G7 PSU Help Needed

Hi - just finished the PSU - in the US so using 110V. 

Getting 123 VAC from the wall;

110:9V transformer is working fine (gives ~10-13VAC when hooked directly to power);

220:15V transformer is working fine (when connected as 110V:15V - gives ~18VAC when hooked directly to power). 

However, once connected together, only getting 74V from the primary of the 220:15V (whether tested directly from the transformer wires, or via the PCB).  The tube is not powering up at all.  Have tried all different combinations and two different 220:15V transformers. 

Any ideas? 

HI, it seems that the 110:9 hasn't enough power
check again the wiring and if it's ok, you have to put a more powerful one

cheers
fred

search for threads about the G7 power supply at this forum
What are the VA ratings of the transformers?

hi - already searched through the messages - but doesn't seem that anyone had the same problem i am having.

VA rating - 9v is 5A, 15v is 5A (i also had a 3A - which is what was called for - but got a second trafo thinking maybe there was something wrong w/ the original 15v)

ersatz007,

It just so happens I am in the process of building my second G7, and am currently bench testing my power supply.  I had the EXACT problem you did, right down to the voltages measured!

You may have already checked for this, but the problem for me was a solder bridge on the bridge rectifier section that feeds the 6.3V rail.  One of the pads for the bridge rectifier is VERY close to the ground trace.  Apparently, it was close enough that when I etched my boards, a tiny trace was created that looked normal, so it escaped notice.  Upon further examination, I caught it.  Now I'm getting 6.3VDC where it belongs, and everything else is working relatively well.  I am getting some very high voltages on Pin 2 and Pin 5 compared to my first power supply; but I think that might be due to a larger second transformer.  I'll be posting another thread on that one.

Hope this helped!

Hi Curt,

I'm near Quakertown (need to update my profile).  I didn't etch my own boards - but I'll check it out anyway.  Thanks!

I double checked it against the trace pattern on the Gyraf website, and I had to zoom way in on that to confirm it.  It's a very narrow gap!

Ironic thing about your profile comment....
It says New Brunswick, and I actually work in Somerset.  (Right next door for those keeping score at home...)