The 811 Amplifier Page.
is a very interesting page because it takes a hard look at all 811 Amplifiers
and the problems they encounter.
are dangerous to work on...please follow the manufacturers
suggestions regarding safety. These voltages are lethal.
I do not
endorse or purchase JAN 811A tubes for replacement in Ameritron
Use these tubes at your own
risk...I recommend RF PARTS Company and the TAYLOR PRC (match sets).
Thank you, W3EUT
The page is short and to the point, but those
points are based upon facts, images and true to life situations
using the 811A tube in RF BEAM POWER applications. These tubes are
capable of Class C or Class AB2
operation for HF amplifiers up to 30MHz. However, these tubes were
more commonly found in
Class A audio applications as power amps and modulators.
Lets us begin. Here is the .PDF file for the 811A
RCA brand tube that is no longer manufactured. This file will open
in a new window so you can follow along as we investigate the trials
and tribulations of this "cheap" amplifier tube.
The 811A as a linear amplifier is not the worst choice, however you
must understand it has weak points. These are cheap tubes to say the
least. The Taylors and Cetrons are not expensive and can be had for
$25 bucks each. This makes them a good choice for the budget
operator. The sockets are also cheap and can be found at just about
any swap meet you attend. They are available on line from places
like RF-Parts and Nebraska Sales. You will pay about $10 - $20 for
four of them. The power supply can be as simple as 1500 VDC at 350
MA and transformers are cheap too. The output capacitors are not big
and the coil can be hand wound or pulled from some old antenna
You could buy a commercial amplifier for anywhere from $700 - $1000
depending, but if you are willing to spend more than $500.00 for an
811A amplifier, may I suggest you speak to your psychiatrist
first. You may have a mental disorder that causes you to waste
money and make poor purchase decisions. Here is one reason why...the
price of a four hole 811 amplifier is around $1000.00. The price of
a NEW single hole 3-500Z is around $1300.00 the difference is not
comparable, but the cost of tubes is. A four hole 811 amplifier cost
$100.00 to replace all tubes; and you will replace them at least
three times during the normal life of a single 3-500Z. The 3-500Z
cost $160.00 NEW and is available almost anywhere you look.
Reason two, even though my "shrink" did not know this, he
agreed...the 811A has a maximum plate dissipation of 65W. Four of
them is barely half the dissipation rating of a single 3-500Z. This
alone should tell you what to buy.
Consider a used two hole 3-500Z amplifier like the Drake L4B or the
Heath SB-220 to name a couple. These amplifiers are out there in
pristine condition for $500 - $700.00. And the two holes will
deliver mountains of RF that the 811A can barely muster. What I want
you to do is look no further and consider these options, but if you
must...go ahead look at the rest of this article.
Sorry to say, if you have purchased an 811A
amplifier, well I am about to knock your socks off. Don't blame me,
I told you to look no further.
Most of the 811A commercial amplifiers are outfitted with Chinese
tubes. That should scare the be-geezes out of you. These tubes are
terrible. They are not worth the glass envelope. When I say these
are bad I mean terrible...is being nice. They sell for around $20.00
and can't deliver $10.00 worth of power under abnormal conditions,
let alone as a simple HF amplifier. There are much better tubes out
there but the RCA's and the Cetrons are damn near exhausted. More on
this JAN tube replacement thing in a moment. When
these tubes are gone, they are history and if they (the good ones)
are in most of the commercial amplifiers built in recent years, they
won't last 48 months if your life depended on it. I would have to
say these tubes can't last four-hundred hours, and that is being
careful how you drive them.
Note: The JAN tubes do not come with a
warranty. If they do not light up you must pull them out and
that means the B+ anode cap comes off...there is no protection for you
against the plate cap coming loose or breaking off. This is because
the glue (epoxy) under the cap has dried and it is brittle now
(after several years). Even the slightest heat on the tube will
render "push/pull" action that will render the cap loose or broken
from the anode lead. The same condition can cause loose sockets at
the base. Follow my lead...do not buy the JAN's (RCA/Cetron) unless
you get a warranty against loose caps and socket bases.
