Premier kit radio - UK Vintage Radio Repair and Restoration Discussion Forum

Sideband · 29th Aug 2008, 4:15 pm

I bought this set a few years ago when another forum member was having a clearout (can’t remember who it was). I’d always wanted one after seeing adverts in the Radio Constructor back in the sixties. This version was white and housed in the usual ‘Pilot’ radio cabinet. It tuned MW, LW and SW.

Anyway the radio had worked some years before and then been stored. When I got it, there was a slight layer of dust and no evidence of previous work underneath. There was, however, a rather mouldy-looking electrolytic with severe corrosion growing out of one end. Most of the capacitors were of the metal-clad ‘Sprague’ type which are usually very good and don’t seem to suffer the same problems of the usual waxy types. There were four valves of the Octal variety namely 6K8, 6K7, an odd Admiralty type marked NR48, and a 6V6. The NR48 was presumably a 6Q7 equivalent and a check on the net showed that it is a Britsh Navy number for an EBC33. The rectifier was two Cen-Ter-Cel contact-cooled selenium types connected in series. There was a mains transformer which was for the valve heaters only. HT was taken from one side of the mains so the radio had a live chassis just like an AC/DC set. Considering it was a kit set, the build quality seemed very good. Judging by the date on two electrolytics, it would appear to have been built around 1953.

Firstly I replaced the mouldy-looking capacitor which was an 8uF electrolytic. The main smoothing can looked good and checked out reasonably well. The audio coupling capacitor was a waxy type and was replaced along with another one connected to the volume control. The others, as stated above were the metal type and they all checked out good on the bridge…..very good as it so happened considering they are 55 years old.

Seeing as there was a contact-cooled rectifier in place, I decided to run the set up slowly on the variac. This was easy and I measured the HT available on the smoothing caps while slowly increasing the mains. At around 200 volts, the radio started working although the HT was quite low at about 120v. Once up at full mains it was obvious that the rectifier was not in good health as I was only getting about 130v on the output valve anode. Everything seemed to be working though apart from low volume. It didn’t like working on SW either and was reluctant to tune above about 8 MHz.

I had no idea what the HT should be as there was no information (yet) on the set. However radio’s of this nature seem to run with an HT at the reservoir of 220 or so. I removed the old rectifiers and used two BY126 rectifiers in series and mounted them on a tagstrip that was already holding the smoothing resistor. I then mounted another tagstrip where the old rectifiers had been, to take the series limiter resistor. I started with a fairly high value for this and worked down and found that 500 ohms gave me just under 220 volts at the reservoir and HT to the 6V6 was now 215v. The set was now much more lively and shortwaves worked right through to the maximum 18Mhz.

Calibration was quite good but I decided to check I.F alignment. Again no information so I decided to check on a signal. The first I.F needed a good half-turn to peak it, the others not so much but now the set was very good indeed. A check with the generator suggested that the I.F was 470kHz so a final fine adjustment at this frequency was made. Calibration was OK-ish but by trial-and-error I was able to identify the MW oscillator padder and the aerial trimmer. This enabled me to get MW very good with an increase in gain and sensitivity. LW was OK already and so was shortwave.

The radio was now working very well and considering it was a kit, it was probably as good as any small superhet available at the time. The only criticism was that it sounded a little harsh.

Having cleaned the cabinet and knobs, the set was put aside for possible further checking later and ended up being displayed with all the others. Apart from being switched on a few times a year, I didn’t do any further work to it.

I always like to have at least a circuit available and during a search around the net, I quite accidently turned up a circuit for a Repanco Hi Gain Superhet 4 (I think I was looking up information on coils at the time). I immediately noticed that the SH4 was, as near as doesn’t matter, the same as my Premier right down to resistor and capacitor values. Only main difference was that mine had the addition of a shortwave band. It didn’t help me with voltages or alignment but at least I had a circuit now.

Armed with this information I decided to see if the harshness could be reduced. This was due no doubt to third-harmonic distortion that is present in single-ended output stages. Most manufacturers reduce this in simple sets by adding a tone corrector across the output transformer primary or (in some cases) adding negative feedback. In this set, there was a 5000pF capacitor from the 6V6 anode to chassis which would have provided some tone correction. However as this set uses a separate triode (in the 6Q7) to provide AF amplification there is a very simple mod that works quite well that just requires the addition of one resistor. All you do is connect a 1 megohm resistor between the anode of the 6V6 and the anode of the 6Q7. This provides a degree of negative feedback without reducing the gain too much…and improves the audio quality. I feel justified in doing this mod as it has removed the harshness and makes the radio more pleasant to listen to. This same arrangement is used in quite a few of the Pilot ‘Little Maestro’ sets.

I think if I had built this set back in the 50’s, I would have been quite pleased with the results.

Rich.

Robert Darwent · 29th Aug 2008, 7:39 pm

Hello Rich,

What a lovely set! Particularly like the louvred cabinet, very similar to a DAC10 in that respect, just splendid!

Quote:

Originally Posted by Richard_Newman

I think if I had built this set back in the 50’s, I would have been quite pleased with the results.

I have to agree with your comments there. Very well put together for a kit, virtually indistinguishable from a factory made set of the time. And you must be very pleased with the result of your efforts too! A first class restoration!

