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Hi 
having some issues with a clone I built. I suspected the volume was rather low on my amp but finally got to test a genuine amp last week. The original has a clean channel with one gain stage into a LTP PI then push pull cathode biased EL34 pair. I get a reading of 17VAC across the speaker with a clean output on my scope and the power tube grids have 20vac signal. When I try to get a clean sine wave on my clone it gives up at about 10vac across the grids of the power tube. If I keep dialling up the volume to reach 20vac on the grids and 17vac across the speaker I get a distorted sine wave that looks like this. The PI output is clean
I've got voltages that match across each stage but the transformer set is different. TDS supplied a laydown set with "MPT 45" on the PT and "OT 30" on the OT after a friend negotiated a Hotcat set from the TDS. These transformers don't look like the original standups but the documentation had the right specs so they were used for the build. I suspect they were meant for a BlackCat 4 el84 build? The power tubes are running at 71ma 29 watts each. The original amp is running at 84ma 30 watts. Rather hot I know.
Sorry if this post is incoherent, rambling etc. I'll attach a link to the only? schem of the amp on the net and at the moment I've taken off the gain channel input and brilliance to keep it simple. I've been over the PI and power tubes several times checking values and possible signal to ground problems. As I said the PI can put 20vac clean into the power tube grids but the output is distorted with a double? peak across the top of the sine wave. Thanks in advance Joe
http://www.webphix.com/schematic%20h..._hotcat_30.pdf
p.s. I was pretty sure that the grid leak bias on the first stage of the gain channel was reversed with the 1 meg but the original amp (early model) has the 5 meg at the input jack to ground and the 1 meg at the control grid. I built mine reverse to the schem and it works fine
having some issues with a clone I built. I suspected the volume was rather low on my amp but finally got to test a genuine amp last week. The original has a clean channel with one gain stage into a LTP PI then push pull cathode biased EL34 pair. I get a reading of 17VAC across the speaker with a clean output on my scope and the power tube grids have 20vac signal. When I try to get a clean sine wave on my clone it gives up at about 10vac across the grids of the power tube. If I keep dialling up the volume to reach 20vac on the grids and 17vac across the speaker I get a distorted sine wave that looks like this. The PI output is cleanI've got voltages that match across each stage but the transformer set is different. TDS supplied a laydown set with "MPT 45" on the PT and "OT 30" on the OT after a friend negotiated a Hotcat set from the TDS. These transformers don't look like the original standups but the documentation had the right specs so they were used for the build. I suspect they were meant for a BlackCat 4 el84 build? The power tubes are running at 71ma 29 watts each. The original amp is running at 84ma 30 watts. Rather hot I know.
Sorry if this post is incoherent, rambling etc. I'll attach a link to the only? schem of the amp on the net and at the moment I've taken off the gain channel input and brilliance to keep it simple. I've been over the PI and power tubes several times checking values and possible signal to ground problems. As I said the PI can put 20vac clean into the power tube grids but the output is distorted with a double? peak across the top of the sine wave. Thanks in advance Joe
http://www.webphix.com/schematic%20h..._hotcat_30.pdf
p.s. I was pretty sure that the grid leak bias on the first stage of the gain channel was reversed with the 1 meg but the original amp (early model) has the 5 meg at the input jack to ground and the 1 meg at the control grid. I built mine reverse to the schem and it works fine
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