Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: Prev 1 ... 4 5 6 7 8 [9]   Go Down
  Print  
Author Topic: Ameritron ALS-1300 Unpacking / Pictures  (Read 74546 times)
ZENKI
Member

Posts: 1636




Ignore
« Reply #120 on: April 02, 2011, 05:52:03 PM »

I agree. The ALC overshoot issue is a problem on just about every transceiver model. This same problem has plagued all the Tetrode amplifiers which are grid current sensitive. These bad radios with overshooting ALC's cause a lot of unnecessary splatter giving many tetrode amplifiers a bad name.

Acom had this problem with most of Icoms radios, and every other radio that caused ALC spike.

Even the Icom 7800 has a overshooting ALC problem. The most notorious is the IC706MK2

http://www.sm5bsz.com/dynrange/pulse.htm

Some hams have used innovative ways of avoiding these spikes and excessive drive problems.

http://www.qsl.net/z/zp4kfx//Antenne/IbrCon/Ibrido.html



What I want to know is if the people who are losing their amps have problems like high power exciter spikes because of ALC issues or improper relay timing, etc.

Logged
N3OX
Member

Posts: 8918


WWW

Ignore
« Reply #121 on: April 03, 2011, 02:51:41 PM »

The guy I mentioned was very careful about drive and never used more than 35 watts with it.

Understood, but some exciters are actually WORSE in terms of spiking when the drive is turned down.  Sometimes the spikes actually exceed the rated output of the exciter.  It's only a few milliseconds so you need a scope to see it.

Other radios start making RF output at exactly the same time they pull the amp keying line low, with no delay!  This is a stupid oversight on the part of the rig's designers, but is actually something that happens in some rigs.  If the relays were timed just so, this could leave the amplifier transmitting briefly into an open circuit.  

These are possibly serious issues if the amp's protection circuitry isn't fast enough to cope.

Anyway, I'm just curious if people who have dead ALS-1300's have verified that the rest of the station's operation is flawless with regard to amp keying and exciter output.  I was having serious problems here with my exciter and amp (AL-811) not so much with the amp getting hurt but with my high-voltage 160m antenna arcing over.  It will handle 400W of output just fine but not the full 600W the AL-811 will do if you drive it too hard.   I had to supply a fixed external ALC voltage to the exciter to stop the arcing.    The ALC from the amp wasn't actually doing anything for whatever reason.

Before I stopped the spikes I could turn down the exciter drive down so low that the steady power output from the AL-811 was just 200W and it would still put out a high power spike that would strike the arc on the antenna.  Now that I have the fixed ALC voltage I can run as much as 500-550W to the antenna with NO problems.  The exciter was briefly driving the amp high enough to arc the antenna even with the drive turned down to something like five or ten watts.
« Last Edit: April 03, 2011, 03:02:47 PM by N3OX » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W8JX
Member

Posts: 13268




Ignore
« Reply #122 on: April 03, 2011, 03:26:11 PM »

I understand where you are coming from but what good is a amp that is so sensitive to input overload if indeed that is part of problem?
Logged

--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
KD8MJR
Member

Posts: 5557




Ignore
« Reply #123 on: April 03, 2011, 09:06:18 PM »

I understand where you are coming from but what good is a amp that is so sensitive to input overload if indeed that is part of problem?

I agree!
But I still think that the overdriving of the FETS is the main issue, but when you get down to it does it really matter?  If this thread has not gotten Ameritrons attention, I guess nothing will! Unfortunately I doubt they have even read the thread, I suspect that nothing really matters too them since they have no real competition at their price point.  It's truly a shame because if the Amp was just slightly redesigned to be a 1kw Amp it would probably have a fair bit of reliability and I suspect almost the same amount of people would buy it.
As I said way back in this post, I think MFJ has gotten away with doing things the way they do because tubes are just so much more forgiving than SS.  I suspect that they might not be very anxious to make another High power SS amp in the future as the returns on this 1300 must be a very expensive undertaking.
Logged

“A lie can travel half way around the world while the truth is putting on its shoes.”  (Mark Twain)
AD5X
Member

Posts: 1623




Ignore
« Reply #124 on: April 04, 2011, 04:18:41 AM »

... some exciters are actually WORSE in terms of spiking when the drive is turned down.  Sometimes the spikes actually exceed the rated output of the exciter.  It's only a few milliseconds so you need a scope to see it.

