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Hi all, looking for advice since I now have some time to focus on getting this amp working right. A quick refresher, I purchased it used but well assembled, nothing looks obviously wrong internally, resistor values are reasonable, no fizz or noise and all switches & pots are functional. Only mod is adding a VRM which works a treat.

Problem is that there is little bottom and it is quite strident - we aren't talking subtle here - bass on max and treble min makes it bearable but still lacks beef. Feels like there is nothing below about 200hz and loads up top. Same problem using the 6V6 or El84 set as well as normal or TMB channels. Tube swaps have no effect. Voltages are within reason. Cabinet choice doesn't do it either, in fact I am using Scumback H55's currently that shift foundations with any other head on top. With the Tone Tubbies nobody can bear to be on the same planet.

I am a bit baffled, is there something that can cause this? I hear great potential in this amp, I must be overlooking something obvious....

Cheers,
Colin

Right values for all caps?
Are the voltages within 10%?

Got some pics of the build? Could be a bad joint somewhere.

Since the problem is on both channels the issue most likely lies in the PI or beyond (output section).

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http://pdfelectronics.com

Thanks, I will get some pics up. I am not sure exactly which version of the schematic it was made too, and I am imagining there have been some revisions over time but the only thing that looks obviously different from the revision 6 schematic I am referencing is that C10 is 220uf instead of the 50uf specified.

220 was used for a while to increase bottom end. check that all the coupling caps are correct.
Check that there is no phase reversal at the PI, I.e. Correct channel goes to correct pin etc.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks for the guidance guys! Finally had a chance to put a 50uf in there and that seems to have been it. A bit counter intuitive since I would have guessed 220 would allow more bottom but for whatever reason it is now sounding like I would expect. Still might tweak the tone stack a bit but otherwise a fantastic amp and headed to the front lines of my gigging setup. The VRM is amazing as well, I want it on all my amps! This will now certainly keep me happy until I can recycle enough beer cans to afford your ODS!

Great to hear All is well. Now's a good time to enjoy it!

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps