Date   
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 Richards
 

Re: Power output tests at 24v PA

Miguel Angelo Bartie
 

Hi Chris

I usually measure RF power with a diode and metal film resistors.
The diode barrier voltage is important for low power (below 2W).
The graph you get shows problems at 1.6, 7 and 10 MHz, in my view is that you are having problems with the low pass filter that has a lower than the expected frequency cut, thus reducing the power in these bands.
If possible change the value of the inductors downwards (by taking a loop, each inductor, for example).
After this measure the power again

73 from py2ohh miguel

Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

Rajendran Mayilsamy
 

Thanks Gorden for info and do post the rough schematic ..tnx n 73 Rajendran

On Sun, Nov 10, 2019 at 2:26 PM Gordon Gibby <docvacuumtubes@...> wrote:
What Allison suggested was to resistively load the transformer upping the impedance of the signal.   So I provided a 2500 ohm load on the hi impedance side.  

I’ll draw up a rough schematic later 

Thanks

Gordon




On Nov 10, 2019, at 03:44, Rajendran Mayilsamy <mrajsuba@...> wrote:

Dear OM Gordon Gibby, pl share the info shared by OM Allision about the using of Heath tube type txcvr final  and me to having a HW101 and would like to modify it..

Allison gave some much needed advice on this crazy idea months back,--This info pse


 73 de Rajendran,VU2SMM

Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

Gordon Gibby
 

What Allison suggested was to resistively load the transformer upping the impedance of the signal.   So I provided a 2500 ohm load on the hi impedance side.  

I’ll draw up a rough schematic later 

Thanks

Gordon




On Nov 10, 2019, at 03:44, Rajendran Mayilsamy <mrajsuba@...> wrote:

Dear OM Gordon Gibby, pl share the info shared by OM Allision about the using of Heath tube type txcvr final  and me to having a HW101 and would like to modify it..

Allison gave some much needed advice on this crazy idea months back,--This info pse


 73 de Rajendran,VU2SMM

Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

Rajendran Mayilsamy
 

Dear OM Gordon Gibby, pl share the info shared by OM Allision about the using of Heath tube type txcvr final  and me to having a HW101 and would like to modify it..

Allison gave some much needed advice on this crazy idea months back,--This info pse


 73 de Rajendran,VU2SMM

Re: Power output tests at 24v PA

Chris [N7CCX]
 

So my pemdas order of operations is wrong! 


I was wondering why I was pulling 16w on a ft60 and my bitx was pushing 70

Re: Using Vacuum Tube heathkit as Linear Amplifier for QRP

Gordon Gibby
 

(The little perfboard circuit in the right foreground is unrelated -- a circuit to deal with transmit/receive problems.....ignore)
The 49:1 balun (really, a Un-Un)  is in the blue electrical box with the banana plug outputs.  

Using Vacuum Tube heathkit as Linear Amplifier for QRP

Gordon Gibby
 



Finally got a chance to try my idea of using a heathkit ssb rig as a power amplifier for a QRP rig.   I've seen "amplifiers" for these rigs going for many hundreds of $$$.  I happen to be swimming in ancient heathkits with 2x6146 linear finals and tuned plate circuits on the driver as well (all good for getting rid of unwanted harmonics.....)

Allison gave some much needed advice on this crazy idea months back, and I finally got the chance to try it:

1 watt output from an exciter [I used an icom 718 that was readily availalbe] -- my only "power measurements" are ancient SWR meters with built in diode detectors so these measurements may be fairly INaccurate.

coax over to a 49:1 homebrew balun our group made for matching resonant half-wave antennas:   ours is a simple autotuner with 14 turns total of #18 teflon wire around a FT-240-43 (or FT-140-43) tapped at turn 2 to give us 7:1 turns ratio, 49:1 impedance ratio, and that checked out roughly with an antenna analyzer and some resistors

I loaded the output with 2500 ohms (temporarily made out of 4 10K resistors in parallel because that is all i had)
output of that via 6 inches of small coax to a 0.01 1kv ceramic capacitor connecting to the PLATE circuit of the removed 6CL6 driver, and to a nearby ground.

Output tested only with very brief bursts of CW -- on 80 meters and 20 meters, got approx 40-50 watts output measured also with an ancient swr meter/wattmeter into a 50 ohm load, everything on the Heathkit peaked for output.   Plate current rose appropriately.   Tuning circuit all appeared appropriately.

