Date   
Re: uBITX Wireup Diagrams on the HF SIGNALS WEBSITE ARE WRONG!! #ubitx #ubitx-help

KG5MG
 

Scott, did you ever get a response from Al, N1AW regarding the CW jack adapter for the uBitx you posted to the group 12/3102018?  I am just starting on my kit and want to use paddles.

Thanks
73
Hamp KG5MG

Re: Wiring question - Nextion case

Mike WA0YCN
 

Looking at the schematic for the front panel board, I’m confused.  Pin 1 of J4 goes to pin 4 of J8 - is that also NC to pin 5 - so its using the speaker output from the ubitx board?

Re: Reducing power

Gordon Gibby
 

I would suggest to just get a non-inductive potentiometer,  put it on the panel, and run tiny coax to it so you have a panel mounted drive controller.  


On Nov 10, 2019, at 14:42, Sascha Bohnet | DL5SMB via Groups.Io <saschabohnet@...> wrote:

There is also another approach by John, VK2ETA, who tried to control SSB and CW power output via software/firmware by changing the clock frequency of the raduino (40 Mhz IF).
I do not understand it fully, but details can be found here.

Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

Gordon Gibby
 

Thanks very much! I think we’ve got a pretty cool project developing here. 


On Nov 10, 2019, at 13:36, ajparent1/KB1GMX <kb1gmx@...> wrote:

Gordon,

Yes don't.  Those vacuum fats have plat to grid capcitance and if not neutralized
(or even if it is) it will take off and get unhappy.

If anything lower might be the thing.  The key is you need enough RF grid voltage
to drive the tube but likley less than the total bias needed to get plate current.
Some tubes gt really unhappy or terribly non linear if they see grid current flow.

Grounded grid has some of the same issues but offers a naturally lower input
impedance and a bit less gain.

Allison

Re: Reducing power

Sascha Bohnet | DL5SMB
 

There is also another approach by John, VK2ETA, who tried to control SSB and CW power output via software/firmware by changing the clock frequency of the raduino (40 Mhz IF).
I do not understand it fully, but details can be found here.

Re: Reducing power

ajparent1/kb1gmx
 

Please observe the schematic of the radio board.

Resistor RV1  is there to serve that function.  

NOTE; if you turn it down (clockwise, yes its odd) for 5W on 80M
you will get less power on successive bands.  

Allison

Re: Wiring question - Nextion case

Justin Phillips K5AXL
 

It's coming from J4 on the front panel mic/key/phones board.

Reducing power

R. Tyson
 

Hi,
I have a uBitX to build over the Christmas period. I will be using the KD8CEC firmware and Nextion 2.8" screen
Is there an easy way of altering the output power, short of dropping the supply voltage ? If I could make this easily adjustable....

I like to run QRP CW so that means no more than 5 watts output.
Any ideas appreciated to save me re-inventing the wheel.

Thanks,

Reg

Wiring question - Nextion case

Mike WA0YCN
 

Folks,

I have the AmatuerRadioKits 3.5 Nextion case kit and a recent v5 ubitx.  I’m trying to determine where to get the audio input for the audio amp board that comes with the kit.  The picture in the downloads shows a connection on an earlier version of the ubitx.

Thanks.

Mike
WA0YCN

Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

ajparent1/kb1gmx
 

Gordon,

Yes don't.  Those vacuum fats have plat to grid capcitance and if not neutralized
(or even if it is) it will take off and get unhappy.

If anything lower might be the thing.  The key is you need enough RF grid voltage
to drive the tube but likley less than the total bias needed to get plate current.
Some tubes gt really unhappy or terribly non linear if they see grid current flow.

Grounded grid has some of the same issues but offers a naturally lower input
impedance and a bit less gain.

Allison

Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

Gordon Gibby
 

Thanks very much for sharing that schematic!   Even with the resistive loading it looked like the grid given PA of heathkit transceiver was doing about 16 dB gain.  I wasn’t brave enough to try it higher than 20 m 

Do you have any advice on whether we should try resistive loading higher impedance than 2500 ohms???

