Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: soapfoot on April 08, 2022, 11:01:32 am
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Hello!
Tired of reflowing solder joints on my 90s Pro Junior, so I'm converting it via the Hoffman turret board.
In the build documents here, (https://el34world.com/Hoffman/files/Hoffman_Pro_Jr.pdf) there are a few deletions.
I wonder if anyone can explain to me the reasoning behind deleting the parts?
The most obvious is the Zobel network on the OT primary (R26 and C11). I know just enough to know thaet such a network would have the effect of evening out load resistance (and therefore frequency response at output).
If I like the sound of the amp as-is, should I at least consider adding this Zobel network back in?
The 47pF snubber cap seems clear enough in function... again, if I like the sound of the amp as-is should I compare and evaluate? Obviously if it was deleted there are no stability issues, but sometimes the snubber removes a bit of blare in a pleasing way.
I also notice that the out-of-phase output of the LTP phase inverter has been switched to a more typical configuration (R17 and R18 have been replaced with a single 82k). I'd love to understand why the 9k1 and 91k in series were originally employed. Does this manage gain staging somehow, or does it perhaps mitigate the impact of the above-mentioned 47pF snubber?