Odd behavior from Ameritron Amplifier

[jackson_r]

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?

[Stretchyman]

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.

[Stretchyman]

May be a case of RTFM!

Is the meter in the Ig or Ip position perhaps?

You have read the manual haven't you?

 

[jackson_r]

Hi Stretchy!  Of course I've read the manual!    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. 

[Stretchyman]

Check for D.C. on the O/P, careful as it may be rather high!  

Check without Tube, this would isolate the valve and anything RF'y

 

[jackson_r]

Sorry, I feel like an idiot for asking...but "check for DC?" 

[Stretchyman]

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!

 

[jackson_r]

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. 

[Stretchyman]

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.

[jackson_r]

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.     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.   

[Stretchyman]

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.

[paranoid dxer]

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.

[paranoid dxer]

personally i would just let it sit and wait until i got a better decent quality meter..

[jackson_r]

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.     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. 

[jackson_r]

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.