Now about tubes...inserting 572B tubes into
an 811 amplifier is useless. You gain "nothing" but headaches. These
tubes do not tune the same and therefore you could run out of tuning
ability on the lower bands. The best thing you can do is buy the RF-PARTS
Taylors. These are PRC, but they are warranted to last and they are
made to Taylor specs, in China. The RF PARTS tubes are less
expensive than the JAN tubes and the Taylors can be installed
without wasting time doing a "getter" charge. (I do not endorse PRC, but they are
all we got outside the JAN tubes.)
The "A" word is not spoken here because it conjures up thoughts of
the "M" company that took over the manufacturing of the "A" line.
That was not a good thing, but still, when you think about it they
make a damn good amplifier. I say that because I have an AL-1500 and
the ATR-30 that runs flawless every night on 75 meters. Remember
these are new days and new ideas. The cost of labor has forced small
manufacturers out of the country, we should be so lucky to have the
"A" company here. Me, I would rather they offer their amps as kits.
This would make them a lot of money and like Heathkit, they can save
the "lousy soldering" to the end-user. Now that conjures up another
set of worms, but I won't mention VE testing or the ARRL either.
The real fix:
Ok you got through all my SOAP BOX rants,
lets look at the 811 amplifier and apply some critical thinking
As I said above...HEAD ROOM is the best way to manage any tube
amplifier. If the plate dissipation is 1500 watts, running 800 or
900 is a walk in the park. A pair of 3-500Z tubes will dissipate
1000 watts, and that relates to 2000 PEP. That is lots of talk
power, and when you come down to it, your average output will be 500
watts if you run the amp within the specifications. Your exciter,
meanwhile is running at half it's 100 watt rating. That saves the
life of your most expensive investments. Plain and simple, that is
like driving your 500 HP street machine at 55 MPH.
What is wrong with the commercial 811 amplifiers offered on the
market ?? Well first of all they are cheap, as in inexpensive, so
they invite sales based upon price and nothing else. They are budget
amplifiers. In as much as they are designed well (simple is better), that brings us to
the bottom-line question. Why do they fail over and over again ??
Well, heat is the answer. They cook themselves and this is not just
the 811A tubes. The 572B is also a heat generator that must be
cooled properly. The SB-200 uses two 572B tubes. There is a PM motor
underneath these tubes that blows air over the envelope and out the
top. The FL-2100 has a similar setup and that amplifier has two
fans, one for each tube. This is enough to allow normal operation,
but if you demand more from the two hole 572B you will have to pull air from the top. A small
muffin fan placed over the cabinet top is all you need. But this is
not quite as simple as that. The relief fan must be LARGER (higher CFM) in air volume than the counterpart below. If it is not, the air
will not be removed and turbulence will create hot spots on the
envelope. What we want to do is force air over the envelope at a
rate that allows the cooling to take effect. If the air volume is
too high, you will create a vacuum around the glass that will
produce hot spots and of course poor cooling. The key is managed
air-flow. The air must flow over the glass and take the heat away.
That means the harder you push the amp, the more heat is removed.
This is not an "air volume" thing, it is a convection thing.
(See my paper on Heat Transfer.)
The 811 amplifiers both three hole and four hole are stuffed into a
desk top box that is about 13 by 15 by 8 inches. They are cute...no,
honestly they are cute. They look real nice on the desk and the
small foot print is popular with the XYL. After all she worries
about the 'lectric bill and your amplifier is not helping.
The stuffing is of course the first problem.
(The Gonset GSB101 uses 811A tubes and is twice the size of the
Ameritron.) The tubes are arranged
so that each one heats the other while generating 160F degrees of
heat at the anode. The heat from the transformer (all in one) and
the diode board is also adding to the problem. This heat is
reflected back onto the components by this "not so roomy" enclosure.
As an example, I checked the Gonset GSB101, an old 811A amplifier
that was built in the 60's. This amp is 13 deep by 17 wide by 10
high. It has a separate 20A filament transformer and a 1500 VDC
power supply. The 811A tubes are located off-center with 1 1/2
inches between each envelope. The FAN is mounted behind the tubes
and heat is carried away through the side louvers. The Ameritron amplifiers designed today have no fan blowing directly on the tubes.
