Topics

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

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.  

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

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

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

Don Richards
 

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

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

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



ajparent1/KB1GMX <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

John Faivre
 

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

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>

ajparent1/KB1GMX <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

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

Robert D. Bowers
 

I've played around with a Kenwood TS520... using a softrock connected in through the filter board.  The combination was in a word AWESOME... if a different radio even thought on frequency, I probably would have heard it (voice QRM became the limiting factor - static and hiss less of a barrier).  I plan on eventually using the softrock as an IF and the filters (and so on) for transmission.  The good thing is that the tuned circuits in the old radio are going to greatly improve the signal, one way or another.  In fact, they should be at least as clean as the best modern unit.

There are more powerful old tube rigs 'out there' - I can think of a KW rig right now that would be awesome as an amp (plus great filtering) for a BitX (or softrock).

Right now I'm trying to get something on the air with 2m SSB/FT8.  Then other projects will follow...

Bob

On 11/9/19 5:01 PM, Gordon Gibby wrote:


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

Attachments:


Richard Spohn
 

Bill, do you have the schematic for the solid-state T/R switch, or
even better, do you still have that switch? I am keenly interested in
an all-electronic (no relays) T/R switch for QSK. Building one from
scratch may be slightly outside my skill set tho. -- Rich WB2GXM

On 11/10/19, 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



Gordon Gibby
 

There is this MFJ pin diode rig that I managed to pick up on ebay for $100.   You might look around for another of those.   They do take some tinkering I'm told.    

An even easier solution is to simply emulate the HW-16 and have TWO devices --- one used for transmit and one used for receive -- and control both of them with the same digitally created frequency (from a Raduino) and just use diode protection of the input of the "receiver" just as many qrp rigs do.    There are probably a lot of schematics out there for creating a diode switch also.   

Gordon


On Tue, Nov 12, 2019 at 4:08 PM Richard Spohn <wb2gxm@...> wrote:
Bill, do you have the schematic for the solid-state T/R switch, or
even better, do you still have that switch?  I am keenly interested in
an all-electronic (no relays) T/R switch for QSK.  Building one from
scratch may be slightly outside my skill set tho. -- Rich WB2GXM

On 11/10/19, 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
>
>
>
>



Richard Spohn
 

MFJ "Pin Diode Rig"....a model or part number?

On 11/12/19, Gordon Gibby <docvacuumtubes@...> wrote:
There is this MFJ pin diode rig that I managed to pick up on ebay for
$100. You might look around for another of those. They do take some
tinkering I'm told.

An even easier solution is to simply emulate the HW-16 and have TWO devices
--- one used for transmit and one used for receive -- and control both of
them with the same digitally created frequency (from a Raduino) and just
use diode protection of the input of the "receiver" just as many qrp rigs
do. There are probably a lot of schematics out there for creating a
diode switch also.

Gordon


On Tue, Nov 12, 2019 at 4:08 PM Richard Spohn <wb2gxm@...> wrote:

Bill, do you have the schematic for the solid-state T/R switch, or
even better, do you still have that switch? I am keenly interested in
an all-electronic (no relays) T/R switch for QSK. Building one from
scratch may be slightly outside my skill set tho. -- Rich WB2GXM

On 11/10/19, 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







Jack, W8TEE
 

Didn't Hans QSX talk at FDIM and reprinted in QRPQ (October issue??) discuss a "relayless" TR switch?

Jack, W8TEE

On Tuesday, November 12, 2019, 4:08:07 PM EST, Richard Spohn <wb2gxm@...> wrote:


Bill, do you have the schematic for the solid-state T/R switch, or
even better, do you still have that switch?  I am keenly interested in
an all-electronic (no relays) T/R switch for QSK.  Building one from
scratch may be slightly outside my skill set tho. -- Rich WB2GXM

On 11/10/19, 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
>
>
>
>




--
Jack, W8TEE

Bill Cromwell
 

Hi Richard,

I copied the whole thing from one of the ARRL Handbooks. I'm sure I can find it again. I will have a look. I do still have the T-R switch and maybe even the coupling capacitor. That cap is a "gimmick" made from about three inches of RG-58. Don't let the "gimmick" label throw you over. It is more than a little twisted pair as sometimes used in receiver circuits for regenerative feedback.

I built mine in an old TV tuner metal box. I don't know what they have in TV sets for a tuner these days but I think it is an SDR front-end. An Altoids tin (or something similar) would work. The transistor is a 40673 dual gate mosfet and is now just about unobtanium. Fortunately there are plentiful substitutes. You could also use a vacuum tube <grin>.

More later after I dig out the details. It is so easy that even *I* could do it.

73,

Bill KU8H

On 11/12/19 4:07 PM, Richard Spohn wrote:
Bill, do you have the schematic for the solid-state T/R switch, or
even better, do you still have that switch? I am keenly interested in
an all-electronic (no relays) T/R switch for QSK. Building one from
scratch may be slightly outside my skill set tho. -- Rich WB2GXM
--
bark less - wag more