Dave thanks for the video. Great stuff. I'll contact the folks at ARBE today.

Great! Tell Pat I said hello!!

There are some very interesting issues that crop up using semiconductors to replace tubes.

Although the Fetrons were a good commercial example, they would not behave normally in some circuits to replace the tube they were intended to. Specifically the effect that occurs when the "Grid" terminal" is taken positive with respect to the "cathode". In a tube there is soft diode conduction, with a semiconductor it is a sharp knee. In a circuit such as a local oscillator with the usual grid bias established by grid current on peaks, they malfunction. You can read about this in the article I wrote on the World's only All Fetron Superhet Radio that I built to evaluate the Fetrons:

https://www.worldphaco.com/uploads/WORLDFETRON.pdf

One other peculiarity is Fetrons must have an earthed body in an RF application. Also I discovered that the isolation of the Fetron, output to input, created by the Cascode variant configuration in the device, was not quite as good as the screen grid pentode it replaced.

Whether any solid state tube replacement works for some type of tube, depends on the application that the tube being replaced is in. For audio it is easy. When it is an RF application it is much more tricky to get all of the parameters, including things like the Miller capacitance correct to match the tube. Then there are power dissipation issues to consider too. You can end up with a situation where in some circuits, the "semiconductor equivalent" could become HF unstable.

So really what is required, for any semiconductor replacement is a full set of graphs to show how it replicates the tube, including what happens in a "grid current" scenario too.

If the requirement is only to make a substitute, say for audio frequencies, the task becomes dead easy and can simply be done with a couple of high voltage NPN transistors, have a look at the E6U7 which is a plug in replacement for a 6u7 tube, but only at audio frequencies:

https://www.worldphaco.com/uploads/Soup ... the_ZC.pdf

Clearly, the logical thing to do in many cases, to avoid all of the troubles that can occur with a semiconductor replacement device, especially an uncharacterized one, is to attempt to find another tube with similar operating parameters, change its base and make arrangements for the correct heater/filament voltage, and a more predictable result will be attained.

Great article

For the $20 difference, I'd just buy a WD-11.

All this input is priceless to me folks. Thank you so much!
The tube kits arrived the other day and I will be doing an unboxing to operation video soon. I am also going to buy the adapters and tube substitutes as well as buy two WD11's (if I don't have to mortgage the house to get 'em).
This way I will get comparisons among the three options.
If anyone has suggestions on what to add to this video, I would appreciate the input.
Thanks for everything folks. Keep it coming!

Rob, real curious how these kits work out. Mr Tell never
responded to Jeff's question on how do the kits work with
regeneration.

While his video shows that the kits work, and work well,
he picks up 3 or so stations with good volume, but never
touched the regeneration control. He controlled the
volume by the filament only. Just makes me wonder.

Jmho. but if you want to experiment, go for it. Seems
like a more viable solution would be to use the UX99
with an adapter. Pretty sure you'll prove this is the best
alternative to WD11's.

try the ux 99, and the 864 tubes; so many different combinations out there just check ebay, a mini 3A4 in an adapter as well.

Well folks I wasn't able to do a video on the tube kit but I did get the kit and finished assembly tonight.
Assembly was fairly simple which is a pleasure in itself. I started by assembling one of the tubes and trying it out in my aeriola sr. Which provided poor results. This I attributed to my own limited experience with tube substitutes.
I then assembled the second tube and plugged them into the radiola III.
At first results were poor producing a heavy motor boat sound. This is because I had the regeneration control set too high.
I turned the Regen control back to zero and slowly adjusted the filament until I heard static. Turned up a little more and it came to life. I had our local villages radio station but it took over the entire dial. After adjusting the antenna connection to long wave single circuit things got way better. Now I was grabbing signals all over the dial.
While the filament adjustment appears to control the volume, the Regen control also controlled the volume to a certain extent. Too much Regen and your ears take a hit.
Slow small adjustments and the experiment seems to go well.
Bottom line is that this is a success but definitely different from traditional vacuum tubes. This kit is definitely worth the money even if you just buy the kit for experimental purposes .

Rob,

Thanks for the info. Good job. Now, at least we know that
they work. JMHO when considering substitutes for the
WD11's, regeneration seems to be the elephant in the
room. Many alternatives have too much gain to be
controlled. Without careful control, the subs break into
uncontrolled oscillation.

Thanks Rob!

My 864 tubes arrived today so I plugged them in with the adapters I bought from the ARBE III site and performance improved greatly. Much more authentic control.
I only have one good WD11 (in my aeriola sr) and the cost is too prohibitive to buy a second so I'll wait until a good deal pops up.
The 864's will do just fine!
I'm thinking about making adapters out of the 2 dud wd11's that I have. Thoughts anyone?

If the dud wd-11's have the large Bakelite base, it is easy with a round ring mount 4-pin socket. The socket will nest inside, using some #12 or #10 solid wire and creative orientation of the new socket, the socket as an assembly with solid lead wires can slip into the cleaned pin holes of the wd-11 Bakelite base. Solder the protruding leads, snip, then file smooth.

Thanks Chas. I'll give it a try as they are the large base
Her is a pic of something adjusting. I discovered a small issue when I was putting new decals on my aeriola. Can you see what I see? Lol

Oops 1, 2, >>8<<, 4, 5, 6, 7, 8, 9...

Doh!

I see autocorrect has butchered my post again! Ugh

Thanks for posting your remarks about the tube substitution performance.

Who was the vendor of that infamous "Tickler" dial plate decal?

Radio daze

Correct. Ain't it a hoot