ameritron al 811x

[airplane1]

I was reading what the designer of the 811 series amps wrote and is saying you can drop in 572b tubes with no mods. it will tune the same and all. no more output but much more bullet proof and in the 811h amp with four tubes only needs 3 572's like hookedon6 said in earlier post. I tend to believe the designer of the amp to know what works in his amps.

I see tons of posts on the net of operators dropping 572's in without modding the amp in any way and having no neg affect.

 

[W5LZ]

Right, no gross negative affects, but also no beneficial affects other than not having to be as careful as you would with the 811's the thing was designed for to start with. I don't see that as a gain. And like it or not, those 572's do have an affect on the quality of the signal. I've been on both sides of that and have seen/heard the difference, I don't care what the designer says/thinks. That designer said that it -could- be done, not that it should be done. If you feel better by using 572's then by all means do so. But you should have bought a different amplifier as far as I'm concerned. Or designed and built your own.
- 'Doc

 

[hookedon6]

there was a thread about this subject about a year ago.

here is a cut/paste from that thread:

here is a link with GOOD(!!!) info on the 811 & 811h. http://www.eham.net/articles/18364 pay particular attention to what Tom (W8JI) says. he knows these amps quite well (for a reason).

if you are going to put 572b's in an 811H, only put 3 in.
use 3 572's replace the four 811's, leave the socket nearest the fan (right rear socket) empty and remove that plate cap.

 

[hookedon6]

... I don't care what the designer says/thinks. That designer said that it -could- be done, not that it should be done...
- 'Doc

actually he says this:

"To: <amps@contesting.com>
Subject: [AMPS] New to the Amps list
From: W8JI@contesting.com (Tom Rauch)
Date: Tue, 22 Jan 2002 14:16:51 -0500

> 1) Is the AL-811H the same copy of AL-811, but
> has an extra matched tube.??

No. The AL811H is neutralized and has a few other changes. I'd go
for the AL811H.

> 2) Can i buy an AL-811 and then later, when i
> retube it, drop in a matched quad of 572B's to
> make it a AL-811H. I assume the 811 will have an
> unused tube socket.

You can drop in 572B's, but it would be a bear to add a fourth tube
to the AL811. Three 811's are just on the edge of not needing
neutralized, add a fourth tube and you would need to neutralize
otherwise you'd have the Clipperton Syndrome.

Even the Collins 811 amps with four 811's are not totally stable
because they lack neutralization.

572B's are a good mod to the 811 amp, they make it almost bullet
proof."


after some "digging around" i found that Tom was TOLD (by the manufacteur) to design an amp around the 811 tube, and that the amp had to be able to sell for a specific price range,..... so the al 811 was designed & built as a "compromise" amp.

if you are doing "light" duty cycle operations, then the 811 tube is fine, but, if you are doing other modes with a full duty cycle, then the 572-b (with about TWICE the dissapation), does make sense.

 

[Captain Kilowatt]

Somewhere on QRZ Tom, W8JI, also said that using the 572B's with that low of a plate voltage will cause an increase in IMD.Not to the point of being unacceptable, just that it got worse.