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

   Home   Help Search  
Pages: Prev 1 [2]   Go Down
  Print  
Author Topic: New AL 572 & IC756 3--snap-no power  (Read 5152 times)
W8JI
Member

Posts: 9296


WWW

Ignore
« Reply #15 on: July 16, 2010, 11:18:02 PM »

One or more of the 572B tubes in the amp will arc again. It's just a matter of time. The question is will the "module" installed in the ICOM protect it?

What appears to happen is the arc energy pings the input Pi network which then rings for one or more cycles at roughly the frequency it is set to. The energy is several kW.

I can send you a circuit schematic that will clamp the ICOM RF output to +/-120 volts while absorbing most of the energy. My simulation shows the circuit reducing the arc-injected total energy by a factor of 10X and the peak energy by a factor of 25X when the amp is set to 160 meters.



You know I'm getting pretty concerned about tube quality for all Chinese tubes these days. I just had a Chinese 3-500Z pop a few times.

I'm going to grab some bad tubes and measure some input connector voltages when they arc. It didn't hurt my FT1000, but the FT1000 is pretty tough for ESD in the neighborhood.
Logged
WX7G
Member

Posts: 6128




Ignore
« Reply #16 on: July 17, 2010, 06:53:42 AM »

Tom, I'll describe the clamp circuit and perhaps you can simulate it and evaluate it. It's along the lines of many other transient absorption circuits I've designed. What I don't know is to what voltage the tube cathode jumps to so I am assuming 1 kV for now. My model also does not include the IC-746 output. That is modeled for now as 50 ohms to GND. The model does include the AL-572 input circuit. A single half sine is produced when arced into a 50 ohm load (IC-746). With the 1 dB pad the AL-572 input circuit is underdamped and it rings for one cycle.

AMP INPUT----1 dB PAD----CLAMP----ICOM

The 1 dB pad it a T with 470 ohm to GND, 4.7 ohm series, 470 ohm to GND. More attenuation would be great for absorbing the energy but I don't think more than 1 dB or 2 dB can be spared from a 100 watt radio and still drive the AL-572 to rated output power.

The clamp consists of two steering diodes to 1 uF of ceramic capacitors maintained at +120 and -120 volts. The steering diode for each rail is made up of six paralleled strings of three series connected 1N4148-type diodes. These diodes survive 10 amp pulses (a few us) in this type of service. Between each 1 uF cap and its 120 volt battery is a 47k ohm resistor. The negative clamp does not appear to be needed.
« Last Edit: July 17, 2010, 06:57:37 AM by DAVE CUTHBERT » Logged
WX7G
Member

Posts: 6128




Ignore
« Reply #17 on: July 17, 2010, 05:11:06 PM »

You probably know this but just in case. To induce arcing in a tube being hipotted or one that is operating tap it with a stick.
Logged
K4FX
Member

Posts: 166


WWW

Ignore
« Reply #18 on: July 18, 2010, 12:59:20 PM »

  I'm having a module put into the 756 which is supposed to guard against spurious amounts of rf getting back into the rig.  I should have it back in about 3 weeks or so, and then I'll know some more I guess.
Thanks for all the input

73  John  n7qx

I also have an Icom 756 and am interested in this module. Is this somthing only offered by Icom. Can one order this and install it themself.

Me too, I would be very interested in that module. I am tired of running my 857D when there is a storm withing 500 miles. Which is most of the time in the spring and summer.

K4FX
Logged
K2QPN
Member

Posts: 70




Ignore
« Reply #19 on: July 19, 2010, 09:26:13 AM »

I too have a Pro3. Please post info on the module when you get it.

