HFU HF Underground
Technical Topics => Equipment => Topic started by: jackson_r on December 07, 2015, 1425 UTC
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I'm a newbie when it comes to amplifiers, and I'm trying to load up my first one with an Ameritron AL-80 connected to my IC-735. I have a wire run from the ALC jack on the back of the amp to the ALC jack on the back of the 735. Another wire runs from the "relay" jack on the back of the amp to the "send" jack on the 735. When trying to load the amp, I confirm that the "XMIT" light on the amp turns on and I can hear the relay click in the amp. So far, so good. But here's where it gets weird...my output meter (which goes in to a dummy load), pegs hard to the left at zero when I turn on the amp. It does this in AM or SSB, and regardless of my drive level. The person I bought the AL-80 from is perplexed as well, but has been trying to help my troubleshoot. So far we've made sure all the RF in/out connections are proper and have also made sure the proper band has been selected on the amp. He also suggested disconnecting the "ALC" connection between the 735 and the amp as he said, "most people don't use it or need it." Still the same result.
I'm beginning to wonder if the 735 might not be capable of properly switching an old amp like this? I'm thinking I might need something like an "ampkeyer" that's supposed to help interface newer solid state rigs with old amplifiers. Does anyone have thoughts on this, or perhaps some other tips I may not have tried?
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Your O/P meter pegs hard to the left?
Surely it should go to the right?
Is that your problem?
If so it sounds like a problem with the meter?
I'm assuming a 'Separate' power meter here.
The 'amplifier' meter has a 3 position switch, please tell the readings in all 3 positions.
Str. :)
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May be a case of RTFM!
Is the meter in the Ig or Ip position perhaps?
You have read the manual haven't you?
???
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Hi Stretchy! Of course I've read the manual! ;D Okay, the three position switch..."V" shows about 2800, IG and IP show 0..this is at startup while preparing to tune. According to the manual, this is how it should be. When I key down without the amp on, I confirm that my meter shows about 40 watts output (swinging to the right, as a normal meter would). Flip the amp on and key down, however, and the watt meter pegs hard to the left. Yes, left. It's the oddest thing I've ever seen. Edit - my watt meter is a separate unit (the old Radio Shack kind) that is downstream of the amp and from there goes in to the dummy load. I get the same meter reaction whether I key down in V, IG, or IP. While the Radio Shack meter seems to work fine barefoot, I do have a new MFJ meter that I have not tried yet (mainly because it won't handle the watts that the RS one will). I'll give that a try later today to see if the RS meter is simply faulty.
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Check for D.C. on the O/P, careful as it may be rather high! :o
Check without Tube, this would isolate the valve and anything RF'y
:)
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Sorry, I feel like an idiot for asking...but "check for DC?"
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DC as in DC voltage the valve uses that should be isolated from the O/P by C15/16, couple of KV?
That would 'upset' your o/p meter.
And you if you touch it!
:(
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I guess I had no idea that DC voltage could be causing problems with the meter. It's one of those cheapo 2000 watt RS watt meters from 20+ years ago. I'll follow your advice and check it without the tube later (what behavior should I expect to see?). I'll also try out the newer MFJ watt meter I have to see if it behaves any differently.
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Does the MFJ handle a KW? I suspect not and it will be blown to bits!
OK not sure of your RS meter?
RS means Rohde & Schwarz over here, I'd need a model number to find a schematic etc.
Negating the meter, how does the amp behave?
With the amp ON and NO drive with JUST the dummy load connected, does the dummy load get HOT (this would indicate DC present on the O/P) if not then you're probably OK for NO DC on the O/P.
There should be NO DC there!
Removal of tube would have no effect on DC but would isolate 'Problem' to valve (i.e. shorted grid etc)
More detail please and we'll get it fixed!
Str.
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Sorry, I was using "RS" to refer to Radio Shack, the maker of the 2000 watt meter I'm currently trying to use:
http://s1361.photobucket.com/user/joe3857/media/DSCF2522_zpscfd91953.jpg.html
The MFJ won't handle 1 KW, but I'm doing all this testing with my drive basically at minimum. My output shouldn't be anywhere near 1 KW with almost zero drive. But I'm new to amps, so I may not know what I'm talking about. ;D Intriguing idea to test the amp just hooked to the dummy with no drive. I'll give that a shot as well and report back whether the dummy gets hot or not. :)
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OK, that photobucket site not good, I cant even zoom into the image, maybe it's just my O.S. (android)
OK it looks like some crappy (sorry) CB thing, hmm, not to be trusted and your not on 27MHz so wont be accurate on 6MHz.
