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Author Topic: Transmitter using Viking Valiant Schema  (Read 2986 times)
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YB1AHY
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« on: March 02, 2023, 02:40:49 AM »

Hi All, greeting from Jakarta

I was in Dayton Hamvention 2022 last year, I saw a lot of boatanchor there. I really want to bring them back to Jakarta but the effort is enormous, so I made my own transmitter instead using the schematic from the EF Johnson Viking Valiant.

At the moment I'm working on the VFO stage.  When the 1.75 MHz tank coil in circuit it works well,  when on a 7 MHz tank coil circuit it doesn't want to oscillate. It will oscillate if I jumped/remove R2 (56 Ohm on grid of 6AU6). Why is that? and what the purpose of R2? reducing feedback?

If any of you know what the real values of inductance on L1A and L1B? I would be very grateful.  I found L1B (1,75 MHz) by reverse engineering about 69 uH and L1A (7 MHz) about 16,7 uH.

Thank You very much
best 73, Agus.
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W4AMV
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« Reply #1 on: March 02, 2023, 08:19:55 AM »

Good day Agus. Congrats in taking on a complex project!

I would study any prior discussions you can find on this particular VFO, which is an ECO configuration.
I suspect that R2 is a parasitic suppressor to prevent spurious oscillations or frequency jumps that occurred
in the design. It will reduce the loop gain of the oscillator slightly. So when you remove it, you effectively
raised the loop gain and oscillation occurs.  If that is the case, then I suspect you do not have the same
loop gain obtained by the Johnson folks at the time of design and this heavily layout dependent.

Very, very important to keep the low frequency, DC resistance of the tank and tube interconnection as LOW
as possible. Just a couple of ohms of DCR will prevent the oscillator from starting or running over the tune range.

Schematic of that VFO section attached here for reference. Good Luck and let us know your progress.

73' Alan

 


* valiant VFO.JPG (194.84 KB, 737x540 - viewed 134 times.)
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W4AMV
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« Reply #2 on: March 02, 2023, 08:37:43 AM »

I get about twice the L value you reversed engineered for the 7 MHz range. You recognized that the feedback C total is about 200 pF... hard to read, is it 500 pF or 300 pF... anyway, the L reactance value is modified as the VFO is tuned as the VFO tank C values are in series with the L tank. So yes, this makes the L required on 40 meters to be LARGER than set by just the feedback C values. Anyway, you are in the ball park with your calculations. Maybe someone who has a Valiant open can measure the diameter and the number of turns and spacing for that VFO coil. Then calculate L.
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W1RKW
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« Reply #3 on: March 02, 2023, 11:16:01 AM »

Agus,
Take a look at this  VFO from a Ranger.  it's very similar if not the same thing.  Author discusses how it works.  It might provide some insight on your VFO.
https://www.frostburg.edu/personal/latta/ee/ranger/schematic/oscillator/rangeroscillator.html
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Bob
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His fear was when I turned it on for the first time life on earth would come to a stand still.
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« Reply #4 on: March 02, 2023, 10:21:56 PM »

Yes, if the schematic is copied 100% it is indeed complex. another thing is that there are many components that don't exist in Indonesia, such as band switches and RF chokes.

My goals are just a few bands that catch my attention are 75 meters, 40 meters and 10 meters. that way I just focus on electronic circuits involving the bands.

Band switches are the most difficult mechanical logic circuits to find, for that I plan to use relays. Electronic components I will use modern components. As an example at this time I use SMPS for tubes to supply 300 volts and filament

The modulator will use solid state with transformer modulation, which is planned to use a tri diode to avoid negative peaks.

Alan and Bob, thank you for your response, the directions and references provided, very useful and make me more excited.

I'm currently using the breadboarding method using a PCB and I'm going to attach it to a metal chassis. I will solve the 40 meter VFO problem in parallel as I will proceed at the next level: buffer, driver-multiplier and final. I will use 2 x 6146B instead of three because my modulation transformer is only capable of up to 250 mA maximum.

In the next stage I will use DDS but it's still a long time, waiting for the main transmitter circuit to run first and be stable.

I've kind of forgotten how to post pictures on this forum so I can show photos of the photos.

