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Old 13th Sep 2017, 6:34 pm   #21
Wishiknewmore
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Default Re: French Miracle 510 1937 too many valves?

Pete
Thank you for the advice, I have a couple of 110v sets and have found a auto transformer,but they are there for another day!
Lawrence
I have tried to follow the capacitors back
The 0.025MF cap that goes to pin 4 on valve 42(A) is connected to via a resistor to pin pin 2 on Valve 42 (B)
The capacitor that goes to valve 42 (B) is connected to a tuning coil ( I think ) with 4 connections the other 3 of which are connected to the unmarked valve which you suggested is a 6A7
Does this help?
I have attached my attempt at a partial circuit for these two 42's
Any thoughts on the suitability of two 473 1KV in parallel as replacements for the 0.025MF caps?
Many thanks
Philip
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Old 13th Sep 2017, 7:28 pm   #22
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Default Re: French Miracle 510 1937 too many valves?

Is your reverse engineered drawing of the output stage starting to resemble the schematic in the link below (scroll/drag down to book page 585, the schematic is Fig. 13.44) Ebb on that schematic means HT:

http://www.paleoelectronics.com/RDH4/CHAPTR13.PDF

Lawrence.
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Old 13th Sep 2017, 7:53 pm   #23
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Default Re: French Miracle 510 1937 too many valves?

Oh!
Yes I think it probably does
I will need an hour in a quiet room with a cup of tea to verify
I will come back to you tomorrow
Thanks
Philip
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Old 13th Sep 2017, 10:28 pm   #24
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Default Re: French Miracle 510 1937 too many valves?

473? I assume you mean, is 0.047uf
Two in SERIES = nearly 0.025uf, not parallel.
Half the value, twice the voltage.
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Old 14th Sep 2017, 12:56 pm   #25
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Default Re: French Miracle 510 1937 too many valves?

Lawrence
Yes, as far as I can work out, except R5 and R6 don't appear to exist .. see pic

Boater Sam...told you I was a novice!
Blue ceramic discs marked as 473 1kv so 47nF 47000pF 0.047uF there two in series equals 0.0235uF ...suitable to replace my "that caps" marked 0.025MF

Opinion..if I replace the 8,16,and 10uF electrolytics (8 and 10 with 10's and 16 with a 15) and the two 0.025uFs is it worth some power on...bearing in mind usual cautions and caveats
Will be via lamp limiter etc.

Philip
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Old 14th Sep 2017, 1:14 pm   #26
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Default Re: French Miracle 510 1937 too many valves?

The non existence of R5 and R6 is of no real consequence, the phase inversion appears to be done by one of the output valves as was suspected earlier, but there's a fly in the ointment, there appears to be a resistor that you've drawn in that connects to C2, is it definitely connected to C2? If so where does the other end connect to?

Yes I would replace the electrolytics and the grid coupling capacitors before firing up.

Lawrence.
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Old 14th Sep 2017, 1:15 pm   #27
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Default Re: French Miracle 510 1937 too many valves?

0.025 is very small for an audio coupling cap, I'd just put one 47n @ 1000v in if you already have it. 400v would do.
Your electrolytic values are fine, does it really need them? They may well reform OK.
Check transformers for continuity, especially the output before getting too involved..


Yes, get it on a lamp as soon as possible, get it working , then find out what it really needs.
Then change one thing at a time so you don't have an introduced error you can't find.

Sam.
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Old 14th Sep 2017, 1:20 pm   #28
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Default Re: French Miracle 510 1937 too many valves?

0.025uF isn't a very small value for a coupling capacitor, I've seen 0.001uF and sometimes lower....

Lawrence.
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Old 14th Sep 2017, 1:33 pm   #29
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Default Re: French Miracle 510 1937 too many valves?

I knew someone would jump on that remark! Just trying to save a few pence that don't need to be spent.
I've seen smaller and larger, not bragging, hey ho.

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Old 14th Sep 2017, 2:53 pm   #30
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Default Re: French Miracle 510 1937 too many valves?

