[Amps] Re: 8171

[David G4FTC]

Hi Rich,

Most of your questions are answered in the following pages:

http://www.qsl.net/g4ftc/amplifiers/8171/8171_circuit_description/8171_circuit_description.htm

http://www.qsl.net/g4ftc/amplifiers/8171/8171_construction/8171_construction.htm

http://www.qsl.net/g4ftc/amplifiers/8171/8171_testing/8171_testing.htm

The operating parameters are the same as my 8170 amp as per:

http://www.qsl.net/g4ftc/amplifiers/8170/8170_testing/8170_testing.htm


>I have used both and I can not see why the SK300 should have less 
>inductance than a SK-300A.

Firstly I must say that I’ve never actually had a SK300 in my hands – it’s 
only my assumptions based on visually comparing the Svetlana SK300As (which 
I use) with the datasheet photos of the Eimac SK300.

(This is really where photos are required to accompany this text – what I am 
trying to describe would then become self evident).

Looking at the filament connection side, the SK300 has 8 radial supports 
whereas the SK300A only has four. Also the SK300 skirt goes the full 
vertical length of the base, whereas on the SK300A this is reduced to zero 
except where the four radials are located, all of which are no doubt to 
improve airflow. Now my background is really VHF/UHF where all attempts are 
made to try and provide the shortest connections to ground to minimise 
inductance. To my way of thinking, the radial supports, which on the SK300A 
are about 2-1/2 inches long from the chassis to the outer filament ring, are 
less than ideal in assuring a good RF ground.

What I would like is a good quality photo of a SK360 base – I have a scan of 
the Eimac datasheet but the detail in the photo isn’t sufficient to work out 
how it’s better at VHF than the SK300/300A.


Regards

David G4FTC