Hi group.
I'm Thomas, La3PNA and I'm in the progress of starting to build an HF
amplifier with 4 811A tubes. I'm gone to use 4 of them because, I got
the tubes, sockets and Plate caps for 4. I have drawn an shematic that
can be found in the folder "LA3PNA 811 amplifier" in the Files section.

I have drawn it as an one band unit, mostly since the rotary switches
in Eagle are stupid drawn, I would like to make it work at all nine
HF bands, from 160M to 10M.

I wrote an e-mail to R L MEASURES and got an nice answer on some of my
questions. He recomended to use 5 of 811, but i think that it is a bit
hard to get 5 matched tubes?

I have found out that one 811 tube has an impedance of 300 ohm's so 4
of them should give an inpedance of 75 ohms. Is this correct? found
the data in an old ARRL handbook, on an article on an one tube amp.

Hope that some of you have time to take an look at my design and
please let me know if there is any errors.

73 de Thomas LA3PNA
PS: sorry for my bad English.

开云体育

Very good English
Anyway I had a Ameratron (sp) AL 811H
This was a 4 tube 811 amp.
Try researching it for CKT diagrams and? ideas.
I think the schematic is on the Ameratron web page.

la3pna wrote:

Hi group.
I'm Thomas, La3PNA and I'm in the progress of starting to build an HF
amplifier with 4 811A tubes. I'm gone to use 4 of them because, I got
the tubes, sockets and Plate caps for 4. I have drawn an shematic that
can be found in the folder "LA3PNA 811 amplifier" in the Files section.

I have drawn it as an one band unit, mostly since the rotary switches
in Eagle are stupid drawn, I would like to make it work at all nine
HF bands, from 160M to 10M.

I wrote an e-mail to R L MEASURES and got an nice answer on some of my
questions. He recomended to use 5 of 811, but i think that it is a bit
hard to get 5 matched tubes?

I have found out that one 811 tube has an impedance of 300 ohm's so 4
of them should give an inpedance of 75 ohms. Is this correct? found
the data in an old ARRL handbook, on an article on an one tube amp.

Hope that some of you have time to take an look at my design and
please let me know if there is any errors.

73 de Thomas LA3PNA
PS: sorry for my bad English.

-- 
de KR4DA Bob Middleburg, FL
HK0/KR4DA J79DA FG/KR4DA

You dont need matched tubes -- just put some resistance in the cathodes and they self match -- rich knows more about how to get the right values of resistance -- im still learning
Steven Grant W4IIV


At 04:54 PM 9/26/2006, la3pna wrote:

Yeah, that's correct.
If you compare them then you would see that I have copyed part's of it.
I think that the Ameritron amp. is running the tubes a bit to hard.
An other thing i have done is that i have added an adjustabile bias and
not an string of diodes like ameritron has done.

73 de Thomas

tir, 26,.09.2006 kl. 17.09 -0400, skrev KR4DA:

--
Best Regards/MVH
Thomas S Knutsen
LA3PNA

Hello Thomas,

A couple of suggestions for your amplifier...

First, I would float the B- to make metering of plate and grid current readily available to you. It takes no more than two resistors and a few diodes to protect the metering to make this big improvement.

Second, I would suggest that you do not do T/R keying of the bias the way that is shown on your schematic. That method is similar to the Clipperton L and a few others. The flaw is that during the transition of the contacts the cathode will rise to near full anode potential and when you make contact with your bias circuit, you are hitting it with a very high voltage at that moment. A simple cure for it without changing the circuit entirely, and this applies to the Clipperton L as well, is to place a jumper across the wiper and the normally closed contact of the keying relay. That will keep the cutoff resistor in the circuit all the time and prevent the cathode voltage from soaring. I would also place a fuse in series with your bias circuit rated at just over your maximum expected plate current. Also, a Metal Oxide Varistor or an NE-2 neon bulb in parallel with the bias circuit will help protect it against transient voltages. You may want to increase the value of the cutoff resistor to about 20K to minimize the current in standby.

73, Tony W4ZT




la3pna wrote:

I have done some modifications to the shematic, so i have uploaded an
revided shematic.