No obvious signs of any instability in this pilot test.    
Did not make any measurements with spectrum analyzer.   (In due time......)

That heathkit has other problems elsewhere but the finals appeared in fine shape.   Earlier VERY CRUDE measuresments with a siglent oscilloscope and some math suggested that the drive required at the INPUT to the 6CL6 stage would be less than 100 milliwatts, and that the drive required at the output of 6CL6 would be in the single digit watts range.    The above test appears to confirm those crude measurements.   Since it appeared the two 6146's could be driven adequately with single digit watts I opted to temporarily just remove the 6CL6 driver and connect to its (DC powered!!!!!!!  High voltage!)  plate circucit with a 1kv .01 blocking capacitor.   

Quite pleased with this very very initial test.   
At some point I'll repeat with a uBitx, but that's all for right now.
Gordon Gibby

Re: Power output tests at 24v PA

Jerry Gaffke
 

That's correct, assuming a forward voltage of 0.4 Volts across the diode.
According to fig 7 of the datasheet, that happens at a current of 20 uA when the temp is 25 C.
   https://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/BAV21.pdf

Dividing the peak voltage (what you measure with a diode detector) by 1.414 
converts it to an RMS voltage, assuming we are dealing with a sine wave.
We must use that RMS voltage when calculating power.

Jerry


On Sat, Nov 9, 2019 at 12:42 PM, Mike Kilpatrick wrote:
I could be way wrong but I measure DC volts, add 0.4V then divided by 1.414.
Multiply the result by itself (square it) and divide that result by the 50 ohms load. Result is power in watts. 

 
 

Re: Power output tests at 24v PA

Mike Kilpatrick
 

I could be way wrong but I measure DC volts, add 0.4V then divided by 1.414.
Multiply the result by itself (square it) and divide that result by the 50 ohms load. Result is power in watts. 


On 10 Nov 2019, at 04:56, Chris [N7CCX] <chriscoel@...> wrote:

Howdy all, I did last night some key down test (keyed the radio with a straight key) into a dummy load and did some power measurements..

I am seeing a bit higher than expected power outputs on 12V and then also 24! I took a single measurement on areas on the bands and then keyed down for a couple seconds and took the average VMM reading, I then took two formulas. One was QRPGuys Dummy load formula (which my dummy load is based on - Except the diode is swapped out for a BAV21 instead of a 72v diode). Other is K4EAA and even Elecrafts Calculations..

My results:
<dummyfile.0.part>




The graph is with the QRPGuys calculations which the formula is shown above.. My question is are these even close or accurate? The forumlas used above base on the exact builds they did. K4EAA uses 20 resistors to achieve a dummy load, meanwhile QRPGuys uses 4 resistors then they originally have a smaller voltage diode... Does someone have a better formula I should use? Signal is dumping into 4 3W 200OHM Resistors, cooled by a fan (cause they def are not rated for 20+ W :) then they feed into a BAV21 Diode with a .01UF capacitor on there to help smooth it out..


Either way the IRF510s didnt seem too upset from the extra power, but I am running a fan on one of the cases Sunil sells and its held up great (minus some fan noise i need to fix). I also need to run a probe on the 510s, since they are still on default heatsinks :)

Any help on confirming a better formula or even if I am accurate with my measurements helps!

Thanks

Power output tests at 24v PA

Chris [N7CCX]
 

Howdy all, I did last night some key down test (keyed the radio with a straight key) into a dummy load and did some power measurements..

I am seeing a bit higher than expected power outputs on 12V and then also 24! I took a single measurement on areas on the bands and then keyed down for a couple seconds and took the average VMM reading, I then took two formulas. One was QRPGuys Dummy load formula (which my dummy load is based on - Except the diode is swapped out for a BAV21 instead of a 72v diode). Other is K4EAA and even Elecrafts Calculations..

My results:




The graph is with the QRPGuys calculations which the formula is shown above.. My question is are these even close or accurate? The forumlas used above base on the exact builds they did. K4EAA uses 20 resistors to achieve a dummy load, meanwhile QRPGuys uses 4 resistors then they originally have a smaller voltage diode... Does someone have a better formula I should use? Signal is dumping into 4 3W 200OHM Resistors, cooled by a fan (cause they def are not rated for 20+ W :) then they feed into a BAV21 Diode with a .01UF capacitor on there to help smooth it out..


