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Author Topic: Seeking assistance with 1965 ARRL SSB Tube transmitter project in 2014  (Read 7863 times)
KB1GMX
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Posts: 772




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« Reply #15 on: February 26, 2014, 04:33:41 PM »

I'm iwth W8JI.

Your picture of it inside the shield is good.

If a loading resistor is needed I'd put it across L5 as the right value may
vary depending on the band.  Also the 6CL6 might benefit from the
added loading. 


A general comment.  Transmitter layout is one of those simple things.
Signals should flow in a linear fashion from low level end to the power end
in a direct way.  Shielding is used to keep the ins and outs apart.  Also
subtle things like socket and coil location and orienttion can result in
shortest path and most direct routing without crossings.  From all
appearances the 6dq5 pin one is near the rear (the right of the picture)
yet the  6CL6 is to the left.  It would seem rotating the tube 90 degrees
makes the layout smoother especially if L5 and its shield is situated
between them.  Looking at the article pictures (magnified) tends to
make that a little clearer, but the article gives little direction.


Allison
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W8JI
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Posts: 9296


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« Reply #16 on: February 26, 2014, 06:56:11 PM »

I thought about that, but then thought it wasn't such a good spot. That tuned circuit:

1.) has a 300 pF cap to ground, which means any resistor there will not load the circuit at all on low frequencies 

2.) depends on the high impedance of that parallel circuit to invert phase for neutralization

I am a little nervous about VLF stuff in that circuit with all the extra large chokes and a fairly large neut cap. I'd feel a lot better for now de-Q'ing the 1 mH on the grid so it is meaningless.

With a narrow band neutralization system like that, he is best to keep the loading at the grid. If he has a gain flatness issue, there are many ways to handle that. I'd get it stable with minimal effect on other things for now.

 
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KB1GMX
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Posts: 772




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« Reply #17 on: February 26, 2014, 07:41:15 PM »

W8JI

The choke is already low Q (Likely under 50) but a 10K across it would be safe.

The 300P to ground is problematic as on 80 its likely too small and on 15 its
maybe a bit large.

The parallel tuned circuit can be fairly high and still loaded (typical in some of
mine were around 33K).  It helps the 6CL6 as sometimes that critter needs a
bit of neutralization, an example of that is the HW101.  The Tempo-One also
loaded the pate of the 12BY7 driver.

The additional problem is the plate of the mixer, grid of the driver and the plate
of the driver are all gang tuned.

I haven't seen enough pictures but subtle layout issue can make the whole amp
an oscillator.  I've seen over the years at least two copies of that TX. one was a
clone of the article and worked with only added bypass caps the other was "laid
out better" and took work to tame. It needed more screening and any changes
in layout are suspect.  In both cases the number and placement of bypass caps
were wanting and many needed were not shown in the schematic.

There was a design variant of that as a transceiver for 40M in the Mobile Manual
and Handbooks.

Allison
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G3RZP
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Posts: 4567




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« Reply #18 on: February 27, 2014, 03:06:27 AM »

There was an article in QST years ago entitled, if I remember correctly, 'Just like QST except....' and it went into problems people have by substituting or changing parts.

KW Electronics in the UK produced a copy of the Swan 350, but so it wasn't so obviously a copy, turned it through 90 degrees - producing a form factor more like Drake. The  transceiver wasn't brilliant in performance and had a reputation for being a bit  unstable. It drifted just like the Swan, too!
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KC9KEP
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Posts: 208


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« Reply #19 on: February 27, 2014, 06:28:05 AM »

Copious thanks again for all the help!  I’m totally amazed by how much “tribal knowledge” that is required to bring these ARRL projects to fruition.  (I guess the information is there if one scours the handbook thoroughly enough and reads between the lines?)

Today, I paralleled the 1 mH choke with a 2.2K 2 Watt resistor.  I do not see any more self-oscillations.
I could not locate a 0.5 uFD capacitor in my junk box, so I simply tried the addition of the resistor.
I will continue looking for an appropriate capacitor.

My front panel meter says that the 6DQ5 is drawing 30mA as recommended in the calibration instructions provided in the Handbook article.  I measure no grid current being drawn.

Here are some images .. Please let me know if anything looks grossly out of order.

Addition of the 2.2K @ W resistor.

http://www.bignick.net/ssb/2200.jpg

Output power into 50 Ohm dummy load (CW Mode)

http://www.bignick.net/ssb/watts.jpg

Output as viewed on a spectrum analyzer (CW Mode)

http://www.bignick.net/ssb/rigol_.jpg

AC Line power consumption with key down (CW Mode)

http://www.bignick.net/ssb/amps.jpg

View of under side of chassis.

http://www.bignick.net/ssb/under_.jpg

When I had built this transmitter, I had tried to follow the mechanical layout as illustrated in the Handbook.  (I can see now where some of my component location choices were poor.)

Thanks again gentlemen and 73,

--Tom KC9KEP
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KB1GMX
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Posts: 772




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« Reply #20 on: February 27, 2014, 03:36:20 PM »

That last picture is nice.  Nice construction.

I would hope that now you have acquired some of the knowledge and the next project
will be less troublesome.   


Allison
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KC9KEP
Member

Posts: 208


WWW

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« Reply #21 on: February 27, 2014, 04:07:13 PM »

Allison,

I hope so too .. But outside of chasing Neutralization and employing better component
layout, I don't know how I would have developed that solution that W8JI graciously supplied.

A big issue for me is my unfamiliarity with how this equipment should behave.  Someone with
experience (such as you fellow eHam participants) can take one look and spot trouble.

There aren't many people that are familiar with this technology any longer.

Anyway, this allows me to go on to the nest steps of getting on the air with this gear!

Thanks again,

KC9KEP

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KB1WSY
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Posts: 776




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« Reply #22 on: February 27, 2014, 04:25:43 PM »

This is amazing stuff, all of you. I am in awe.

73 de Martin, KB1WSY
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W8JI
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Posts: 9296


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« Reply #23 on: February 27, 2014, 07:48:40 PM »


There aren't many people that are familiar with this technology any longer.

Anyway, this allows me to go on to the nest steps of getting on the air with this gear!

Thanks again,

KC9KEP



I'm glad it worked out.

If the rig has any gain-flatness issues, we can work them out while improving IMD at the same time.

When I was 11 or 12, I wanted desperately to be a Ham. We were very poor, with dirt floors in some rooms, so I had no choice but to build things. Since I couldn't buy parts, I had to get them from the dump and from people's throw away stuff.

Since I wanted to get on the air, and I could not copy any article, I had to read and experiment and learn how this old stuff worked.  It kept me alive and out of trouble, most of my friends were dead by the time I was in my 20's. This is why I really love seeing someone else build stuff from that era. I'm just so envious of you, Tom, and the neat work you do.

If you lived near me, I'd be a real pest. We'd start a new company, like Collins. Smiley
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