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Author Topic: Goodbye tubes.  (Read 7189 times)
KM4AH
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Posts: 963




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« Reply #120 on: August 15, 2019, 01:28:24 PM »

Now we can argue about whether or not you can discern the difference in the transmit audio quality of a transistor amplifier versus a tube amplifier.
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KD8MJR
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« Reply #121 on: August 15, 2019, 03:45:47 PM »

Now we can argue about whether or not you can discern the difference in the transmit audio quality of a transistor amplifier versus a tube amplifier.

Probably in AM or FM mode their might be a slight difference but I doubt in SSB that anyone could ever tell.
I have never seen any test done so I am just guessing.
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“A lie can travel half way around the world while the truth is putting on its shoes.”  (Mark Twain)
K6BRN
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« Reply #122 on: August 15, 2019, 04:41:14 PM »

Off topic triggered by Carl's old cars OT commentary....

Quote
With a lot of bodies framed in wood as late as 1935 those loosened up and added a lot of creaks and groans plus many roofs were tar covered cloth inserts as full body stamping/welding into one piece was playing catch up. 

The reason most "hard top" cars from the '20s and early '30s had flat, canvas covered  roof cutouts was to prevent annoying "oil-canning" when the body flexed.  It was not until the late '30s that makers realized that simply putting a gentle curve fore and aft and side to side in the steel roof would solve the problem.  No more canvas roof cutouts needed.

It had nothing to do with that eras metal stamping and forming technology, which was pretty good.

Brian - K6BRN
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ZL1BBW
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Posts: 1374




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« Reply #123 on: August 15, 2019, 08:19:10 PM »

GENEROUS OFFER  Grin Grin Grin


Being as Toobes are so outdated, old fashioned, carbon hungry etc, as a kind hearted person if anyone has some good 3-1000's they wish to donate to me, I will plant some carbon absorbing trees on their behalf.

 Roll Eyes  Gavin  ZL1BBW
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ex MN Radio Officer, Portishead Radio GKA, BT Radio Amateur Morse Tester.  Licensed as G3YCP ZL1DAB, now taken over my father (sk) call as ZL1BBW.
KM1H
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Posts: 5534




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« Reply #124 on: August 16, 2019, 01:07:48 PM »

Quote
The reason most "hard top" cars from the '20s and early '30s had flat, canvas covered  roof cutouts was to prevent annoying "oil-canning" when the body flexed.  It was not until the late '30s that makers realized that simply putting a gentle curve fore and aft and side to side in the steel roof would solve the problem.  No more canvas roof cutouts needed.

It had nothing to do with that eras metal stamping and forming technology, which was pretty good.

Brian - K6BRN

More misinformation here from Brian folks.

The well rounded and curved, called streamlining back then, 1934 Chrysler Airflow had a roof insert as did the the 1935 VW Beetle prototype, 1936 Toyota and Volvo that was inspired by Chrysler.

The insert remained due to production limitations until wide sheet handling metal drawing and stamping came along. Welding small individual pieces was costly and often came out warped. As bodies were slowly rounded the inserts shrunk in size. GM tested the public reaction to no insert in the 1933 Oldsmobile and the full line was all steel by 1936 as was Chrysler. Ford followed in 37.
The 1935 Chevrolet Standard had an insert and the Master was the first from GM to use the all new body.

Some luxury cars and coachbuilt models kept the insert a little longer as customers were often tradition bound.

Carl

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W1BR
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Posts: 4196




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« Reply #125 on: August 16, 2019, 03:08:13 PM »

Now we can argue about whether or not you can discern the difference in the transmit audio quality of a transistor amplifier versus a tube amplifier.

Probably in AM or FM mode their might be a slight difference but I doubt in SSB that anyone could ever tell.
I have never seen any test done so I am just guessing.

FM mode?Huh
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K6AER
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« Reply #126 on: August 16, 2019, 04:21:53 PM »

An amplifier does not have to be linear for FM.
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KM1H
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Posts: 5534




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« Reply #127 on: August 16, 2019, 05:20:30 PM »

Nor for AM, CW, RTTY, SSTV, Digi.  Just for SSB and that can tolerate going rather deep into Class B before it becomes objectionable and there are ways to use it in Class E.
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G3RZP
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Posts: 1320




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« Reply #128 on: August 17, 2019, 02:34:20 AM »

Quote
Nor for AM, CW, RTTY, SSTV, Digi

That depends on exactly what you mean by 'digi'. OFDM requires linearity, for example, while high order QAM has an appreciable amplitude component.
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AH7I
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Posts: 136


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« Reply #129 on: August 17, 2019, 06:30:47 AM »


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.

The single band amp makes a lot of sense when using single band antennas.
No worries about band switching followed by antenna switching.
No worries about broadband transformers or broadband feed back.
With inexpensive active devices, for CW power on a few favorite bands, band specific or antenna specific amplifiers are more attractive for my application than spending $5k to $10k on an auto switching, auto tuning, idiot proof, computerized tube amp.