Other radios start making RF output at exactly the same time they pull the amp keying line low, with no delay!  This is a stupid oversight on the part of the rig's designers, but is actually something that happens in some rigs....

I have an IC-706MKII that overshoots to 140 watts for 2ms when set at any power level.  Even setting it for 5-watts output results in the 140 watt spike.  I would never use this radio with any amplifier.  My IC-706MKIIG overshoots 7-10 watts regardless of power setting, which is much better.  My K3 has no overshoot at any power setting.

Also, some transceivers unkey the amplifier 5-7ms before RF has decayed to zero (IC-706/7000/7600 are examples).  This can result in hot-switching on un-key when operating QSK if the amplifier's switching is faster than this (like in a QSK-capable amplifier).  A few tube amps on the market have input RF sensing that prevents switching when RF drive is present regardless of the state of the amp-key line - though there is always some sensing threshold below which you can't see the RF and hot-switching could occur at lower power levels.  The only solid-state amp I know of that addresses this issue is the new Elecraft KPA500.  It has a menu setting for drop-out time after un-key in milliseconds, and it also has both input and output RF sensing to prevent switching when RF is present.

Phil - AD5X
« Last Edit: April 04, 2011, 04:49:47 AM by AD5X » Logged
N3OX
Member

Posts: 8918


WWW

Ignore
« Reply #125 on: April 04, 2011, 07:04:22 AM »

I agree!
But I still think that the overdriving of the FETS is the main issue, but when you get down to it does it really matter? 

The objective facts about the failures are important to an appropriate discussion of the real-world limitations of the ALS-1300.  It matters a lot to some people if the active devices are really being pushed  by Ameritron's claims and/or the users or if they are being hammered by station glitches.

The latter is neither Ameritron's fault nor is it really the users' fault.  But it's easy enough to fix if you know about it ahead of time.

I did what you said before and read the data sheet and formed my own opinion about whether the FETS are being pushed.   I don't really understand how running eight MRF-150's at 150W to get 1200W power output is a problem.  That's pretty much where the devices were run for characterization of many of the specs in the data sheet.  300W dissipation is the maximum, and that happens at about 245W output power, assuming 45% efficiency.  150W doesn't sound like "pushing" to me.  There are several plots on that sheet where the devices were putting out over 200W.  What WX7G is saying seems right to me: 150W is more like the last reasonable recommended operating point if you want better than 30dB IMD suppression.

There's a lot of heat to get rid of with 1200W out and 45% efficiency, but for some people, like me, that's not an issue even if the amp's thermal design is inadequate.  I don't transmit much. 

So I don't get it.  Seems to me like 1200W is fine.   But some people's amps are still blowing up.  So I think it's something else.

Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KD8MJR
Member

Posts: 5557




Ignore
« Reply #126 on: April 05, 2011, 12:43:27 PM »

"Seems to me like 1200W is fine."

I am not going down that road again Lips sealed

"The objective facts about the failures are important to an appropriate discussion of the real-world limitations of the ALS-1300.  It matters a lot to some people if the active devices are really being pushed  by Ameritron's claims and/or the users or if they are being hammered by station glitches."

Why is the reason so important to you?
If you bought a new Nissan electric car and the engine blew up after 2 months, you sent it back and got it fixed then it blew out again after 3 more months, would you care if the mechanic told you that the Motor gears in sub section 3 had gone bad or would you feel better if it was a mismatch in the Cell outputs that spiked the motor?
I would guess pretty much "NO", all you would want is your money back or a car that stopped blowing up engines!

