Pilot Little Maestro cap dropper query - UK Vintage Radio Repair and Restoration Discussion Forum

Malcolm G6ANZ · 10th Jul 2020, 12:27 pm

My next on the to do list is a Pilot 'Little Maestro' from around 1939. Although designed for 240v, it says so on the data plate, it has a line cord dripper. This cord is very tangled and twisted so I am going to replace it with a capacitor dropper and a resistance. Searching through this site I found that the hard work had already been done way back in 2007 by 'Radio Dave', and the revised circuit and values were available.
My question is what type of 4uF capacitor should I be using? A big motor run type https://www.ebay.co.uk/itm/4uF-Motor...cAAMXQ-KRRhOQ2 that might prove difficult to fit in the chassis or a smaller type used for small fan running https://www.ebay.co.uk/itm/CBB61-1-1...AAOSw5Ylb7ARb?
I'm using Ebay as an idea of the correct type I need.

boxdoctor · 10th Jul 2020, 1:01 pm

When renovating a small Portadyne table radio a couple of years ago, I used exactly the first type of capacitor you have given a link to. As I had replaced the rectifier with a silicon diode, I fitted the 4uf capacitor over the hole in the chassis where the valve had been.
There was a thread on here fairly recently about the choice of capacitor for this job, and I do remember the concensus was that the smaller ones you mention were not very reliable in ths position. The set is occasionally used, and has been Ok so far. Tony.

davebms · 10th Jul 2020, 1:35 pm

hello all,, I have nearly finished my 39 pilot. the reservoir cap was dead
so I put a motor run in its place, and the HT dropper behind it

dave

Malcolm G6ANZ · 10th Jul 2020, 2:04 pm

That's exactly what I intend to do. The HT smoothing caps can fit under the chassis asa they are much smaller than the 1939 style.
Cap and resistors on order from CPC.

paulsherwin · 10th Jul 2020, 3:53 pm

There's an old article by Paul Stenning on dropper calculations if you don't know it: https://www.vintage-radio.com/repair...per-calcs.html

Malcolm G6ANZ · 10th Jul 2020, 4:37 pm

I saw that and calculated the cap and resistor values. Then I found ,via a search, that it had already been done. My results tallied with theirs.

Malcolm

FERNSEH · 10th Jul 2020, 7:07 pm

The calcs for the heater dropper capacitor work out to something like 4.4microfarads. You can get away with a 4uF motor start capacitor.

Link to the Little Maestro I serviced last year:https://www.vintage-radio.net/forum/...d.php?t=161165

DFWB.

Ed_Dinning · 10th Jul 2020, 7:37 pm

You can also use classX types that may be a bit smaller.

Ed

10th Jul 2020, 12:27 pm	#1
Malcolm G6ANZ Octode Join Date: Feb 2006 Location: Bristol, UK. Posts: 1,042	Pilot Little Maestro cap dropper query My next on the to do list is a Pilot 'Little Maestro' from around 1939. Although designed for 240v, it says so on the data plate, it has a line cord dripper. This cord is very tangled and twisted so I am going to replace it with a capacitor dropper and a resistance. Searching through this site I found that the hard work had already been done way back in 2007 by 'Radio Dave', and the revised circuit and values were available. My question is what type of 4uF capacitor should I be using? A big motor run type https://www.ebay.co.uk/itm/4uF-Motor...cAAMXQ-KRRhOQ2 that might prove difficult to fit in the chassis or a smaller type used for small fan running https://www.ebay.co.uk/itm/CBB61-1-1...AAOSw5Ylb7ARb? I'm using Ebay as an idea of the correct type I need.

10th Jul 2020, 1:01 pm	#2
boxdoctor Rest in Peace Join Date: Sep 2010 Location: Ripley, Derbyshire, UK. Posts: 785	Re: Pilot Little Maestro cap dropper query When renovating a small Portadyne table radio a couple of years ago, I used exactly the first type of capacitor you have given a link to. As I had replaced the rectifier with a silicon diode, I fitted the 4uf capacitor over the hole in the chassis where the valve had been. There was a thread on here fairly recently about the choice of capacitor for this job, and I do remember the concensus was that the smaller ones you mention were not very reliable in ths position. The set is occasionally used, and has been Ok so far. Tony.

10th Jul 2020, 1:35 pm	#3
davebms Pentode Join Date: May 2017 Location: Ware, Hertfordshire, UK. Posts: 215	Re: Pilot Little Maestro cap dropper query hello all,, I have nearly finished my 39 pilot. the reservoir cap was dead so I put a motor run in its place, and the HT dropper behind it dave Attached Thumbnails

10th Jul 2020, 2:04 pm	#4
Malcolm G6ANZ Octode Join Date: Feb 2006 Location: Bristol, UK. Posts: 1,042	Re: Pilot Little Maestro cap dropper query That's exactly what I intend to do. The HT smoothing caps can fit under the chassis asa they are much smaller than the 1939 style. Cap and resistors on order from CPC.

10th Jul 2020, 3:53 pm	#5
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: Pilot Little Maestro cap dropper query There's an old article by Paul Stenning on dropper calculations if you don't know it: https://www.vintage-radio.com/repair...per-calcs.html

10th Jul 2020, 4:37 pm	#6
Malcolm G6ANZ Octode Join Date: Feb 2006 Location: Bristol, UK. Posts: 1,042	Re: Pilot Little Maestro cap dropper query I saw that and calculated the cap and resistor values. Then I found ,via a search, that it had already been done. My results tallied with theirs. Malcolm

10th Jul 2020, 7:07 pm	#7
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Pilot Little Maestro cap dropper query The calcs for the heater dropper capacitor work out to something like 4.4microfarads. You can get away with a 4uF motor start capacitor. Link to the Little Maestro I serviced last year:https://www.vintage-radio.net/forum/...d.php?t=161165 DFWB.

10th Jul 2020, 7:37 pm	#8
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Pilot Little Maestro cap dropper query You can also use classX types that may be a bit smaller. Ed