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Old 23rd May 2020, 11:00 am   #41
poppydog
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Default Re: Ferranti 925 mains lead

The link below is to Radio Constructor from 1966 containing a piece from the Dickie and Smith sagas and was kindly sent to me by Geoffk.
It has a uncanny relevance to the issues I have at the moment, starts from page 696.

https://www.americanradiohistory.com...RC-1966-06.pdf
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Old 23rd May 2020, 7:08 pm   #42
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Default Re: Ferranti 925 mains lead

I note the circuit indicates 7V on mains and explains the anode & screen currents, shows the ballast resistors.

I liked reading that column.
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Old 23rd May 2020, 7:10 pm   #43
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Default Re: Ferranti 925 mains lead

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Originally Posted by poppydog View Post
Any recommendations what diode/s I could use in place of the old rectifier please?

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1N4007 and maybe 220 Ohm 5W.
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Old 25th May 2020, 11:22 am   #44
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Default Re: Ferranti 925 mains lead

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Quote:
Originally Posted by poppydog View Post
Any recommendations what diode/s I could use in place of the old rectifier please?

poppydog
1N4007 and maybe 220 Ohm 5W.

Thanks for the suggestions Mike.

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Old 26th May 2020, 2:17 pm   #45
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Default Re: Ferranti 925 mains lead

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Re: Post#35:

Possibly not, but if you do decide to replace the existing rectifier with a silicon rectifier I would fit a 33uF for C25, and the same value for C24.

Lawrence.
Could I use 47uf here?


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Old 26th May 2020, 3:06 pm   #46
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Default Re: Ferranti 925 mains lead

It should be alright if you can't get a 33uF, an important thing to remember is selecting a suitable value (and wattage rating) for the silicon rectifiers limiter resistor, according to the valve data the voltage across the filament chain should be approx. 7 volts if everything's ok.

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Old 26th May 2020, 3:42 pm   #47
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Default Re: Ferranti 925 mains lead

Thanks for the reply. I try to get everything from rs, but every thing I want is on back
order at the moment due to the circumstances we are in and I don't really want to start getting cheap and nasty components.

I have some 47uf 450v nichicons here that were too big to use for restuffing on a grundig so Its good to know I can use these. I'll be careful with the limiter resistor.
Back in post 34 you said that you thought that the voltage out of the rectifier was low, what should I have had out of that rectifier?

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Old 26th May 2020, 3:57 pm   #48
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Default Re: Ferranti 925 mains lead

The Trader sheet quotes 100 volts across the reservoir capacitor.

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Old 26th May 2020, 4:05 pm   #49
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Default Re: Ferranti 925 mains lead

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The Trader sheet quotes 100 volts across the reservoir capacitor.

Lawrence.

"The unsmoothed voltage across C25 was 100v"

Ok thanks, I did'nt see that

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Old 31st May 2020, 5:21 pm   #50
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Default Re: Ferranti 925 mains lead

Regarding the voltages that I'm trying to measure at the moment, I'm measuring with my neg test lead connected to ground via chassis, It's not supposed to be via the neg of c24/25 is it as would r23 not affect my results??

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