Brand Philips
Type BG500A
Source: Alan Lord    
Power AC
Bands SW, MW, LW
Cabinet Walnut veneered Plywood Cabinet
Tubes ECH42 ( mixer )
EF41 ( if amp )
EBC41 ( demod + af amp )
EL41 ( output )
EM34 ( tuning Indicator )
EZ40 ( rect )
Notes This set came from a local market , complete and working ( but sounding very rough),cabinet in very good condition .There was two reasons for the rough sound -----first there was a 100hz hum due to inefficient smoothing capacitors. Secondly there was bad modulation hum ( if you have not come across this it is hum that is only heard when a station is tuned in ) .The frequency was 50hz so could not come from the .The only source of 50hz is the heater supply so an insulation test was carried out on the EBC41 demod and af amp ( the demodulator stage is the most likely source of modulation hum ) sure enough the valve had leakage between the heater and the anodes of the diodes and the control grid of the triode! This range of valves are very prone to this fault---it is caused by the glass around the base being coated by emission from the heater , this coating is conductive hence the leakage, it can be removed ( I built a unit for this ) the valve was connected to my machine , a blue light appeared around the inside of the base , it travelled around the pins then faded away. When the valve was tested again there was no leakage and re-fitting it to the set produced clear sound.,there was still some distortion at high volume due to the output valve's grid running positive.Not due to the coupling cap this time---it was due to the EL41 suffering from the same leakage problem.It was cleared the same way. The set's performance is now O.K.
Data source Alan Lord

(c) 2000-2019 Mario Huizinga

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