Regards

Sideband · 29th Aug 2008, 11:01 pm

....If I had built the set in June 1953 it would have been very remarkable indeed as I would have been 6 months old!!

Rich.

29th Aug 2008, 4:15 pm	#1
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,571	Premier kit radio I bought this set a few years ago when another forum member was having a clearout (can’t remember who it was). I’d always wanted one after seeing adverts in the Radio Constructor back in the sixties. This version was white and housed in the usual ‘Pilot’ radio cabinet. It tuned MW, LW and SW. Anyway the radio had worked some years before and then been stored. When I got it, there was a slight layer of dust and no evidence of previous work underneath. There was, however, a rather mouldy-looking electrolytic with severe corrosion growing out of one end. Most of the capacitors were of the metal-clad ‘Sprague’ type which are usually very good and don’t seem to suffer the same problems of the usual waxy types. There were four valves of the Octal variety namely 6K8, 6K7, an odd Admiralty type marked NR48, and a 6V6. The NR48 was presumably a 6Q7 equivalent and a check on the net showed that it is a Britsh Navy number for an EBC33. The rectifier was two Cen-Ter-Cel contact-cooled selenium types connected in series. There was a mains transformer which was for the valve heaters only. HT was taken from one side of the mains so the radio had a live chassis just like an AC/DC set. Considering it was a kit set, the build quality seemed very good. Judging by the date on two electrolytics, it would appear to have been built around 1953. Firstly I replaced the mouldy-looking capacitor which was an 8uF electrolytic. The main smoothing can looked good and checked out reasonably well. The audio coupling capacitor was a waxy type and was replaced along with another one connected to the volume control. The others, as stated above were the metal type and they all checked out good on the bridge…..very good as it so happened considering they are 55 years old. Seeing as there was a contact-cooled rectifier in place, I decided to run the set up slowly on the variac. This was easy and I measured the HT available on the smoothing caps while slowly increasing the mains. At around 200 volts, the radio started working although the HT was quite low at about 120v. Once up at full mains it was obvious that the rectifier was not in good health as I was only getting about 130v on the output valve anode. Everything seemed to be working though apart from low volume. It didn’t like working on SW either and was reluctant to tune above about 8 MHz. I had no idea what the HT should be as there was no information (yet) on the set. However radio’s of this nature seem to run with an HT at the reservoir of 220 or so. I removed the old rectifiers and used two BY126 rectifiers in series and mounted them on a tagstrip that was already holding the smoothing resistor. I then mounted another tagstrip where the old rectifiers had been, to take the series limiter resistor. I started with a fairly high value for this and worked down and found that 500 ohms gave me just under 220 volts at the reservoir and HT to the 6V6 was now 215v. The set was now much more lively and shortwaves worked right through to the maximum 18Mhz. Calibration was quite good but I decided to check I.F alignment. Again no information so I decided to check on a signal. The first I.F needed a good half-turn to peak it, the others not so much but now the set was very good indeed. A check with the generator suggested that the I.F was 470kHz so a final fine adjustment at this frequency was made. Calibration was OK-ish but by trial-and-error I was able to identify the MW oscillator padder and the aerial trimmer. This enabled me to get MW very good with an increase in gain and sensitivity. LW was OK already and so was shortwave. The radio was now working very well and considering it was a kit, it was probably as good as any small superhet available at the time. The only criticism was that it sounded a little harsh. Having cleaned the cabinet and knobs, the set was put aside for possible further checking later and ended up being displayed with all the others. Apart from being switched on a few times a year, I didn’t do any further work to it. I always like to have at least a circuit available and during a search around the net, I quite accidently turned up a circuit for a Repanco Hi Gain Superhet 4 (I think I was looking up information on coils at the time). I immediately noticed that the SH4 was, as near as doesn’t matter, the same as my Premier right down to resistor and capacitor values. Only main difference was that mine had the addition of a shortwave band. It didn’t help me with voltages or alignment but at least I had a circuit now. Armed with this information I decided to see if the harshness could be reduced. This was due no doubt to third-harmonic distortion that is present in single-ended output stages. Most manufacturers reduce this in simple sets by adding a tone corrector across the output transformer primary or (in some cases) adding negative feedback. In this set, there was a 5000pF capacitor from the 6V6 anode to chassis which would have provided some tone correction. However as this set uses a separate triode (in the 6Q7) to provide AF amplification there is a very simple mod that works quite well that just requires the addition of one resistor. All you do is connect a 1 megohm resistor between the anode of the 6V6 and the anode of the 6Q7. This provides a degree of negative feedback without reducing the gain too much…and improves the audio quality. I feel justified in doing this mod as it has removed the harshness and makes the radio more pleasant to listen to. This same arrangement is used in quite a few of the Pilot ‘Little Maestro’ sets. I think if I had built this set back in the 50’s, I would have been quite pleased with the results. Rich. Attached Thumbnails __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman..... Last edited by Sideband; 29th Aug 2008 at 4:31 pm.

29th Aug 2008, 11:01 pm	#3
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,571	Re: Premier kit radio ....If I had built the set in June 1953 it would have been very remarkable indeed as I would have been 6 months old!! Rich. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....