OK plug another radio in there and see if it works, any old .... a CB, anything, does the meter respond normally?
OFF now see you tmrw.
Str.
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JACKSON
you say you are a newbie to amps. don't go poking around inside that thing. if you have to do something in there get a hold of someone who knows what they are doing and learn from them.
try taking that rs watt meter out and tuning with just the meter on the amp .
tune it by the numbers in the manual.
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personally i would just let it sit and wait until i got a better decent quality meter..
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personally i would just let it sit and wait until i got a better decent quality meter..
Believe me, I have no intention of poking around inside the amp. The lights in the house dim momentarily when I turn it on and I can "feel" the electricity in the air. No earthly good can come from opening up the innards of something like that. :D Yeah, the Radio Shack meter is definitely cheap and mostly used by CB'ers, but I also note that it's well spoken of by Hams as well so I thought it would be worth a shot. Outside of trying a couple of things Stretchy mentioned, I think you're right that I should just unplug the thing and wait until I get a bombproof watt meter. I'm also going to look at getting a soft key installed so I don't kill my rig.
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Been doing some more research this afternoon about wattmeters showing reverse deflection on key down. Multiple sources seem to indicate that this can occur during overmodulation. I'll also go back and recheck my amp tuning procedure and also that pesky little "mic gain" slider, which I hadn't paid much attention to during this tuning process.
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Toss the ratt shack meter until proven useful otherwise...
Do your tune up in the CW mode first...
Sounds like some sort of screwy RF feed back thingie going on... are all your connections solid? good coax cables properly soldered etc... poor connectors and cables are demons and need to be placed in the hell box and buried in a pit outside.
Point is: check everything before powering up... every connection every piece of equipment in-line... when all is proven well connect each piece of gear one by one, (one at a time that is) until the gear works properly.
let me think on this...
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If it's used, it's hard to tell how much it's been knocked around, misused and modified over the years.
If the fellas here can't help you try someone near you who knows about linear amps and have them help you. You can always use the "aspiring ham" excuse if the person suspects you of being an evil CB'er or worse. Repair the mod on the transceiver before asking for help, that's a red flag for the more persnickity hamsters.
Ham radio clubs are full of old guys with a lot of knowledge about such things who are more than willing to walk you through it. You could probably pick up a good working power meter and heavy duty dummy load for testing cheap there too. Again the aspiring ham angle is the way to go.
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Ham radio, Old Guys, Yep I'm here already :)
Ha! :) :)
Re the 'Over modulation' you should be tuning it up with an unmodulated carrier BTW! (I'm sure you are)
You don't have to 'aspire' to be anything either, I'll help coz your into RADIO, that's enough for me!!
Str.
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Okay, second round of tests on a fresh day.
- Tried stretchy's recommended test about running the amp straight in to the dummy load to see if it got hot (from possible high DC). No heating occurred.
- Part of the tuning procedure states, "idle current (Ip) should be just under 150 ma with no drive when the XMIT light is on." The meter sits at zero and doesn't twitch when doing this.
- Next part of tuning procedure states, "With the transciever on tune and the AL-80 on OPT, slowly advance the drive control until (in the Ip meter position) a reading of between 150 and 300 ma occurs." Once again, the meter doesn't move at all when advancing the drive. I ran it slowly all the way up to maximum drive and then back down, no reaction from the Ip meter. (I tried in CW, AM, and SSB modes, with the mic keyed and no modulation). The troubleshooting section of the manual says this about and Ip meter that sits idle when on standby: "filament to ground short, socket, tube." In other words, it's saying there could be something wrong with the tube?
If it's of any consequence, I'm not getting the backwards deflection of the watt meter when running these tests this morning. So something either fixed itself, or I was doing something wrong yesterday. But on the other end, there's no positive deflection either. Wattmeter shows power output just fine when barefoot. Run it through the amp and there's nothing. At the end of the day, still a non-working amplifier that requires some more prodding. ??? I'm back to wondering if my 735 is even keying the amp properly to be able to tune it. The XMIT light on the amp does turn on when I key the mic (and I believe I hear a relay clicking inside it), so I think that means I'm keying it properly, but I'm not certain.
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Quite simple then.......................
If it's not taking any current the valve is NOT working.
Not too difficult to work that one out!!
OK, could be many things and as the manual suggests, the valve or socket or anything actually as the amp is just, simply a valve oh and a power supply too.
Has the meter (the one on the amp) got 2 other positions to indicate H.T. and I.G?
What do they say?
???
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No, it doesn't seem to. Very basic meter that is simply labeled "plate voltage."