73s, Agus
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W4AMV
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« Reply #5 on: March 03, 2023, 09:51:54 AM »

The site Bob mentions is a good breakdown of the VFO and the Ranger. I looked at some ECO literature but came up empty on the series RC to the control grid. I decided an easy quick approach would be a simple model. The 6AU6 has a model, not perfect but provides some insight. I built a simple schematic and set the padder caps to nominal. Iterated the tank L and C to achieve center of 40 meters. I tried to choose a reasonable tuning C for the VFO and arrived at about 10 uH. The series gate R C affect loop gain. I suspect it is a method the designers used to fine tune VFO operating point and likely improved stability. You can see how the VFO start up and amplitude gets shifted with R. I had to get pretty aggressive to see that effect. The gm on the 6AU6 is good so the tank losses before killing startup were about 10 ohms. That's huge. Lower gm causes the tank losses to be quite small, 3 ohms is not unusual. I hope you find your issue with the current build.  


* 6AU6_VFO2.JPG (319.58 KB, 684x580 - viewed 117 times.)

* 6AU6_VFO.JPG (229.83 KB, 1364x579 - viewed 128 times.)
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« Reply #6 on: March 04, 2023, 12:49:42 AM »

Hi All, greeting from Jakarta

I was in Dayton Hamvention 2022 last year, I saw a lot of boatanchor there. I really want to bring them back to Jakarta but the effort is enormous, so I made my own transmitter instead using the schematic from the EF Johnson Viking Valiant.

At the moment I'm working on the VFO stage.  When the 1.75 MHz tank coil in circuit it works well,  when on a 7 MHz tank coil circuit it doesn't want to oscillate. It will oscillate if I jumped/remove R2 (56 Ohm on grid of 6AU6). Why is that? and what the purpose of R2? reducing feedback?

If any of you know what the real values of inductance on L1A and L1B? I would be very grateful.  I found L1B (1,75 MHz) by reverse engineering about 69 uH and L1A (7 MHz) about 16,7 uH.

Thank You very much
best 73, Agus.

R2 is in the feedback path and it is a parasitic suppressor but a 22 ohm should suffice. Of course C18 can a be a modern 47-50pF 500V silver mica for best RF transfer.

Phil - AC0OB
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K9MB
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« Reply #7 on: March 04, 2023, 10:08:12 AM »

I do not have any advice on the vfo, but I do have a question.
Why did you choose the Valiant- particularly?
The fact that it looks like a Ranger on Steroids give a cool looking radio dial, but then you decided to not use 3-6146 tubes, which makes it look more like a Viking II.
I personally like tue concept that the Viking II used in having a separate VFO.
Easier to stabilize it if the heat in the cabinet is stable and fairly low.

Second question. Why not just buy an ANTEK 8T800 and put it in a bridge?
A choke input filter will give you about 700volts at more than 500mA.
You could run 4-6146s with that power supply.
It would take some design arrangement, but you are not starting with a Valiant chassis. It would be different if you were trying to exactly replicate the Valiant, but that would mean vacuum rectifiers like 5R4s, so the question becomes- where do you stop modernizing?
If that line is fuzzy, then why not get a DDS generator VFO and be dome with it?
Stability not an issue and only the noise floor need be of concern, so buying a quality unit the main focus…
Or you could air freight a good Valiant in for about $1000.   Might be worth it.😉
73, Mike
Just wondering
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YB1AHY
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« Reply #8 on: March 07, 2023, 12:55:50 AM »

I do not have any advice on the vfo, but I do have a question.
Why did you choose the Valiant- particularly?
The fact that it looks like a Ranger on Steroids give a cool looking radio dial, but then you decided to not use 3-6146 tubes, which makes it look more like a Viking II.
I personally like tue concept that the Viking II used in having a separate VFO.
Easier to stabilize it if the heat in the cabinet is stable and fairly low.

Second question. Why not just buy an ANTEK 8T800 and put it in a bridge?
A choke input filter will give you about 700volts at more than 500mA.
You could run 4-6146s with that power supply.
It would take some design arrangement, but you are not starting with a Valiant chassis. It would be different if you were trying to exactly replicate the Valiant, but that would mean vacuum rectifiers like 5R4s, so the question becomes- where do you stop modernizing?
If that line is fuzzy, then why not get a DDS generator VFO and be dome with it?
Stability not an issue and only the noise floor need be of concern, so buying a quality unit the main focus…
Or you could air freight a good Valiant in for about $1000.   Might be worth it.😉
73, Mike
Just wondering

Hi Mike, thanks for sharing your thoughts. I can't answer your question, maybe I often watch on YouTube channels that do restorations.

