[Amps] Alpha 87 (not 87A)

[Jim Thomson]

Date: Tue, 7 Nov 2017 11:36:49 -0800
From: Jim Brown <jim at audiosystemsgroup.com>
To: amps at contesting.com
Subject: Re: [Amps] Alpha 87 (not 87A)


On 11/7/2017 10:28 AM, Steve Wright wrote:
> On 08/11/17 07:21, Jeff wrote:
>> [..] Over the following week I collected an OO card and a few FYI 
>> email from guys nice enough to mention that my CW 2nd harmonic was 
>> being copied in the low end of the SSB 80m band.
>
> Any actual complaints? 

<A neighbor about 15 miles away is an active contester, as am I. It is 
<not unusual to hear his second harmonic loud enough (S6 or louder) to 
<make me stop on his signal when looking for someone to work. In past 
<years that neighbor had a LOT of IMD on his signal (splatter and clicks) 
<that made him a very bad neighbor. It was common for him to chew up 10 
<kHz of a band on CW! In the last year or so, he's cleaned up a LOT. By 
<contrast, K6XX, only 3 miles away, is only 600 Hz wide, 70 dB down!

<73, Jim K9YC

## Excess  drive to a GG amp will produce splatter + imd on ssb.   And so will
insufficient loading... on the load cap of the same GG amp.   By increasing the loading a bit,
IMD will improve a bunch..  and harmonic suppression will also  improve. 

##  But the above paragraph I just wrote pertains to  tuning the amp correctly.   The loaded Q of the same
GG triode amp can be varied greatly, by changing the tap on the tank coil, with no ill effects on IMD.
I have tested this several times in the past, by manually changing taps and also using a heavy duty roller inductor. 
Higher loaded Q is capable of greater harmonic suppression,  but higher loaded Q does not improve IMD one bit. 

##  The touted  PI-L has greater harmonic suppression  vs the simpler plane jane PI..into a dummy load,  but the PI-L  doesnt have
better IMD.    A PI-L appears to have good to excellent harmonic suppression into a dummy load, since the harmonics are 
loaded by 50 ohms and no reactance. The harmonic suppression, right out of the amp, using the same PI-L, but into a mono band ant, appears
to have increased harmonic level, at least for the 2-4-6 th harmonics..vs the dummy load.   A PI net provides  for somewhat decreased harmonic
suppression vs  PI-L... into a dummy load, but the simple PI has excellent harmonic suppression, measured right out of the amp..when  the 
same monoband ant is used. 

##  The  slide show was good,  but lets not get off onto a tangent.  Every SS xcvr and also SS power amp typ has a slew of LP filters, like
at least 6 of em, and 7 if 6M is included.  The LP filters typ have  50-60db of harmonic attenuation.   SWR may well affect IMD on these SS
xcvrs and power amps, so the advice to use a tuner is probably well founded.   Swr on a GG tube amp  will not de-grade IMD one bit, as long as
the GG tube amp is correctly tuned up.   IE: no excess drive, and no under loading. 

## As far as key clix goes, its an easy fix on both my FT-1000D..and also my FT-1000-MP-MKV.  Another method is to REDUCE the damned drive
levael on the FT-1000D.  No need to be wailing away  with the ALC running full scale on CW mode.  Reduce the DRIVE control till NO alc action is
displayed, yet PO remains the same.    The  ... Drive control on the FT-1000MK-V is found in the hidden menu.   Same deal, turn it WAY down, until
either NO alc action is displayed, or a miniscule amount.

## The K3 on ssb, with its paltry –29db pep for IMD3  is nothing to brag about.  All of these SS xcvrs will have improved imd, when power out reduced. 
Thats fine if you have an amp that only requires 40-50 watts of drive..and your 100w xcvr is a IMD garbage truck when run at 100w pep out.    Some amps
require a good 100 watts of drive.  The typ 200 watt xcvr..when run at 100-130 watts out, is very clean. 

##  The ANAN 7000 is typ  –72 db pep  for imd3..for the 200 w xcvr itself.   If the GG triode amp is also included in the loop, and the sampled 0 dbm 
signal is derived from the GG amp..then fed back to the 7000’s main  sample input, the  IMD of the tube amp can be greatly  improved, typ  by 14 db
over just the amp alone..which is a huge improvement.   The pre-distortion technique works on ssb or any linear mode, albeit the main drawback is the
20 msec delay.... which will sure to drive  one nuts when trying to monitor yourself on headphones...on SSB. 

##  Correctly set up 7000,  +  wide band ESSB is a thing to behold.  No more splatter  from lousy xcvrs being run full bore.  

##  If your SS xcvr does not have a power output control, no big deal, a simple  9 vdc battery + 100K pot..with divider of pot fed back to the xcvrs 
ALC input will work just fine.  Then you can dial up precisely the po you want.   Set it for say 87 watts, and scream all you want, it will never exceed 87 watts. 
It cant, you have already developed the ALC voltage externally, and its present on the xcvrs  ALC input at all times, including TX  + RX. 

later.... Jim   VE7RF