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Yes OK PLATE VOLTAGE
What does it read.
???
+ send a shortcut to a picture of the EXACT model of your amp as all the ones I can see read 'Ig' too.
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Ok... now the picture is getting clearer...
It will be a great help for you to post a diagram of the amp, including the PSU...
I'm keeping my fingers crossed that it isn't the tube...
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Yes OK PLATE VOLTAGE
What does it read.
???
+ send a shortcut to a picture of the EXACT model of your amp as all the ones I can see read 'Ig' too.
Here is the meter from my exact model: http://s28.postimg.org/jz7rxstod/Untitled.jpg
Again, when in the "V" position, voltage reads about 2700, as the manual says it should. When in Ig or Ip, however, it sits at zero.
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Ok... now the picture is getting clearer...
It will be a great help for you to post a diagram of the amp, including the PSU...
I'm keeping my fingers crossed that it isn't the tube...
I appreciate the continued help, ka1iic! Here is a link to the manual for the AL-80, which also includes a schematic of the innards:
https://qrzcq.com/pub/RADIO_MANUALS/AMERITRON/AMERITRON--AL-80-User-Manual.pdf
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tanks... military tanks... I will check it out and add it to my collection of diagrams...
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OK well you have VOLTS but NO CURRENT.
However you still have to make sure the volts are getting to the tubes ANODE, that's the top connection and with close to 3KV on it your going to have to be careful you don't touch it.
There are two chokes that could be O/C and stopping the volts reaching the anode.
Just get a meter that will measure such a voltage and measure it. Probably best to get someone else to do that.
You could also turn it off (you have to make sure the PSU is completely discharged) and buzz out this connection. Again get someone else if your not sure.
I want to help and not be responsible for your demise!
3KV is VERY dangerous, I cannot emphasise that enough!
The HEATER also needs 5V at lots of amps and probably glows a bit (you can see in a darkened room).
Provided both voltages are present you should get current flow and if you don't the valve is shot.
BTW I did ask if the switch read HT and IG, you said NO, should have been YES I believe, HT, PLATE, V all the same BTW as IG is Ig is it not?
Kind of thought you maybe had a different amp for mo!
Would have saved some time......
We'll get there.....
Eventually.
:)
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jackson_r;
I've been racking my memory banks here. In my shop, we used a couple of AL1200s in an industrial process, and IIRC, one of them exhibited a similar problem. I have a sneaking suspicion that what stretchyman sez about an open choke is spot on, and was the cause of the problem I found with the AL1200.
Again, IIRC, PC1 in the schematic you posted may be a strip wound choke using a high value power resistor as a form; this is probably pretty rugged. RFC2 was a larger choke wound on a ceramic form, and this was the culprit; the winding had burnt out and needed to be re-wound.
This was quite a while ago, but I'm pretty sure that's how things went down.
Please exercise due caution around HV; it can be quite unforgiving!
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Sorry, Stretchy! They very well could be the same and I just didn't realize it because I'm a newbie to this whole amp thing. :)
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Cool, no worries ;)
Mr Farley's reply is a good one....
That's it for tonight from me, you have enough info, you're going to have to measure stuff now.
Good Luck!
Str.
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jackson_r;
I've been racking my memory banks here. In my shop, we used a couple of AL1200s in an industrial process, and IIRC, one of them exhibited a similar problem. I have a sneaking suspicion that what stretchyman sez about an open choke is spot on, and was the cause of the problem I found with the AL1200.
Again, IIRC, PC1 in the schematic you posted may be a strip wound choke using a high value power resistor as a form; this is probably pretty rugged. RFC2 was a larger choke wound on a ceramic form, and this was the culprit; the winding had burnt out and needed to be re-wound.
This was quite a while ago, but I'm pretty sure that's how things went down.
Please exercise due caution around HV; it can be quite unforgiving!
I'll take a look under the hood later tonight for any obviously burned out or damaged chokes (from a safe distance). I know all sorts of nasty things hide inside a tube amp like this that can hurl my fried carcass across the room long after it's been unplugged, so if I see anything that looks wrong I may just have to see if it's worth getting repaired by someone else. I don't want to be poking around in there with a screwdriver, or anything for that matter. :-\
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I looked at the diagram and sometime my eyes fixate on...
The centre tap from the filament transformer to the tube goes to a relay... bad relay contact... perhaps... if that relay doesn't make contact to ground then no plate current...
That relay contact is taking all the current that the amp draws so there is a possibility that it is charred up/burnt etc etc
I may be wrong (most likely) but I am still praying it isn't the tube...
