More Photos & schematic here: www.clickernet.net
Amp is based on Dave Hunter's Two-Stroke using his original design utilizing one or two power tubes, in single-ended Class A mode. I used a Weber 5E3 chassis, W022772 power transformer and WSE15 OT.
Most significant change from "stock" Two-Stroke is the negative feedback circuit. I replaced the 68K resistor with a 1K resistor and a front panel mounted, switched 1M pot. This allows the NFB circuit to have resistance from about 2K to 1M, or be completely open. It is connected to the active impedance tap of the OT, rather than to a fixed tap.
Other changes are replacing the.47uf cap on the V1A cathode "boost circuit" with a .68uf cap, and ability to switch between 120v & 125v primary coils on PT. In the 125v setting I am reading 336VDC on the power tube plates, 303VDC on PT grid(p4) and 151 VDC on V1A plate.
Problem is a hum as soon as amp is turned on, at about 115hz. Amp volume control or guitar input does not affect hum. The NFB control DOES affect it. The higher the NFB pot is turned, increasing the resistance, the hum gets quieter. If the NFB pot is switched off so the circuit is open, the hum almost disappears.
Any ideas appreciated. Photos & schematic here: www.clickernet.net
Thanks - Bil
New Build Hummmmmmmmmm
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New Build Hummmmmmmmmm
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Last edited by bclick on Thu Aug 12, 2010 2:29 pm, edited 1 time in total.
