![OPERATIONAL NOTES](/images/new-backgrounds/12631/1263115x1.webp)
OPERATIONAL NOTES
SWITCHING
SWITCHING VARIABLE FEEDBACK The variable feedback can be changed in 1 dB steps from zero to 10 dB. The most obvious effect of changing the amount of negative feedback is the gain change. The more feedback - the less gain but also less distortion and a flatter frequency response. You should be able to hear that with less feedback, the tonality is more aggresive but the imaging may have greater detail. As you increase feedback, the amp gets smoother and softer and slightly brighter. Towards the maximum amount of feedback, the amp may begin to sound like a good solid state amp. Virtually all solid state amps need large amounts of feedback in order to sound acceptable. Maximum feedback also corresponds to maximum damping factor. This control not only affects the tonality of the amp but also of the speaker. The optimum setting depends on the speaker, the room, and your tastes. Experimentation will be necessary but also fun and educational.
ADJUSTING BIAS This does more for tube life than it does for sound quality. You will need a DC voltmeter and a small flat screwdriver. This should be checked every few months but does not need to be necessarily checked and adjusted unless the 300Bs are replaced.
1) Let the amp warm up in
2) Put negative or black probe of the voltmeter to a chassis screw (ground) and the red or positive probe in the small black socket near the FEEDBACK switch below the tube to be adjusted.
3) It should read 740 mV or .74 volts DC. If not
4) Now adjust the other 300B bias. Use the other black probe socket and the right side trimmer and adjust the same way. A little "drift" is normal .
5) Switch to PUSH / PULL - you should measure each tube again. The meter should now read
640 mV but more important should measure the same as the other tube. If not adjust one tube to match the one closest to .64 volts. This cancels hum in
TUBE LIFE
You should expect many years of life from the tubes in your MANLEY SE / PP if you adhere to the procedures described above and check your bias at least once every
FUSES
The fuses used in your amplifier are standard 1/4" x 1 1/4"