By using the tuned plate circuit of the 6cl6 driver, I guess we are already dealing with any grid capacitance in the process

I never did anything like this before (since I home brewed a 3x 811 a amplifier in high school ) it’s pretty cool for me to get back to this


On Nov 10, 2019, at 11:59, ajparent1/KB1GMX <kb1gmx@...> wrote:

The attached image was the solution of the 60 and 70s for hams (and CBers)
for 100W amp. it was cheap 10-13DB of gain.  Alas sweep tubes got expensive 
as people burnt them all up pushing those.  There were generations of them with
up to 6 (SIX!) for a KW input peak.  Not all were clean.

Some did grid driven and they worked save for over drive the grids and the
tubes protest by going away.  At 25$ each that is a bad thing.

For laughs a decade ago I took a 4CX250  and ran it grounded grid like that
and it was good for about 80W (on 6M) out in a simple circuit without forced
air cooling. The tube with screen bias (its a ceramic metal power tetrode)
added did an easy 300w out at 2000V (a very lethal power supply).  The
amp was terminally simple save for a typical tube amp tapped load coil
Pi network for multi-bands.  There are a long list of tubes that can can
be used for that that..

Allison
<courier_bl100_sch.pdf>

Re: Power output tests at 24v PA

Chris [N7CCX]
 

@mIguel, it is not designed to do 160, this was just a test.

7/10 ill check..


@mark variable multi meter

Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

John Faivre
 

I have a HW104 with solid state finals and was thinking of doing the same thing. 
--
John Faivre WA9SGD

Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

ajparent1/kb1gmx
 

The attached image was the solution of the 60 and 70s for hams (and CBers)
for 100W amp. it was cheap 10-13DB of gain.  Alas sweep tubes got expensive 
as people burnt them all up pushing those.  There were generations of them with
up to 6 (SIX!) for a KW input peak.  Not all were clean.

Some did grid driven and they worked save for over drive the grids and the
tubes protest by going away.  At 25$ each that is a bad thing.

For laughs a decade ago I took a 4CX250  and ran it grounded grid like that
and it was good for about 80W (on 6M) out in a simple circuit without forced
air cooling. The tube with screen bias (its a ceramic metal power tetrode)
added did an easy 300w out at 2000V (a very lethal power supply).  The
amp was terminally simple save for a typical tube amp tapped load coil
Pi network for multi-bands.  There are a long list of tubes that can can
be used for that that..

Allison

Re: Power output tests at 24v PA

ajparent1/kb1gmx
 

A note on 24V operating...

If you do that there will only be a bit more power is the result.
Since the gain of the finals does not increase with greater
applied voltage you still need more drive to take advantage
of it.  It only enables it to produce more power.

That goes back the the initial problem, not enough drive on
the higher bands from the decaying gain from the 3904s.

As to dummy loads and detectors,  Diodes are terrible load
and when connected to dummy load they change the
effective impedance presented back to the radio.
They also have a hard to predict offset (threshold)
that at best is approximated and untested.  Above a
few watts its not a big deal unless some one can show
a significant difference for 15V vs 15.5V (peak)
across a 50 ohm load. 

Then we get into peak vs p-p and RMS power.
Note most diode detectors are usually PEAK so
the actual is .707(give or take considering diode
offset) times the peak voltage (correct only for
sine wave). 

Also detected waveform makes a difference and assuming
a sine wave is not always valid.

Its those details that impact read power and why many people
get sometimes wildly different numbers. 

the simplest test is pit a fresh 1.5V battery across hte dummy load.
That should cause 30mA to flow and the diode detector if perfect
(and DC connected) will read 1.56V (fresh alkaline cell).  Likely
it will be a diode drop lower and that depends on the diode and
meter load presented to the diode.  Typical for 1n34 is about
1.45V,  1n5711 Schottky maybe 1.35V, and 1n4148 silicon
about .96.   FYI the resistor in the load if 50 ohms is dissipating
.045W (45 milliwatts) DC.  If it was 1.56V AC P-P its a lot less
(about 6mW).

