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Author Topic: 811A 'venture'  (Read 6724 times)
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K9MB
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« Reply #25 on: July 03, 2023, 11:31:16 AM »

Here's one that caught my eye:..attached
ARRL handbook 1968 pages 187 - 190
Single 811

I'd like to 'keep' my homebrew "as is"...with only the necessary internal changes.
That should be no big problem...esp since the power supply would be external.
And...I'd like to use the 'smallest' power supply as necessary....'small' in cost as well.

And...I really don't need much QRO

Firstly, you *REALLY DO* need much QRO if you go to the trouble of adding a linear amplifier.

1-Your transceivers are capable of 80-100 watts output on CW and SSB
2- the maximum output from a single 811a at 1500volts on the plate is about 150-175 watts including feedthrough power.
That means that- at best- you are getting 3dB more signal.
3- 3 dB is insignificant in terms of actual signal at distance
4- The minimum increase that is useful is 6dB (4x power) which is one S-unit.
This means that the threshold for justifying an amp is 4x 100watts = 400 watts output.
5- You can get 400-450 watts from 3-811a.

Finally- if you ever want to be successful at building anything, you should:
1- Read about amplifiers and understand a little about how they work, including high voltage power supplies and input and output matchung networks.
2- read articles on well designed amplifiers using the tubes you are considering.
4x811a amps are easy to build and relatively cheap, if you look for the parts pm EBAY and trade threads on Ham sites or tap into the really generous hearts of old timers who love to help a you g guy willing to work hard and do it right.
3- Ask guys who have actually done it and if you do not understand, ask more questions.
4- Think about it and plan your project
    A. Accumulate parts-it might take a year- be patient and keep at it.
    B. Make a schematic and a parts list and get what you need
    C. Plan the physical layout- it matters, because it affects stability and
         and performance.
    D. Measure three times, cut once- chassis are expensive to destroy without
         thought.
    E. Seek help all the way to assure best practice in the details. Vast experience
        lives here.
Failure to plan and educate yourself is not only prone to fail, but with high voltages, it can kill you.
Read the story of Icarus the Greek who preceded the Wight Brothers by 2500 years, but less successfully….😉

It us an interesting thread and you have received good advice, but failure to follow some method like I have outlined is just churning words and goes nowhere.
Follow it and you will be amazed at what might be accomplished.
A lot of us built a knowledge base in Ham Radio that powered our engineering careers. Be assured, it came with much effort and a lot of failures along the way, but grit and never give up attitude succeeds every time. Decide which road you will take and follow your dream… MB
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wa2tak
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« Reply #26 on: July 03, 2023, 12:20:07 PM »

Hello MB:

Appreciate your detailed critique.
All is good advise...for a rookie.

Permit me this reply.

I really do NOT need 'high power' in this venture.
I simply want to get it 'working'...whatever the watts.
AND..I did 'succeed'...my 10 watts out makes me most likely the only guy
to have a QRP linear 811 'amplifier'... Smiley

AND....it WILL be working properly eventually!!

I can also understand you 'seeing' my ignorance in my text.
My experience and confidence allows me to speak 'simply'
regarding the DETAILS on the matter at hand.
It's darn hard to make 'things' simple!!...esp in electronic and electrical engineering.
Having a Masters in Engineering leads to try to UNDERSTAND 'everything' I can.

Over these MANY years...licensed in 1963...I have:
Made my first novice homebrew 2 x 807 xmtr;
Made a homebrew 1937 AM transmitter using contemporary components;
Restored a 1948 homebrew ( 500 pound ) AM rack rig...photo attached.
just to mention a few.
( got it for $10...at an estate auction...when I 'cried' when the other $5 bidder said he was buying it for scrap...think they felt sorry for me. )

Was a F-102 jet interceptor RADAR TECHNICIAN.

I've always been one for traveling my own path...and..enjoy the fruits of doing so...
like antenna patent number 7,586,462..as shown on www.tak-tenna.com

Lastly...and most importantly...I THANK YOU for your generous help.

Steve






* ER Calendar 4close.jpg (45.36 KB, 480x640 - viewed 315 times.)
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K9MB
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« Reply #27 on: July 03, 2023, 12:36:02 PM »

Hello MB:

Appreciate your detailed critique.
All is good advise...for a rookie.

