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Author Topic: Goodbye tubes.  (Read 6744 times)
SM0AOM
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Posts: 256




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« Reply #30 on: July 14, 2019, 08:45:21 AM »


It is well known that playing with reflected harmonics can make a meaningful difference to efficiency, but I do wonder if there is another point where they can make a real difference to linearity? Anyone got a reference to the theory on this?

I have not seen any theory reference, but when designing HF MOSFET PA:s in the late 80s, ITT-Standard Radio ran into problems with both stability and linearity unless harmonic-dump LPF:s were used.

In their previous bipolar (BLX15) realisations, they did not have to use these measures to obtain ISB performance.

Marconi also ran into similar problems in their 500 W PA somewhat later.
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AH7I
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Posts: 128


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« Reply #31 on: July 15, 2019, 02:50:50 AM »

The problem with stability circles on a Smith chart is that it can be tricky to tell which side of the curve is the stable one...

The basics don't change and a newbie could still do worse then reading F.Termans magnum opus (Also, Langford-Smith).

73, Dan.

Thanks. 73, -bob ah7i
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KB1GMX
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Posts: 1803




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« Reply #32 on: July 15, 2019, 09:53:13 AM »

I read the data sheet...

Its not wow neat!   It's rediscovered.  With many wrong assumptions.

First watch the rating for dissipation plastic tab cases have very high
thermal resistance so really good thermal design is a must.  Big
heatsink and fan.  However for the people that want to get their
QRP radio to impressive power it has possibilities.

As to paralleling, seriously?   The same guys make 1.5KW parts
and a pair of them combined would be far more resilient.
Generally paralleling at HF and up is not desirable as it
introduces more copper on the board with its issues, never
minding the paralleled parameters you don't want to increase.
I hold the MRF150 x4 amps that tend to sometimes do nasty
things.

Try to not apply 1980s design and devices to modern parts,
you will hurt yourself.  Newer parts are more robust and
have far better gain.  Also things like feedback are more
commonly used now.  The whole design process is more
sophisticated as well using modern simulation tools and
test techniques.  To me the 1970s was the beginning of
the big move to both bipolar power and various forms the
the VMOS first generation.

The biggest killer is far too much power in.  Maximum power
input the narrow band model is under a watt at then its over
driven!   That means the average (typically most) transceivers
the power spike will kill them before you get to say hellooo. 
Even a FT817 may be far too much!   Pin based limiters and
input attenuators are required as most 100W radios also are
not as nice and clean at low power if we ignore the ALC spiking
on key down.

Getting low IMD takes work as been said.  Also enough
standing current (BIAS) to required monitoring the heat.

Also even at 50V you want a low impedance load to the gates
and drains for stability and to keep on the linear part of the curve.
Been doing it for while like others here.  Going for max smoke is
usually a result without taking in all considerations.

An aside stage gain is not limited by the FCC for user designed
and built gear.  It was instituted to prevent US CB ops from
getting to the kilowatt level with COTS/HAM amps in one hop.

Allison

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KM1H
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Posts: 5259




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« Reply #33 on: July 15, 2019, 06:18:58 PM »

Quote
An aside stage gain is not limited by the FCC for user designed
and built gear.  It was instituted to prevent US CB ops from
getting to the kilowatt level with COTS/HAM amps in one hop.

Allison

Which was aimed specifically at the National NCL-2000 with a pair of swamped grid driven 8122's. On 10M about 15-20W drive would provide ~1200W out. Ive run one on 6 since 1965 with a tuned input and a 270 Ohm resistor and run 1200W output with ~8W drive, No neutralization required and completely stable.

The FCC rule killed that amp for the ham market and left an almost complete production run in limbo. So National got even by moving production to North Central Maine and selling direct to the CBers, some hams, and also direct into Canada. The FCC never caught on and they were still producing them in Maine in small runs up to the IRS auction in 1992 Grin

Carl
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KB8VUL
Member

Posts: 297




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« Reply #34 on: July 21, 2019, 08:06:00 AM »

When building solid state amps, and this will raise some eyebrows, look at what the CB guys are doing.
There are guys out there running solid state amps at AM radio station power levels from vehicles. 

THe biggest historical issue with high power solid state at home was the power supply required. 
Tube stuff was easy, big transformer, some diodes, a filter cap and you had a plate supply.
Generating 48 volts at 50 amps was expensive.  Now, you can get switching power supplies and parallel them to produce any currnet level you could reasonably want.

The OP mentioned that he was looking to build a single band amp.  Why settle for single band, unless that's all you want.  The bandpass fillers are not hard to construct if you want multiband operation.
Solid state devices are here to stay, and they are in alot of applications better than tubes. 

