Harman Kardon tube pre/amplifier
caseymou
Posts: 327
I just bought a working HK A500 preamp/amplifier. Tubes consist of
4x12AX7
1x12AU7
4x7355
I have downloaded a wiring schematic but have no idea where to go from there as far as tuning/maximizing potential. Any links to reading which I should do? I graduated with an Electrical Engineering degree but suprisingly vacuum tubes were never mentioned except to say they were "old tech" and replaced by SS. So much for a well rounded teaching approach. So I have a background and should be able to comprehend technicial information if presented.
4x12AX7
1x12AU7
4x7355
I have downloaded a wiring schematic but have no idea where to go from there as far as tuning/maximizing potential. Any links to reading which I should do? I graduated with an Electrical Engineering degree but suprisingly vacuum tubes were never mentioned except to say they were "old tech" and replaced by SS. So much for a well rounded teaching approach. So I have a background and should be able to comprehend technicial information if presented.
Post edited by caseymou on
Comments
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It's probably worth replacing the coupling caps. You can go as fancy as you want, but the Sprague 716 or 715 "orange drops" sound great IME and they're inexpensive and readily available.
Tube electronic circuits are simpler and MUCH more robust than ss (IMNSHO). The only drawback is the high voltages involved... you have to be a little more careful under the hood than you may be used to being.
If it hasn't run in a long time, you should bring it up slowly on a Variac to reform the power supply capacitors.
There is fun to be had "rolling" tubes, e.g., different kinds of 12AX7's... take a look at the "Tube FAQ" at www.audioasylum.com
As to a primer on tube amplifier circuits: look for a copy of the old US Navy intro electronics book (at a library or a used book sale) --- I forget the title -- or buy a copy of Bruce Rozenblitz' "Beginners Guide to Tube Audio Design". http://www.audioxpress.com/bksprods/books/bkaa42.htm
