[Amps] Overdrive protection

[Jim Thomson]

Date: Fri, 27 Jul 2012 10:28:49 -0400
From: "Roger (K8RI)" <k8ri at rogerhalstead.com>
Subject: Re: [Amps] Overdrive protection

On 7/27/2012 10:11 AM, Jim Hargrave wrote:
> Duh...
> Why not just use the RF PWR adjustment on the front of the transceiver and
> save all that costs and wasted heat dissipated by the attenuator.
>

That is the problem. With the power turned down, the first dit comes 
through at full power on some rigs. This approach works just fine in 
both of my rigs.

Although the 756 Pro line is notorious for this, mine does not do it, 
nor does my FTDX5000MP.

As to ALC I do not use it. The amp has its own internal ALC so the 
tiniest Amount of grid current will not only shut it down, but requires 
a reset and wait for the tube warmup cycle again. It is protected for 
about any thing I can think of.

Other than During a tune-up I've never had it kick out.

73

Roger (K8RI)

##  No roger, your amp does NOT have internal ALC,     What it has is grid overcurrent
protection !   Some SS amps  will switch in a pad asap, if too much drive applied... and –or
kick the amp  offline.  And ditto with tube amps, like tetrodes. 

##  stick the wrong xcvr on there..like an icom 775, and it will trip all the time..and be kicking itself
offline  as soon as you apply drive, regardless of where u set the power output control.  A buddy here
in town had a 775dsp xcvr... and it put out well over 260 watts for the spike,  regardless of where the
po was was set to...even if set for 20 watts out.   It fried his  AL-80bx amp too.  250 watts into a tube amp
=  fried bandswitch. 

##  in any case, I would suggest tweaking  the LOAD control  such that the¨PO  drops 2%.    Tune ur amp
up to say 1550 watts pep out,, THEN increase the loading ( decrease the C of the load cap), so the
PO  drops down to  1500 w pep out.  ( 3.7% drop)  Or tune up to 1600 pep out..then tweak load cap
for 1500w pep out.   Then its linear..and will absorb  most spikes. 

## see my other post on how to get rid of the spikes.

##  Im surprised alpha has not made  a list  of lousy xcvrs .  “warranty void if ICOM 775 used”   etc. 
That would smarten up the  xcvr makers real fast.   “ warning, do not use the following xcvrs, due to their 
poor  IMD.  These IMD products will be amplified by your Alpha linear amplifier to a much greater level” 

later........ Jim  VE7RF

Jim  VE7RF