I can't see the reason for floating the B-, to mesure the current i
would just add an 0.1 ohm resistor between the PSU's - tab and ground.
It sould be easy to mesure the current over that? or is it somting I
have missed?

I also have to order an transformer, since there are just 2 producers
of small transformers, i would have to order an 600V and use an
voltage doubler. I could get an 700VA transformer realy cheap, but is
it enoug? I've read that SSB only has an dutty of about 20%.

73 de Thomas.

--- In ham_amplifiers@..., Tony King - W4ZT
<w4zt-060920@...> wrote:

Hello Thomas,

A couple of suggestions for your amplifier...

First, I would float the B- to make metering of plate and grid current
readily available to you. It takes no more than two resistors and a few
diodes to protect the metering to make this big improvement.

Second, I would suggest that you do not do T/R keying of the bias the
way that is shown on your schematic. That method is similar to the
Clipperton L and a few others. The flaw is that during the

transition of

the contacts the cathode will rise to near full anode potential and

when

you make contact with your bias circuit, you are hitting it with a very
high voltage at that moment. A simple cure for it without changing the
circuit entirely, and this applies to the Clipperton L as well, is to
place a jumper across the wiper and the normally closed contact of the
keying relay. That will keep the cutoff resistor in the circuit all the
time and prevent the cathode voltage from soaring. I would also place a
fuse in series with your bias circuit rated at just over your maximum
expected plate current. Also, a Metal Oxide Varistor or an NE-2 neon
bulb in parallel with the bias circuit will help protect it against
transient voltages. You may want to increase the value of the cutoff
resistor to about 20K to minimize the current in standby.

73, Tony W4ZT

I guess i need 8 resistors? but, how about the voltage drop over the
resistors? or should the resistors be so small that I don't need to
worry about that?

Since i have about 75 ohm input impedance, do I need an tuned input or
is there an easyer way to do it?

73 de Thomas

On Sep 29, 2006, at 1:08 PM, la3pna wrote:

I guess i need 8 resistors? but, how about the voltage drop over the
resistors? or should the resistors be so small that I don't need to
worry about that?

The V-drops across the cathode resistors is what helps to equalize the cathode currents in the 4, 811As. However, 4, individual bifilar filament chokes and 4. DC blocker/coupling caps are needed.

Since i have about 75 ohm input impedance, do I need an tuned input or
is there an easyer way to do it?

There is no substitute for the flywheel effect of a Pi-network tuned input with a Q of 2 to 3.

73 de Thomas

--- In ham_amplifiers@..., Steven Grant <w4iiv@...> wrote:

You dont need matched tubes -- just put some resistance in the
cathodes and they self match -- rich knows more about how to get the
right values of resistance -- im still learning
Steven Grant W4IIV


At 04:54 PM 9/26/2006, la3pna wrote:

Hi group.
I'm Thomas, La3PNA and I'm in the progress of starting to build an HF
amplifier with 4 811A tubes. I'm gone to use 4 of them because, I got
the tubes, sockets and Plate caps for 4. I have drawn an shematic that
can be found in the folder "LA3PNA 811 amplifier" in the Files section.

I have drawn it as an one band unit, mostly since the rotary switches
in Eagle are stupid drawn, I would like to make it work at all nine
HF bands, from 160M to 10M.

I wrote an e-mail to R L MEASURES and got an nice answer on some of my
questions. He recomended to use 5 of 811, but i think that it is a bit
hard to get 5 matched tubes?

I have found out that one 811 tube has an impedance of 300 ohm's so 4
of them should give an inpedance of 75 ohms. Is this correct? found
the data in an old ARRL handbook, on an article on an one tube amp.

Hope that some of you have time to take an look at my design and
please let me know if there is any errors.

73 de Thomas LA3PNA
PS: sorry for my bad English.

Yahoo! Groups Links

--- In ham_amplifiers@..., R L Measures <r@...> wrote:


RICH SEZ.. The V-drops across the cathode resistors is what helps to
equalize the cathode currents in the 4, 811As. However, 4,
individual bifilar filament chokes and 4. DC blocker/coupling caps
are needed.

