What is a tube extension

As a power supply I quickly fetched an old one from a telephone system (?) From the basement, at least it has an ISDN plug. Just run an old ISDN socket and the terminal connection is ready. It supplies approx. 40V and 14V DC as well as approx. 55V AC, which I did not use. I operate the heating on the 14V with a series resistor. The 40V for the anode also go through as "safety extra-low voltage". Because the voltage is so buzzing, I temporarily hung a CRC element over it. Strangely enough, better reception is also possible with the second Siebelko (10,000µF).

A two-core wire is used as the antenna, which I have stretched in the living room with as little contact as possible. The earth hangs on a radiator. - Unfortunately, while I was writing, I remembered that it has plastic connections, but it worked anyway.
Last night I listened to some stations, including Deutschlandfunk, BBC, Radio Slovenia (or something like that), which was Italian, Russian etc ...
This morning the reception was much worse. Unfortunately, you have to constantly readjust the feedback, it works with the core, but a second Dreko would be nicer, as has already been noted.

I have now drawn the circuit diagram:


The whole story is emotionally quite "low resistance", but those are the available values ​​from the box.
I also tried adjusting the feedback using a trimmer. You can either swap the 270k with the 100k trimmer or connect a 10k trimmer parallel to the coupling coil, then the feedback can also be adjusted via the trimmer.
However, when you touch the trimmer, the resonant circuit changes and the overall sensitivity seems to decrease, which is why I preferred to tune the coil core again with a long screwdriver.

The trimmer as a volume control did not do that much. You can use the 100K trimmer as a grid lead-R to place the LF from the coupling capacitor on the tap, but it should be a logarithmic potentiometer. The volume can be adjusted via the feedback anyway.

I'm trying to clean the contacts in the ultrasonic bath tonight, there wasn't much time on the weekend, the garden and girlfriend were more important ... GS's idea of ​​using shampoo sounds very plausible, the stuff sometimes really "squeaks".
The EF98 have also arrived, let's see when I can try something, an EL95 power amplifier should also be tested.
- So much for me about the "Polytronic" project.

Greetings, Tommes

Wolfgang Holtmann put the following circuit diagram in the forum with the following words:

Today I rebuilt the "Triodon" audio circuit with 2x EC92 and Ub = 42V.
I was able to find confirmation of my proposed change requests. Greetings, Wolfgang Holtmann