Allison

Re: Power output tests at 24v PA

 

Hi Chris,

In your first column of power calculations, the formula is correct but you must have made a mistake in the spreadsheet calculation.  Either that or you didn't take into account the the probe gives Vpeak not Vrms so it must be converted.

This is shown correctly in the second column formula:  your reading squared divided by 100.  In converting Vpeak to Vrms you divide by the square root of 2.  However, since this is subsequently being squared, you can just put that in the divisor with the 50 and that makes it 100.

Of course both voltage measurements should have the diode voltage drop correction added back in before and any calculations are done.

Be aware that dummy loads/detectors can be built in different configurations so the formulas may vary (e.g. Elecraft's DL1 where the probe is measuring across only half the load).

73,


Mark

PS:  What is a VMM?

Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

Gordon Gibby
 

Fantastic!   part of the magic of ham radio is experimenting and developing more personal knowledge of radio and electronics.   

On Sun, Nov 10, 2019 at 8:38 AM Bill Cromwell <wrcromwell@...> wrote:
Hi,

In the 80s I built boots for an Ten Tec Argonaut 509 using the carcass
of a Heathkit DX-35. There is no receive circuitry involved. I biased
the single 6146 for class AB1 operation. I built a solid state T-R
antenna switch to keep the QSK feature of the 509. It served me for a
several years and then the 509 moved to a new home. The remains of the
DX-35 also went to another ham.

I have the CW portion of a Heathkit DX-100 down for overhaul. The AM
phone parts were all gone when I got the DX-100. I am going to dpo the
mods to include the linear operation in phone mode to amplify SSB
signals and keep the class C operation for it's CW operation - ala the
Apache (TX-1). Grid block keying has already been part of this
particular DX-100.

Sometimes QRP is just not enough.

73,

Bill  KU8H

On 11/10/19 7:35 AM, Don Richards wrote:
> Hi Gordon
> I ran across this a while back but never tried it.
>
> https://www.google.com/url?sa=t&source=web&rct=j&url=https://frrl.files.wordpress.com/2008/09/hotwaterforthek2.pdf&ved=2ahUKEwjwzsTQ09_lAhWsmuAKHQ1MCyYQFjACegQIARAB&usg=AOvVaw1PdjqVxSUEw-wayoqwuZyO
>
> 73 Donve3ids

--
bark less - wag more



Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

Bill Cromwell
 

Hi,

In the 80s I built boots for an Ten Tec Argonaut 509 using the carcass of a Heathkit DX-35. There is no receive circuitry involved. I biased the single 6146 for class AB1 operation. I built a solid state T-R antenna switch to keep the QSK feature of the 509. It served me for a several years and then the 509 moved to a new home. The remains of the DX-35 also went to another ham.

I have the CW portion of a Heathkit DX-100 down for overhaul. The AM phone parts were all gone when I got the DX-100. I am going to dpo the mods to include the linear operation in phone mode to amplify SSB signals and keep the class C operation for it's CW operation - ala the Apache (TX-1). Grid block keying has already been part of this particular DX-100.

Sometimes QRP is just not enough.

73,

Bill KU8H

--
bark less - wag more

Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

Gordon Gibby
 

FABULOUS!!!!!!   That is way ahead of me, and probably an even better way to do exactly what I was doing!!!!!   Thank you for providinig that information!   

It looks like this works quite well.   I saw that in the schematic but buzzed past, never realzing that was probably the exact type step-up transformer just like what I was using!!!    

An even easier way to do what I was working on.    I'll be talking about these amplifiers to our local ham club on Wednesday.   What a great addition, your article makes.    

To resurrect these ancient and great transceivers, generally all one has to do is replace their electrolytic compacitors in the power supply.   And there are two on the main transceiver board as well.    Just that simple work (I'm going to make a printed circuit board for myself to make it easier) gives you what may be a very cheap power amplifier for the wonderful bitx devices.   

I've been able amazingly to get the transceiver for $100 and the power supply for $100 also, often.    What a huge amount of radio for such little $$.    Replace the VFO with a signal from the Raduino (it works great) and you have a computer controllable radio.    I've written that up before.   

Gordon

Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

Don VE3IDS