| Author: | Asdain (registered user: 169 posts ) |
| Date: | Wed, May 23rd, 2012 @ 01:18 ( . ) |
On 05/22/2012 @ 19:27, Dan McCormack wrote :
On 05/22/2012 @ 16:08, Steavis wrote :
: yes I was thinking the same thing. : : : : Dan: just thinking out loud: is the amp fixed biased or cathode biased? A common mistake is not to ground the point where the 2 220K resistors meet in the PI section when it's cathode biased. Check a 5E3 deluxe schematic (cathode biased) vs a AB763 schematic.. : : : : But since you were talking about adjusting the bias you probably have an adjustable fixed bias.. : -- : : : : Yes, it's adjustable fixed bias. : : Chris, it turns out a 6v lantern battery couldn't put out enough current either, but I unsoldered the heater supply wires from my pilot light and powered them from the 5v DC power tap on my bench power supply, and the hum was still there (It settled down at around 3.7 amps of draw at 5v, btw). So that seems to exonerate the heater supply. : : You guys seem to be agreeing that the most likely location of the problem is in the heater network for the long tailed pair. I already went over it and it all looked correct, but I'll take another look and see if I can find a problem. Here's another [link] to the picture of my power section (giant version: [link] ) -- does anything stand out to you guys? : : I appreciate the help in narrowing this down. Can't wait to solve the problem and hear this thing in its full glory. : : Dan -- The heater wiring definitely doesn't look very tidy, keep the wires twisted tightly right up to the socket. How the Heater circuit is grounded is also important. Don't just ground one side of the heater supply. better use an artificial center tap and put it on an elevated potential (or ground if you have to). if you still have hum after that, at least your heater wiring is neat then ;) |
5/23/2012 @ 11:26----Dan McCormack --- 13 Users Online --- 42 Recent Unique Posters |