Pilot Little Maestro pre war AC/DC 1939 restoration project. - Page 7 - UK Vintage Radio Repair and Restoration Discussion Forum

Radio Scotland · 12th Nov 2021, 1:31 pm

New tone correction capacitor fitted, Dropper caps in parallel come out around 3.8UF So i'm either gonna be low on voltage or high and they're to big to fit on the valve base, Plan B i suppose, Mounted on the old smoothing can space.

Still waiting on the bleed resistor, So nothing being fired up yet

Radio Scotland · 12th Nov 2021, 3:15 pm

Quick summary of the work done today for anybody that's interested.

Built cap dropper ''block'' 2 X 2.2uf safety caps in parallel, Working voltage 305 Volts, Actual capacitance measured in pic below.

Across the line cap replaced with an X2 ...275 Volts rating.

Tone correction cap replaced..

Thats it for today, No bleed resistor yet..

Any mistakes feel free to comment

Cheers
jay

Radio Scotland · 12th Nov 2021, 4:56 pm

Dropper too near rectifier valve ? Heat shield needed ?

agardiner · 12th Nov 2021, 5:30 pm

Quote:

Originally Posted by Radio Scotland

Dropper too near rectifier valve ? Heat shield needed ?

I would say that the dropper is far enough away to be OK.

Radio Scotland · 12th Nov 2021, 6:13 pm

Quote:

Originally Posted by agardiner

Quote:

Originally Posted by Radio Scotland

Dropper too near rectifier valve ? Heat shield needed ?

I would say that the dropper is far enough away to be OK.

Wasn't happy so i moved it farther way..

Radio Scotland · 12th Nov 2021, 9:15 pm

Any boffins out there that can tell me what voltage 3.8uf of capacitance will give me on the heaters ?

ms660 · 12th Nov 2021, 9:24 pm

Quote:

Originally Posted by Radio Scotland

Any boffins out there that can tell me what voltage 3.8uf of capacitance will give me on the heaters ?

Hard to say for sure because the heater filaments are Non Ohmic.

Lawrence.

Radio Scotland · 12th Nov 2021, 9:27 pm

Quote:

Originally Posted by ms660

Quote:

Originally Posted by Radio Scotland

Any boffins out there that can tell me what voltage 3.8uf of capacitance will give me on the heaters ?

Hard to say for sure because the heater filaments are Non Ohmic.

Lawrence.

Cheers

Read about guys having no issues using a 4uf (Stated value) motor run cap..

paulsherwin · 12th Nov 2021, 9:46 pm

Measure the voltage. Start with a lower capacitance and then increase it if necessary.

Valve heaters are quite tolerant of being run slightly over voltage, though obviously it's not desirable.

Radio Scotland · 12th Nov 2021, 9:49 pm

Quote:

Originally Posted by paulsherwin

Measure the voltage. Start with a lower capacitance and then increase it if necessary.

Problem is paul i wanna be sure i'm in the ball park before applying power, Don't wanna hear the valves go pop pop pop

Jay

Radio Scotland · 13th Nov 2021, 1:20 pm

Well plugged it in, No bangs or blue flames, But no heaters or lamp either, And 240v on the output of the dropper, Kinda like there was no load on it, Checked the heaters and they're ok, Maybe a break in the chain some where.

Radio Scotland · 13th Nov 2021, 2:30 pm

Turned out one of the valve heater pins was needing tightened up, 56 VOLTS output from the dropper and a rather dim dial lamp

More capacitance on the dropper ?

Well its a start..

Jay

davebms · 13th Nov 2021, 5:48 pm

hello all. if you have a surge limit resistor in the heater chain, possibly reduce its value ?

dave

Radio Scotland · 13th Nov 2021, 5:51 pm

Quote:

Originally Posted by davebms

hello all. if you have a surge limit resistor in the heater chain, possibly reduce its value ?

dave

I had 14 volts sitting across it dave 50 ohms/5 watts, Weird thing is when i bypassed it the output didn't go up, Still 56 volts

Jay

Radio Scotland · 13th Nov 2021, 5:55 pm

I'm missing something

davebms · 13th Nov 2021, 6:36 pm

hello all . thats strange,what voltage have you got going into the cap dropper
? is dial bulb in series with heater string ?
dave

Radio Scotland · 13th Nov 2021, 6:42 pm

Quote:

Originally Posted by davebms

hello all . thats strange,what voltage have you got going into the cap dropper
? is dial bulb in series with heater string ?
dave

Yeah it's in series dave although its been moved to the end of the filament string, 240v going in,

I wonder if the 100k bleed resistor is the wrong value and its loading the voltage down

Jay

davebms · 13th Nov 2021, 6:48 pm

hello all , try to disconnect bleed resistor, it should still work BUT give things
time for cap discharge, before touching set after switch off

dave

Radio Scotland · 13th Nov 2021, 6:51 pm

Quote:

