Bridge or Center Tap?
Hey Paul, I think I may have corresponded with you a few years ago with
regard to my take on Crowhurst's Twin Coupled Amp. Was that you?
Anyway, here is my take on the FWB as opposed to the FWCT systems. An
important consideration for PS designers is something called 'Utility
Factor' of the various windings on the PT. Others have already noted the
FWB to be better if that connexion is possible. I've attched a numerical
example here for the secondary winding UF for the FWB with cap input
filter. Since there are no other windings the primary & secondary UF's
are equal.
Other examples will follow but in following posts since file size is
limited here in AudioBanter. But in summary the best UF for single phase
work is the FWB with choke input to filter. The lost power during the
conversion from AC to DC is in the form of the even order harmonics
(2nd, 4th, 6th...Etc) generated by the rectifying process.
You could check for the possiblity of circulating currents in the
parallel connexion of your PT secondaries as follows. Connect one end of
the secondaries in series opposition. Then with an AC VM check for any
voltage differance.
My guess is the voltages are near equal but with somewhat different
resistance, all OK to parallel permanently. Sounds like you have a PT
built from the core up to be series or paralleled, commonly available.
For example, Hammond lists many such devices.
Cheers to all, John
+-------------------------------------------------------------------+
|Filename: 100v Bridge BW.jpg |
|Download: http://www.audiobanter.com/attachment.php?attachmentid=300|
+-------------------------------------------------------------------+
--
John L Stewart
Hi, John. Yes, that was me who contacted you about the Twin Coupled amp. That project remains the best sounding stereo amp I've built yet. Thanks for your help.
I love choke input filters and use them as much as possible both for the greater current capability as well as the better voltage stability.
The pentode PP parallel amp I am currently building has two high voltage power supplies, one of each type: One FWB feeds a cap input for about ~600v on the EL34 output plates. A second FWB feeds a choke input for ~400v on the EL34 screens plus the input, gain, splitter, and driver stages.
The transformer is from Antek. This is the first project I have tried with one of their products.
Thanks to all of the RAT responses that convinced me to go with the parallel secondaries and FWB rectifiers.
- Paul
|