Go Back   WorldwideDX Amateur Radio Forums > Amateur Radio Related > Amplifiers


Amateur Callsign Lookup
Enter Callsign:

Ameritron AL-811 problems

Reply
 
LinkBack Thread Tools Display Modes
  #9  
Old 06-10-2005, 08:38 PM
Captain Kilowatt's Avatar
Professional Amateur
iTrader: (1)
 
Join Date: Apr 2005
Location: Nova Scotia,Canada
Posts: 10,571
Captain Kilowatt is on a distinguished road
Default


That amp should not require any mods to convert to 572B's.572B's are like 811A's on steroids.Electrically the same but with 160 watts plate dissapation instead of the 65 watts for an 811A.

I'm confused by a couple of your statments:
First you said:

Okay, I checked it out last night and here are my results, everything was done into a dummy load with a bird 43, with 10 watts carrier in on am I got 40 watts out, plate current-75ma grid current-30ma.


Then you said:

increasing the drive to 25 watts got 60 watts out but the grid current won't go over 80ma and the plate current won't go over 35ma.



Are you sure that is right because more power output should result in more plate current,not less.Either way something is wrong with the bias because the plate meter should read around 110mA +/- 25 % (according to the manual) with the amp switched inline and with no drive applied.

Try reducing the loading control somewhat and see if that raises the grid current.It may be loaded too heavily.

Check R12 and R13 in the ALC circuit as well as the setting of R14 which is the ALC adjust pot.If it is set wrong it will limit the amount of drive from the radio regardless of what the radio is set at.That is of course if you have the ALC line connected to your driver radio.

After that :?: :?:

Reply With Quote
  #10  
Old 06-10-2005, 10:07 PM
KD7UGY
Guest
 
Posts: n/a
Default

Sorry for the confusion, I meant that the plate current won't go over 80ma and the grid current won't go over 35ma. I'm not sure on the ALC adjustment, when I bought it the guy told me that the ALC had been defeated when they changed the relay to be keyed by receiving RF instead of being operated by a relay cable, so I don't have the ALC hooked up. Does that sound right? I'll look inside of it tonight and see what I can find. Thanks again for all the input.

Reply With Quote
  #11  
Old 06-11-2005, 03:08 AM
Captain Kilowatt's Avatar
Professional Amateur
iTrader: (1)
 
Join Date: Apr 2005
Location: Nova Scotia,Canada
Posts: 10,571
Captain Kilowatt is on a distinguished road
Default

I forgot about the amp being modded to accept RF keying.If the ALC circuit was defeated then that is not a factor.If an amp is loaded too heavy it will prevent it from drawing much grid current.That amp should see about 550mA plate current and 150mA of grid current with +/- 1600 volts on the plate.These values are with the max of 70 watts drive.What radio are you driving it with and what is the input SWR going into the amp?

Reply With Quote
  #12  
Old 06-11-2005, 11:03 PM
Senior Member
iTrader: (1)
 
Join Date: Apr 2005
Location: Louisville, KY
Posts: 464
nomadradio is on a distinguished road
Default

Uh, you're not running this from a 120-Volt 15-Amp outlet, are you?

With adequate filament voltage on that tube, a 572B should last more or less forever in that box. It's like running a box meant for the 572B on "low" side all the time.

If you're running it on 120 Volts, and the outlet circuit isn't stout enough, you'll see the color of the filaments inside, dim noticeably with full drive.

This would indicate that the line voltage was falling under load, causing the 6.3 Volts on the filaments to fall, as well. This dimming of the yellow-white filament color indicates that the filament temperature is falling.

Running that filament at too low a temperature can and will cause the tube to go "soft", and appear to be worn out and weak.

If this is in fact the root of the trouble, you won't see those filaments dim when you key it now. If you remember seeing that happen when they were 'fresh', that would be a clue.

And if you're running it from a stout 240-Volt circuit, this is probably not the cause.

73
__________________

These are not the 'droids you've been looking for.