Originally Posted by davebms

hello all , try to disconnect bleed resistor, it should still work BUT give things
time for cap discharge, before touching set after switch off

dave

Was thinking the same, I'll try that tomorrow dave,

Cheers

jay

Ed_Dinning · 13th Nov 2021, 7:42 pm

Hi Jay, note that in this setup Vmains does not equal Vcap + Vhtrs. It is actually what is called a vector sum and takes a while to explain and get your head round
Ed

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12th Nov 2021, 1:31 pm	#121
Radio Scotland Heptode Join Date: Jul 2020 Location: Larkhall, South Lanarkshire, Scotland. Posts: 671	Re: Pilot Little Maestro restoration project. New tone correction capacitor fitted, Dropper caps in parallel come out around 3.8UF So i'm either gonna be low on voltage or high and they're to big to fit on the valve base, Plan B i suppose, Mounted on the old smoothing can space. Still waiting on the bleed resistor, So nothing being fired up yet __________________ Help!! I've been electrocuted by a glass thing that glows Last edited by Radio Scotland; 12th Nov 2021 at 1:36 pm. Reason: Extra info

12th Nov 2021, 3:15 pm	#122
Radio Scotland Heptode Join Date: Jul 2020 Location: Larkhall, South Lanarkshire, Scotland. Posts: 671	Re: Pilot Little Maestro restoration project. Quick summary of the work done today for anybody that's interested. Built cap dropper ''block'' 2 X 2.2uf safety caps in parallel, Working voltage 305 Volts, Actual capacitance measured in pic below. Across the line cap replaced with an X2 ...275 Volts rating. Tone correction cap replaced.. Thats it for today, No bleed resistor yet.. Any mistakes feel free to comment Cheers jay Attached Thumbnails __________________ Help!! I've been electrocuted by a glass thing that glows

12th Nov 2021, 4:56 pm	#123
Radio Scotland Heptode Join Date: Jul 2020 Location: Larkhall, South Lanarkshire, Scotland. Posts: 671	Re: Pilot Little Maestro restoration project. Dropper too near rectifier valve ? Heat shield needed ? Attached Thumbnails __________________ Help!! I've been electrocuted by a glass thing that glows

12th Nov 2021, 9:15 pm	#126
Radio Scotland Heptode Join Date: Jul 2020 Location: Larkhall, South Lanarkshire, Scotland. Posts: 671	Re: Pilot Little Maestro restoration project. Any boffins out there that can tell me what voltage 3.8uf of capacitance will give me on the heaters ? __________________ Help!! I've been electrocuted by a glass thing that glows

12th Nov 2021, 9:46 pm	#129
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: Pilot Little Maestro restoration project. Measure the voltage. Start with a lower capacitance and then increase it if necessary. Valve heaters are quite tolerant of being run slightly over voltage, though obviously it's not desirable.

13th Nov 2021, 1:20 pm	#131
Radio Scotland Heptode Join Date: Jul 2020 Location: Larkhall, South Lanarkshire, Scotland. Posts: 671	Re: Pilot Little Maestro restoration project. Well plugged it in, No bangs or blue flames, But no heaters or lamp either, And 240v on the output of the dropper, Kinda like there was no load on it, Checked the heaters and they're ok, Maybe a break in the chain some where. __________________ Help!! I've been electrocuted by a glass thing that glows

13th Nov 2021, 2:30 pm	#132
Radio Scotland Heptode Join Date: Jul 2020 Location: Larkhall, South Lanarkshire, Scotland. Posts: 671	Re: Pilot Little Maestro restoration project. Turned out one of the valve heater pins was needing tightened up, 56 VOLTS output from the dropper and a rather dim dial lamp More capacitance on the dropper ? Well its a start.. Jay __________________ Help!! I've been electrocuted by a glass thing that glows

13th Nov 2021, 5:48 pm	#133
davebms Pentode Join Date: May 2017 Location: Ware, Hertfordshire, UK. Posts: 215	Re: Pilot Little Maestro restoration project. hello all. if you have a surge limit resistor in the heater chain, possibly reduce its value ? dave

13th Nov 2021, 5:55 pm	#135
Radio Scotland Heptode Join Date: Jul 2020 Location: Larkhall, South Lanarkshire, Scotland. Posts: 671	Re: Pilot Little Maestro restoration project. I'm missing something __________________ Help!! I've been electrocuted by a glass thing that glows

13th Nov 2021, 6:36 pm	#136
davebms Pentode Join Date: May 2017 Location: Ware, Hertfordshire, UK. Posts: 215	Re: Pilot Little Maestro restoration project. hello all . thats strange,what voltage have you got going into the cap dropper ? is dial bulb in series with heater string ? dave

13th Nov 2021, 6:48 pm	#138
davebms Pentode Join Date: May 2017 Location: Ware, Hertfordshire, UK. Posts: 215	Re: Pilot Little Maestro restoration project. hello all , try to disconnect bleed resistor, it should still work BUT give things time for cap discharge, before touching set after switch off dave

13th Nov 2021, 7:42 pm	#140
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Pilot Little Maestro restoration project. Hi Jay, note that in this setup Vmains does not equal Vcap + Vhtrs. It is actually what is called a vector sum and takes a while to explain and get your head round Ed