14-07-2011, 07:32 AM
An intersting post Alan - you'll be pleased with this radio. Once more, your post shows how handy it can be to have a lathe for such things as knob brights and other little radio related tasks.
The little Pye R33 table radio is one of my favourites. I came across two last year which I restored - very easy set to work on. It was produced in 1964, towards the end of the valve era and has some interesting features, with an eye to production costs. It used a PCB to reduce point-to-point wiring, making voltage and resistance checks much easier as the PCB-mounted valveholder connections and other components can be accessed from the top of the chassis.
Unlike many small radios, it doesn’t use AC/DC techniques (which obviates the need for a mains transformer but have undesirable heat-producing mains droppers a la DAC90A). As Alan says, instead, it uses an auto transformer, (no secondary – just a primary tapped at 66 Volts for the series heater chain). Thus, the HT is direct from the mains, so the usual precautions about live chassis apply.
Because the twin core brown flex - which appears to be original - isn’t colour coded, I checked the polarity and found that the line went to the chassis, so I reversed that. Although there are no exposed metal parts, the grub screws on the three knobs would have been live.
The set uses only three valves – UCH81 Frequency changer; UBF89 IF amp, detector and AGC, and UCL83 AF Amp and output. For rectification, it uses a small contact-cooled half wave metal rectifier, which curiously, is referred to as ‘V4’. The UCH81 and UBF89 have 19V heaters – the UCL83 is 38 Volts (all at 100mA) making a total of 66 Volts.
The second of the two sets I restored needed minimal work.
The smoothing and reservoir caps and one other are in one small can – two at 32uF, one at 8uF. Before being tempted to switch on, I reformed all three till the leakage was negligible, did a few checks, such as the continuity of the heater chain, and switched on. The first set worked, but at low volume, and with distorted audio. The input to ‘V4’ – the rectifier was 230V AC, but the output – which should have been 225V DC - was only 125V. Initially I thought the rectifier might be faulty, so I substituted it for a 1N4007, which brought the voltage up a bit, but not significantly, so I reverted back to the metal rectifier.
Then I did what I ought to have done in the first place – checked the smoothing and reservoir caps on my ESR meter. No wonder the leakage was low when I ‘reformed’ the caps. Two were fine, but the ESR on one of the 32 uF sections was so high it might as well have been open circuit. I therefore mounted a new replacement 33 uF under the chassis, and left the other two sections in use.
This brought the HT up to spec.
When new, the stated tolerances of most of the 16 resistors was 20%, with just two at 10%. I checked them all and found that four were out of tolerance by a good margin – 53%, 40% and 35%. One of the 10% resistors was 18% so I change that too, as it was across the reservoir and smoothing caps and may have had a slight bearing on the HT voltage.
I checked the ESR of the 25uF 25 V cathode bypass cap on the output valve (one of those red/black plastic encapsulated jobbies). Unsurprisingly, it was duff, so I replaced that.
There were two Hunts waxies, which I changed as a matter of routine (one had deposited all of its wax on the floor of the set, so had been getting hot). In this set, ‘that cap’ was in fact a 1000V disc, so I left it in situ as they seem not to suffer breakdown in the same way as waxies do.
I switched on and the set gave a very good account of itself, especially on MW. The audio quality and volume from the 6 x 4 speaker was excellent. All of the voltage checks showed that the set was now bang on spec – anode voltages up from 106V as found, to the correct level of 192V.
The last task was to fill the grub screws of the knobs with wax.
It’s clear that some of the design features, such as the use of an auto-transformer, metal rectifier and PCB had an eye to costs – perhaps in the face of rising competition from 'the land of the rising sun', and cheaper to produce transistor radios, but this also helped keep the set compact, and overcame the heat problems that would have arisen with a mains dropper and a valve rectifier, given that the cabinet is injection moulded plastic.
By 1964, the transistor era was well established (the Bush TR82 series was launched in 1959 and the Roberts R200 in 1960) so this little Pye was perhaps one of the last valve models to go into production.
The replaced components above and below chassis can be seen on the pics, as can the metal rectifier on the rear apron of the chassis.
Beauty is in the eye of the beholder, but I think it’s a very attractive little set which deserves its place on my now cramped display shelves. I rather like little sets such as this, the Murphy 198 and the KB Toaster.
