Carl wrote:
>
>
> For several reasons I take anything from that source with a huge grain
> of salt.
>
Carl, I don't think I ever saw you and Tom agree<:-))
> There also appear to be several definititions of ICAS with the first
> going back to the Class C AM days. Without a running time meter
> attached to an amp its a lot of guesswork how emission life was
> affected. BUT, the typical tube seemed to be no worse for wear at
> slightly elevated voltages.
>
Those were back in the days where we pushed to get every watt we could,
even knowing a watt or two made no difference at all
> When SSB came along voltages were raised to and sometimes above CW
> ratings and robust tubes from the 813 to 4-1000A seemed to flourish
> without complaint. Lesser tubes such as the 811A and 572B suffered;
> especially the 572B which is an 811A with a graphite plate and is run
> well beyond what its basics emissions capability would indicate.
>
> The next stage is where some tubes appear to have specs written by the
> marketing department, especially the Class C Russian tubes that have
> been reinvented for linear SSB service. Toss in the 3CX800 and 8877
> pulse versions with the former being run on CW at 3500V. IMO, that is
> way beyond ICAS.
I always look for CCS. They tell me I talk too long.
Weren't the ratings changed on the 3CX800, for political reasons? I
think they did the 8877 too. OTOH the 8877 has gone through several
incarnations that weren't always successful. I liked the one where they
took much less drive
>
> One huge reason for tube failures is that the average ham doesnt have
> a clue how to tune an RF stage be it in a DX-100 or a brand new amp.
They are stuck on tuning for maximum output, but it has to be carefully
peaked to get that last watt out. Going back and fourth with tune and
load to get another 5 or 10 mills while they could put a frying pan on
top to cook breakfast at the same time.
> A 6146 is easily fried by excessive grid drive as well as excessive
> screen current which isnt even measured. A modern tetrode amp is no
> different and its questionable how good the protective circuits perform.
>
I thought we tuned for maximum blush<:-)) OTOH that's hard on the solder
with the modern, external anode tubes. That and many don't realize
Tetrodes are tuned differently than triodes. As for protective circuits,
I can say without doubt they sure work on the new solid state amps.
> With fragile triodes its excessive grid current that does the damage.
>
> Ive watched many hams over the past 50+ years tune up and I'll tell
> you that grass grows faster. Then they have to do it again every time
> they do a small QSY. The ones using antenna tuners are the worse of
> the bunch.
>
We have a local pilot who does runups the same way. We all try not to
get behind that plane when it's headed down the taxiway because we know
we'll be sitting at the hold line for a very long time.
> I do a lot of amp repairs here for customers and its obvious why they
> failed. Trying to convince many that their long ingrained tuning
> procedure is wrong is a waste of time so after a year or two its back
> again and they are cursing the tube or amp manufacturer.
Or blaming it on parasitics.
73
Roger (K8RI)
>
> Just my nickels worth.
>
> Carl
> KM1H
>
>
>
>
>
>
>
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