Same thing here, I would not care in the least why!   This is a new Amp, if it was some second hand older Amp I certainly would want to know why.  Also I would keep in mind that if my Amp was one of the only ones to blow out; then yeah I might want to know why, but with the 1300 all one has to do is look at the review section to realize it's not my system at fault, something is up with the Amp!  I certainly don't care what it is, I would just want it fixed properly or my money back.
IOW I am not comforted by knowing if it's input glitches, overdriven FETS or badly machined heat sinks, bad soldering or bad application of Thermal paste. Just get me an Amp that works.
« Last Edit: April 05, 2011, 01:56:57 PM by KD8MJR » Logged

“A lie can travel half way around the world while the truth is putting on its shoes.”  (Mark Twain)
K6AER
Member

Posts: 5720




Ignore
« Reply #127 on: April 05, 2011, 01:31:56 PM »

I have been reading this thread for some time and many good points have been brought up.

First running the transistors at 150 watts out is not pushing the devices but that is not without some understanding.

The devices are designed for a certain thermal coefficient between the heat sink, the heat spreader and the actual devices die. The assembly is critical to obtain the maximum thermal coupling from the device and the heat sink. A ruff or uneven surface, too much thermal or too little compound will affect the ability of the transistor to dissipate heat. Heat sink dust will insulate the heat sinks ability to dissipate heat and solid state amplifier must be kept clean. All of these areas could be the difference between one amplifier surviving and the other heading back to Mississippi.

Drive levels the user puts into the amplifier are critical. 5 mS of over drive will blow the gates in some cases. Sometimes the protection circuits are fast enough and sometimes not. How much overdrive is too much? 1 dB, 2 dB or 3 dB can be the difference. The manufactures skip lightly over this area and most of the time do not give much data. Class C amplifiers used in repeater service generally are run no more than 70% of the device rating for high reliability.

Don’t depend on the ALC feedback from the amplifier to the radio to save you. Many circuits are not fast enough. Newer radios have very good ALC control and do not exhibit power overshoot. Radios made before 1997 are all over the map. Only a spectrum analyzer or a good peak reading watt meter will give you a clue.

IMD, known as intermodulation distortion is the ability of the device in the amplifier to remain linear and this is expressed in a dB ratio during a two tone signal test. Transistors and FET’s have a harder time of it for they cannot have soft compression like a tube amplifier. Typical solid state amplifiers that are run near their maximum output will have IMD numbers below 30 dB from second to third harmonics. This will earn you the bandwidth splatter award. In order for your solid state amplifier to have low IMD number the output in SSB (complex modulation) needs to be run a couple of dB below your 1 dB compression point. Typical well designed tube amplifier at rated output will be in the 42-46dB range. At 1500 watts out this can place some of you sideband noise from S7 down to S1 or into the noise. This is the effect of higher IMD ratios. Note I am not referencing an S unit at 6 dB but real world signal strength as it appears on today’s radios. This is why many 1500 watt tube amplifiers are capable of 2400 watts out. This is necessary to have sufficent headroom for low IMD numbers.

One of the understandings of amplifiers that comes with time is not trying to squeeze every last watt out of the device. An amplifier needs to be operated in its most linear region where the unit will produce a clean signal.
« Last Edit: April 07, 2011, 07:56:53 AM by K6AER » Logged
W4AMP
Member

Posts: 6




Ignore
« Reply #128 on: July 24, 2011, 12:45:13 AM »

An excellent and informative thread.
Logged
K8AXW
Member

Posts: 7038




Ignore
« Reply #129 on: July 25, 2011, 08:48:43 PM »

Looks like they still haven't fixed the "Refected" Power typo that I noted like about a year ago.

They have a problem with Cheveray and Caderac.
Logged

A Pessimist is Never Disappointed!
Pages: Prev 1 ... 4 5 6 7 8 [9]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!