Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Tubed PS for Tubed Guys- Two Improvements
I've made two changes to the circuit, one of them rather important.
Goto ABSE & ABPR for the revised schematic & parts list. As any practitioner of electrical theory will tell you, the current once established in a conductor likes to keep on flowing. This is very noticeable in an inductor such as the piece of Hammond iron I used as a choke in the power supply. If 100 ma of load current is being delivered to the load, what happens when the standby switch is opened? I didn't think about things like that 40 years ago when I was building the original version of this PS. Aside from burnt contacts in the switch, the stored energy in the choke magnetic field needs to be dissipated somewhere. No problem when the L/C switch is set for C filter input during operation. A serious problem occurs when set for L filter input operation, since when the switch is opened there is nowhere for the current to go. As a result a very large negative going voltage occurs at the switch end of the choke as it is wired in the diagram. The very fact that the choke insulation has not yet failed after more than 40 years operation is an attestation to the reliability of Hammond products. This same phenomena is used in your car's ignition to provide the spark (unless you have compression ignition). The fix is quite simple, that being a diode & resistor from the loose end of the choke to the common lead. Some of the stored energy is dissipated in the choke resistance while the remainder shows up in the filter caps. I've included a 10R resistor for my own interest in order to monitor the transient at switch off. For the other change I've moved the DC ON-OFF switch to the transformer HV secondary, as I've also done on some other recent projects. That makes life easier for the switch since it now has to interrupt AC rather than DC. Since AC passes thru zero at twice the line frequency any arc will be self extinguishing (we hope). Cheers, John Stewart |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
What do you guys think of these speakers? | Car Audio | |||
Tubed Car Amplifiers | Car Audio | |||
Rockers Unite to Oust Bush | Audio Opinions | |||
White van guys | Pro Audio |