First tube amp al-80b questions

**Kf7ilp** · Sun 18th Dec 2011, 17:36

I recently got an al-80b ameritron amplifier. It seems to work very well however I have a small concern. Beeath the tube socket is a small white bead looking component with leads on either end. It appears to be ceramic. This bead illuminates breifly when keying and unkeying and sometimes flashes during high modulation on Ssb. Is this normal? What is this thing? Should I be worried?

**5B4AJB** · Sun 18th Dec 2011, 21:03

Sounds like a capacitor, which does not illuminate under normal conditions

On the other hand it may be a ceramic LED, but, I have only used this amp, I don't know it very well...

**G4LNA** · Sun 18th Dec 2011, 21:28

Looking at the circuit diagram there are a couple of capacitors underneath the tube socket. It is possible the one of the leads have become un-soldered on the end of the capacitor and its arching, that isn't good news and it needs a serious looking at. I have attached a copy of the circuit diagram for you if you don't have one.

**Kf7ilp** · Sun 18th Dec 2011, 23:03

Crap, that's not what I was hoping to hear... I will have to call ameritron tomorrow. It almost seems as if the light is coming from within the component. Thanks for the quick replies and schematic. Any other input is much appreciated.

**5B4AJB** · Mon 19th Dec 2011, 00:29

The dielectric has burned away. it's a 5 min / $1 fix... look on the circuit diagram for the capacitor, find one the same value with the same or higher Voltage rating and solder it in...

**Kf7ilp** · Mon 19th Dec 2011, 03:02

I figured out what was causing the issue during keyup, it seemed to be the contact distances on the relay. However it is still doing it under modulation. Could this happen from too much drive as it seems to happen during the peaks. Otherwise power out is right where it should be. Should I even worry about this?

**G4LNA** · Mon 19th Dec 2011, 06:46

As Dem says, I have had this happen before on one of my amplifiers. You can probably get a better component from RF Parts in California. It might be worth replacing both the capacitors in that circuit, you can bet your bottom Dollar that if one has gone the other could be going the same way, it might be a batch problem.

**G6NHU** · Mon 19th Dec 2011, 09:19

I hope you get it fixed quickly, I'd not be happy with that.

When I was looking at amplifiers a couple of months ago I discounted Ameritron out of hand as soon as I realised they're under the MFJ umbrella for just this reason. They don't have the nickname 'Made From Junk' for nothing.

**Kf7ilp** · Mon 19th Dec 2011, 17:21

Update:

Called ameritron and it turns out that the components are actually arc arresters.
The three diagnosises given were:

Bad tube trying to arc out
Oscillation that can be fixed by bending the parasitic choke coil
Bad arc arresters.

They sent me new arc arresters for free and were quite helpful and concerned. Sounds like its not a huge problem but they are going to take care of me.

Thanks for all of the help!