Permit me this reply.

I really do NOT need 'high power' in this venture.
I simply want to get it 'working'...whatever the watts.
AND..I did 'succeed'...my 10 watts out makes me most likely the only guy
to have a QRP linear 811 'amplifier'... Smiley

AND....it WILL be working properly eventually!!

I can also understand you 'seeing' my ignorance in my text.
My experience and confidence allows me to speak 'simply'
regarding the DETAILS on the matter at hand.
It's darn hard to make 'things' simple!!...esp in electronic and electrical engineering.
Having a Masters in Engineering leads to try to UNDERSTAND 'everything' I can.

Over these MANY years...licensed in 1963...I have:
Made my first novice homebrew 2 x 807 xmtr;
Made a homebrew 1937 AM transmitter using contemporary components;
Restored a 1948 homebrew ( 500 pound ) AM rack rig...photo attached.
just to mention a few.
( got it for $10...at an estate auction...when I 'cried' when the other $5 bidder said he was buying it for scrap...think they felt sorry for me. )

Was a F-102 jet interceptor RADAR TECHNICIAN.

I've always been one for traveling my own path...and..enjoy the fruits of doing so...
like antenna patent number 7,586,462..as shown on www.tak-tenna.com

Lastly...and most importantly...I THANK YOU for your generous help.

Steve






😂😂
Steve, hey- I get it- Since you have had all this experience, you certainly must have realized all I wrote you and if you want to build an 811a parasitic active dummy load that put out less than goes in, it is your choice- no matter the reason. 😉😁
It does beg the question, however, that you would start a thread leading anyone to believe you to be clueless on these matters and elicit the perfectly good advice you have received, only to reveal that you already knew better, but wanted to run the experiment anyway?
I am sure we all learned from your experiment, however..
As the Scots say, “fool me once- shame on you, fool me the second time, shame on me…”
But I enjoy a good joke, so knock yourself out. 😂😂😂
73, Mike
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wa2tak
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« Reply #28 on: July 03, 2023, 01:01:23 PM »

Hi Mike:

I do know a few things...like all of us.
But, I've never had HANDS ON with a LINEAR amplifier...
...the DETAILS of which I knew zip..as you can see from my texts.

I've not a shy guy.

My FIRST task was to see 'what's up' with this rig.
NOT having PROPER power supply...and...seeing the 811 specs...I 'figured' I'd get something out?
Why the heck not try?
And...don't even know if my 811 conducts even with good filaments.
( jsut put a want ad for one )

I did NOT know better at the START of this thread.

And, feel bad that folks think they were misled.
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K9MB
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« Reply #29 on: July 03, 2023, 02:09:02 PM »

Hi Mike:

I do know a few things...like all of us.
But, I've never had HANDS ON with a LINEAR amplifier...
...the DETAILS of which I knew zip..as you can see from my texts.

I've not a shy guy.

My FIRST task was to see 'what's up' with this rig.
NOT having PROPER power supply...and...seeing the 811 specs...I 'figured' I'd get something out?
Why the heck not try?
And...don't even know if my 811 conducts even with good filaments.
( jsut put a want ad for one )

I did NOT know better at the START of this thread.

And, feel bad that folks think they were misled.

Steve,
I enjoy a good joke as well as another, so I- myself am mostly amused by the exercise.
It does- however- seem inconsistent with your list of accomplishments that you seem unaware of triode diode saturaio voltage, plate load impedance and the necessary plotting of load lines that are the ABCs of running modulators and amps.
Your assertion and rhetorical question- “why not?” has been sufficiently answered in this thread, so we will leave it as an orphaned rhetoric.
As for “thinking they are mislead”, others must express their own feelings regarding that.
In my own case, a series of naive actions coupled with revealing questions and comments must demand a decision whether it was innocence or amusement that would motivate the record.
I am content that my own advice might help s person who actually wishes to learn something of the process snd discipline required for constructing and testing of good designs. Nothing is wasted as long as some may profit from the process.
I- myself appreciate the opportunity to recall and express that which
Might become otherwise forgotten or corrupted by neglect and time.
Please accept my own gratitude for that.
73, Mike
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wa2tak
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« Reply #30 on: July 03, 2023, 04:02:48 PM »

Hi Mike:

Enlightening comments!

