Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Archives of favorite topics => Topic started by: EL34 on June 15, 2005, 07:49:14 am
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I see many post regarding scratch built amp problems that the owner cannot find. They get stumped and give up and then come here asking if we can find it for them. The problem is always this, we cannot see the amp from here. You are the only one that has the amp in front of you.
The time that is spent posting here and waiting for an answer that may never come could be spent looking for the actual problem. I am not saying that you should not post your problem here, I am saying that you need to buckle down and try harder to find the problem.
Many people here have been in this situation. Some even swear that they have done everything correctly only to find that indeed they have connected something wrong. Logic dictates that if everything is correct, then the amp would be working, right?
A bad tube or transformer is about the only thing that cannot be checked by using the method below. Tubes can be swapped for known good tubes, one at a time.
Here are some tracing tips.
#1 - Print out a layout diagram or schematic of the amp!
#2 - Take a yellow Hi-Liter and trace every connection and component in the amp as you check it. Start at the input jacks and work towards the power transformer.
Check all component values as you pass through them. Make sure that 470 ohm resistor is not a 470K resistor. Double check the resistor color bands to make sure all resistor values are correct.
If your path ends at a chassis ground, take your meter and make sure that you really do have a ground connection. Do a continuity check or a DC resistance check with your meter from the power trans main ground point to your ground and make sure you actually have a good ground connection.
When you are finished, your layout drawing should have a yellow Hi-Liter line over the top of every possible wire/circuit path and every component will have been checked for proper placement.
(http://www.el34world.com/Misc/images/trace.gif)