Thanks, Bob K2QPN
Logged
N7QX
Member

Posts: 21




Ignore
« Reply #20 on: August 04, 2010, 02:14:33 PM »

Regarding the IC756 Pro protection module referred to earlier---
   My rig is being repaired at Burghardt's.  When I called to tell them I was sending it in,  I was asked if I would like this protection module. They said they had installed over 400 of them to date.  I believe the cost was somewhere around $70-75-part and labor...
   I don't have the rig back yet--due sometime around Aug 11 or so.  Once I get the repair sheet,  I'll post the info here....Meantime,  I guess you could contact Burghardt's if you need to know right away....
    My 572 went back to Ameritron after 2 weeks.  All the trouble shooting they had me do at home did not solve the issues..Don't know when that will be back to me.
Logged
W8JI
Member

Posts: 9296


WWW

Ignore
« Reply #21 on: August 06, 2010, 07:08:21 AM »

Tom, I'll describe the clamp circuit and perhaps you can simulate it and evaluate it. It's along the lines of many other transient absorption circuits I've designed. What I don't know is to what voltage the tube cathode jumps to so I am assuming 1 kV for now. My model also does not include the IC-746 output. That is modeled for now as 50 ohms to GND. The model does include the AL-572 input circuit. A single half sine is produced when arced into a 50 ohm load (IC-746). With the 1 dB pad the AL-572 input circuit is underdamped and it rings for one cycle.

AMP INPUT----1 dB PAD----CLAMP----ICOM

The 1 dB pad it a T with 470 ohm to GND, 4.7 ohm series, 470 ohm to GND. More attenuation would be great for absorbing the energy but I don't think more than 1 dB or 2 dB can be spared from a 100 watt radio and still drive the AL-572 to rated output power.

The clamp consists of two steering diodes to 1 uF of ceramic capacitors maintained at +120 and -120 volts. The steering diode for each rail is made up of six paralleled strings of three series connected 1N4148-type diodes. These diodes survive 10 amp pulses (a few us) in this type of service. Between each 1 uF cap and its 120 volt battery is a 47k ohm resistor. The negative clamp does not appear to be needed.

That's a good clamp.

I have a patented clamp in a receiving antenna system that uses a single reference voltage. It is a hard clamp with peak voltage set by a single zener. The zener can be fed from a 1-5 mA source, just enough to overcome leakage.

It's really odd the amp won't pop 1N4148's inside the amp but the Pro can't handle the transient.

I'm experimenting with a different approach. I have little gas clamp protection devices rated at 150-175 volts peak. I'm running tests on them now.  I'm doing one at the filaments, and across the input jack. It's tough to measure the pulse level because it is so narrow and random.

73 Tom

Logged
WX7G
Member

Posts: 6128




Ignore
« Reply #22 on: August 06, 2010, 08:15:30 AM »

I always employ a two stage clamp when using a gas gap. The gas gap is followed by a solid state clamp. For high energy sources the voltage rail used as a clamp has an amplified zener (MOSFET and zener).

A gas gap alone takes time to fire but when it does the current risetime is very fast. And the voltage when fired is about 15 volts. This can form a transmission line pulser that sends a nice fast pulse into the transceiver. There's a trick to using gas gaps that might be used. The gas gap is connected in series with an MOV or TVS. The gas gap isolates the high capacitance of the TVS. The TVS keeps the voltage from clamping too low.

As you know gas gaps take time to fire. This has been called the lucky electron theory. If there is an electron in the gap it fires fast. If not it can take microseconds. There are gas gaps with radioactive sources to keep the gas ionized but these are not common items.

Logged
N2JXN
Member

Posts: 189




Ignore
« Reply #23 on: August 07, 2010, 05:36:14 AM »

Love this thread. Could someone explain what a Clamp is and maybe provide a simple circuit drawing for the hams out here tring to learn. Thanks
Logged
N7QX
Member

Posts: 21




Ignore
« Reply #24 on: August 24, 2010, 10:38:57 AM »

There were a couple of inquiries about the ESD protection circuit that Burghardt's installs in icom rigs, particularly the 756 and 746 pro models.
As I just received my 756 back from Burghardt's,  the name of the part they installed is called  BEV-756.   While I don't know for sure,  I would hazard a guess that the part for the 746 Pro is probably BEV-746.  HOpe this is all helpful to those who were asking...73
Logged
Pages: Prev 1 [2]   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!