The AM Forum
March 29, 2024, 05:53:24 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Amplifying a low level signal...  (Read 12399 times)
0 Members and 1 Guest are viewing this topic.
N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« on: November 23, 2015, 09:51:04 PM »

What would be the best way to amplify a 20 watt PEP (5 watt carrier) to higher power levels using tubes?
I have a new toy coming (ANAN 10E) which puts out about 5 watts carrier and I wonder if I can plug it into a pair of 4X150 tubes running AB1.
As modulators, they run 2000 volts and about 500 ma on peaks, about 600 watts out, no driving power, -50 volts bias, 350 volts on the screens.
That would be about 150 watts (carrier) output.

Can I just put the signal into the grid, turn down the grid leak resistor, turn down the screen dropping resistor, set the resting current to 200ma, (fixed bias at -50 volts), screen voltage to 350, and drive it to maximum power output?

Pure signal can clean it up a bit.

Will this work?
Logged
W3RSW
Contributing
Member
*
Offline Offline

Posts: 3308


Rick & "Roosevelt"


« Reply #1 on: November 23, 2015, 10:00:42 PM »

Just about all the ARRL handbooks of the 40's through 60's will have your answer, some articles of which almost exactly describe your amplifier line-up, driving requirements, grid, screen and operating conditions.  Virtually all have link coupled inputs to the final stage, which is essentially the amplifier section you desire. Not much modification required here except possibly a 3 to 6 dB network to attenuate the signal if required.

Logged

RICK  *W3RSW*
N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #2 on: November 23, 2015, 10:11:21 PM »

The designs I have seen use a load resistor instead of a tuned input, or grounded grid.
Bill Orr had some water cooled 4wx300's and they had the load resistor input.
With only 5 watts carrier, it needs to not have much loss involved.
Logged
KD6VXI
Contributing
Member
*
Offline Offline

Posts: 2648


Making AM GREAT Again!


« Reply #3 on: November 23, 2015, 11:02:00 PM »

4cx250b

2 kv loaded,  2.2kv unloaded

300 to 350 on the screen

-65 to - 80 on the grid.

450 ohm grid to ground resistance with a 9 to 1 input xformer.   

That will amplify 12 watts to 650 pep or more.

Put a 8930 in,  change the grid to - 80 to - 120 and you can see almost a kilowatt.

These output levels are not at the cleanest level.....   


I have an amplifier based on the above parameters for the 10e coming here.

--Shane
KD6VXI
Logged
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 8308



WWW
« Reply #4 on: November 23, 2015, 11:06:10 PM »

I have a nice SDP-1000L amp with two 4X150's. It will make about 500W PEP on SSB and a nice 100W carrier on AM without overheating the tubes. Be careful with those tubes, the grids are not designed for any dissipation, maybe 1W max.. and the screens are delicate too, so metering both screen and grid current is a very good idea. The screen meter is well to be a center zero meter because the screen current can go negative under certain conditions.
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #5 on: November 23, 2015, 11:16:11 PM »

What does a 9-1 input transformer look like?



4cx250b

2 kv loaded,  2.2kv unloaded

300 to 350 on the screen

-65 to - 80 on the grid.

450 ohm grid to ground resistance with a 9 to 1 input xformer.   

That will amplify 12 watts to 650 pep or more.

Put a 8930 in,  change the grid to - 80 to - 120 and you can see almost a kilowatt.

These output levels are not at the cleanest level.....   


I have an amplifier based on the above parameters for the 10e coming here.

--Shane
KD6VXI
Logged
W1ITT
Member

Offline Offline

Posts: 573


« Reply #6 on: November 23, 2015, 11:18:31 PM »

Definitely get a coupler working and implement PureSignal.  The IMD numbers I have seen for 4x150 / 4cx250 series are generally low 20 db range numbers.  They are good Class C tubes, and were used for a lot of "linear" implementations but they leave a bit to be desired in that department.  
The 4cx350A or F tubes are a horse of another color, having been designed for very linear service, up around -40 db, but they are scarce and the socket is more so.  But keep your eyes open.
Logged
W3RSW
Contributing
Member
*
Offline Offline

Posts: 3308


Rick & "Roosevelt"


« Reply #7 on: November 24, 2015, 07:52:50 AM »

Well if you want to go grounded grid, get a high mu triode.
Overkill with a sledgehammer ( esp. In Efficiency) and repeating essentially what I posted some time ago.

Here's what an Alpha 89 that just happened to be laying around produces with two Tone  PEP via an LP 100 A.  Each output point loaded as though the feeding power was max., I. E. Everything lesser at that point is amplified linearly.  You'll notice that I didn't manage to accurately reset some of the loading.  All traces were observed for sharpest peaking on a scope.  The Pi L output tune/load of the Alpha is co- respondent to a wide range of settings at low powers and interacts a good deal.  Looks like I forgot to retune at a couple of the points.  (7200 kHz)

Pin.      Pout
4.   355
5    433
6.   511
7.   556
8.   653
9.   653
10. 660
12. 816
16. 921
19. 1020

Your Anan 10 makes about 15 pep clean watts on bands down to 15, maybe 10 meters.  The HRPD team Apollo amplifier was originally rated at 20 pep on most of the bands. Anan knowing 6 meters yielded only 10 pep, listed it as such.

