811 no output

[Mudfoot]

Well, I was on 75 meters last night. Wasn't talking to long. Everything was working OK.

Just tried to tune up on 40 meters. I noticed all the meter readings were OK. When I slowly increased the drive to get 100mA of grid current or 450 mA of plate, the amp meters were acting normal, but I'm not seeing any output from the amp. Zero output.

Did I poof it. I baby the damn thing and follow instructions to the tee. Radio, antenna, tuner and jumpers all check out good. Would this be a fuse?

 

[Shadetree Mechanic]

Did you kill your watt meter?

 

[Mudfoot]

That's what it acts like. I'm using an MFJ-998 Autotuner. It's internal meter is working. When I put amp in bypass, then I see power out from the radio. The amp keys up and everything, and when I increase drive, the grid and plate meters act normal, but just zero output on the tuner meter. I thought the amp bypass in the tuner was kicking in, but I just hooked relay cable directly to the radio. I have been using the ARB-704 buffer. Thought it my be it, but bypassed it. The amp acts normal, but just zero output. I have little knowledge of tube amps, but can follow instructions.

Irritation is increasing.

 

[Shadetree Mechanic]

Do you have a dummy load?

 

[Mudfoot]

Yes, shows zero output. Bypass shows output from rig.

 

[NightThumper]

When you key your rig, do you hear the amp relays clicking?

 

[Mudfoot]

Yes

 

[NightThumper]

Did you change the band switch from 75/80 to 40 meters? I know dumb question

 

[Mudfoot]

Yes, even trying different bands. Amp acts like it wants to work. Meters act normal when applying power, but just zero output. Radio works fine on bypass. Tuner is working as normal.

 

[NightThumper]

Ok so you tried tuning on different bands and going back to 75/80 that you were running last night. What does High Voltage show? Does the voltage dip when you try to tune up. Remember tune for max power output not just grid/plate current

 

[Mudfoot]

It just started to show output on 40 when I slowly brought power up from 5 watts. Then, it just started dropping in and out. Weird, but sounds like something is loose or shorting out. Gonna see if I can get my buddy to come look. Something isn't right.

 

[NightThumper]

I’ve owned a lot of amps including an AL80B, AL82 and AL1500. I’ve never start with a drive of 5 watts. Generally at least 10-20

 

[NightThumper]

Test on SSB using MOX or push-to-talk with no mic gain. With no RF drive power, but the amplifier keyed, the amplifier’s grid current meter deflects about the same as the plate current meter. This is a common problem

• D16 shorted (811), D117 in AL80 series mainframe, including AL572. Negative rail meter protection diode. This will also cause the plate and grid current meter to track each other, and indicate false grid current
  • This problem is almost always from a defective tube or tubes that have flashed over internally, generally from excessive internal gas
  • This problem occurs after HV has been shorted, arced, or discharged to chassis
  • In older AL811H and AL572 amplifiers, grid circuits using resistors should be modified to current production

 

[Mudfoot]

I'll start at that level when I get this figured out. There's so many variables from each operator. Even MFJ has 3 different sets of instructions. Online video, manual, and a one page addendum. Lol, guess I'll somehow average everything out and come up with my own spin.

Thanks for helping me.

 

[NightThumper]

Did you happen to adjust the ALC on the back of the amp?