Odd behavior from Ameritron Amplifier

[ka1iic]

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...

[Pigmeat]

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.

[Stretchyman]

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.

[jackson_r]

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.  

[Stretchyman]

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?

 

[jackson_r]

No, it doesn't seem to.  Very basic meter that is simply labeled "plate voltage." 

[Stretchyman]

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.

[ka1iic]

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...

[jackson_r]

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.  

[jackson_r]

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

[ka1iic]

tanks... military tanks... I will check it out and add it to my collection of diagrams...

[Stretchyman]

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.

[jFarley]

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!

[jackson_r]

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.   

[Stretchyman]

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.