Another Pilot Little Maestro. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Sideband · 12th Nov 2019, 10:22 pm

Quote:

Originally Posted by Neil Purling

ECH35, 6K7, 6Q7 PL36 and PY33. That case must be unusual.

That can't be right....PL36 is a TV line output valve and PY33 is a TV rectifier. If they are fitted it seems like someone has been trying substitutes. The PL36 has a top cap.

I've heard of PL36 being used as output valves in high power amplifiers but never in a domestic radio....quite difficult to use as an audio valve. It would need special biasing.

FERNSEH · 12th Nov 2019, 10:30 pm

Did try a PY33 in my series 2 Little Maestro as a temporary replacement for the 25Z6 and it worked OK. Marconi-Osram U31 works OK as well.
Might try a PL36, it's got the same heater voltage as the 25L6.

DFWB.

Neil Purling · 13th Nov 2019, 12:52 pm

It IS a PL36. The changed valves are there to save the originals without having to change the capacitive dropper. The PY33 and PL36 were suggested to me on this Forum & are used examples obtained from members.

FERNSEH · 7th Jan 2020, 12:56 am

Before the Pilot Little Maestro and the Ultra EU4052 are dispatched to the set's owner we decided an internal fuse should be fitted inside the cabinet rather than just rely on the fuse in the plug.
The attachment shows how it was done in the Pilot. The fuse has a rating of 630mA.
At first I considered fitting the fuse holder on the heater capacitor clip but quickly decided against doing that because it would be all to easy to come into contact with the connections which are at mains potential. The position chosen behind the valves is much safer.

With a mains supply of 240volts the voltage at the top of the heater chain is 70V. Measure the voltage across the heater supply capacitor and the reading is 235volts. How about that?

DFWB.

stuarth · 7th Jan 2020, 2:11 am

Because the heaters are resistive and the capacitor is, well, capacitive, the two voltages have a 90 phase difference.

Think of a right angle triangle, the two sides adjacent to the right angle have a length proportional to the voltage across the heaters and the capacitor, the length of the hypotenuse is proportional to the supply voltage.

From Pythagoras, the adjacent side lengths of 70 and 235 give a hypotenuse of 245, ie the supply should be 245V.

Stuart

12th Nov 2019, 10:30 pm	#22
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Another Pilot Little Maestro. Did try a PY33 in my series 2 Little Maestro as a temporary replacement for the 25Z6 and it worked OK. Marconi-Osram U31 works OK as well. Might try a PL36, it's got the same heater voltage as the 25L6. DFWB.

13th Nov 2019, 12:52 pm	#23
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,086	Re: Another Pilot Little Maestro. It IS a PL36. The changed valves are there to save the originals without having to change the capacitive dropper. The PY33 and PL36 were suggested to me on this Forum & are used examples obtained from members.

7th Jan 2020, 12:56 am	#24
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Another Pilot Little Maestro. Before the Pilot Little Maestro and the Ultra EU4052 are dispatched to the set's owner we decided an internal fuse should be fitted inside the cabinet rather than just rely on the fuse in the plug. The attachment shows how it was done in the Pilot. The fuse has a rating of 630mA. At first I considered fitting the fuse holder on the heater capacitor clip but quickly decided against doing that because it would be all to easy to come into contact with the connections which are at mains potential. The position chosen behind the valves is much safer. With a mains supply of 240volts the voltage at the top of the heater chain is 70V. Measure the voltage across the heater supply capacitor and the reading is 235volts. How about that? DFWB. Attached Thumbnails

7th Jan 2020, 2:11 am	#25
stuarth Heptode Join Date: Feb 2010 Location: Heysham, Lancashire, UK. Posts: 668	Re: Another Pilot Little Maestro. Because the heaters are resistive and the capacitor is, well, capacitive, the two voltages have a 90 phase difference. Think of a right angle triangle, the two sides adjacent to the right angle have a length proportional to the voltage across the heaters and the capacitor, the length of the hypotenuse is proportional to the supply voltage. From Pythagoras, the adjacent side lengths of 70 and 235 give a hypotenuse of 245, ie the supply should be 245V. Stuart