So this is what a pair of 3cx800 a7's at the original data sheet specs will get you.
For one tube, I guess you cut the outputs by 2 or 3 dB.

There is an ARRL single 3cx800a7 amp article , July '88, that describes a one tube circuit. That amp however uses the derated HV tube spec data points. Much literature on web for the supposed cut in tube specs.

As per article.

5.    230
10.  440
15.  575
20.  750

Might be fun to build one up using GM3SEK's triode control board or his tetrode control board with a 4cx350 , do it right ( the HV thing) and have one very nice Anan 10 post amp.  The triode of course has less power supply complexity.
Logged

RICK  *W3RSW*
N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #8 on: November 24, 2015, 08:27:10 AM »

Guess I will be experimenting.
I want to use what I have on hand and see what it will do, not buy expensive amplifiers or their tubes.

Yes, a pair of 3cx800's would be nice, and I used to have a bunch of pull outs but gave them away, and have no sockets anyway.
And, I would likely get bored running an sdr into an amplifier to get low/medium power output.
It might be fun to get it working and experiment though.

Logged
w4bfs
W4 Beans For Supper
Contributing
Member
*
Offline Offline

Posts: 1433


more inpoot often yields more outpoot


« Reply #9 on: November 24, 2015, 11:11:40 AM »

Brett, the king of home brew !  .... man, when you get after sumphin, you just don't mess around do ya .... maybe run a pair of 4x150 in the 30S1 circuit ...gain around 25 which would be just about right for yer drive level .... very clean
Logged

Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #10 on: November 24, 2015, 12:40:28 PM »

Yes, I have a mess o sockets for 4x150's and a bunch of the tubes also.

30S1 circuit, I need to look that up...

Logged
KD6VXI
Contributing
Member
*
Offline Offline

Posts: 2648


Making AM GREAT Again!


« Reply #11 on: November 24, 2015, 06:37:45 PM »

30S1  Pride dx300, and a couple other amplifiers use the same or similar tubes.

The 4x150s should sing about the same as the 250Bs with the voltages and specs I posted above.

Pretty much the same tube.

--Shane
KD6VXI

Logged
N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #12 on: November 24, 2015, 08:38:34 PM »

30S-1 diagram I found on the web used a 4cx1000.
Looked at and printed out the diagram for a KWS-1, a pair of 4x150/4cx250b tubes driven by a pair of 6cl6's in parallel.
Logged
KD6VXI
Contributing
Member
*
Offline Offline

Posts: 2648


Making AM GREAT Again!


« Reply #13 on: November 24, 2015, 10:27:46 PM »

The 1000 and 250b are close animals,  from the amps I've fooled with.   

The 4x150 and 4cx250 are also very close animals.

And depending on which flavor of 4cx1k you've got,  it might even be whimper grid than a 150 or 250.

Australia also uses a pair of 250s and a quad.   500 and a kw pep rated output.

--Shane
KD6VXI
Logged
w4bfs
W4 Beans For Supper
Contributing
Member
*
Offline Offline

Posts: 1433


more inpoot often yields more outpoot


« Reply #14 on: November 26, 2015, 10:24:18 AM »

look closely at 30S1 schematic .... screen is hard grounded ... screen supply is - thru the cathode ... see divider network in control grid for negative feedback .... innovative circuit !

see WCHB 14th edition .... also works with 4-400
Logged

Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #15 on: November 26, 2015, 09:02:33 PM »

That 30s-1 diagram confuses me!
Logged
KD6VXI
Contributing
Member
*
Offline Offline

Posts: 2648


Making AM GREAT Again!


« Reply #16 on: November 26, 2015, 10:49:05 PM »

DTS,  check rich measures website...   In particular his plywood box amp.   He uses the same circuit on a 4cx5k.  I duplicated that amp,  mono band,  in the past.   Great design,  with the screen grid grounded,  your tetrode is VERY stable.

Billy Orr describes it as well...   

It also took me a bit to understand the schematic,  looks wrong and confusing.   But,  when you realize you are just floating the cathode,  putting + for the screen to ground,  directly grounding the screen,  then run all voltage references back to said floating cathode,  it starts to make more sense.

Done it from 250Bs to 8170s.

--Shane
KD6VXI
Logged
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 8308



WWW
« Reply #17 on: November 26, 2015, 10:53:19 PM »

It's very simple. Take a normal 4CX1000 amp. The screen is of course properly bypassed for RF to GND, so it acts like a shield. as it should.

plate V = 3000
screen V = 200
grid V = -50
cathode V = 0 (GND)

Now, make the power supply and tube float and move the GND to the screen terminal, directly instead of through capacitors.

plate V = 2800
screen V = 0 (GND)
grid V = -250
cathode V = -200

The ratio of potentials remains the same, as does the class of operation, etc. This is more common as a technique than it seems, and is used for many applications.

