[Amps] Tube amps are not a thing of the past

[w8hw at comcast.net]

I am very familiar with that as I built one also, The issue is anyone who 
builds one must face that issue one way or the other. Any mistake and it is 
over.

As I said, I have both LDMOS and Tube amplifiers. One of the tube amps (Two 
3-500 is 40 years old, I re built the power supply and runs like new. The 
other Ameritron AL-1500 runs 8877 and is 20 years old and with rebuilt power 
supply and it too runs like brand new. I do not expect that from the dual 
BLF188 LDMOS because of parts availability even 5 years from now.

Good luck on your KPA1500. That looks like a good amp. Let me know how that 
works out for you.

73, Bruce, W8HW
=============================

-----Original Message----- 
From: Paul Christensen
Sent: Sunday, June 04, 2017 14:06
To: amps at contesting.com
Subject: Re: [Amps] Tube amps are not a thing of the past

">Another disadvantage of LDMOS is the input side of the LDMOS has a “Glass 
Jaw”. If you over drive them it can be a quick death, while a tube will take 
an occasional over drive."

Current SS amp protection circuity is very good and getting better all the 
time.  In the case of the SPE 1K-FA - a design that's already a decade old, 
I cannot force it to fail with direct output shorts, nor pulsing the input 
with high exciter input power of 150W.  The amp uses a 7-point summing 
circuit that quickly biases off the MOSFETs.  Concerning VT amps, it doesn’t 
take much abuse to destroy the control/screen grids of many hi-mu types.  At 
this point of LDMOS development, I don’t think we can say that today's SS 
amps are any less reliable than their VT counterparts in their respective 
power class.  We cannot ignore the accelerating use of SS in broadcast RF, 
medical, commercial, and military applications.

>"Amplifier Life and longevity is strongly on the side of the tube 
>amplifier. If you want it to last 25 to 40 Years."

Possibly true of the older VT amps that don’t use obsolete semiconductors 
and proprietary firmware code.  The B26 uses a RaspberryPi for control and 
is thus easy to hack, manipulate, and clone.  My SPE and newer Alpha amps 
all use proprietary firmware.  If the final round of support on those amps 
dries up, I think we can forget about 25-40 year longevity when we're 
cannibalizing old amps for spare parts.  Of course, LDMOS devices face the 
same problem with obsolescence.  Only time will tell if newer, better 
devices will be made with the same component footprint and operating 
parameters.

I think the contesting argument is a good one.  But concerns in a contest 
environment may be more dependent on the quality of other components like 
those used in ultra-fast RF switching, cooling, and the power supply.  And 
that’s a shared concern across any type of SS or VT amplifier.  Assume for a 
moment that a SS amp fails during a contest.  Do we say it failed because it’s 
a SS amp, or because some other component failure that has no relationship 
with active RF device(s)?

The remote site that N4CC and myself share on the FL/GA state line uses two 
desk-crushing Alpha amps: a 9500 and 8406.  Our plan is to replace both with 
one Elecraft KPA1500.  Will the KPA1500 be more prone to problems?  We 
honestly don’t know.  However, based on what's been made public about the 
LDMOS design and PIN diode T/R design, I'm comfortable with the change --  
especially since the root of the design can be seen in the time-proven 
KPA500.   Ultimately, it may be the wrong decision, but for every new 
technology that comes along, someone needs to take that risk and for us, the 
risk is acceptable.

Paul, W9AC

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