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Author Topic: If you were going to build a tube CW xmtr for HF what tube line up wld you use  (Read 1903 times)
AK0B
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Posts: 269




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« on: December 02, 2017, 12:12:58 PM »

I have been considering many different ones in the hand books an old issues of QST.  I have, 6AG7, 6L6, 807,1625 and newer tubes 6CL6,5763 available.

Expect it will have Pi network, but have coil forms so could be something else.

I want a good oscillator and no clicks or chirping.

Let me know your choice.   Thanks

73, AK0B  Stan
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G3RZP
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Posts: 8142




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« Reply #1 on: December 03, 2017, 02:46:41 AM »

6SJ7Y or 6AU6 high tuning C, low inductance Colpitts electron coupled VFO. 6C4 cathode follower, 6AG7  or 6CL6 buffer/amplifier, 6AG7 or 6CL6 multiplier, 807 (or two or three of them) in the PA.

Or there are more complex ways, mixing a crystal and VFO, which can be really chirp and click free.
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KM1H
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Posts: 2622




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« Reply #2 on: December 03, 2017, 07:09:56 AM »

12AT7 Vackar VFO, 6V6/6AQ5 buffer-multiplier, 6V6/6AQ5 amp-multiplier, 6146/807/1625/4D32 final should cover 160-10 with 40-120W out and 600-750V on the anode. With the driver stage having a screen voltage control a huge range of finals can be used. The first 2-3 stages can also be used as the full TX if 5-10W is OK

http://www.w7ekb.com/glowbugs/VFOs/vackar_vfo.html   A 6SN7 may work, Ive only used 12AT7's.

A few seldom seen output tubes these days would be 814, 815, 829B, 5894, 8072 with the latter a sleeper requiring a scrapped Motorola UHF TX/RX or Heath SB-230 for socket and BeO thermal block.

Carl

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KC2ZFA
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Posts: 22




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« Reply #3 on: December 03, 2017, 09:09:28 AM »

the first question should be what bands one wants and how
complex a transmitter one is willing to brew.

Peter
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KM1H
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Posts: 2622




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« Reply #4 on: December 03, 2017, 01:45:49 PM »

Quote
the first question should be what bands one wants and how
complex a transmitter one is willing to brew.

Only ONE appears to care for now.

My reply covered many bases for thinking about and the details can come once they are digested.
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AE7TE
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Posts: 57




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« Reply #5 on: December 03, 2017, 10:50:25 PM »

6C4 oscillator buffer - I'm using an outboard signal generator for a signal source. The plate voltage on this stage would be low enough I'd be able to use it with modern, HC-59 crystals if I had to.

6CL6 driver. Multiplication would be available but not necessary.

6DQ6B final. These tubes are robust and would give me a good 20 watts on any HF band.

Ed
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N2DTS
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Posts: 744




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« Reply #6 on: December 04, 2017, 05:32:43 AM »

I would think the tube line up matters very little, its the design that counts.
The 6C4 makes a good vfo tube at low voltages, I use one for my receiver LO and its very stable, and works down to something like 10 volts on the plate!


I use the lo circuit as a vfo for transmitters as well.

For the output tube, a tube with a plate cap works much better then an audio tube as you can keep the plate and grid separate.
All you need is a LO tube, a buffer, and an output tube (2E26, 6146, 807, 1625) to get 30 to 40 watts out.
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KX4OM
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Posts: 210




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« Reply #7 on: December 04, 2017, 09:36:29 AM »

Stan,

6CL6 oscillator, 5763 amplifier. Because the 6CL6 is the modern version of the 6AG7, which is the best tube to use for low crystal current (in the right circuit.) It will handle HC49-U crystals. The 5763 because I used it in the 60-70s handbook "Novice Special" back in 1972, and because I have several of them. If I decide to go with a 3-tube rig, a 5763 driver (I would key the driver) and 6DQ5 PA, which is currently $12.50 unused at my favorite tube vendor:

http://www.pacifictv.ca

Ted, KX4OM
« Last Edit: December 04, 2017, 09:43:28 AM by KX4OM » Logged
GW3OQK
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Posts: 394




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« Reply #8 on: December 04, 2017, 11:05:07 AM »

Stan, for me a small chirp is an advantage for it says "I am a home-brewer or using vintage gear" which attracts like minded folks for a ragchew. I have a rig with 5763 VFO, grid-block keying for full break-in, and it's stable enough on 80 and 40.
Good luck, 73
Andrew
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AK0B
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Posts: 269




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« Reply #9 on: December 04, 2017, 02:30:33 PM »

Several good suggestions. I like the idea of running low plate power to allow the use of current crystals.  I do have a good supply of old WWII ones.  A 6C4 or 6CL6 will be my oscillator unless i find a good 6AG7 in the bottom of my tube box.  5763 I like for the 2nd stage.  I also like the idea for grid block keying. I have to chuckle at the idea for a little chirping. Final - I am leaning toward what ARRL calls inverted amplifiers.  I think any amplifier with a driven cathode should be called ground grid even if does draw a few mills via a resistor.  Might be a fun place to use a 829. I am only interested in 160, 80 and 40.  I expect 30 would be close enough my coils should be able to tune 30 meters.  I don't have a suitable modulation transformer for AM unless I went with cathode modulation of the final. I have good variables so I could use push-pull as the final stage. If i use the 5763 which I like for the second stage it would look funny with a 6AG7 for osc and 807/1625 or 829 final.  Should use a 6L6 their instead I think. Decisions - decisions...   