Reply With Quote
  #13  
Old 06-13-2005, 10:25 PM
KD7UGY
Guest
 
Posts: n/a
Default

Thanks for all the help guys, I think nomadradio figured out my problem though. I am running it on a 120-volt 15 amp circuit and I didn't see the filaments dim but that sounds like what I probably did. So if I want to run it could I get by with running it on a better 120-volt circuit like say 20 amps or should I run the amp on 240 or should I put 811 tubes back into it?

Reply With Quote
  #14  
Old 06-13-2005, 11:48 PM
Senior Member
iTrader: (0)
 
Join Date: Apr 2005
Posts: 701
paws264 is an unknown quantity at this point
Default

Quote:
Originally Posted by KD7UGY
Thanks for all the help guys, I think nomadradio figured out my problem though.
I'm glad we have a handle on the situation however, I have a problem with this conversion; there are circuit differences in the amps constructed to run 572B's and the amps constructed to run 811's

572B amps

Heathkit SB-200. 572 B amp

Yaesu 2100B w 572B's

All the 572B amps have a grid leak resistor in the control grid circuit to provide "self bias' for the tube.

811A Amps

Ameritron 811

The 811 circuit has the control grid grounded; if a 572B tube is put in that circuit without the proper modifications done for the grid leak resistors then that tube (the 572B) IS gonna draw more current than it should and it's gonna draw current when it should n't.

When the RF sensing keyer was put in there I wonder what was done to the center point of the filament circuit; I wonder if it is still switched thru a relay or is it hard grounded.

I wonder why it was only doing 100 watts when it was sold to him?

.

Reply With Quote
  #15  
Old 06-13-2005, 11:54 PM
Senior Member
iTrader: (1)
 
Join Date: Apr 2005
Location: Louisville, KY
Posts: 464
nomadradio is on a distinguished road
Default

I predict that the damage has been done to that set of tubes. Just changing the line voltage will NOT undo the damage. Might have prevented it, had you done so in the first place.

You can run 120 Volts, so long as you hold the drive down to about half-throttle. If you draw less current from the wall, the voltage drop won't be that bad.

A 20-Amp 120-Volt circuit will be wired with #12 wire. A 15-Amp circuit with #14, usually. The fatter wire will have a smaller voltage drop at the same current draw. The reason the problem is worse on a 120-Volt circuit is that you need TWICE the amperage on a 120-Volt circuit as you need on the 240. This causes twice the voltage drop in the same size wire, for the same output wattage on the linear. Turn the drive down, and the current demand drops with it. So does the voltage drop on the outlet wiring.

If the 811A tubes haven't had this same (mis)treatment yet, try them on a 240-Volt circuit, if you can. Or hold back to about half of full power. Either strategy will work.

The old textbooks describe a procedure to "rejuvenate" the thoriated-tungsten cathode in a tube like that. I have had pretty poor results on the ones I have tried to bring back to life. Mostly it involves turning up the filament voltage on a test rig. More often than not, the filament just burns out.

You DO have to blow air on them when trying this trick. The heat from the filament alone gets out of hand when you turn up the filament voltage, even for 15 or 20 minutes.

If you placed larger wires in the wall, and fed your 120-Volt outlet with #8 or #6 wire, the problem would be partly fixed. Trouble is, most building codes forbid using wire larger than #12 for a 120-Volt circuit. Might void your homeowner's insurance if they discovered it after a house fire.

Besides, wire that large won't fit under the screws on a 120-Volt outlet.

Here's hoping the 811A tubes haven't been "flattened" yet.

73
__________________

These are not the 'droids you've been looking for.

Reply With Quote
  #16  
Old 06-14-2005, 04:02 AM
Captain Kilowatt's Avatar
Professional Amateur
iTrader: (1)
 
Join Date: Apr 2005
Location: Nova Scotia,Canada
Posts: 10,571
Captain Kilowatt is on a distinguished road
Default

I have a ham buddy that runs an AL-811H off the 120 volt line and has no problems other than a very slight flicker of the ceiling light on voice peaks.He runs about 700 watts pep out and has done so for several years on the original tubes.Admittedly 240 volts would be better but it should run half decently on a 120 line.

Reply With Quote
Reply

Bookmarks
Worldwide Radio Forum



Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -7. The time now is 10:02 PM.


Powered by vBulletin®
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Search Engine Optimization by vBSEO 3.6.0
Worldwide Radio Forum