

In theory you need to disconnect one end of the resistor to measure it accurately.

Many original resistors in valve radios were manufactured with a 20% tolerance.

Looking at your spreadsheet, I see no reason to investigate further providing the radio works correctly.
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Old 25th Jan 2022, 11:42 am   #15
Biggles1998
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Default Re: BC5639 on the bench

Thanks for the comment, it looks as if all the resisters i have are silver banded at 10% tolerance.. using the link (calculator)

is what you are saying that silver was 20% back in the day??

edited ( after seeing this discussion (https://antiqueradios.com/forums/vie...?f=19&t=373767

i read that three bands where 20% and that four bands, as such that i have seem be rated at 10%

so would this difference need addressing?

thanks
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Old 27th Jan 2022, 5:01 pm   #16
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Default Re: BC5639 on the bench

i didn't realise that starting this little project that i'll have to start being proficient and cabinet repairs, veneer touch up and a varnish expert LOL....
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Old 14th Feb 2022, 4:30 pm   #17
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Default Re: BC5639 on the bench

Hi - just catching up and though id post the final entry on this my first refurb attempt, i looked at placing caps inside the old shells, but i look like ii was going to make a pigs ear out if it so just did the replacements until i get the technique
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Old 14th Feb 2022, 5:50 pm   #18
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Default Re: BC5639 on the bench

Well Mike, You look to have made a good job of the cabinet, congratulations. Are you pleased how it sounds? One suggestion, for your next set is take plenty of photos, they don't cost much if anything and are invaluable if you think, or have actually made a mistake in wiring.

John.
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Old 16th Feb 2022, 11:49 am   #19
Biggles1998
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Default Re: BC5639 on the bench

hi - thanks, yes i was a bit unsure of the veneer being in a bad state, but gritted teeth and fine sandpaper brought it back to life .. and replaced the cork lining around the grill as this had become brittle over time, the grill had some chips, but trusty airfix paint box had an exact match !

the sound i must admit is really nice, i took the tone completely apart and cleaning it up as this had some crackling in use, and now its nice and smooth all the way round.

i hooked it up to a long wire for SW, and signals where coming in really good, so as a first revamp i'm pretty pleased, and nice for a keeper rather than refurb and sell..

the next one, will be photos at every step..
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