73 -Bob

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KM1H
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Posts: 5534




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« Reply #130 on: August 17, 2019, 08:23:06 AM »

Quote
That depends on exactly what you mean by 'digi'. OFDM requires linearity, for example, while high order QAM has an appreciable amplitude component.

Im referring to the common ham band modes Peter. I had enough of that high level stuff at work where linearity specs for the multi channel TX was extreme. This was for Alcatel in the 23 -38 GHz segments for EU cell phone towers/poles. This was in the late 90's so Im sure the gear is more sophisticated these days.
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K6BSU
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Posts: 66




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« Reply #131 on: August 17, 2019, 08:36:40 AM »

The only place where "high fidelity" audio is even considered is 75M AM, where hams fo on for hours discussing audio quality.

Otherwise, the goal is audio "punch", where distortion is tolerated, and even encouraged in order to increase readablity.
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W0BTU
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« Reply #132 on: August 17, 2019, 08:55:04 AM »

I don't think that we are all on the same page.

Any mode that is generated in a transceiver and amplified by an external non-linear Class-C amplifier must have a steady carrier which never varies in amplitude, or IMD products will be transmitted with a resulting increase in bandwidth.

That includes CW and AM.

And I am not speaking of a class-C output stage where the plate is directly modulated by an audio amplifier in AM, nor a directly-keyed Class-C output stage which properly shapes the rise and fall times of a Morse transmission.
« Last Edit: August 17, 2019, 08:58:56 AM by W0BTU » Logged

SM0AOM
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Posts: 259




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« Reply #133 on: August 17, 2019, 09:35:56 AM »

Previously, some "hard statistics" about power tube reliability compared to transistors was requested.

Here is what I can come up with, from about 35 years of my own and others practice:

- Low and intermediate power tubes;
receiving and up to 6146 class, closely following the predictions in the tables of the "Reliability Engineering" textbook and the ARINC Report 411 "Investigation of Electron Tube Reliability in Commercial Airline Applications" a wear-out life of about 8000 to 13000 hours of H24 operations.

- Medium power tubes up to the 4CX250B/4CX350A class;
depending of usage profile, up to about 12000 hours when the tube quality was good such as in Eimac, ITT-STC and English Electric, but then declining to about 4000-5000 hours when "no-name" tubes came on the market.

8877s were used in about 20 AL-1500 amplifiers for maritime radiotelex channels during the time-period of 1993-2015.

Average tube life in the beginning around 12-15000 hours of H24 operation, later below 10000 hours but showed quite a lot of "outliers"

- Higher power tubes, P290A, 4CX5000A, 4CX10000D and 4CX15000A

The oxide cathode P290A, mostly around 18000-25000 hours in the beginning. Some late tubes went "gassy" already at
6-7000 hours averaging around 12000, but a select few survived for more than 80000 hours.

Without filament voltage management and reduction of idle current in SSB, 4CX5000As and 4CX10000Ds lasted for about 10000 hours in the 70s. When VOX relays and filament voltage management were introduced in the 80s, the life increased to about 12-14000 hours.

The original RS2793 (approx 4CX15000J) final in the Telefunken 30 kW amplifiers originally lasted for about 8000 hours, but after retrofit with 4CX15000A and VOX relays together with filament voltage reduction in the idle periods they lasted for about 13000 hours on average.

Now for transistors.

Smaller and early production power transistors in the BLX15 class, showed scattered ageing related (probably metal migration) failures after around 150000 hours of operation.
No definitive patterns were observed before finally retiring the transmitters in 2014, after a service life of over 30 years.
It appears that later production with ceramic cases had somewhat more stable characteristics.

Higher power transistors such as the ST TH430 and the 300 W Motorola type used in the Collins HF-80 and Spectrum 2000 system have not shown any systematic wear-out signs yet.

One system I am responsible for has been in H24 operations since 1996. It contains 6 Collins PA-2250 amplifiers (closely related to the HF-8023) each with 24 final transistors. Over 22 years of operations have netted 0 (zero) final transistor failures during about 27 million transistor-hours of operations.

Logged failures have been a few cases of worn-out electrolytics in DC-DC converters, and one (1) transistor failure in a driver amplifier,
possibly caused by a ripple-effect from a "blown-up" DC-DC converter.

Attempting to scale the field reported final transistor reliability to an amateur radio usage profile and to a typical amplifier design would point to a predicted MTTF of around 500 000 hours of H24 operations or 50 years.

However, it is likely that power supplies and other peripherals will have worn out before the final transistor MTTF is even approached.

The experience gained from using the smaller 8xBLX15 equipped amplifiers points in the direction that about 20 years of H24 operation is able to approach their MTTF.
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G3RZP
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« Reply #134 on: August 17, 2019, 10:23:34 AM »

Somewhat off topic, how do they protect the PA transistors from lightning induced EMP surges coming back down the transmission line?
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