You can read the history on Tube Audio Design in my TAD-150 Preamp post. This is the amp that pairs with it. The cool thing about this amp is that it can be used as a standalone integrated amp if you need it to. With 1 input, if you move the volume button all the way to max, it opens a direct path for the preamp when used. It has 4 & 8 ohm speaker connections. This amp is built like a tank. It weights just about 50lbs!
The amp is very versatile. It comes standard with EL34 power tubes, but can use a variety of others as well, including KT-66, KT-77, KT-88, and more. The best tubes that have made the amp simply amazing are some Genelex Gold Lion KT-88′s. Push-Pull Class-A Design, UL or Triode Mode, Variable Feedback, and has external easy biasing. I’m using a pair of Amperex 12AU7′s, and a single NOS Sylvania 5751 Black Plate Triple Mica.
If you have any questions about this awesome amp, please feel free to leave a comment or contact me.
Push-Pull Tube Biasing (based on 2000mV reading):
6550, KT88, KT90: 600-620
Class A biasing:
EL34: V1+V3 @ 200mv; V2+V4 @ 500
6CA7: V1+V3 @ 300mv; V2+V4 @ 500
KT66: V1+V3 @ 250mv; V2+V4 @ 450
Here is the complete BIAS instructions from Paul Gryzbek:
TAD-60 BIAS INSTRUCTIONS Very important :
Tube bias must be set immediately when tubes are first installed. Excessively high tube bias will burn output tubes in a matter of minutes. Output tube glass gets very hot and will burn your skin – be careful. T AD-60 bias adjustments are very precise 25-turn pots. Turning right raises the bias. Please read instructions below.
WITH NEW TUBES INSTALLED:
1. Start with the amplifier off and cold, all tubes properly installed. Turn all 4 bias adjustment screws to the left 3-5 complete turns. Speakers do not have to be connected to set the idle current bias. Make sure music is not playing during the adjustment.
2. Set the supplied digital meter to the marked 2000m V range. Clamp the meter black probe into any speaker terminal post – or simply place the black probe into one of the brass top cover mounts. Place the red meter probe into one of the top chassis gold RCA bias jacks, notice screw adjustments next to each test jack (see picture).
3. Now power up the amplifier NO music playing. Watch the meter – if the meter reading quickly rises above 600 IMMEDIATELY switch the amplifier power off – the bias adjustments are not set to a low initial bias adjustment starting point and need to be turned left a few more turns. Once the amplifier is switched on you should see a relatively low reading:(1 to 300) in 15 seconds. Adjust each corresponding bias screw for this meter reading: EL-34 tubes set to 350, 6550 or KT -88 tubes set to 550. Set the remaining 3 bias adjustments in the same manner by moving the probe to the corresponding bias gold jack and turning the adjustment screw.
4. Let the amp idle for 10 minutes (or longer) at this setting. Watch out, tube glass gets very hot (up to 300 deg. F)
5. After 10-minutes (or longer) of idle time, final adjust all 4 settings: EL-34 set to 350-370. 6550, KT -88 or KT -90 tubes set to 600-620. + or – 20 is accurate enough. Final test and adjust all 4 test points two or more times till all look identical. The bias is now properly set and will not need attention for 6-months.
the correct 4 or 8-0hm + post. Speaker minus – wire goes to the amp 0 ground post. Connect the amp input to your preamp output. The adjustment can be performed with or without speakers, or input connections – just so no music is playing during the adjustments.
Check the bias every 6 months.