[Heath] SG-7 Help

[G3OOU at aol.com]

Hi Ron
 
I have now had a chance to study the circuit diagram for the SG-7 in  
detail:
 
1. The HT electrolytic smoothing capacitors are 20uF 150V so the 600v  
working potential that you mentioned is way over what is actually required. The  
anodes of the two valves are shown as having 60-80V potentials on them but 
this  will be higher when first switched on and the valves not conducting 
any anode  current. The two capacitors across the mains supply should 
certainly be  adequately rated for AC working and allowing for additional spikes.
 
2. As already stated by another contributor MMF is the old fashioned way of 
 stating pF - the original designation stood for micro micro farad.
 
3. Decoupling capacitors in the RF oscillator can be disc ceramic types but 
 the tuning capacitors in the AF oscillator should be film types.
 
4. Any fixed tuning capacitors in the RF oscillator could be NPO disc  
ceramic types although my preference would be for silver mica. The photo of the  
coil pack in my copy of the manual is not very clear.
 
73

Bob

Bob F Burns
C Eng,  FIET, MSE
Amateur Radio Callsign: G3OOU
Registered RSGB  Instructor
G-QRP Member No: 6907; Zone: 14, QRA: IO91WH; WAB:  TQ25
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