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Old 17th Feb 2019, 10:57 pm   #1
Wishiknewmore
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Default Pye "Slim Six" P128B

I have started to have a look at my first transistor set, based on the things I had read I expected that there would be failure of one or more of the germanium transistors….but maybe not!
I have supplied 6 volts to it and initially I had some signs of life from the speaker, but little if any reception, but after an hour or so a very quiet Radio 5 sport (I think), so prodding around to see any loose connections I discovered that touching the main variable tuning capacitor that instantly more stations (gain/sensitivity) and volume, so then attached a makeshift 4 meters of aerial to the terminal (as per picture) and now I have a moderate level of reception
Current draw is about 20mA , no reception on LW at all
Serial Number 973879
I have sprayed the wave change switch with switch cleaner, but not yet done any stripping down
So before I start randomly replacing capacitors what are the suggestions to move forward?
Philip
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Old 17th Feb 2019, 11:29 pm   #2
AD360 Rob
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Default Re: Pye "Slim Six" P128B

First I would double check the wave change switch, they sometimes need repeated applications of switch cleaner, then, I see it has a couple of those plessey black & red electrolytic, change those as they'll most likely be way out of spec and possibly leaky too. Next check if the local oscillator is running on long wave, you can use another radio to check. If it is running then chances are it's very insensitive (which you've sort of proved on mw by clipping that extra wite to the variable capacitor) does the set look like it's been got at previously?

Rob
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Old 18th Feb 2019, 9:10 am   #3
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Default Re: Pye "Slim Six" P128B

I seem to recall this set has a fixed long wave (not tunable.)

When I restored mine many years ago I had to retune it by moving the LW coil on the ferrite rod.

They are quite lively when working properly.

Cheers

Mike T
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Old 18th Feb 2019, 10:10 am   #4
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Default Re: Pye "Slim Six" P128B

Thanks for that
Rob
I will order up some new electrolytics and spend a little more time on the wave change switch, the set does not look as it has been got at before except for repeated resoldering of the wires from the battery tube
I am not 100% sure how to check that the local oscillator is working on long wave (ignorance exposed!) but shall see what new capacitors does for me

Mike
You are indeed correct it is a fixed LW tuning supposed to be 1500m

Philip
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Old 18th Feb 2019, 10:28 am   #5
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Default Re: Pye "Slim Six" P128B

The IF of this set is 470 kHz, so when the set is tuned to 198 kHz (BBC R4 Long wave) the Local Oscillator will be running at 198+470 kHz or 668 kHz. This corresponds to a wavelength of 300,000/ 668 metres or 449 metres. You should be able to hear the LO as a hiss as you tune through 449 metres on another radio in close proximity to the Pye.
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Old 18th Feb 2019, 10:49 am   #6
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Default Re: Pye "Slim Six" P128B

Graham
So obvious when you put it like that
Thank you
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Old 22nd Feb 2019, 8:29 pm   #7
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Default Re: Pye "Slim Six" P128B

Update

The local oscillator does appears to be working on LW at about 668kHz as I found the "lo hiss" on another radio
I replaced the 100uF caps,C16 and C23, this in itself seemed to make little difference (although they read 142uf and 25 pF on my cheapo Chinese component tester)
Next I replaced C11 with a 10uF, schematic shows 10uF, actual component marked 8uF tested at 750nF, this made a significant improvement to the gain/sensitivity, no need for my aerial wire
Then, I replaced C21 4uF on component and schematic with 2 x 10uF in series (5uF?), the existing cap measured 9831nf.
Is the 5uF a problem or near enough?
The set is very much better than it was, but still no long wave.
Comments, observations or suggestions
Many thanks in advance
Philip
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Old 23rd Feb 2019, 10:02 am   #8
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Default Re: Pye "Slim Six" P128B

The values of the electrolytics are not likely to be important if it works on MW.
The wavechange switch is more likely to be the problem or the LW aerial coil open circuit.
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Old 23rd Feb 2019, 1:40 pm   #9
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Default Re: Pye "Slim Six" P128B

I have had a fairly good go at the wavechange switch, but I will have a go at "hard wiring" in the LW position

Philip
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Old 23rd Feb 2019, 1:53 pm   #10
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Default Re: Pye "Slim Six" P128B

If the LO is running at the correct frequency, which you say it is, the fault must be with the LW aerial coil or switching. Have you checked the LW coil for continuity?
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Old 23rd Feb 2019, 2:42 pm   #11
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Default Re: Pye "Slim Six" P128B

If all else fails check C1 if it's a polystyrene type.

Lawrence.
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Old 23rd Feb 2019, 4:58 pm   #12
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Default Re: Pye "Slim Six" P128B

Update
The LW coils has continuity
I have removed C1, It was polystyrene , however I managed to break a lead off it while removing, It has been replaced by2x3300pf cobbled together in series (reading 1639pF)
Result is that I now have, at a very very low volume LW, although it seemed to increase slightly by itself over the last hour, may be my imagination
Should I change C6 also polystyrene?
And /or should I have a twiddle with C4 or will I live to regret it?
Thanks again
Philip
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Old 23rd Feb 2019, 5:21 pm   #13
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Default Re: Pye "Slim Six" P128B

Try adjusting the longwave coil (L3....R&TV Servicing schematic ref.) along the ferrite rod.

Post#7 suggests that the osc on LW is more or less on frequency so C6 is probably ok along with the setting of C4.

Lawrence.
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Old 23rd Feb 2019, 6:38 pm   #14
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Default Re: Pye "Slim Six" P128B

I tried moving the coil, it can make it worse but not better
I have had another go at the wavechange switch, I took it apart and although a very simple one I am not in a hurry to do it again!
To confirm post no 7 I definitely get a hiss on the second radio when switching to LW somewhere just below 700KHz as per the radio scale
Suggestions
Philip
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Old 24th Feb 2019, 1:42 pm   #15
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Default Re: Pye "Slim Six" P128B

What's MW and LW like now without an external antenna?

Lawrence.
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Old 24th Feb 2019, 2:28 pm   #16
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Default Re: Pye "Slim Six" P128B

The MW is quite respectable,the aerial doesn’t improve it
But on long wave the volume is very very low and the aerial does not improve this
Philip
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Old 24th Feb 2019, 2:32 pm   #17
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Default Re: Pye "Slim Six" P128B

I would check the LW osc frequency, try tweeking C4, if it starts to improve keep tweeking, if it doesn't peak check C6.

Lawrence.
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Old 24th Feb 2019, 2:45 pm   #18
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Default Re: Pye "Slim Six" P128B

Ok Lawrence
I will try that,but it will be tomorrow
Many thanks for your help
Philip
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Old 24th Feb 2019, 11:17 pm   #19
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Default Re: Pye "Slim Six" P128B

Just tried tweaking C4 ...Instant improvement

So I think that's it fairly well sorted electrically, thanks to all

Now to work on the cosmetics........any suggestions for a lacquer for polished brass?

Thanks again

Philip
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Old 25th Feb 2019, 3:00 pm   #20
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Default Re: Pye "Slim Six" P128B

Just wax the brass?
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