HV B+ problem with Marshall Power Tran

[Gibson924]

Hi, just finished a jcm800 clone and I am having a voltage problem on the main HV secondary. It's a hammond replacement 290HX. I am only getting 185v and 185v on each of the blue/gray taps. I have 120v on the prim. flipping the standby with normal full rectifing it comes out to ~220. the bias and heater taps all test fine.
when I use a typical marshall style diode bridge the amp shorts out and blows the main 5A fuse.
I've gone over and redid all the grounds and center taps and still can't seem to figure out why my voltage is so low or then blows. Can anybody offer advise to help troubleshoot. I built this real quick yesterday during the Packer game and maybe spent too much time hooting and hollering and missed something simple, but I also have never used this tran. Thanks

[rhinson]

if you're getting only in the mid 200's voltage wise you have chosen the wrong style of rectification. 100w marshall's typically use a full wave voltage doubler circuit. your diagram below show this trannie to have a 350vct hv sec winding---ie, a 175-0-175 winding. doing the normal full wave on this will get you 245v unloaded and a 20-40v drop underload with the standby disengaged. look at the schemo for a 100w marshall and see how they do it (the ct is not grounded using this method). alternatively, you could just use a simple bridge and ignore the ct. -----you'll come out with pretty much the same voltage
(350 x 1.4 = 490v unloaded, about 460 - 470 under load). rh

[Gibson924]

Thank You!! I knew I was doing something boneheaded. I was using the center tap with the diode bridge. Thanks again