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Old 20th May 2018, 5:49 pm   #21
victor54
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Default Re: Restaurare Leak III ST Refurbishing

Nice case Ken, congratulations for your work.
By the way, did you change the ancien antena conector for a modern 75 ohms? How?
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Old 20th May 2018, 7:16 pm   #22
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Default Re: Restaurare Leak III ST Refurbishing

No, I have a ribbon aerial connected across the 300 ohm
Screws. It's all l need as I'm only a quarter of a mile from the local repeater transmitter.
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Old 20th May 2018, 7:22 pm   #23
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Default Re: Restaurare Leak III ST Refurbishing

You are using the One Thing.... decoder? are you happy with?
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Old 21st May 2018, 12:19 pm   #24
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Default Re: Restaurare Leak III ST Refurbishing

Yes. I should really do a write up and post it in success stories. This was my first restoration and l spent almost 60 hours on it, spaced over a seven week period.
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Old 21st May 2018, 12:25 pm   #25
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Default Re: Restaurare Leak III ST Refurbishing

What do you think about Neville Roberts restauration kit? published on HIFI-Collective

Has anyboady an oficial part list for the Leak III ?
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Old 21st May 2018, 12:38 pm   #26
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Quote:
Originally Posted by Kentode View Post
Yes. I should really do a write up and post it in success stories. This was my first restoration and l spent almost 60 hours on it, spaced over a seven week period.
How did you conect it? directly to the MPX out using a coupling capacitor, or throu the cathode follower?
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Old 21st May 2018, 2:53 pm   #27
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Default Re: Restaurare Leak III ST Refurbishing

I honestly don't remember! I'll dig out the notes and write it up next week!
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Old 21st May 2018, 3:25 pm   #28
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OK, thanks.
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Old 23rd May 2018, 4:27 pm   #29
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Default Re: Restaurare Leak III ST Refurbishing

Parts are ariving, first the PSU capacitors from F&T
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Old 11th Jun 2018, 11:17 am   #30
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Default Re: Restaurare Leak III ST Refurbishing

Now I stared up with my restoration.
First stepp was measuring resistors (all of them) Pulling out the tubes I asume i can check all of them without unsoldering. The result was not verry promising as many of them were out of 10% tolerance.
The worst were:
R2=166k(220k)
R3=115k(100k)
R5=30,7(33)
R7=380k(680k)
R8=378k(680k)
R9=14k(68k) can be a mesuring fault, I have to unslder
R10=41k(33k)
R11=18k(47k) can be a mesuring fault, I have to unslder
R15=123k(100k)
R19=206k(470k)
R25=452k(470k)
R25=121k(100k)
R27=52k(47k)
R30=815k(680k)
R36=56k(47k)
R38=12k(10k)
All cheramic capacitors I asume are all right
The electrolotics I have allready changed all with modern one as well as the C47 and C53 with MKp.
As I intend to use an external MPX decoder from Fisher(MPX 100) I did not care about the internal decoder compoments.
Your opinion shall be usefull to me. Shall I change all resistors or else?
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Old 11th Jun 2018, 12:44 pm   #31
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Default Re: Restaurare Leak III ST Refurbishing

If you are measuring the resistors with them still connected in circuit there will be some parallel resistance paths.

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Old 11th Jun 2018, 5:01 pm   #32
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Default Re: Restaurare Leak III ST Refurbishing

I knew it from the beginning, but having a close look to the diagram and excluding the tubes, only the capacitors can make some changes but not too significant. I marked the nevralgic points where I have to unsoler.
Unsoldering such a spatial structure, can damage sometimes much more than out of tolerance resistors.
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Old 11th Jun 2018, 5:23 pm   #33
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Default Re: Restaurare Leak III ST Refurbishing

Quote:
Originally Posted by victor54 View Post
Unsoldering such a spatial structure, can damage sometimes much more than out of tolerance resistors.
That is true, but if the original resistor is well outside it’s tolerance range, it should be replaced. If the original was a carbon composition type (most are), I would fit a modern one of the same type, to avoid adding inductance with carbon or metal film types. This is only really important in the RF stages.

