Speaker transformer is an Astor part probably from the 60's

Yes, that transformer looks correct for the radio.

In order mainly to save on cathode resistors & reduce cost lots of strange things happened.

The back bias was a way of developing a fixed bias using the current from the cathodes, in most cases the voltage between CT and chassis was that of the output tube. The current draw of the tubes had to be right for it to be right. Also making it handy for diagnostics.

The individual cathode resistor is "self bias" and that sets the tubes bias relative to the cathode.

The CT is the most negative point in the set. Therefore the chassis is positive relative to it and the grids negative.

Do note most of those speakers are "mid range" and that does have an effect on how low and how high they can go, which is not Hi-Fi.

This has been really educational all around. I think I’ll drop the back bias cap slightly as occasionally there is a bit too much bass making the speaker bottom out / Rattle but overall it sounds about as good as you’d expect for a 1950s mantle! I can easily adjust tone too with the adjustable resistor I put into the ‘bass boost’ - but that really only touches the super high frequencies.

Reception isn’t great but I have that issue with all the mantle radios I’ve tried here - the Kriesler stereogram is the only one that is nearly distortion free with the reception here. (I tinkered with the antenna trim too but that was pretty much spot on).

Incidentally since I know a bit more about the cathode bypass caps I revisited the Kriesler & note that I replaced the two output tube 25μF with 22μF - I didnt appreciate the affect that could have at the time….so I put in some 30μF and gee it vibrates the floor now!

Deaf sets are normally related to poor antenna's (less than 25ft) and IF alignment, which is recommended if you mess with parts in the IF: Which is unavoidable.

Speaker may be overloaded or there's a "motor boat" (oscillation). There should be no DC component from a speaker transformer to cause pulling in. Correct polarisation on DC pushes the cone outwards.

I think the speaker was a little overloaded - I tried a 10μF instead & it is a good balanced sound now.

My antenna is only about 5ft so I need to work on that but the reception here isn’t great on any radio really - the Kriesler is the best but that could be the inbuilt ferrite rod antenna it has.

Incidentally while working in the Mickey again I turned on the hmv little nipper to listen to & realised just how bassy the Mickey was by comparison….

So not being able to help myself I increased the bypass cap on the hmv to a 30μF instead of 25μF - and now it sounds quite similar to the Mickey! It doesn’t have the ‘bass boost’ though so I guess listening loud may distort but these radios aren’t really for loud listening anyway...so thanks everyone I have some great sounding tube radios to listen away to

City dwelling is not good for radios; Lots of RFI.

My biggest source of RFI is RF riding on the mains & lightning and it creating spikes. That means filters on mains lines, along with MOV's to kill the spikes & surges.

Bench antenna is around 37m on dedicated poles. Insulators and fittings: Electric fence. Tied to ground in thunderstorms to disperse lightning.

Marc