Ameritron 811 problem

[Mudfoot]

My 811 has been working pretty good. Now, when I try to load up on 80 meters, I have an issue.

Following the manual, I'm to apply just enough drive to see 100 mA of grid current or 450 MA of plate, whichever comes first. I don't see either, even at full input of 100 watts. I'm using FM and I see 50 MA grid and 250 MA of plate max.

If I adjust plate and load, I see output power rise, but the load control bottoms out on zero.

Other bands seem to load. All my cables are OK. My dipole is 1.3:1. No tuner is inline. I didn't pop cover and gander. With my recent luck, I'd get kilt. Would dust and cat hair cause an issue? My back porch is really dusty and fans draw hair and crap inside my stuff.

Any ideas? Damn thing is only a few months old.

 

[nomadradio]

Damaged contact point on the 80-meter position of the band selector.

Probably.

73

 

[Mudfoot]

What would cause that?

 

[groundwire]

Google the problem. Lots of different forum threads with same issue. Most seem to agree its a normal problem on 80m with the al-811h, not enough capacitance. You need to add more by switching in a capacitor. Oh yea, and switching the band selector while transmitting, poof

 

[Mudfoot]

Worked absolutely fine until this morning. Don't need to Google. All the experts are right here. Definitely never switched bands while transmitting. Just a drag.

 

[Mudfoot]

I posted my issue in the Ameritron Facebook group. Tom Rauch runs the group. One answer, mentions the capacitance topic. Strange how it just surfaced. It's seen daily/evening use on 80 and was running great. I suppose it's got to go for warranty repair. Likely going to be a long time before it's fixed.

Guess I'll have to find a replacement.

 

[fogdog]

Let's hope for a speedy recovery.

 

[Mudfoot]

Let's hope for a speedy recovery.

Me too, I just ordered an ACOM to replace it. Once the 811 is repaired, it's going down the road.

 

[DainBramage]

... its a normal problem on 80m with the al-811h,....

He has an 811, not an 811H

 

[kopcicle]

Well lets clarify
Mud, 811 or 811H?
While we're at it , C23-24, and 25 in the -H all have proper capacitance in and out or circuit?
Any resistance on the band switch?
Are you using full drive or reduced drive power?
Wilma or Betty?
Ginger or Maryanne?
Peg Bundy or Betty White?

inquiring minds want to know...

 

[fogdog]

Me too, I just ordered an ACOM to replace it. Once the 811 is repaired, it's going down the road.

That Acom will be awesome.

 

[Mudfoot]

That Acom will be awesome.

I hope so. It made my wallet skinny. It appears bulletproof, which is what I need.

 

[ExitThirteen]

Wilma or Betty?
Ginger or Maryanne?
Peg Bundy or Betty White?

inquiring minds want to know...

Betty, MaryAnn, and Betty White. And it's not even a contest.


~Cheers~

P.S. --------> Gnorph

 

[nomadradio]

A chronic failure like this amplifier's band selector still boils down to "not enough".

Not enough current rating to the switch?

Not enough capacitance in that side of the pi-network circuit?

Not enough coil to keep the circuit Q (and circulating currents) down to a safe level?

Plenty of room to argue about specifics.

Not much room to argue that the design has "almost enough" of something important.

Every real-world design has at least one weak link in the chain.

Some have more than one.

73

 

[BlowinSmoke]

There are padding caps that get switched in on the lower bands. If the padder caps are missing, open, or if the contacts that switch them in parallel with the variable load cap are bad, you will never have enough capacitance to get the variable from going less than full mesh. When the amp is being driven with low levels of drive on the bands that require lots of load C, the amp requires lots of capacitance. As the drive level increases the tank circuit needs less capacitance (heavier loading). At some drive power the tank will require less and the load cap advances. If you see that load variable cap not going lower in capacitance (advancing clockwise) that would indicate that the padding cap(s) are not doing their job, hence they are missing, open or not being switched in. They are easy enough to check and test.