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Old 6th Nov 2021, 1:12 pm   #41
Simon Gittins
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Default Re: Pilot Little Maestro restoration project.

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And the pilot lamp seems to be in parallel with one of the heaters
Originally, one end of the line cord went to one side of the rectifier heater and the first 15 ohm section was anchored at some point (possibly a spare tag on the rectifier) with the pilot lamp wired across these two points.
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Old 6th Nov 2021, 1:18 pm   #42
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Default Re: Pilot Little Maestro restoration project.

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I noticed this odd 50 ohm 5 watt ''made in uk'' resistor which seems to be taking the full mains input on one side and the other side of it is hooked to the valve next to the rectifier.
The output valve socket tag 6 that the 50 Ohm is connected to doesn't connect to the valve itself according to the valve data (6 = no pin) If the 50 Ohm is in circuit trace where in the circuit it's connected to in the schematic.

Lawrence.
The resistor in question is wired to the points shown in the pic below,


Cheers.
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Old 6th Nov 2021, 1:26 pm   #43
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Default Re: Pilot Little Maestro restoration project.

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The resistor in question is wired to the points shown in the pic below
If the mains is/was connected to tag 6 of the middle valve socket then it's looking like a surge limiter for the rectifier:

https://www.vintage-radio.net/forum/...6&d=1636039756

?

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Old 6th Nov 2021, 1:30 pm   #44
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Default Re: Pilot Little Maestro restoration project.

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Quote:
And the pilot lamp seems to be in parallel with one of the heaters
Originally, one end of the line cord went to one side of the rectifier heater and the first 15 ohm section was anchored at some point (possibly a spare tag on the rectifier) with the pilot lamp wired across these two points.
Pilot lamp is tied to the point illustrated by a piece of solder, Rear valve between tuning cap & speaker

Cheers.
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Old 6th Nov 2021, 1:58 pm   #45
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Default Re: Pilot Little Maestro restoration project.

It looks as though the pilot lamp wiring has been altered as V3 (6Q7G) was the last valve in the chain with one side connected to chassis. Where does the other side of the pilot lamp go? It may be going to chassis via the holder and there may or may not be a shunt resistor across the pilot lamp.
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Old 6th Nov 2021, 2:03 pm   #46
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Default Re: Pilot Little Maestro restoration project.

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Originally Posted by Simon Gittins View Post
It looks as though the pilot lamp wiring has been altered as V3 (6Q7G) was the last valve in the chain with one side connected to chassis. Where does the other side of the pilot lamp go? It may be going to chassis via the holder and there may or may not be a shunt resistor across the pilot lamp.
Yup tied to the chassis and no shunt that i can see


Jay
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Old 6th Nov 2021, 2:10 pm   #47
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Default Re: Pilot Little Maestro restoration project.

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Originally Posted by ms660 View Post
Quote:
Originally Posted by Radio Scotland View Post
The resistor in question is wired to the points shown in the pic below
If the mains is/was connected to tag 6 of the middle valve socket then it's looking like a surge limiter for the rectifier:

https://www.vintage-radio.net/forum/...6&d=1636039756

?

Lawrence.
Mains was tied to the point shown below
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Old 6th Nov 2021, 2:15 pm   #48
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Default Re: Pilot Little Maestro restoration project.

Where did the right hand Red wire shown in the photo in the link I posted connect to apart from tag 6 of the output valve socket and one end of the 50 Ohm resistor?

Lawrence
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Old 6th Nov 2021, 2:20 pm   #49
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Where did the right hand Red wire shown in the photo in the link I posted connect to apart from tag 6 of the output valve socket and one end of the 50 Ohm resistor?

Lawrence
The answer to that is i'm not sure, Since been snipped off, In hind sight not a good idea
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Old 6th Nov 2021, 2:27 pm   #50
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Default Re: Pilot Little Maestro restoration project.

The red wires had been taped on to the original cord or at least it looked like the original cord or what was left of it, Wanted it gone asap due to any asbestos risks
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Old 6th Nov 2021, 3:24 pm   #51
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Default Re: Pilot Little Maestro restoration project.

Looks like the 50 ohm resistor is in series with the mains input and the heater of the 25Z4 rectifier
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Old 6th Nov 2021, 5:31 pm   #52
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Looks like the 50 ohm resistor is in series with the mains input and the heater of the 25Z4 rectifier
Forget the above its hooked to the plate of the 25Z4 Rectifier. Tap from what i believe was the original mains cord goes to one side of the 50 ohm resistor other side to the plate.. The heater chain appears to have been wired to the original line dropper. The pilot lamp taps V4 heater other side of the lamp is chassis grounded.

Believe the above to be correct after a bit of googling valve pinouts and testing various points of the circuit,


Quote:
Oscillator section of the tuning cap seems to have a DC Short
Is this on both positions of the waveband switch? If so, there could be a problem, especially as you mentioned in Post 16 that the tuning shaft is bent.