Of course, in the RF stages, you must be very careful to fit the new resistors in exactly the same positioning as the originals. Make careful drawings, before fitting replacements, to avoid disturbing the RF circuit’s alignment.

Last edited by dazzlevision; 11th Jun 2018 at 5:25 pm. Reason: Added text.
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Old 11th Jun 2018, 5:47 pm   #34
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Default Re: Restaurare Leak III ST Refurbishing

Just to be clear, if measuring the resistors while connected in circuit R2, R7, R8 and R19 in your list all have parallel resistance paths in the schematic, for example:

R2 has a resistance in parallel due to R19 and R20.

R7 has a resistance in parallel due to R8, R6 and R9 (R9 is connected across the HT for temperature compensation)

R8 has a resistance in parallel due to R7, R6 and R9.

R19 has a resistance in parallel due R20 and R2.

There are others too, notably around the discriminator.

Lawrence.
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Old 11th Jun 2018, 7:58 pm   #35
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Default Re: Restaurare Leak III ST Refurbishing

I cant say contrary, but what do you suggest......unsoldering all my cause a mass....what shall I do?
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Old 11th Jun 2018, 8:57 pm   #36
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I cant say contrary, but what do you suggest......unsoldering all my cause a mass....what shall I do?
To measure them properly if there's a resistance in parallel they need to be disconnected but you can get a go/no go idea by comparing the measurement in circuit to the parallel combination, eg: the resistance of two resistances in parallel is R = R1*R2/R1+R2, take your measurement across R19 as an example which was 206k....R19 = 470k, the resistance in parallel with it is 100k + 220k which = 320k, so 470*320/470+320 = 190 (approx.) your measurement across the 470k was 206k, we have just calculated 190k using schematic values so all in all not far out, resistors probably ok, eg: the difference is less than 10%.

You can do the same calculation for the others, here's the calculator I use:

http://www.sengpielaudio.com/calculator-paralresist.htm

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Old 11th Jun 2018, 9:02 pm   #37
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Default Re: Restaurare Leak III ST Refurbishing

Quote:
Originally Posted by dazzlevision View Post
Quote:
Originally Posted by victor54 View Post
Unsoldering such a spatial structure, can damage sometimes much more than out of tolerance resistors.
That is true, but if the original resistor is well outside it’s tolerance range, it should be replaced. If the original was a carbon composition type (most are), I would fit a modern one of the same type, to avoid adding inductance with carbon or metal film types. This is only really important in the RF stages.

Of course, in the RF stages, you must be very careful to fit the new resistors in exactly the same positioning as the originals. Make careful drawings, before fitting replacements, to avoid disturbing the RF circuit’s alignment.
Thanks Lawrence, I started to get curage to make a total restoration takin care at the architecture. In that case, what about the old ceramic capacitors? Shall I recuperate and use the same?
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Old 11th Jun 2018, 9:32 pm   #38
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Default Re: Restaurare Leak III ST Refurbishing

You cannot check a capacitor properly if there is a parallel path unless you disconnect it, to test for leakage it should be tested at it's rated voltage or at least it's working circuit voltage if possible.

Ceramic capacitors are usually reliable, especially in tuned or low voltage circuits.

Lawrence.
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Old 13th Jun 2018, 8:02 am   #39
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Default Re: Restaurare Leak III ST Refurbishing

Hi Lawrence,
I had remake the calculations, you was right, large part of resistors revial better tolerances than 10%. Nevertheless R9 was too low and athers where too high especialy R3, R10, R26, R27, R30, R36 R38, Which I suppose are out of range. I shal start slowly, slowly to unsolder and change them with Kiwame as they are carbon type and claim to be noninductive. I can use also AB as I have a lott but I am afraid not to be so stabile.

Last edited by victor54; 13th Jun 2018 at 8:12 am.
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Old 14th Jun 2018, 6:22 pm   #40
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Default Re: Restaurare Leak III ST Refurbishing

Having a look inside
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