But for some, nothing beats the glow of a tube.  And that's ok too.
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K2FW
Member

Posts: 218




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« Reply #35 on: July 21, 2019, 02:29:19 PM »


The Chinese FU728F Tetrode is rated for 1800 watts continuously and only cost about $400. Gain is about 15-16 dB depending on screen current. I have seen these tubes put out easily 2.3 KW in SSB mode with 60 watts drive. This tube was modeled after the 4CX1500B.

Mike, do you happen to know the "real" plate dissipation on the FU728F tube.  It must be more than 1500 watts since the tube is larger than a 4CX1500.
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KM1H
Member

Posts: 5259




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« Reply #36 on: July 21, 2019, 03:11:06 PM »

The REAL rating is 1200W and it took about 2 seconds to find that spec sheet on Google. Since the tube is used for commercial and military amps that is a CCS rating.

You are welcome to apply any ICAS or Hammy Hambone IVAS rating you wish.

Carl
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K2FW
Member

Posts: 218




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« Reply #37 on: July 21, 2019, 06:00:54 PM »

The REAL rating is 1200W and it took about 2 seconds to find that spec sheet on Google. Since the tube is used for commercial and military amps that is a CCS rating.

You are welcome to apply any ICAS or Hammy Hambone IVAS rating you wish.

Carl

Thank You oh Humble one!
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KM1H
Member

Posts: 5259




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« Reply #38 on: July 21, 2019, 06:12:39 PM »

Quote
Thank You oh Humble one!

Im always glad to be of service massa
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W3RSW
Member

Posts: 606




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« Reply #39 on: July 22, 2019, 08:17:04 AM »

W6ASI’s  Eimac Amateur Service Newsletter AS40 article
“Intermittent Voice Operation” and reprinted in Ham Radio Mag. Jan 1971
Defines such as a more realistic set of operating parameters to be found for Only specific tubes, the 8873/4/5 set in particular in this article.  Bill Orr writes that any other tube must be determined Individually; the parameters are not a universal set for all power tubes.

As such the IVAS rating is valid for SSB and CW for the particular oxide cathode ceramic triodes Specified and with reasons clearly outlined.

Tune up time limits and average operating power limits are defined.

https://archive.org/stream/hamradiomag/ham_radio_magazine/Ham%20Radio%20Magazine%201971/01%20January%201971#mode/2up
« Last Edit: July 22, 2019, 08:21:19 AM by W3RSW » Logged

Rick, W3RSW
KM1H
Member

Posts: 5259




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« Reply #40 on: July 22, 2019, 08:30:16 AM »

And here is what ICAS is really all about from the horses mouth. IMO IVAS is simply a hammy hambone way to further decrease tube life especially with oxide cathode tubes. Those running the YC-156/YC-179 pulls have found that out the hard way.

https://www.americanradiohistory.com/ARCHIVE-RCA/RCA-Ham-TIps/RCA-Ham-Tips-39-10.pdf

Carl
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KOP
Member

Posts: 346




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« Reply #41 on: July 22, 2019, 09:51:36 AM »

W6ASI’s  Eimac Amateur Service Newsletter AS40 article

W6SAI perhaps?
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I considered a microwave oven magnetron and a 4' dish as a drone-killer. The ERP would be on the order of a hundred thousand watts or so. ~anon

November 28, 2018, 09:16:04 AM
W3RSW
Member

Posts: 606




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« Reply #42 on: July 23, 2019, 08:15:51 AM »

Certainly, Bill Orr himself, “Mr. Eimac”
 Wink And the modern, well reasoned article in the reprint bears reading, starting page 24.
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Rick, W3RSW
K2FW
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Posts: 218




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« Reply #43 on: July 23, 2019, 08:22:40 AM »

Certainly, Bill Orr himself, “Mr. Eimac”
 Wink And the modern, well reasoned article in the reprint bears reading, starting page 24.
An excellent read.  I've had many Bill Orr books over the years.  What I really would like to know is how does the plate dissipation of the FU728F compare to the 4CX1500?  The tube is much larger in size than a 4CX1500.
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KM1H
Member

Posts: 5259




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« Reply #44 on: July 23, 2019, 10:19:15 AM »

Certainly, Bill Orr himself, “Mr. Eimac”
 Wink And the modern, well reasoned article in the reprint bears reading, starting page 24.
An excellent read.  I've had many Bill Orr books over the years.  What I really would like to know is how does the plate dissipation of the FU728F compare to the 4CX1500?  The tube is much larger in size than a 4CX1500.

Are you saying the spec sheets arent sufficient for you?

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