I keep a look out for Pye 33s and if I see another, I'll snatch it - you can't have too much of a good thing!
David
The little Pye R33 table radio is one of my favourites. I came across two last year which I restored - very easy set to work on. It was produced in 1964, towards the end of the valve era and has some interesting features, with an eye to production costs. It used a PCB to reduce point-to-point wiring, making voltage and resistance checks much easier as the PCB-mounted valveholder connections and other components can be accessed from the top of the chassis.
Unlike many small radios, it doesn’t use AC/DC techniques (which obviates the need for a mains transformer but have undesirable heat-producing mains droppers a la DAC90A). As Alan says, instead, it uses an auto transformer, (no secondary – just a primary tapped at 66 Volts for the series heater chain). Thus, the HT is direct from the mains, so the usual precautions about live chassis apply.
Because the twin core brown flex - which appears to be original - isn’t colour coded, I checked the polarity and found that the line went to the chassis, so I reversed that. Although there are no exposed metal parts, the grub screws on the three knobs would have been live.
The set uses only three valves – UCH81 Frequency changer; UBF89 IF amp, detector and AGC, and UCL83 AF Amp and output. For rectification, it uses a small contact-cooled half wave metal rectifier, which curiously, is referred to as ‘V4’. The UCH81 and UBF89 have 19V heaters – the UCL83 is 38 Volts (all at 100mA) making a total of 66 Volts.
The second of the two sets I restored needed minimal work.
The smoothing and reservoir caps and one other are in one small can – two at 32uF, one at 8uF. Before being tempted to switch on, I reformed all three till the leakage was negligible, did a few checks, such as the continuity of the heater chain, and switched on. The first set worked, but at low volume, and with distorted audio. The input to ‘V4’ – the rectifier was 230V AC, but the output – which should have been 225V DC - was only 125V. Initially I thought the rectifier might be faulty, so I substituted it for a 1N4007, which brought the voltage up a bit, but not significantly, so I reverted back to the metal rectifier.
Then I did what I ought to have done in the first place – checked the smoothing and reservoir caps on my ESR meter. No wonder the leakage was low when I ‘reformed’ the caps. Two were fine, but the ESR on one of the 32 uF sections was so high it might as well have been open circuit. I therefore mounted a new replacement 33 uF under the chassis, and left the other two sections in use.
This brought the HT up to spec.
When new, the stated tolerances of most of the 16 resistors was 20%, with just two at 10%. I checked them all and found that four were out of tolerance by a good margin – 53%, 40% and 35%. One of the 10% resistors was 18% so I change that too, as it was across the reservoir and smoothing caps and may have had a slight bearing on the HT voltage.
I checked the ESR of the 25uF 25 V cathode bypass cap on the output valve (one of those red/black plastic encapsulated jobbies). Unsurprisingly, it was duff, so I replaced that.
There were two Hunts waxies, which I changed as a matter of routine (one had deposited all of its wax on the floor of the set, so had been getting hot). In this set, ‘that cap’ was in fact a 1000V disc, so I left it in situ as they seem not to suffer breakdown in the same way as waxies do.
I switched on and the set gave a very good account of itself, especially on MW. The audio quality and volume from the 6 x 4 speaker was excellent. All of the voltage checks showed that the set was now bang on spec – anode voltages up from 106V as found, to the correct level of 192V.
The last task was to fill the grub screws of the knobs with wax.
It’s clear that some of the design features, such as the use of an auto-transformer, metal rectifier and PCB had an eye to costs – perhaps in the face of rising competition from 'the land of the rising sun', and cheaper to produce transistor radios, but this also helped keep the set compact, and overcame the heat problems that would have arisen with a mains dropper and a valve rectifier, given that the cabinet is injection moulded plastic.
By 1964, the transistor era was well established (the Bush TR82 series was launched in 1959 and the Roberts R200 in 1960) so this little Pye was perhaps one of the last valve models to go into production.
The replaced components above and below chassis can be seen on the pics, as can the metal rectifier on the rear apron of the chassis.
Beauty is in the eye of the beholder, but I think it’s a very attractive little set which deserves its place on my now cramped display shelves. I rather like little sets such as this, the Murphy 198 and the KB Toaster.
I keep a look out for Pye 33s and if I see another, I'll snatch it - you can't have too much of a good thing!
David
