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Upgrade Kit AL811 and AL811H amplifier
Information in this modification manual is copyright 2021 by W8JI and CTR Engineering. I understand people like to
share things, but please remember we have several weeks’ labor composing this document.
Please consider a
when using these instructions if you do your own kit.
Thank you for purchasing this kit (and/or modification manual). These kits and this technical manual are intended
to help fellow Hams understand failures and reduce expensive damage. This technical instruction manual and kits
bring 811 series amplifiers up to latest revisions. With basic hand tools and soldering skills anyone should be able
to upgrade or service their own amplifier.
Please order via email links on
https://
www.ctrengineeringinc.com
/ameritron-811-811h-upgrade-
kits/
or email order query only to
This modification manual is also the result of feedback, questions, and suggestions by fellow Hams. More
suggestions are always welcome. The overriding philosophy is everything reasonably possible should be done to
prevent expensive or annoying damage, especially to expensive radios. An amplifier should work as well as
possible for the cost.
These kits come in two basic forms with one add-on:
(Power Supply rebuild) 811KS
1.) four better sized higher-voltage much longer-life 5000 hours 105c rated electrolytics
2.) four improved bleeder/equalizer resistors
3.) one large 6A grid meter protection diode
4.) four 499K 1% 1kV rated two-watt temperature stable meter multiplier resistors. These resistors also correct a
slight meter error
(Protection Kit) 811KP
1.) three application tested GDT tubes
2.) one large 6A meter protection diode
3.) one 100k 2-watt resistor
4.) two 3.9V 5-watt Zener diodes
5.)
10-ohm 9-watt CCS 10kV rated fault resistor
Add on part:
811R200K
200-ohm 25-watt non-inductive TO-220 case load resistor kit with hardware
Overview
I designed the AL811 series many years ago. It was intended to be a minimal cost reasonable power level
SSB and
CW only
amplifier. The initial design request was for just two tubes, but that obviously would have been
inadequate. As a result, I added a third tube as a bare minimum cost amplifier, and pushed to have a better but
still not too expensive four-tube amplifier. The better version became the AL811H.
The initial schematic circulating for these amplifiers was hand drawn on a drafting table by pencil around 1990!
This instruction manual and the 811 kits are the result of direct feedback from servicing several dozens of
amplifiers. Read these instructions thoroughly before you start working on your amp. Make sure you understand
every step to avoid errors or omissions.
AL811 Stability
Tubes with long thin grid leads and large internal structures sometimes have significant anode-to-cathode
feedthrough. This can destabilize amplifiers at upper HF. 811 and 572 tubes are particularly bad about this.