I have a good junk box; back in the early 80s I started picking up parts for that rig I would build when I retired. Never did really retire.  It is boring as hell.  I have R390 which I could use as the companion receiver. 

Appreciate all the good ideas. thanks.

Stan AK0B
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KX4OM
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Posts: 210




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« Reply #10 on: December 04, 2017, 04:04:59 PM »

A 6C4 or 6CL6 will be my oscillator unless i find a good 6AG7 in the bottom of my tube box.  5763 I like for the 2nd stage. 
...

If i use the 5763 which I like for the second stage it would look funny with a 6AG7 for osc and 807/1625 or 829 final.  Should use a 6L6 their instead I think. Decisions - decisions...

Stan AK0B


You might look for a design using the 6AG7 oscillator, a 6V6 beam power tube for the buffer/driver, and 6L6 or 807 or 6L6 beam power tube as the PA. The cost is going to creep up if you use the 6L6 and even the 6V6. Check Pacific TV for prices. 807s are not currently available from them.

When I was the editor of of a QRP magazine, one of my favorite projects we ran was a rig using a 6AQ5 beam power tube as the PA, and a 6AQ5 as the oscillator. It was from a long time ham who was experimenting with QRP design for the first time. The GE data sheet shows it to be the equivalent of a 6V6. I got so excited when I reviewed the design for publication, I ordered a few of the 6AQ5 tubes Smiley

Another tip: while you are deciding on your project, check out the prices of used and tested tubes. The prices for the 6AG7, 6V6 and 6L6, for example of octals are really low from PacificTV. They test before shipping. Once you have it built and working, then you can spend the bucks for the long run.

You probably have looked at some of AA8V's designs.

If you are not 12V-averse, check out the "Inexpensive 75 Watter" from the 1964 ARRL Handbook. 12BY7 oscillator and 1625 PA, each with regulated screens. I have a clone of that rig, including the plug in coils in cans, and the meter propped up front center of the chassis. My chassis is painted black, and the last time I plugged it in, I blew a fuse, so it is in the refurb stack of projects. 'Round tuit, whenever.

Ted, KX4OM 
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WA5VGO
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Posts: 39




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« Reply #11 on: December 05, 2017, 07:23:57 AM »

Although it wasn't used as often as the other mentioned tubes, the 5763 is an equally effective crystal oscillator. Many years ago I ran tests replacing the 6V6 in a Globe Scout with 6AG7, 6CL6, 12BY7 and 5763. There wasn’t any meaningful difference between any of them. However, all of them were vastly superior to the 6V6. I suppose the 5763 wasn't used more often for oscillators because they weren’t as available and cost a bit more.
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K5DH
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« Reply #12 on: December 05, 2017, 10:43:13 AM »

6AG7 crystal oscillator and 6146 PA based on an old ARRL Handbook circuit.  I'm about to start constructing one!  I think I have all of the part kitted up for it. 
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WA2ISE
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« Reply #13 on: December 05, 2017, 01:05:17 PM »

I'd use the "antenna" grid of the 6BE6 as the grid that could turn on and off the oscillator output, ie, where to do the keying.  The oscillator keeps running, so that should avoid chirping.  The key would ground out a negative bias on this grid, thus allowing the oscillator RF to get to the plate and then to the output tube. 

I vaguely remember an article in a magazine like 73 or CQ, how to build a "pennywhistle" novice CW transmitter.  A "hot chassis" design, only issue is to how to key it without the key being "hot".  Assuming a solution to that (maybe a relay driven by the key and a battery), you could use tubes from an old AM tube radio, the 12BE6 the xtal osc and keyed gate, the 50C5 the power output stage (capacitor coupling to the antenna) , 25w4 the rectifier, and maybe use the 12BA6 as a low power rectifier to develop the negative bias to cut off the RF in the keying circuit above. 
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N2DTS
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« Reply #14 on: December 06, 2017, 08:54:26 AM »

I can likely help you with any parts or tubes you need to build the rig.
I like a vfo, but crystals are easy to do....
Changing bands with a VFO circuit is a bit more complex then crystals....

This is my homebrew exciter/transmitter, its very stable, and keys well as the VFO operates all the time, its just well shielded and the buffer tube is keyed:



Only does 40 meters though...
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