A small fan mounted behind, outside or inside depending on the
model, blows air onto the core of the main transformer. What that
accomplishes is nothing, or nothing more than increasing the heat
inside the cabinet. This fan blows IN not OUT like PC powers
supplies. Even if it did pull air out, it is too low in volume and
can't move enough air to cool the cathode seals. So the tube cooks
from the inside out.
If you IR the tubes, with the case off, you can register temperatures
as high as 200F degrees at the envelope, times four !! Same with the
three hole unit. The tubes are barely 1/4 inch apart. There is
simply no way you are going to prolong the life of these tubes. The
constant high to low swing of these envelopes will sooner or later
distort the tube and you end up with this...
A PLATE to GRID short. Look at the warped plate element. There is
nothing to stop this from happening, time and time again. Short of
not using the amplifier, it is simply a matter of when not why. The
real problem is HOW can I fix this ?? Well it is going to require
some work and a few good tools. But before I begin take a look at
this next image.
this picture you see a poor solder connection. This is very typical,
and failure is certainly possible if the heat on the tube base reaches
temperatures that are capable of turning a good connection cold.
Just the heat alone can render a poor solder connection worthless and the
results look like the joint was never soldered at all. These solder
joints can not take the heat of these 811A bases. Now imagine what
goes on inside the tube.
If nothing at all, cool the base of the tube. That will help
dramatically. This amplifier is less than 100 hours old; and I have
seen more than one!!!
Look at the grid connection. That small ground lug will not last if
this base gets any hotter. Like the cathode lead in the image. The
black wire is not capable of carrying off heat. These wires are
stranded and cannot dissipate the heat this tube is generating. Just
thank God that pin two has no connection (under my thumb). The
sockets are mounted on standoffs and they do not radiate heat away
from the base. The four hole unit has a sub chassis. This is worse,
because there are no vent holes located around the sockets. However
the side fan conversion will force some air under that sub and cool
the sockets as well.
this amplifier now:
The image shows a case cabinet that I folded to specifications in my
shop. Mine is made from .060 aluminum sheet. It fits exact according
to the OEM case cover. You can buy the cover for $27.00 plus
shipping, from the manufacturer. That is the best thing you can do;
buy a new cover and start in on the old unit. This way you can
always sell the amplifier and certainly get more for it if the cover
is clean, not butchered.
The hole size should be 4 1/2 inches; both at one side and on the
top. The side hole can be cut from the openings that exist. The top
hole must be punched. The Greenlee punches will work fine or you can
get a cheaper version at Harbor Freight that will not cost an arm
and a leg. I suggest you do not use a hole saw, unless you can mount
the cover on a drill press. Last resort...use a "nibbling tool".
These are also available at reliable tool shops. You can order a
good one from Studer Industrial Tool (on the Internet).
you nibble out the side hole, it should look something like this.
The four hole amplifier will require the hole to be placed 1 3/4
inches offset to the front. More on this later...
The air we will force in will concentrate on the base and the
cathode elements. This air will be forced up and out of the amp so
it will carry off the anode heat as well. The hole size should not
vary from side to top. That way we have an even flow in and out.
Less turbulence the better the flow and the cooling.
The fan is a simple 80 CFM ThermalTake model TC-1225A (red) that is
available at most all Radio Shack locations. The 12VDC for the fan
can be brought out of the amp or you can use an external 12VDC
source. Air is directed IN over the tubes. The fan mounts nicely
over the entire grate and you can place an external fan grate over
The top hole must be screened. You can purchase COPPER or BRASS
screening at any hobby shop. The screen can be mounted using pop
rivets or small aluminum strips 1/4 inch wide by 5 inches long. Bolt
the strips over the screen to hold it in place. Do not glue the
screen. Prior to mounting the screen and the fan, you should paint
the inside of the cover with FLAT BLACK HIGH TEMP paint. This is
available at hardware or automotive parts stores (exhaust header
paint). The black surface will absorb the radiated heat and the case
will become a radiator to help lower the over all temperature. This
step eliminates the inside case reflection.
is the mock-up as tested. The amplifier ran much cooler than it did
with the OEM case cover in place. I tested the air flow and found
that I could extinguish a lit match at 12 inches above the top cover
hole. That more than satisfied me. The real problem was finding the
best configuration for the three hole vs. the four hole model. I
started with a simple cardboard template, and worked at it until I
created the best flow.