For me the end product is not that important i really enjoy the process while immersing myself in what the designer thought of the design, doing reverse engineering and calculations. The final product maybe I just enjoy it for a while after that I store it.

DDS is already on my agenda, maybe later I will use it for CW mode

ANTEK 8T800, I can't find it in Indonesia, maybe it's a local home factory here. True, because the transformer power is quite large.

The effort to import is huge. the first is the shipping cost, the second the most important problem is regulation. I can't import used goods.

73s Agus
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YB1AHY
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« Reply #9 on: March 07, 2023, 01:02:55 AM »

The site Bob mentions is a good breakdown of the VFO and the Ranger. I looked at some ECO literature but came up empty on the series RC to the control grid. I decided an easy quick approach would be a simple model. The 6AU6 has a model, not perfect but provides some insight. I built a simple schematic and set the padder caps to nominal. Iterated the tank L and C to achieve center of 40 meters. I tried to choose a reasonable tuning C for the VFO and arrived at about 10 uH. The series gate R C affect loop gain. I suspect it is a method the designers used to fine tune VFO operating point and likely improved stability. You can see how the VFO start up and amplitude gets shifted with R. I had to get pretty aggressive to see that effect. The gm on the 6AU6 is good so the tank losses before killing startup were about 10 ohms. That's huge. Lower gm causes the tank losses to be quite small, 3 ohms is not unusual. I hope you find your issue with the current build.  

Hi Alan

sorry I haven't been active lately. taking my project to the next level is buffers and drivers.

thank you for busy making a simulation for me. I'm not very familiar with using LTSPICE, I usually design and directly assemble in the real world. i appreciate your efforts.

I think I've found the problem, tonight I'll try to re-examine the VFO circuit, I'll let you know later.
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YB1AHY
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« Reply #10 on: March 07, 2023, 01:05:42 AM »

Hi All, greeting from Jakarta

I was in Dayton Hamvention 2022 last year, I saw a lot of boatanchor there. I really want to bring them back to Jakarta but the effort is enormous, so I made my own transmitter instead using the schematic from the EF Johnson Viking Valiant.

At the moment I'm working on the VFO stage.  When the 1.75 MHz tank coil in circuit it works well,  when on a 7 MHz tank coil circuit it doesn't want to oscillate. It will oscillate if I jumped/remove R2 (56 Ohm on grid of 6AU6). Why is that? and what the purpose of R2? reducing feedback?

If any of you know what the real values of inductance on L1A and L1B? I would be very grateful.  I found L1B (1,75 MHz) by reverse engineering about 69 uH and L1A (7 MHz) about 16,7 uH.

Thank You very much
best 73, Agus.

R2 is in the feedback path and it is a parasitic suppressor but a 22 ohm should suffice. Of course C18 can a be a modern 47-50pF 500V silver mica for best RF transfer.

Phil - AC0OB

Hi Phil.

thanks Phil, I tried it with 10 ohms it still doesn't oscillate, or it stops oscillations very easily

73, Agus
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W1RKW
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« Reply #11 on: March 07, 2023, 08:32:05 AM »

Agus,
when the VFO is oscillating and you tune the VFO from one end of the band to the other, does the amplitude of the VFO remain the same?
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Bob
W1RKW
Home of GORT. A buddy of mine named the 813 rig GORT.
His fear was when I turned it on for the first time life on earth would come to a stand still.
W4AMV
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« Reply #12 on: March 07, 2023, 10:10:27 PM »

Hi Agus.

If I use your 16.5 uH, I see the VFO running at about 5 MHz. I am using all the schematic values that are shown in the design. The pad C values are at mid value and the main tank C is reasonable, 50 pF to 100 pF. I think a tank L of 9 uH would be closer.

Also there is no need at this point for placing a proper tank in the plate. You can AC short the plate and extract the signal voltage off the cathode. That is a low Z point and easy to monitor with a scope. Once you get the VFO running properly, than work out the details of the plate circuit. Also for now, put aside that series RC in the grid.

