Features:

• OTL Class A Cathode Follower Output
• 2 x 1 Watt RMS Output @ 250 Ohms Impedance
• SRPP gain stage
• Line level input sensitivity
• Drives 80-2000 Ohms Headphones

Fig.3 Power Supply Circuit Version 2.

Construction
The two channel amplifier circuit and the PSU can be assembled using the traditional point-to-point wiring method. However, for our prototype, we designed a PCB. We have some PCB's available for purchase (see below).
We are still working on an electronic voltage regulator PCB which may be available in the future. In the mean time there is a regulated PSU available at Ebay that may be utilized for this project: item number 120366398663 Store name: tubeshunter http://stores.ebay.com/tubeshunter
However, we did not test it for fittness in this project!

Testing
It is highly recommended to test the PSU voltages with load resistors first before connecting it to the OTL Amp. Use the following load resistors for PSU testing:

U1=92V output: 635 Ohms 15W or 2 x 1.270k Ohms 7W ( for PSU version II 1350 Ohms 8W or 2 x 2.7k Ohms 4W)
U2=230V output: 47k Ohms 2W
U3=6.3V filamenrt output: 5 Ohms 10W or 2 x 10 Ohms 5W

Be prepared to do the tests rapidly as the load resistors will dissipate a lot of heat. The accuracy of the output voltages is importand for the OTL performance and tube longelivitity. Voltages should be as follows:

92V +/- 1 Volt
220V +/- 15 Volts
6.3V +/- 0.1 Volt

Connect the load resistors to the appropriet outputs. Make sure that the correct fuses are in place. Apply power and measure the output voltages. If measurements are within limits, the PSU is ready to be connected to the OTL amp. Otherwise the voltages must be corrected.

OTL Amp Testing
Apply power and let the tubes warm up for 3-5 minutes (Stand-By ON). Next switch Stand-By switch to "operate". Immidiately measure the cathode voltages of each output tube. Cathode voltage should be 17V DC +/- 1V. If not within limits, turn off power quickly and look for wiring errors, solder shorts. Otherwise watch the tubes for any signs of overheating. Only the filament and the cathode (center part of the tube) should glow orange. Any other part of the tube should remain dark. The amp is ready for listening tests.

	COMPONENTS: (numbers in brackets = right channel)

	Resistors (0.25W 5% unless noted otherwise):			Capacitors
	R1 (R7)  = 820k							C1  (C5)  = 0.22uF 100V plastic film
	R2 (R8)  = 180R							C2  (C7)  = 0.15uF 630V plastic film
	R3 (R9)  = 680R 0.5W						C3  (C8)  = 47uF 16V electrolytic
	R4 (R11) = 820R 0.5W						C4  (C9)  = 4.7uF 350V electrolytic
	R5 (R12) = 220R							C10 (C11) = 220uF 50V electrolytic
	R6 (R10) = 330K							C12 (C13) = 1uF 250V plastic film
	R13 R16 (R19 R22) = 10K						C14 = 10uF 350V electrolytic
	R14 R15 (R20 R21) = 470R 3W-4W
	R18 (R24) = 15K 0.5W
	R18 R16 (R19 R22) = 10K
	R30 = 4.7k 0.5W