My recent adventure with Vacuum Tubes suggested the theme of todays' posting. Yes, CW transmitters. Who does CW? Well, not a lot of hams but it is like climbing Mt. Everest... some make the effort.
I am appalled at the cost on junk type CW transmitters on eBay and even after spending a King's Ransom for one you are not done. Many of the parts like capacitors have reached their end of life and likely the tubes are flat. So, more costs.
There is a bonus to building a homebrew CW transmitter and that is the low cost, small sized power supply from Amazon. You can buy a supply for less (a few pennies less) than $30. There is enough juice in that supply to deliver more 5 to 10 watts to the antenna. That will net pages full of contacts! The linear hunk of iron supplies cost a fortune but with this Amazon supply... it plain works and NO SWITCHING noise in the receiver. You don't have to hit send as I am sure that was a burning question. In one of my earlier blog posts I covered that supply.
There are plenty of good candidate tubes for such a rig and I recommend two: the 6AQ5 as the oscillator driving a 6DQ6 as the final. RF Chokes used to be a problem but with the FT-82-43 cores and 73 Turns of #28 you have an instant 2.5 Millihenry choke. The Mini-Ductor stock can be replaced with the T-68-2 powdered iron cores which easily will take 10 watts (or more). BTW the Amazon supply also provides 6.3VAC at 5 amps which is plenty for the filaments.
A 40M Starter Transmitter
Here is the reason why I suggested the 6AQ5 as it can be used as a standalone rig and then once that is working you can add the 6DQ6 for more power.
If I am not mistaken the older ARRL handbooks (before the handbook became an advertising medium for "Foreign Radio Manufacturers") used to have such a design and it was quite popular.
I replaced the Air-Dux Coil with 22T #20
on a T-68-2 Core and a Better Match!
Since crystals from AF4K cost about $26 I suggest getting the Frequency 7030 kHz as later on you can build this same circuit as a oscillator doubler and now you have two QRP frequencies... 7030 and 14060 kHz.
For those who have two left thumbs or are just plain lazy the Antique Wireless Association (AWA) sells a 6AQ5 Transmitter PCB on eBay for about $14 and one You Tube video of the AWA rig uses the Amazon power supply. So, no excuses.
Them that know can make things go.
73's
Pete N6QW