[Amps] Solid State Amps-v- Tube Amps

[Jim Thomson]

Date: Mon, 19 Jun 2017 03:31:19 +0000
From: Bill Turner <dezrat at outlook.com>
To: Amps group <amps at contesting.com>
Subject: Re: [Amps] Solid State Amps-v- Tube Amps

<There is one thing about tube amps that is not often mentioned  and
<that is the multiple functions of the pi- or pi-L network, something
<that is not applicable to solid state amps. 

In one simple circuit you can do all of the following:

1.  Tune out the effect of the tube's output capacitance.  It simply
becomes part of the pi-network tune capacitor.

2.  Suppress harmonics, given sufficient Q.

3.  Match the tube's impedance to the load impedance.

4.  Compensate for odd values of load resistance and reactance.

5.  Supply the "missing" half cycle of RF in a single ended amp, given
sufficient Q. 

And by use of a small coil in the anode lead, step down the tube's
impedance to a low value which allows use of an output circuit at high
frequencies which other wise would have excessive Q. 

Just something to keep in mind when choosing your type of amp. 

73, Bill W6WRT


###  JI and I got into it on another forum about the small  coil  b4 the
main C1 cap.    He claims it will lower the harmonic suppression on 
the lower bands.    I find that hard to believe.... but I have not measured
harmonic suppression on the lower bands, when the small coil is installed
on the higher bands, like 10 or 15m.  Harmonic suppression is not high on my list.

## The coil  b4 the  PI net is called an L-PI.... or a L-PI-L  if a PI-L is used.  If anything
I would have thought that the harmonic suppression on the upper bands would increase.
The shunt tube C  + the small coil  form  step down L network..followed by the PI or 
PI-L.   The shunt C  from the tubes anode to grounded grid  followed by the series L,
on paper should provide for a harmonics redux  on 10 + 12 M..and perhaps a bit on 17+20m.  

##  If a lower band, monoband amp was built,  and the normal PI coil was  center tapped 
with the hot side of the C1 tune cap,  Im betting the  harmonic suppression would increase
a bunch.      And thats with an L-PI  alone, never mind a L-PI-L .   The concept would be easy
enough to test...provided you had enough C in the tune cap to resonate with a now smaller coil.  
40m might be a good band to test the concept on.   For my application, anything over 30 db for
2nd harmonic suppression is ample,  36 db is plenty.  The 3-4-5 would be more than that of course. 
None of my ants are resonant on their 2nd harmonic, nor their 3rd, plus I use a LP filter with
a 33 mhz cut off.   With 1.5 watts into a sky high swr on the 2nd harmonic, with just 30 db of
2nd harmonic attenuation on  1.5 kw po  is not going to get very far. 

Jim   VE7RF 

Jim   VE7RF