First air gap output transformer listening tests

At your risk. Safety precautions should be followed. Any voltage or current can be dangerous. A fuse should always be used in series with a battery.


The core used is made of 2 E type 3C85 ferrites.


Electron tube used is DC33 triode connected.


V filament is 2.8V from 2 AA rechargeable batteries.


Just about 30V was tried on the anode trough the output transformer. Anode current is just about 2mA.


To Have and Not to Hold - Madonna song was playing in CD.


A 1:7 Sowter microphone trasformer gets the signal from Walkman CD player line out bridged mono to grid through a coupling capacitor. Centre tap of filament is connected to ground Vb minus. Grid was most of the time floating at space potential or through a 10MΩ resistor to cathode or anode.


First the Sowter SK05 output transformer was connected.


Speaker is the Zeiss Ikon baffle with 7in Dew drive unit or the linoleum Pleiades Auratone 5C type with Tesla 5in.


Sound level is very low as expected but the quality is exceedingly high. Compared to the one transistor Pleiades BD139 power amplifier connected to a non air gaped transformer there is a velvet quality without any compromise of bandwidth. Like being in another planet.


The Tesla 5in linoleum speaker sounded even less loud.


Then the ferrite about 5cm x 5cm transformer was connected (much smaller than the Sowter transformer).


While the 2 Es were separated by hand it was amusing to hear the bass disappearing due to the decrease of primary inductance (Pleiades filter).


It was also very amusing once the 2 Es touched how difficult it was to separate them due to the DC quiescent current magnetization. Class A operation means electrons flowing all the time. The amplifier is single ended so DC (0th order) does not cancel, 2nd harmonic distortion does not cancel, 4th harmonic distortion does not cancel so everything good does not cancel. Why should DC magnetization be a good thing? Could it be that domains do not have to reverse direction while music is playing?


It was also amusing to hear a buzzing sound once Es were separated closely and hand feels the vibration. A thicknes of ordinary A4 paper was placed between the 2 Es on one side of them only. Sound was nice. For the moment it is left as is.


Sound was somewhat more clear than the bigger transformer. The bigger transformer had somewhat more bass and perhaps going a bit more at the highs.


Promising result.


An ordinary type of cathode resistor bias would be possibly tried with more potential at the (plate) anode.