The four hole unit, the top hole should be 4 1/2 inches and cut
directly above the RF choke. The three hole can be similar in size
but cut this directly over the center tube in line. I tested a
rectangle opening. It came to 3 inches deep by 7 inches wide. A
rather massive opening, but this may be the only way to go on these
models. The screen and aluminum strips can be added for strength.
Problem will be...making it look neat. If you have a 3 inch
Greenlee, you can cut two holes and nibble along a line drawn
between. It will look more oblong than rectangular. This will work
as long as you maintain a larger volume opening than you are forcing
into the amp.
test results are here...Using an IFR thermometer, you can test the
temps before and after. With the fan running and the cover removed,
these 811A tubes were 35% cooler than without the fan. I tested the
temperature on the glass with the case cover on and the plate was
almost 180F degrees for the tube closest to the air opening on the
side. This was using SSB with 40 watts input. The stock fan was
doing nothing. You can remove it and not hurt anything that is not
already over-heated now.
There are more tests to be considered. I will leave them up to you,
but for a 50.00 bill you can save the life of one set of tubes
during the normal life of another. That is a pretty good return on
NOTE: If you run the amplifier with the
cover off, be sure to clamp down the interlock, or you may damage
the amplifier power supply. Keep your fingers out of the amp when
it is on with the cover off. You could kill yourself...always let
the bleeders function properly do not short the HI-VOLTAGE to ground
!!! The amp will take 4-5 minutes to clear of any voltage.
If you have any questions, or you want this
work done for you, contact me. I do not want your amplifier, you
only have to tell me the model and I will perform surgery on your
old case cover. You order a new one. Place your old one in that box
and ship to me. I will do all the work and ship it back with the fan
mounted and the screen in place. It will cost about $89.00, but if
you do not have the equipment to do the job, this is well worth your
time and money.
The base operation is 59.95 less the fan. You can handle that and
save a bunch...My turn-around is 2 to 3 days, so you won't miss
Good luck with your issue and remember...COOL IT DUDE !!!
I have added a couple of pictures since the article above was
written. Look at this tube. It came directly from an Ameritron three
hole 811 amplifier. This was the center tube in the chain...
Yes. that is a HOLE blown in the plate of an 811 Cetron. The tube
code is that of a JAN. This tube got so hot that the plate cap
solder melted. How did this happen?? No not poor tune up, the tube
heated and one of the grid connections (those little ground lugs)
failed at the solder connection. This is a regular failure and
replacing the tubes will not eliminate the problem. The filament
leads can also come loose and either way, you have a failure of the
is my cover modification on an 811A. This one the user will buy his
fan and mount it himself.
In this case, the amplifier was so hot that the solder connections
failed during tune-up. The result of poor SWR and now the PLATE tune
capacitor must be replaced. The solder connection failed on the tube
and the 3 HOLE turned into a 2 HOLE and the result was catastrophic.
The tank circuit arced over and the result is a costly repair.
Ameritron gets big bucks for this fix, but, they will not do my
wiring repair, so you are back in trouble again after the amp is
returned on line.
These fixes are "required" in order for the unit to function
properly over time. You can ask my customers all you want about
their 811 amplifiers after my repairs...and, yes they are working
I apologize to Ameritron, but this is un-called for. You
cannot have little old ladies wiring these "hot boxes" they should
be knitting a sweater...not building RF amplifiers!!
If you are an Ameritron 811 user you must prepare for this issue.
This is not about using a cheap amplifier, it is about fixing an
economical amplifier so the damn thing will last.
Oh yes...one more side bar...The 811H four hole
amplifier uses "neutralizing". Something that 811's like. There is
no neutralizing cap in the 3 hole version. The 4 hole unit also has
a better input impedance than the 3 hole amp. These are tips you
might consider if you plan to buy one of these low ball amps.
Thanks, The RFampGUY.