Just shift the point of ground, whether for DC, RF, or other needs! It can be applied to many circuits, only the imagination is the limit.

Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #18 on: November 27, 2015, 12:48:39 PM »

Part of the problem is looking at diagrams on line and only being able to see a part of it at one shot.

Everything has a trade off, you then put high voltage on the filament transformer and other issues.
It may be important in some applications (tube choice, operating frequency) and not so much in others.

Since 4X150's need no driving power, I suppose driving two, three or four is about the same.
I have a deck (screen modulated at the moment) that does 200 watts carrier and should do 100 watts or more as an amplifier for the ANAN.
100 or 150 watts will do fine on 40 meters.
Logged
W1ITT
Member

Offline Offline

Posts: 573


« Reply #19 on: November 27, 2015, 01:19:13 PM »

Brett..
I agree with you about trying to look at schematic diagrams online.  Give me a book made out of dead trees every time.  I think Shane alluded to the Bill Orr "West Coast Handbook", actually titled "Radio Handbook".  It has an excellent description of the grounded screen tetrode amplifier.
The reason for its being is that screen bypass capacitors (or any other capacitor for that matter) don't always act like pure capacitors and the effect varies across wide frequency spans.  The screen bypass capacitor that looks pretty good on 40 meters may be a terror at 100 mhz, where your amplifier just might want to be a parasitic amplifier if left unsupervised.  A fat copper strap has much less inductance.  So you just reorient the relationships between the tube elements, referencing the screen to ground instead of the cathode.
I did this for many years with a 4-1000.  It was stable as a church.  The cathode sat at 500 volts (screen voltage value) below DC ground.  With any decent quality filament transformer even twice that is unlikely to pose a problem, and many are specified as such.
Treat yourself to a copy of the "Radio Handbook" by William Orr.  I have a few of them.  My 22nd edition was published by Howard Sams, but I think others were published by Editors and Engineers.  They show up cheap at hamfests,  Mine will be for sale when they settle my estate.
Logged
N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #20 on: November 27, 2015, 01:37:18 PM »

I have the Bill Orr handbooks, and many others including the very hard to follow RSGB handbooks.
Why can't they draw tubes like other countries?
And I thought an ariel was a brand of motorcycle...

Never noticed the grounded screen designs as I never really looked at amplifiers much before.
And most modern ones are grounded grid designs.
Logged
W1ITT
Member

Offline Offline

Posts: 573


« Reply #21 on: November 27, 2015, 02:58:47 PM »

Brett..
The British don't draw tubes the way we do because they don't have any.  Over there, they are "valves", and they don't even have high voltage on them.  It's "high tension".
What is even more astounding is that they don't start their hamfests before the first glimmers of dawn.  The ones I attended there start at 10 AM on Sunday morning, and they all show up dressed spiffy.  It's all very other worldly, but they seem to be fine chaps.
Logged
flintstone mop
Contributing
Member
*
Offline Offline

Posts: 5055


« Reply #22 on: December 01, 2015, 12:50:01 PM »

Here's something to tickle your fancy
The Harris RF 110A linear amp. Will amplify a 750mw signal to legal limit. Yea it costs a few dollars!!

Big Dollars at Surplus Sales, of course.

https://www.surplussales.com/RF/RFamp.html
They pop up on ebay and various Ham "for Sale" sites, QTH dot com and Eham. Festers,etc etc


Logged

Fred KC4MOP
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 8308



WWW
« Reply #23 on: December 01, 2015, 05:18:28 PM »

If you are going to pay like that and not even get the power supply then go ahead and get a 208U-3.

https://www.fairradio.com/catalog.php?mode=search&keywords=208U-3A&submit.x=0&submit.y=0

4CX5000 are cheap enough and I'd bet it can be run on single phase at reduced power.

I've wanted one of these forever. Like to have the manual or schematic if it could be found -a good read being auto-tune.

208U-3A   -   Collins 208U-3A Power Amplifier automatically tunable linear PA operates over 2.0-29.9999MHz SSB-AM-CW; output 2.5KW PEP using 4CX5000A tube driven by two 4CX350A tubes. Requires RF input from 0.025 to 0.1 watts for rated output; upto 2W input acceptable. Tune time 6 sec nominal, 10 sec max. Other features Internal Gain Control, Automatic Load Control, & Transmitter Gain Control. Has Collins URG-11 compatible modules 333H-2 Electronic Control Amp, 309F-1 Digital to Analog Converter, 915V-2 Amp Control, 652J-13 Power Supply, 599Z-1 Test Panel, and 915X-1 Control Monitor. Input imped: 50 ohms, max VSWR 1.3:1. Output imped: 50 ohms, max VSWR 3:1. Power input: 200-250VAC line-to-line, 3-line & ground, 3-phase 30 amps 47-63Hz; 1200W Standby, 9100W single tone CW @ 2.5KW. Includes manual copies for all components except 915X-1 & 599Z-1. 72.5x32.6x31: 1200 lbs sh. Used not tested, less 4CX5000,
$3,700.00 each

:drool
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone © 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.084 seconds with 19 queries.