Yea short goes away when the band selector is switched S4 Shunts one of the coils to ground which appears as an almost DC Short
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Last edited by Radio Scotland; 6th Nov 2021 at 5:39 pm. Reason: correction
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Old 6th Nov 2021, 5:39 pm   #53
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Default Re: Pilot Little Maestro restoration project.

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Originally Posted by Radio Scotland View Post
Quote:
Originally Posted by Simon Gittins View Post
It looks as though the pilot lamp wiring has been altered as V3 (6Q7G) was the last valve in the chain with one side connected to chassis. Where does the other side of the pilot lamp go? It may be going to chassis via the holder and there may or may not be a shunt resistor across the pilot lamp.
Yup tied to the chassis and no shunt that i can see


Jay
The pilot lamp has been moved to the bottom of the heater chain instead of the top; I don't see any point in moving it back again but putting the 15 ohms shunt back would stop it glowing too brightly and make it last longer. The original bulb was 7.3V 0.25A is this still what is fitted and is it still ok? It may be hard to find an exact replacement.

Just seen the post above, I think you meant the pilot lamp goes to V3 heater from your description earlier.

Last edited by Simon Gittins; 6th Nov 2021 at 5:44 pm. Reason: Addition.
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Old 6th Nov 2021, 5:42 pm   #54
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Default Re: Pilot Little Maestro restoration project.

Quote:
Originally Posted by Simon Gittins View Post
Quote:
Originally Posted by Radio Scotland View Post
Quote:
Originally Posted by Simon Gittins View Post
It looks as though the pilot lamp wiring has been altered as V3 (6Q7G) was the last valve in the chain with one side connected to chassis. Where does the other side of the pilot lamp go? It may be going to chassis via the holder and there may or may not be a shunt resistor across the pilot lamp.
Yup tied to the chassis and no shunt that i can see


Jay
The pilot lamp has been moved to the bottom of the heater chain instead of the top; I don't see any point in moving it back again but putting the 15 ohms shunt back would stop it glowing too brightly and make it last longer. The original bulb was 7.3V 0.25A is this still what is fitted and is it still ok? It may be hard to find an exact replacement.
Its working and looks like new, Its not the original, Its 6.5v 0.3a
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Old 6th Nov 2021, 5:46 pm   #55
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Default Re: Pilot Little Maestro restoration project.

That's good. You may want to try it with and without a shunt when you get it going.
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Old 6th Nov 2021, 5:51 pm   #56
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That's good. You may want to try it with and without a shunt when you get it going.
If i get it going But i'm slowly putting the puzzle together.

Currently waiting on a new audio coupling cap and 2 x smoothing caps.


Cheers
jay
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Old 6th Nov 2021, 7:03 pm   #57
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That's good. You may want to try it with and without a shunt when you get it going.
Any idea of the shunt wattage rating ?

Quote:
I think you meant the pilot lamp goes to V3 heater from your description earlier.

Yea my mistake lamp is in series with V3 Heater
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Old 6th Nov 2021, 7:46 pm   #58
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Default Re: Pilot Little Maestro restoration project.

The 15 ohm 2.5 watt resistor you suggested should be fine.
The heater chain current is 0.3A and the resistor should be able to handle this current if the bulb fails; the wattage is the current squared times the resistance which works out at 1.35W.
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Old 6th Nov 2021, 7:56 pm   #59
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Default Re: Pilot Little Maestro restoration project.

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Originally Posted by Simon Gittins View Post
The 15 ohm 2.5 watt resistor you suggested should be fine.
The heater chain current is 0.3A and the resistor should be able to handle this current if the bulb fails; the wattage is the current squared times the resistance which works out at 1.35W.
Thanks for that I Have two power resistors i can parallel to get the required 15 ohms.

One last thing (i think) Which of the following capacitors would it be advisable to change ? Obviously C10 Audio coupling for starters..And C13/14 Smoothing caps

Wont touch anything frequency related unless need be,

Cheers
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Last edited by Radio Scotland; 6th Nov 2021 at 8:12 pm.
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Old 6th Nov 2021, 9:01 pm   #60
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Default Re: Pilot Little Maestro restoration project.

Yes, C10 is the most important one. C13 and C14 might be reformed but changing them is an option. C15 is worth changing (it needs to be a Class X type as it's filtering the mains) also C12 as if it fails the output transformer is at risk.
We normally suggest not changing too many capacitors at once as it's easy to make a mistake so you could try the set after changing those five and then change others as required.
At some point C1 should be changed in case someone touches the end of the throw-out aerial (needs to be a Class Y type).
C6 will probably reduce the screen voltages and C4 will probably mean the AGC won't work properly. C11 will probably be causing low volume. C5, C7, C8 and C9 could cause trouble as well.
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