23-01-2016, 08:23 PM
Servicing the FB10. As mentioned in a previous post about this set, it works in a fashion but the sensitivity on the Medium Waveband could be better. After the cabinet was removed it was evident that this set is a late production model, the FB10/2 The output valve is a Brimar 6BW6 and the HT rectifier is a Brimar 6V4/EZ80. These valves replace the older octal 6V6GT and 6X5GT.
For starters I found that the 6BE6 frequency changer valve had been replaced by a EH90, you can get away with using this common pin compatible valve but the performance is not as good as the 6BE6/EK90.
Fitting a 6BE6 has improved the performance considerably and tweeking up the aerial and oscillator trimmers effected a further improvement.
Distortion on strong stations was caused by excess negative volts on the grid of the AF amplifier, a 6AT6.
The grid coupling capacitor C15 is leaky, replacing it improves matters considerable, but there is still overloading on strong signals. The AVC decoupling capacitor, C9 is leaky. Now almost 5 volts of negative AVC is now available to reduce the gain on strong signals.
That taped up mains lead is definitely not a good thing. Sometime long ago the mains lead had been replaced with one with the brown and blue leads.
So now there just the damaged cabinet to attend to.
Geordie McBoyne.
For starters I found that the 6BE6 frequency changer valve had been replaced by a EH90, you can get away with using this common pin compatible valve but the performance is not as good as the 6BE6/EK90.
Fitting a 6BE6 has improved the performance considerably and tweeking up the aerial and oscillator trimmers effected a further improvement.
Distortion on strong stations was caused by excess negative volts on the grid of the AF amplifier, a 6AT6.
The grid coupling capacitor C15 is leaky, replacing it improves matters considerable, but there is still overloading on strong signals. The AVC decoupling capacitor, C9 is leaky. Now almost 5 volts of negative AVC is now available to reduce the gain on strong signals.
That taped up mains lead is definitely not a good thing. Sometime long ago the mains lead had been replaced with one with the brown and blue leads.
So now there just the damaged cabinet to attend to.
Geordie McBoyne.
