[Amps] Hard bus bar copper and inductor Q

Conrad PA5Y g0ruz at g0ruz.com
Thu Aug 31 16:48:37 EDT 2017

Hello again, I have gathered almost everything that I need for my 
3CX800A7 conversion from 2m to 6m.

I have choice of materials for L1.

I have some 6mm soft copper pipe, some 4mm soft copper pipe and some 3mm 
silver plated copper wire. All the tubing is C102 copper and forms very 
nicely. VE7RF suggested that I use some flat strap and make L1 a flat 
wound coil to reduce capacitance between turns, it is also very easy to 
drill for blocking caps.  This makes sense to me.

The strap that I have is 17mm wide and 1.5mm thick but I have some 
concerns. It was used as bus bar material and is much harder than the 
C102 copper tube that I have. It is also considerably darker in colour. 
It forms into coils quite easily and is not particularly springy so I am 
fairly sure that it is not Beryllium copper. I suspect that it has been 
annealed. I am worried that the resistivity will be high but surely as 
it was used for busbars it won't be lossy, will it?

Soon I will have a DER EE DE-5000 LCR meter which I am told are very 
good value for money and I can measure component Q so I should see the 
difference between the flat bar and the copper tube, if there is a 
problem. I know for sure that the copper tube is C102 soft copper. I 
would be interested in hearing from anyone who has this instrument and 
what they think of it.

Any advice? In the past I have made a number of QRO VHF amps for 6m and 
without exception the efficiency has been good. This is the first one 
that I have actually designed myself and I expect the loaded Q to be 
10-12, previous amplifiers had big tubes, lots of stray C and had a 
higher Q and were mainly copies or adaptations of published designs. 
This time I want to design and truly understand what I am doing.

I am still somewhat mystified by Anode RFCs for VHF amplifiers, I can 
plug numbers into the GM3SEK spread sheet but I do not know exactly how 
to design a good choke. Most of the stuff that I found on google was 
concerned with multi-band HF amplifiers and the perils of series 
resonance. What are the rules of thumb. I can do the calculations but 
what are my goals?

Hopefully this will give the reflector a kick and start some interesting 


Conrad PA5Y

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