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A very good idea, Jackson. I had an Uncle by marriage who was TV repairman via correspondence school. Fred was a poke with one hand, keep the other in his back pocket kind of repairman. Hanging around his shop was a primer in self electrocution.
Good luck and be careful.
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Jackson, did you observe this amp working, putting out full power into a dummy load or antenna before you bought it?
Also, in the beginning, when your watt meter was pegging backwards, what did the meter on the amp read at that moment in the Grid (ig) and Plate (ip) positions?
Can you actually see the filament glowing?
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Jackson, did you observe this amp working, putting out full power into a dummy load or antenna before you bought it?
Also, in the beginning, when your watt meter was pegging backwards, what did the meter on the amp read at that moment in the Grid (ig) and Plate (ip) positions?
Can you actually see the filament glowing?
James - Did I actually witness it working in person? No. I purchased it from a reputable online dealer of used Ham radios, parts, etc. In fact it was guaranteed to be working so I could return it if it's truly DOA. But given the hassle that would be involved in returning this boat anchor, I'd rather get it working if it's something easily fixed (or if it's something I'm doing wrong). The grid and plate were both reading "0" during my initial tests. I have not checked to see if the filament is glowing yet. Somebody else recommended that as well and I think I'll do that tonight.
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So as far as whether the tube is glowing at all...negative. I even took off the cover part way so I could visualize it (yes, I'm a death rebel!) and except for the light from the meter, it's as dark as a well digger's arse in there. :-\
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DING!
That's the lightbulb coming on type noise BTW!
And Yes, twas I who recommended the Heater be checked glowing.
More time wasted.....
It's a valve and needs to have a glowing heater, so simple to check and as per a previous suggestion could well be the relay.
I think we're there now and think it probably could have taken a fair fewer thoughts.
Q, is Heater Glowing?
A, NO.
As per my previous suggestion check for 5V across the heater terminals of the valve.
No scary voltages on the valve base so you should be OK.
OK!
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Sorry again, stretchy. The cabinet on this thing is such that you have absolutely no way to see if the tube is glowing without at least partially removing the top. I had to work up the courage to remove the top part way and plug it in an turn it on. I'll check the tube and the relay a bit later today.
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NO Worries, Bud, but remember its a valve, they 'GLOW'........ Nicely!
;)
You will get it working and in doing so will learn from the experience!
Most worthwhile!
:)
Str.
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Hi Everyone - I went to run a few more recommended tests this morning and found out my multimeter isn't up to the task. I'll buy a new one on my lunch break today. I took a few photos of the innards and noticed something:
https://drive.google.com/folderview?id=0B1Sx8UoqolwlWnVJVDdZZG5walk&usp=sharing
In one of the photos, you'll see that I circled an area in red. That's a connection for the wire that goes to the tube "cap." The solder joint is loose. Not broken off completely, but loose. I believe the wire is still making sufficient contact, and I'm not even sure it would stop the tube from working if it was broken completely, but I thought I'd point it out.
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Tube appears to be "good" from a continuity standpoint. However, testing probe "flickers" on the pin depending on where it's placed. Makes me think there's some corrosion that could be causing some problems with conducting voltage to the tube. Socket seems to be fine at right around 5 volts. Weekend project will be to clean up the pins on the tube, re-solder the connection to the tube cap and then see where we're at.
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First time in over a week that I've had to try to dink around with this thing. I spent about an hour giving it the twice over today, and here is the only thing that I found that looks amiss:
http://s14.postimg.org/6ib0d08gx/IMG_5549.jpg
The circled connection in red looks fried. Charred with the insulation of the wires melted. This goes in to what the manual describes as the "primary connections terminal board." Here it is, as seen from the rear of the unit:
http://s30.postimg.org/uwwri08gh/IMG_5550.jpg
This is over on the high voltage side of the amp, so I've yet to poke around for continuity with a tester. Anyone have advice on my next step?
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I got in late but let me try some comments
1) that fried wire is likely due to someone changing the primary voltage from 240 to 120 (I'm guessing since you said the lights dim, that it's running off a 120V line). My guess is it has nothing to do with the issue you're observing.
2) Cleaning the socket pins is a good idea, as is tightening up the plate connections that you said that you've done.
Now that you've gotten as far as you have (reseating the 3-500, cleaning the pins) put the cover back on and see if the filaments light up when you have the amp ON but without any drive?
There's not much use going beyond that point.
Be very careful with this (and any) amp. Keep in mind that plate voltage can stay in the filter caps for quite some time after you've shut the power off , depending on the condition of the bleeder resistors and the internal resistance of the capacitors.