### Well... that sucks !! I suppose you require the same deal on
just balancing TWO tubes ???? [2 x fil chokes + 2 x
blocker's]............ even the 2 x tube senario sucks.

I remember building a 2 x 4-1000 amp... with two of
everything in it.... fil xfmrs... fil chokes... 2 x fil variacs...
separate adjustable bias....... and 3 x plate + 3 x grid current
shunts..... Tube 1.... Tube 2..... Tube 1+2. Then cross ur
fingers... and hope the drive split's into two equal parts...
ditto with airflow.

After that... I said I'd never build / design another 2+ tube
linear again..... I didn't. Just trying to trbl shoot a 4 x tube
amp is not fun. Still, I did have a 4x 811A linear.... and
the tubes never gave me any problems........ the rest of that
Dentron amp was pure junk.

later.... Jim VE7RF

On Sep 29, 2006, at 4:16 PM, pentalab wrote:

--- In ham_amplifiers@..., R L Measures <r@...> wrote:


RICH SEZ.. The V-drops across the cathode resistors is what helps to
equalize the cathode currents in the 4, 811As. However, 4,
individual bifilar filament chokes and 4. DC blocker/coupling caps
are needed.

### Well... that sucks !!

That's the awful reality of adding cathode RF-NFB with thoriated tungsten tubes in parallel

I suppose you require the same deal on
just balancing TWO tubes ???? [2 x fil chokes + 2 x
blocker's]............ even the 2 x tube senario sucks.

With multi-tube indirectly-heated cathodes, adding cathode RF-NFB is a piece of cake, but with directly-heated cathodes it's a bucket of snakes.

I remember building a 2 x 4-1000 amp... with two of
everything in it.... fil xfmrs... fil chokes... 2 x fil variacs...
separate adjustable bias....... and 3 x plate + 3 x grid current
shunts..... Tube 1.... Tube 2.... Tube 1+2. Then cross ur
fingers... and hope the drive split's into two equal parts...
ditto with airflow.

After that... I said I'd never build / design another 2+ tube
linear again..... I didn't.

Smart move. If one needs more suds, go for One tetrode with handles.

Just trying to trbl shoot a 4 x tube
amp is not fun. Still, I did have a 4x 811A linear.... and
the tubes never gave me any problems........ the rest of that
Dentron amp was pure junk.

Amen, Jim. Dennis Had is reportedly now in the AF amp business -- which is where he pretty obviously should have gone in the first place.

later.... Jim VE7RF








Yahoo! Groups Links

R. L. Measures, AG6K, r@somis,org, 805-386-3734

R L Measures wrote:

I suppose you require the same deal on
just balancing TWO tubes ???? [2 x fil chokes + 2 x
blocker's]............ even the 2 x tube senario sucks.

With multi-tube indirectly-heated cathodes, adding cathode RF-NFB is a piece of cake, but with directly-heated cathodes it's a bucket of snakes.

Amen!! So true so true.

I remember building a 2 x 4-1000 amp... with two of

Smart move. If one needs more suds, go for One tetrode with handles.

Thats why I built a 8171! At one point Rich also gave me some help,
now it runs like a charm!

73 Jim SM2EKM

On Sep 30, 2006, at 10:46 AM, Jan Erik Holm wrote:

R L Measures wrote:

I suppose you require the same deal on
just balancing TWO tubes ???? [2 x fil chokes + 2 x
blocker's]............ even the 2 x tube senario sucks.

With multi-tube indirectly-heated cathodes, adding cathode RF-NFB is
a piece of cake, but with directly-heated cathodes it's a bucket of
snakes.

Amen!! So true so true.

I remember building a 2 x 4-1000 amp... with two of

Smart move. If one needs more suds, go for One tetrode with handles.

That?s why I built a 8171! At one point Rich also gave me some help,
now it runs like a charm!

And in the Winter it keeps you warm.

73 Jim SM2EKM






Yahoo! Groups Links

R L Measures, AG6K, 805.386.3734
r@...