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Old 30th Aug 2019, 10:37 am   #37
Leon Crampin
Octode
 
Join Date: Nov 2005
Location: Surrey, UK.
Posts: 1,869
Default Re: Philips 170A restoration

The 170A chassis utilises the EF39 IF amplifier as an audio preamplifier stage on "gram". The anode supply is disconnected and the screen grid of the EF39 is used, effectively as a triode anode. The screen grid decoupling capacitor is then used to couple the audio to the EBL31 control grid.

This arrangement gives rather limited gain on "gram", but should be sufficient if a large input signal is available, such as from a CD player or 'phone. It also explains why the "gram" switch is separate from the wavechange switch and has a number of contacts. Sets as supplied new had a tie-on label fixed to the "gram" switch, reminding users to select "radio" when needed.

Leon.
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