Discussion in 'Amateur Radio Amplifiers' started by W9RAC, Nov 17, 2019.
I'll get it fixed and sell it , might be ok for SSB guy but not so sure about CW. I might consider a solid state amplifier. Thanks for comments. 73 Rich
Roger I have given it lots of thought and decided to move away from the 811H for CW. I had sent it to Ameritron to check out. They said one of the tubes were bad. I had them replace all four, return the other 3 as spares and are shipping it back with a clean bill of health. I'm going to sell it. I bought it new little over a year and half ago. I do not think it makes a good dedicated CW amp even at 20/30 watts in with the 811A tubes. The guy at Ameritron said the 811A tubes are just not what they use to be. I even run the Ameritron 704 relay and Ameritron inrush 240 protector with it. I'll be listing the entire package as I ordered a solid state Acom today. I could have put 572's n it but I just decided to move on, I believe they are good SSB amps but not up to being a dedicated CW amp even at very low power, with 811A's anyway, tnx, Rich
They're fine CW amps when equipped with decently robust tubes. There's nothing inherent in the design of that amp that causes tubes to fail other than the use of somewhat sensitive 811 tubes.
I kind of gathered that Dave. I could have had them install 572's but I have wanted to try and move over to solid state anyway so I figured this might be a good time. I'm not degrading the 811H amp in general. I believe like you the tubes could be better chosin for CW work. I knew that it could be a issue when I purchased the amp with that purpose in mind so I run it lite, very lite but it still just did not play out for me. 743 Rich
Are you watching when it goes "poof"? Sounds like something else is happening that causes excessive plate dissipation in the 811s.
Im running it on 240v and pretty low input, 25w or so. I have decided to move on to a little better quality piece for my CW work. Not knocking it but its pretty low quality overall. I happen to have it here as a backup amp for a couple better quality ones so thought Id use it. Pretty good entry level amp or the like SSB but I do not think its up to CW duty. Its on its way back from Ameritron, Just my thoughts. Thanks, Rich
I use my AL80B at 20-25W input sometimes. But it required an extra doorknob cap in the tuning circuit to get it off 0 for Load on 80 & 40M. Still works fine at 70W input too. You should be able to pick up a used one for $8-900. But you'd want to see it in operation.
Thanks. I am going to give a solid state amp a shot. I ordered a Acom 1200s. Been wanting to try solid state and maybe move away from tube amps so this should be a good test. 73 Rich
Holes in the plates?
Holes in the anodes indicate excessive plate dissipation -- like red to orange anodes. The 811A anode color should not exceed a dull red at the center. Holes can be burned during tune up and this can be prevented by tuning in pulse mode sending dits. At 350 watts on-off-keyed CW each tube will dissipate only 25 watts average.
When sending CW do the anodes show any color? They shouldn't.
I'm sure you already know this but just in case, apply 25 watts drive and peak the RF output with the LOAD and PLATE controls. Don't tune up with higher RF drive and then back the drive down to reduce RF output to 350 watts. Doing so leads to low efficiency and high anode dissipation.
I replaced the 811A tubes in my AL-811 amp with 572B tubes and I no longer have to be careful tuning up.
Here is the AL-811H tuning supplement by W8JI, the AL-811H design engineer: