Kit Radio Performance - UK Vintage Radio Repair and Restoration Discussion Forum

Neil Purling · 22nd Oct 2017, 11:51 pm

There must be a few Forum members out there with one of the DIY kit radios in the case copied from the Pilot 'Little Maestro'.
I know there are the basic 3 valve TRF and the 4 valve Superhet.
I am specifically referring to the TRF type.
How do you find that they perform in comparison to other sets in your collection?
I have got an example that appears to be pretty deaf, needing about 30ft of wire to do anything.

Obviously there's no 'Trader' sheet to go by, only a diagram here: http://vintage-radio.net/forum/attac...0&d=1144184530.

I have had a few of these through my hands and this example just doesn't seem right.

G6Tanuki · 24th Oct 2017, 4:46 pm

I've played around with numerous obes of these in the past: typical valve-lineup 6K7 6K7 6V6, EF39 EF39 6V6, or Mazda equivalents. One even had a CV309 VHF power-tetrode as the output-valve.

Given that they're essentially 1-V-1 they can be surprisingly sensitive if the regen is wound up - and with a RF amp you don't need to worry much about radiating oscillations if the detector does go into howl-mode.

My ones were as sensitive as a typical 4-valve superhet of the era: a few feet of wire as a 'throw-out' antenna used to be just fine for receiving Luxembourg and Caroline in the Midlands,

Does yours go into oscillation when you wind it up full? If not then check the detector. You can also get a feel for what's going on by connecting the antenna wire straight to the detector grid-cap through a small (50pF) capacitor - if that gives good results but the 'official' antenna socket gives poor results suspect the RF amp.

I've seen a few of these where the isolating capacitor between the antenna terminal and the RF-stage coil has failed, and taken the primary of the RF-stage coil with it [remember they're live-chassis radios...]

Neil Purling · 24th Oct 2017, 7:06 pm

These kits have anode-bend detection, no reaction is used.
That loctal tetrode is one of the odder outputs. I had a Premier with a 717A 'doorknob', VR116 and ATP-4 o/p, which was even weirder as the ATP-4 has a 2V heater.
The present example has 6K7G , 6J7 (metal) and 6V6G, which is boringly normal.

22nd Oct 2017, 11:51 pm	#1
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,087	Kit Radio Performance There must be a few Forum members out there with one of the DIY kit radios in the case copied from the Pilot 'Little Maestro'. I know there are the basic 3 valve TRF and the 4 valve Superhet. I am specifically referring to the TRF type. How do you find that they perform in comparison to other sets in your collection? I have got an example that appears to be pretty deaf, needing about 30ft of wire to do anything. Obviously there's no 'Trader' sheet to go by, only a diagram here: http://vintage-radio.net/forum/attac...0&d=1144184530. I have had a few of these through my hands and this example just doesn't seem right.

24th Oct 2017, 4:46 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: Kit Radio Performance I've played around with numerous obes of these in the past: typical valve-lineup 6K7 6K7 6V6, EF39 EF39 6V6, or Mazda equivalents. One even had a CV309 VHF power-tetrode as the output-valve. Given that they're essentially 1-V-1 they can be surprisingly sensitive if the regen is wound up - and with a RF amp you don't need to worry much about radiating oscillations if the detector does go into howl-mode. My ones were as sensitive as a typical 4-valve superhet of the era: a few feet of wire as a 'throw-out' antenna used to be just fine for receiving Luxembourg and Caroline in the Midlands, Does yours go into oscillation when you wind it up full? If not then check the detector. You can also get a feel for what's going on by connecting the antenna wire straight to the detector grid-cap through a small (50pF) capacitor - if that gives good results but the 'official' antenna socket gives poor results suspect the RF amp. I've seen a few of these where the isolating capacitor between the antenna terminal and the RF-stage coil has failed, and taken the primary of the RF-stage coil with it [remember they're live-chassis radios...]

24th Oct 2017, 7:06 pm	#3
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,087	Re: Kit Radio Performance These kits have anode-bend detection, no reaction is used. That loctal tetrode is one of the odder outputs. I had a Premier with a 717A 'doorknob', VR116 and ATP-4 o/p, which was even weirder as the ATP-4 has a 2V heater. The present example has 6K7G , 6J7 (metal) and 6V6G, which is boringly normal.