Reflex receiver sensitivity, normal work regimen

Hi!

I am restoring a reflex radio from year 1938. It is made in Estonia by RET. Model name is "Sangar" or "Sangar 1" (the model does not exist on Radiomuseum yet) Originally it had 5 tubes. one to rectify anode voltage, probably 80 (original transformer and power supply is lost unfortunately), 6A8G as a mixer tube, 6B8G as a IF stage, detector and first audio amplifier stage and 6F6G as a Audio power tube. There was also a Magic Eye, but I am not sure what was the original tube. Some sources say it was Philips EM1. 

So, what have I done so far is, a replacement of all electrolytic and paper capacitors, potentiometers are cleaned, and circuit diagram is drawn, as RET factory archive was destroyed during the war. No official circuit diagram remain. most inductors, capacitors and resistors left in circuit were measured, bad ones replaced. It doesn't give any quarantee that no bad elements exist, as some elements may fail in rather curious way. Audio amplifier tube works. IF is readjusted with the help of generator and oscillograph to 128kHz as a most probable IF frequency. Original IF frequency is not known unfortunately.
IF tube is Mullard 6B8G, 6A8G is replaced with russian 6A8. And Audio tube is also russian 6П6C.

But I am stuck with interesting problem in IF stage. I made a video about that video to be more clear. I speak there in Estonian, but the situation is clear anyway.

I explain it here:
First, radio is turned on, it warms up and very weak signal is heard. Oscillograph gets its signal from IF stage output. There is almost no clear IF signal visible either.
But, when I touch one of IF transformers (second one, connected to anode of 6B8G) audio becomes suddenly loud and clear and also strong signal appears on oscillograph. Receiver becomes much more sensitive. When I take my fingers away it remains loud and clear.
Now my question is if that effect is simply due to IF stage self oscillation which was induced by my fingers, or is it some tube specific effect, like DC regimen change? 
Has anyone seen similar effects?

video is here:

youtube video
 

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Hi Peep,

you will have a better chance to get an answer, if you first add this model to our database. When accepted, please add your circuit diagram to the sheets section and add some pictures of the chassis and the housing. When done, start this thread again at the model page. Without knowledge of the circuit, it's hard to find out, why the oscillation does not start properly.

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