World Designs KT88 amplifier

[Murphyv310]

Looking good Trevor not only in looks but function too.  I have tried all the various hum reducing techniques in the past, most more trouble to wire than the reduction they give.  One of the simplest was a 'hum dinger' where a 100 ohm pot connected between the floating heater wires and the slider down to the star point earth.  I must admit never tried them with an EF86 renown for being fickle where noise is concerned especially microphony.

Dave.

Thanks Dave.
I must say that I've never had any problems with the EF86 and like the EF37A it is a low micro-phonic valve.
I have tried DC feeding the heaters, that along with different smoothing values have resulted in virtually imperceptible hum. I have two GZ34's each rectifying the opposite phases from the mains TX, the anodes are strapped with 50 ohm limiters, the Reservoir is 47 uf and the smoother 100uf both rated at 500v.
The changes on the 5-20 circuit are:
C5, 50uf. C4, 10uf. R14 & 15 500 ohm otherwise as the Mullard diagram