Icetech wrote:well.. thing is.. this is without any filter caps grids or anything even hooked up....just the PT and rect...
on the up side i just redid the tone stack and its sounding pretty good:)
way too much gain on the clean channel though:( thinking the low voltage might not be helping that
You will not develop the full DC until you have the filter caps in the circuit. Right now you are measuring a Full wave rectified signal (120hz) that has a RMS level lower due to no smoothing/storage from the caps.
Gary
Located in the St Croix River Valley- Afton, MN
About 5 miles south of I-94
aka K0GWA, K0 Glas Werks Amplification www.glaswerks.com
Are the filter capacitors as old as the diodes? If so It could be that their value has gone way down and they are acting like much smaller value caps.
In that case you would have widely fluctuating dc that your meter might be reading as a lower value of DC.
Then a leaking first cap can be the problem, change it too with a new one, if still unsuccesfull try to remove all the basic supply components from that chassis (trans, diodes and first cap) and test them separately.
If diodes are new and 1N4007, cap is new and voltage is still 400vdc the last thing to try a change is the transformer...
when i get some real odd stuff going on likethis tx problem , i replacxe everything and rebuild the section ( my PI comes to mind ! )
this way you usually find the problem - swapping out things one at a time or just replacing the "whole bloody lot" , as we say in blighty.
try replacing stuff - starting with the mains TX.
Sometimes a TX looks Ok- and behaves OK - but has a short in the windings somewhere which makes it do strange things - esp under any load.
Icetech wrote:
And i would like to think bad transformer also if it wasn't putting out 330+ on each tap...
I agree with you, it's last thing to swap but it could be faulty in a way that it's ok with no load and then sags too much under even the minimal load.
Before swapping first cap have you tried to measure how much (ac) current flows through it under no-load condition? Does the cap get warm?
Actually it looks like i got it last night.. first cap was fine.. it is one of the later ones.. i disconnected the rest of the system cept the first cap and bam.. 442V..
i shoulda done this sooner i guess. but didn't know it wouldn't give full votlage without load til i think it was gary mentioned it..
i finally hopped outa bed and tried that bout 1am.. so tonight ill figure what is bad:)
