7 Tube Stereo Output Amplifier

Posted on Feb 6, 2014

This is a 7 tube 20 watt amplifier that must be used in conjunction with a pre amplifier having volume an tone controls. For this, I recommend this 6 tube pre-amp. With this amplifier you may use 6BQ5 output tubes. A 5U4-G rectifier is used so that the power supply will have plenty of pep to run the amp. This amplifier is basically a Magnovox amp

7 Tube Stereo Output Amplifier
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lifier I bought on ebay years ago and rebuilt after building the 6 tube amp. It is really amazing how it sounds, and the circuit is very minimalist, as you can see. Because of the output setup, you must use a quartet of matched 6BQ5 tubes. You will notice in looking at the schematic my preference for the balance control. I find this a convenient way to compensate for less than optimal speaker placement in my living room Above, the amplifier`s schematic. In addition to the 6BQ5 output tubes, a 6EU7 dual-triode is used in each channel. This amplifier also uses a curious phase-inverter circuit I have heard described as a "paraphase" inverter. *Note R4 and R24, optional fixed balance control, omit 750 ohm 1/2 watt pot. The original balance control was mounted inside the tuner. When I began using this amplifier without the tuner, I had to add two resistors in place of the connections to the pots. For whatever reason, I installed two 330 ohm resistors and used the amp this way for years before the rebuilding when I added a balance control pot. I was lucky to find a pot with the same value as the original at a real electronics parts store. Many readers have emailed saying they are having difficulty finding a 750 ohm pot. If this is the case for you, just omit the pot and use the 330-ohm resistors as shown. You may want to install a 3-prong line cord and connect the chassis to ground. Make sure the fused and switched side of the...

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