Assuming no wire or component value errors, this VFO should run well. The usual easily overlooked culprit is excessive loss between the tank network and the active element, the tube! You must keep the losses to a minimum.
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K9MB
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« Reply #13 on: March 07, 2023, 10:14:32 PM »

I do not have any advice on the vfo, but I do have a question.
Why did you choose the Valiant- particularly?
The fact that it looks like a Ranger on Steroids give a cool looking radio dial, but then you decided to not use 3-6146 tubes, which makes it look more like a Viking II.
I personally like tue concept that the Viking II used in having a separate VFO.
Easier to stabilize it if the heat in the cabinet is stable and fairly low.

Second question. Why not just buy an ANTEK 8T800 and put it in a bridge?
A choke input filter will give you about 700volts at more than 500mA.
You could run 4-6146s with that power supply.
It would take some design arrangement, but you are not starting with a Valiant chassis. It would be different if you were trying to exactly replicate the Valiant, but that would mean vacuum rectifiers like 5R4s, so the question becomes- where do you stop modernizing?
If that line is fuzzy, then why not get a DDS generator VFO and be dome with it?
Stability not an issue and only the noise floor need be of concern, so buying a quality unit the main focus…
Or you could air freight a good Valiant in for about $1000.   Might be worth it.😉
73, Mike
Just wondering

Hi Mike, thanks for sharing your thoughts. I can't answer your question, maybe I often watch on YouTube channels that do restorations.

For me the end product is not that important i really enjoy the process while immersing myself in what the designer thought of the design, doing reverse engineering and calculations. The final product maybe I just enjoy it for a while after that I store it.

DDS is already on my agenda, maybe later I will use it for CW mode

ANTEK 8T800, I can't find it in Indonesia, maybe it's a local home factory here. True, because the transformer power is quite large.

The effort to import is huge. the first is the shipping cost, the second the most important problem is regulation. I can't import used goods.

73s Agus
Hi Agus,
Well you gave the very best possible reason for build9mg anything-  because you love the challenge of getting something going and learning in the process.
It is almost,the only reason that I am an active Ham.
I own a nice Ameritron AL80B, but I am immersed im building a super low IMD
3-500z (my motivation😉) to drive a pair of 4-1000As or a pair of 3-1000z tubes in AM linear and SSB.
I can afford to buy any commercial Amp I want- but, then what?
The process is all the fun and the Old Timers and younger geniuses on this forum are more than willing to help out and that helps forge froemdships- my second motivation. It is a great privilege to get advice from literally centuries,of total experience on here. I will be a ham for 60 years-myself- in 2024 and still learning and making chuckle headed assumptions….😉
Go for it. Johnson made some beautiful stuff amd built like battleships too.
73, Mike
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YB1AHY
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« Reply #14 on: March 07, 2023, 11:15:19 PM »

Agus,
when the VFO is oscillating and you tune the VFO from one end of the band to the other, does the amplitude of the VFO remain the same?

Hi Bob.

hi Bob. answering your question from end to end the VFO frequency does change but not much around 1 Volt (RF)

73s Agus
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YB1AHY
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« Reply #15 on: March 07, 2023, 11:48:52 PM »

I think I've found the problem, tonight I'll try to re-examine the VFO circuit, I'll let you know later.

Hi Alan and everyone maybe since I'm not young anymore I've done some stupidity in soldering a VFO circuit. I assembled the VFO series with a 80 meter coil tank correctly. But the VFO circuit with a 40 meter tank I soldered the 500 pF feedback capacitor incorrectly which should be at the end of the 50 Ohm resistor I soldered at the end of Grid no1 from 6AU6.

Last night I fixed it and BOOM 40 meters immediately oscillated even though I disturbed it by touching it (the tank is not the plate) it still oscillated. R2 50 Ohm remains in the circuit. WOW how happy I was and slept well

My 40 Meter VFO CASE is closed! I obtained an inductance of 7.5 uH for the tank coil as Alan calculated.

I have another topic to confirm, that is the frequency multiplication scheme from VFO to Final. From tuned circuit driver stage to Final is easy just the same resonance frequency at working frequency. Earlier stage is still bit confused, visually i follow the movement of wafer switch and is not that easy for me.

73s Agus.
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W1RKW
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« Reply #16 on: March 08, 2023, 03:20:36 PM »

Excellent that you found the problem.
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Bob
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Home of GORT. A buddy of mine named the 813 rig GORT.
His fear was when I turned it on for the first time life on earth would come to a stand still.
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