1939 Pilot Maestro - UK Vintage Radio Repair and Restoration Discussion Forum

davebms · 14th Apr 2020, 5:27 pm

Hello all, I got this set from a member here. It's been modified with a 6volt transformer for heaters, and a metal rectifier for ht. The volume pot has been changed for a 1meg double pole, and the output valve to a 6v6. Pin 5, diode section 6q7g, has its resistor wedged in the fixing screw of T1 that turns out to be a really good earth !! so I marked it with red marker. All the chokes and coils checked out ok (once I worked out the loud speaker windings). I rewired the heaters so that they were not connected to earth to stop possible Ht to Lt shorts. I wired the transformer to a plug so its got its own supply. 6q7g has open heater, 6k7g very low emission the other all good, ordered two replacement valves. I replaced the caps on v4, that took a long while as I double checked looking for problems, so isolation transformer variac dim bulb (clean sockets). I tried to reform the smoothing cap but no go, tacked in two new ones heaters on HT up, Nothing !!! FORGOT to connect the resistor to t2 (yes it took ages to follow diagram) BUT it works

I will change the rest of the caps one at a time /check resistors LOTS to clean !! I want to put a valve rectifier back in probably a capacitor dropper (when I work it all out) but so far so good

thanks dave

vinrads · 15th Apr 2020, 8:55 am

That looks very clean under the chassis Dave ,good luck with the rest of the restoration .Mick.

davebms · 28th Sep 2020, 5:30 pm

hello all. the pilot is all done (I had more photo but cant find them) ive just
re fitted to back into cabinet ,, all went ok. I used the capacitor dropper for
heaters. experimenting with some caps that I had to hand it was as per the calculations on Pauls web page, but with motor run cap no resistor required
(different type dielectric) heater volts a little low ,but set works well I used scotch pad to remove surface rust. tuning capacitor removed and cleaned,
masked and sprayed chassis with gloss lacquer no real problems all coils speaker all good . I disconnected v4 cathode bypass capacitor , less distortion (well to my ears) tone capacitor up to .03 . I used my Tech TE 20D
and a frequency meter and checked /adjusted alignment that made a good improvement !! I will put pictures of finished radio in success section
thanks all dave

Herald1360 · 28th Sep 2020, 7:29 pm

Did you go back to the original series heater type valves?

A capacitor dropper will have saved around 50W of resistive losses (at the expense of a poorer power factor) and the set will run as cool as with the heater transformer mod.

Was the 6V TX not up to the extra heater load of something like a 6X5GT or did you want to go back nearer to original?

davebms · 28th Sep 2020, 8:54 pm

hello all. yes went back to original valves , got a good working out put
for £1 plus post , I had a rectifier and socket . the 6 volt transformer that the set came with, pushed out 7.5 volts (probably why one valve heater dead) I resisted down,, when working to sort HT and after a few hours it got very hot and lost volts, plus it was BIG and mounted on the back cover

dave

14th Apr 2020, 5:27 pm	#1
davebms Pentode Join Date: May 2017 Location: Ware, Hertfordshire, UK. Posts: 215	1939 Pilot Maestro Hello all, I got this set from a member here. It's been modified with a 6volt transformer for heaters, and a metal rectifier for ht. The volume pot has been changed for a 1meg double pole, and the output valve to a 6v6. Pin 5, diode section 6q7g, has its resistor wedged in the fixing screw of T1 that turns out to be a really good earth !! so I marked it with red marker. All the chokes and coils checked out ok (once I worked out the loud speaker windings). I rewired the heaters so that they were not connected to earth to stop possible Ht to Lt shorts. I wired the transformer to a plug so its got its own supply. 6q7g has open heater, 6k7g very low emission the other all good, ordered two replacement valves. I replaced the caps on v4, that took a long while as I double checked looking for problems, so isolation transformer variac dim bulb (clean sockets). I tried to reform the smoothing cap but no go, tacked in two new ones heaters on HT up, Nothing !!! FORGOT to connect the resistor to t2 (yes it took ages to follow diagram) BUT it works I will change the rest of the caps one at a time /check resistors LOTS to clean !! I want to put a valve rectifier back in probably a capacitor dropper (when I work it all out) but so far so good thanks dave Attached Thumbnails

15th Apr 2020, 8:55 am	#2
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,763	Re: 1939 Pilot Maestro That looks very clean under the chassis Dave ,good luck with the rest of the restoration .Mick.

28th Sep 2020, 5:30 pm	#3
davebms Pentode Join Date: May 2017 Location: Ware, Hertfordshire, UK. Posts: 215	Re: 1939 Pilot Maestro hello all. the pilot is all done (I had more photo but cant find them) ive just re fitted to back into cabinet ,, all went ok. I used the capacitor dropper for heaters. experimenting with some caps that I had to hand it was as per the calculations on Pauls web page, but with motor run cap no resistor required (different type dielectric) heater volts a little low ,but set works well I used scotch pad to remove surface rust. tuning capacitor removed and cleaned, masked and sprayed chassis with gloss lacquer no real problems all coils speaker all good . I disconnected v4 cathode bypass capacitor , less distortion (well to my ears) tone capacitor up to .03 . I used my Tech TE 20D and a frequency meter and checked /adjusted alignment that made a good improvement !! I will put pictures of finished radio in success section thanks all dave Attached Thumbnails

28th Sep 2020, 7:29 pm	#4
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: 1939 Pilot Maestro Did you go back to the original series heater type valves? A capacitor dropper will have saved around 50W of resistive losses (at the expense of a poorer power factor) and the set will run as cool as with the heater transformer mod. Was the 6V TX not up to the extra heater load of something like a 6X5GT or did you want to go back nearer to original? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

28th Sep 2020, 8:54 pm	#5
davebms Pentode Join Date: May 2017 Location: Ware, Hertfordshire, UK. Posts: 215	Re: 1939 Pilot Maestro hello all. yes went back to original valves , got a good working out put for £1 plus post , I had a rectifier and socket . the 6 volt transformer that the set came with, pushed out 7.5 volts (probably why one valve heater dead) I resisted down,, when working to sort HT and after a few hours it got very hot and lost volts, plus it was BIG and mounted on the back cover dave