Either way the IRF510s didnt seem too upset from the extra power, but I am running a fan on one of the cases Sunil sells and its held up great (minus some fan noise i need to fix). I also need to run a probe on the 510s, since they are still on default heatsinks :)

Any help on confirming a better formula or even if I am accurate with my measurements helps!

Thanks

Re: Self Promotion

Tom, wb6b
 

On Fri, Nov 8, 2019 at 06:09 AM, Charles Hill wrote:
latest STM32F SDR Project
That is totally cool. I just bought the same STM32F769I-DISCO board for a data acquisition and controller project. Now I going to need to use all my willpower not to get diverted from the project at hand to making an SDR out of it, or connecting it to my uBitx. 

This is a great board has lots of audio processing capability and double precision floating point. Plus four mems microphones on the board. I suppose there is some software that processes the four microphones to create a directional or other composite microphone from the four. 

For those that don't want to spend $80, there is a STM32F429I-DISCO board that has a smaller touch screen LCD display, but still has way more computing power than the Blue Pills. It, also, has some audio specific features. 

In my case the choice was made because the UI with the capacitance touch screen is much better than the resistive touch screen of the lesser expensive board.

Charles, please let us know where to find the code for this and the SDR project you mentioned in the video. I'd love to learn more about the SDR capabilities of the STM32F769 and STM32F429 chips with some examples I can relate to-- Ham Radio. 

Is the project done (or importable into) in STM32Cube or Mbed? Those are the two development environments I'm currently using. 

Thanks,

Tom,
wb6b

Re: OT - EMRFD

K5ESS
 

I got it and joined. It's just a mailing list as far as I can tell but it does archive messages. No file or picture storage I believe unless they would be stored as attachments tp messages. Members of note are Hans Summers and Allison Parent.
Mike
K5ESS

-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Vince Vielhaber
Sent: Friday, November 8, 2019 11:32 AM
To: BITX20@groups.io
Subject: Re: [BITX20] OT - EMRFD

I got it but didn't join. Had he done it at groups.io I probably would
have, but I've never heard of the site he chose so I didn't, and
probably won't.

I did, however, download all the content from the emrfd group before it
goes away.

Vince - K8ZW.


On 11/07/2019 09:34 PM, Ken wrote:
Sorry to post this here.

Is there anyone here who belonged to the EMRFD yahoo group and was
contacted by a Andrea Baldoni to join his group?

Just wanting to find out if this is a valid group.

Sorry for the OT.

73

Ken VA3ABN
--
K8ZW http://www.metalworkingfun.com http://www.hamradio.fun

Re: Does anybody know how to calibrate CEC firmware ?

Adrian Chadd
 

On Fri, 8 Nov 2019 at 09:22, Adrien F4IJA <@Adrien_Grelet> wrote:

OK so the Set calibration is used for the Master calibration upon frequency and BFO for the decoding of signals if I'm right?
The BFO needs calibrating to make sure the signals you're trying to
receive are in the passband of the IF filter.

That's why you can calibrate it quickly by looking at your audio
output and just looking for the noise passband. The filters vary board
to board, so the BFO calibration can't be to a specific frequency - it
is a frequency based on what the matched crystals in your ~12MHz
filter centre on.


-adrian
(kk6vqk)

Re: OT - EMRFD

Vince Vielhaber
 

I got it but didn't join. Had he done it at groups.io I probably would have, but I've never heard of the site he chose so I didn't, and probably won't.

I did, however, download all the content from the emrfd group before it goes away.

Vince - K8ZW.

On 11/07/2019 09:34 PM, Ken wrote:
Sorry to post this here.

Is there anyone here who belonged to the EMRFD yahoo group and was
contacted by a Andrea Baldoni to join his group?

Just wanting to find out if this is a valid group.

Sorry for the OT.

73

Ken VA3ABN

Re: Does anybody know how to calibrate CEC firmware ?

Adrien F4IJA
 

OK so the Set calibration is used for the Master calibration upon frequency and BFO for the decoding of signals if I'm right? 
--
73's
Adrien F4IJA
https://www.qrz.com/db/F4IJA

Re: Self Promotion

Roy Appleton
 

Charles, I sent you an email asking for more info on this project!

Roy
WA0YMH

On Fri, Nov 8, 2019, 8:10 AM Charles Hill <chillmf20@...> wrote:
To All,

I am pleased with the results of my latest STM32F SDR Project which I have documented with this utube video:

https://www.youtube.com/watch?v=D4lKBUj9MAw

Regards.

Charley