Let us know what you find....
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I got in late but let me try some comments
1) that fried wire is likely due to someone changing the primary voltage from 240 to 120 (I'm guessing since you said the lights dim, that it's running off a 120V line). My guess is it has nothing to do with the issue you're observing.
2) Cleaning the socket pins is a good idea, as is tightening up the plate connections that you said that you've done.
Now that you've gotten as far as you have (reseating the 3-500, cleaning the pins) put the cover back on and see if the filaments light up when you have the amp ON but without any drive?
There's not much use going beyond that point.
Be very careful with this (and any) amp. Keep in mind that plate voltage can stay in the filter caps for quite some time after you've shut the power off , depending on the condition of the bleeder resistors and the internal resistance of the capacitors.
Let us know what you find....
I agree with you Syfr 100 %. The connection in question looks like a re-connection from 220 v to 120 v and the melting was caused by a heavy duty soldering gun. Also notice rosin specks on the chassis, that is a good indication of a soldering for the voltage change.
Syfr is also very very correct about the high voltage capacitors holding voltage for a long time after the amp is shut down... handle with great care. Sure there are bleeder resistors but still the voltage is slow to discharge.
With something like this I would dis-able the high voltage totally because that doesn't seem to be the problem. Dis-able-ing the High Voltage makes it much safer for you to poke around in the unit. But you will still have to use great care as to where or what you poke.
If I were faced with this problem I would apply a very low amount of RF drive to the unit and put the Amp in the transmit mode and use an RF probe to see if the RF is getting to the input of the tube (cathode). If RF is getting to the tube the next thing to check would be the connection of the tube grid to ground, if that connection is OK then.... errrrr... the tube might have a problem with the Grid... no Grid, no amplify... That's never a good thing, in the past I have vaporized the Grid element in tubes... Yes it can be done and much easier than you might think...
Check the relays, mechanical things tend to be a very weak point in any device. Look at the contacts of the relays they should be shiny but if they are black then they need cleaning. If they are silver then they can turn black just by sitting around... many years ago I used mercury to clean up relay contacts but mercury is something you really shouldn't play with. Sometimes relays just get tired (the springs and alignment) and don't do what they should.
I have a gut feeling the RF drive just isn't getting to the tube so check the schematic and look at the RF input flow, all circuits and connections from the RF input to the cathode of the tube. If RF is getting to the tube and the connection from the tube's grid to ground are ok... then the tubes grid might be the problem.
Anyway.... have a Merry Christmas and a happy new year!
later...
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C/P from somewhere:
Carefully remove # 500Z tube..check... amp plate volts should be indicated. Key amp and observe reading on volt scale..should be same as unkeyed amp with tube Removed. Continue to move meter switch to current ranges..no idle current 150/200 indicates that the 3 500Z is the shorted proublem...D117 is also the meter protection diode and the 2 small caps beside often fail together (tube arking inside, tube short's ,to lite of loading control can cause arcking inside tube and tank stage. B+ is on tube at standby or operate, "operate switch" controls the bypass relay remote key line and with tube removed the procedure will help pin down what often is a internal tube defect that is a shorted 3 500Z.
KC7QNM, Apr 28, 2011
Any updates?
rgg
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Thank you, sir, for the advice! No updates as of late. The boat anchor is sitting in the corner of the office collecting dust right now as I prepare to leave on a month long trip to South America. I'll have to get poking around when I get back. By then those capacitors should all be well discharged. ;D
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I use to have an insulated screwdriver where the entire length of the shaft, about 1 foot, was insulated except for the tip and at the handle there was a very heavy wire, about 20 inches long, with a huge alligator clip on it for connecting to ground. The handle appeared to be doubled insulated.
It was great for discharging caps but I never used it for PSU's over 1KV... When I made supplies of 1KV or higher I had huge dropping resistors that would kick in on time delay relays to discharge the caps when the unit powered down. Also I used sequencers on power up slowly... in some cases I would use variacs for power up. The variacs came in handy for gear that I just picked up and was questionable for operation. I considered everything that came in as "questionable" in quality...
And don't get the idea that it is just high voltage that can be dangerous I had a 24 volt supply that had a current output of 50 amps... It had 10 @ 100,000 MF caps in parallel and that thing tossed a pair of vise grips that got dropped accidentally on the caps connecting straps and it flew 5 feet into the air and stuck in the ceiling of my lab... It sounded like a 12 ga shot gun blast...
Point is... use great care with any PSU... never take anything for granted... EVER!
Have a great and safe New Year...