I do add humor in my comments...think it lightens things up a bit...and, hopefully...makes reading a little more
fun.

I do NOT take myself seriously...never did.
Must be naive! ..a naive Vietnam Vet at that.

Regarding load line etc...had 'wondered' how my Pi output - designed for 2 x 811's plate load resistance...apprx 5000 / 2 would 'work' with my ONE 811...

Putting that 'reading' aside...'reading' is dandy...but hands on IS the candy...esp if if you make the thing work.
Naturally, learn MORE by 'mistakes'!!

As we know..."there's alllllllllllllll kinds on Planet Earth"...makes life interesting, huh?
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wa2tak
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« Reply #31 on: July 03, 2023, 04:45:28 PM »

PS
Here's some icing on this cake.
Tubes do not 'work' without vacuum.

Given a tube at whose 'vacuum' is ground level pressure...
...how MUCH will it 'not work'??

Can't seem to find any data on 'tube conduction vs vacuum level'.

Sooooooooooooo...grab this...I will 'see' with my one 811 with a glass hole in it.
The filiament IS giving off electrons...

How's this for being serious???
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K9MB
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« Reply #32 on: July 03, 2023, 04:52:17 PM »

Plate load impedance is approximately:

(Plate Voltage - Diode Saturation voltage)/ 1.8 * plate current

For two 811a at 1500 plate voltage, we get:

(1500- 100)/ 1.8 * 0.35
= 1400/0.63 = 2200 ohms plate load for class B or AB2
For AB1, the multiplier is 1.6 and for class C, it is 2.0

There are charts snd calculators to give you values for C and L for output tank.
Operating Qs between 10 and 20 are customary,
73, MB

As previously stated, unless you are driving the amp with a low powered (25-50 watts) rig, it is not going to boost your signal much at 300 watts output.
Of course- modern rigs can set output to whatever you like and 35-40 watts will work well.
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KA3EKH
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« Reply #33 on: July 05, 2023, 03:15:07 PM »

Man, you all are too smart for me, I would just put the 400 volts to the one good tube you got and see what happens. Curves, conductance and everything else aside. Still think it was a quick built grounded grid amplifier built up for SSB and think that without hitting it relatively hard and with a high plate voltage may not be that impressive, but enough talking it to death, just do it and let us know what happens.
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K9MB
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« Reply #34 on: July 05, 2023, 11:53:54 PM »

Man, you all are too smart for me, I would just put the 400 volts to the one good tube you got and see what happens. Curves, conductance and everything else aside. Still think it was a quick built grounded grid amplifier built up for SSB and think that without hitting it relatively hard and with a high plate voltage may not be that impressive, but enough talking it to death, just do it and let us know what happens.


😂😂😂
And thus 100 years of Radio Amplifier design technology goes down the  hole after the rabbit.… “eat me!”, “drink me”! What could go wrong???  🤪😉😁
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KD6VXI
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Making AM GREAT Again!


« Reply #35 on: July 06, 2023, 06:14:52 AM »

Reminds me of the 11 meter forums.

Where 'Real Whirl' don't be coincidin' with that book lernin'.

I get it, hands on learning is how some of us learn, vs being able to read it and go 'DING'.

But that doesn't negate the fact that you aren't going to beat physics.

--Shane
WP2ASS / ex KD6VXI
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K9MB
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« Reply #36 on: July 06, 2023, 10:30:46 AM »

Reminds me of the 11 meter forums.

Where 'Real Whirl' don't be coincidin' with that book lernin'.

I get it, hands on learning is how some of us learn, vs being able to read it and go 'DING'.

But that doesn't negate the fact that you aren't going to beat physics.

--Shane
WP2ASS / ex KD6VXI

Hi Shane,

Well, most of us had mentors who helped us not kill ourselves and rescue our half cocked knuckle headed projects. I had several guys from “the 160 meter days” serve to help me and I still got nearly killed on a floating center tap from a tv transformer power supply. Yes- experience does serve a purpose, but deciding to jump off a tall building to find out if a person dies on the way down or upon impact may not benefit the experimenter as much as listening to good counsel…..😉😂😂😂

It reminds me why this forum even exists. The wiser heads on here have saved my axx a number of times when I proposed a chuckle headed idea and I have 65 years experience.
Glad I stayed away from the edge until I heard from older and or better heads. 😉
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