View Single Post
Old 14th May 2018, 12:23 pm   #35
GeorgeChristofi
Triode
 
Join Date: Apr 2018
Location: Northampton, Northamptonshire, UK.
Posts: 41
Default Re: Jonell Radio. A cheaper version of the Ace 50.

Quote:
Originally Posted by crackle View Post
Wasn't the transformer originally only supplying 6.3v for the valve heaters.
It is likely to be a smaller transformer (mounting holes) than one which can supply the HT and LT voltages on an isolated winding from the mains.
In other words is the replacement transformer you have able to supply the additional power for the HT as well as the LT without over heating.
Yes, the only thing the original was supplying was 6.3v for the heaters with the incoming mains tied to the chassis on one side and direct to the two diodes on the 6x5 on the other through a 50 ohm resistor.

I have a replacement transformer that is taller and has an ht winding on it as well as the 6.3v for the heaters but it is 250-0 rather than a centre tapped 250-0-250. This certainly seems to be man enough for supplying the required HT (70mA ) as well as the heater current from the other valves (2A).

Quote:
Originally Posted by TrevorG3VLF View Post
A hybid circuit is good, it takes out any DC component from the transformer so less likely to put the core into saturation. This would cause less primary heating.
That is good to know, hadn't thought of the dc feedback into the transformer from the use of the chassis as a dc ground. I think I shall go with the hybrid bridge then. I have enough 1n5408's in stock to do the job of finishing the bridge configuration.
GeorgeChristofi is offline