Lawrence
The said resistor (orange body, black end I think yellow dod, it pinged off) measures 330kohm
Is connected via the yellowish wire to pin 4 and one end of the 0.025uF cap, the other end of the resistor goes to the chassis.
Is this a problem? All seems very untouched ? ( except for choke and replacement 16 uF cap)

Boater Sam
I've already got the electrolytics, and the rubber insulation on the 8 and 16 have perished, so I will replace, makes me feel like I've done something

Philip
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Old 14th Sep 2017, 3:06 pm   #31
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Default Re: French Miracle 510 1937 too many valves?

Quote:
Originally Posted by Wishiknewmore View Post
Lawrence
The said resistor (orange body, black end I think yellow dod, it pinged off) measures 330kohm
Is connected via the yellowish wire to pin 4 and one end of the 0.025uF cap, the other end of the resistor goes to the chassis.
Is this a problem? All seems very untouched ?
That 330k resistor isn't the one I was on about, that 330k is the usual grid resistor to complete the grid bias circuit (cathode bias)

The resistor I was referring to is the hand drawn one that's running north south in the top left hand side of the annotated schematic in post#25.

Lawrence.
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Old 14th Sep 2017, 5:05 pm   #32
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Default Re: French Miracle 510 1937 too many valves?

Whoops, I have gone back to the chassis rather than my wiring sketches, and I now don't know where I thought that hand drawn was, sorry
Philip
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Old 14th Sep 2017, 8:32 pm   #33
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Default Re: French Miracle 510 1937 too many valves?

Update
Electrolytics replaced, "coupling' capacitors replaced ,mains lead replaced, power applied via lamp limiter......
Result..crackly wave change switch,scratchy volume control and a significant amount of hum,but reception on all the wave bands, a very pleasing result
But more questions,
Can I use the earth from the domestic mains supply as the ground for the aerial?
The house has an earth rod type earth?
I have read elsewhere that one end of a long wire antenna should be grounded..to reduce the risk from lightning is this correct?
My plan is now to clean wafer switch,valve pins and volume control with switch cleaner and search for the reason for the hum...any suggestions
Many thanks in advance
Philip
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Old 14th Sep 2017, 10:29 pm   #34
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Default Re: French Miracle 510 1937 too many valves?

Mains earth is sometimes disappointing when used for a radio, as it can be electrically noisy. You may get better results with a separate earth stake. But, there is no harm in trying ..... But consider yourself lucky, if it's any good. Do not make any connection to the live or neutral pins of the plug.
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Old 15th Sep 2017, 8:24 am   #35
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Default Re: French Miracle 510 1937 too many valves?

Long wire aerials used to have a shorting link to ground for use in thunder storms. It is doubtful if it would have made any odds in the event of a strike and of course the aerial would not work shorted to ground.
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Old 15th Sep 2017, 10:28 am   #36
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Default Re: French Miracle 510 1937 too many valves?

The difference a night makes!
Returned to set this morning, no radio signals at all! Any band
Set works on gram / pick up with iPod, but the volume control has very little effect, more like a tone control
Suggestions?
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Old 15th Sep 2017, 11:08 am   #37
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Default Re: French Miracle 510 1937 too many valves?

Is the set now on full mains, without the lamp?
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Old 15th Sep 2017, 12:05 pm   #38
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Default Re: French Miracle 510 1937 too many valves?

Yes, on full mains
But there are developments
I ran with iPod for about an hour till the battery ran out and turned in to long wave..and there is radio 4 ( and others)
Thoughts?
Dry joint?, bad contact?
Philip
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Old 15th Sep 2017, 12:15 pm   #39
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Default Re: French Miracle 510 1937 too many valves?

Dirty wave change switch?
Without checking voltages when not working it's hard to guess. Intermittent faults are the devil to fix.
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Old 15th Sep 2017, 4:15 pm   #40
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Default Re: French Miracle 510 1937 too many valves?

Quote:
Originally Posted by Boater Sam View Post
Long wire aerials used to have a shorting link to ground for use in thunder storms. It is doubtful if it would have made any odds in the event of a strike and of course the aerial would not work shorted to ground.
A direct hit would vaporise it anyway, but static build up as a nearby flash gets its act together would be dissipated, rather than biting either the radio or anyone touching it.

Even in clear weather you can get quite a belt sometimes from contacting an ungrounded aerial.
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