Skip to main content

Acorn Tubes. QRP with tubes that are only a bit bigger than fat Transistors

 














Acorn Tubes are really small tubes that were designed during WWII for use at UHF frequencies. I got my 1st Acorn Tube when I bought a WWII surplus Radiosonde Transmitter. 


Needless to say, long ago, when hams would build things and not just do contests, POTA/SOTA or plain operate, these Acorn tubes found their way into homebrew QRP CW transmitters. Several years ago, I even saw a radio set using an Acorn Tube CW Transmitter complete with a matching Regen Acorn Tube Receiver. What a hoot.



Rex Harper, W1REX, during the virtual 2020 FDIM Buildathon (you know that COVID 19 Crap) used this schematic as the project foundation. I think it got close to a watt output with this lash up.

I didn't participate in that event but did build my version using scrap stuff I had lying around the garage. The tube filaments are wired in series so I could simply supply 12 VDC through a three-terminal regulator. 




Since Cycle 25 has been sub-par (a highly touted but major disappointment) and given the MUF yesterday was no higher than 30M then this jewel would be FB on 40M.

Before anyone gets their underwear in a knot about high voltage DC and the need for a special power supply... Think 20 Transistor Radio Batteries in series. The current draw is less than 10Ma so as they say in Italy -- Non è un grosso problema.

Or in plain English -- "Ain't no big deal". I checked Amazon and twenty 9VDC batteries cost less than $15.

An overwhelming resource on simple vacuum tube receivers can be found here thanks to K3UH. You could get lost on his site for weeks at a time.

Band conditions are supposed to be better today so maybe we can test the ZIA. The MUF is better but unsure about the other one.

Them that know can make things go.

73's
Pete N6QW


Popular posts from this blog

January 26, 2024. A simple CW Transceiver/Transmitter

Cruise through the lower part of the ham bands bands and what do you hear? Well, FT-8 and CW. Often you will not hear any SSB stations yet go to the lower part of the bands, and it is a cacophony (I love that word) of bad sounding signals and some high-speed keying. Fast is not so much of the issue as is bad, run together and jerky keying. But none the less our hobby started there.    So, you could crank down your ICOM 7300 and watch the waterfall on CW or you could homebrew a radio. Actually, to do CW right you need more thought up front than you do with a SSB transceiver. Often, I will state that a CW Transceiver is much more difficult to build than a simple SSB rig. I published two articles in QRP Quarterly on CW transceivers and all I got was a yawn so maybe history will repeat itself.  Yawn!   30M CW Transceiver with RIT!   Of interest is that the LO is a Varactor tuned LC oscillator using a NE602. Look closely at the RIT circuit which is only activated on ...
Read more

March 31, 2024. Happy Easter to those who celebrate this day.

What a great day to Binge on Chocolate and experience the pain of that filling that has been leaking.  I would be in that category with the leaking filling(s) had I not just spent an amount equivalent to one of the fancy new uptown appliance box transceivers on two filling repairs. Well at least I can binge on the Chocolate bunnies without fear of pain. Regrettably everything appears to have jumped in price including the price of parts. Well not so much the parts as the shipping costs.  That notably is seen in the eBay treasures. I spotted a nice heathkit DX-20 for about $50 and the shipping was $65. Likely it is a twofer with part being a way to in effect charge a higher price by inflating the shipping and in part by increased shipping costs. Shipping with insurance across the US was about $150 for this jewel and that was three years ago. 6AM on the Left Coast ~ 20M Easter Sunday! My only hope is the cost of Chocolate Bunnies remains steady although a pound of See's Candies f...
Read more

August 30, 2024. A PNP 20M SSB Transceiver

Shown below is the Block Diagram for the 20M PNP SSB Transceiver steered in the  Transmit Mode . The components shown in the dotted block are relay steered so that the block module is single pass and amplifies in a single direction. The Block diagram show steered in Transmit.  Essentially the steering process works so that the IF Module input follows the Balanced Modulator on Transmit and then the input side follows the Receive Mixer on Receive. All done with some relays and a bit of RG174U coax. For those who count things in detail, this block diagram is not unlike what was used for the PSSST Transceiver which can be found on my website . Yes, a warmed over P3ST only using PNP devices. TYGNYBNT. 73's Pete N6QW
Read more