HiFi Tube Amps

Here are just some of the amplifiers we have built

5 watt single ended EL34

Here is a 5 watt per channel single ended EL34 stereo amplifier we previously built, chassis, all transformers and choke are Hammond Manufacturing. Mundorf Evo Oil silver coupling capacitors , Alps volume pot and all wiring is point to point. All components used are of top quality including manufacturers like Solen, Vishay, Nichicon. Rectifier tube is a 5AR4 and driver tubes are 6SQ7.

6SN7 Simple Pre-Amp

Here is a preamp we built running a single 6SN7 tube per channel, it is a very simple circuit which a lot of the time sound better as there is less in the signal path. The circuit is a voltage amplifier as the first triode and a cathode follower as the second. This preamp uses a regulated power supply, running a voltage regulator tube. The rectifier tube is a soviet 5C4S, it is an indirectly heated cathode for a slower warmup, it has similar ratings to the western 5Y3. Alps volume pot and again all parts are great quality. 3 selectable inputs in the back. The power transformer is a vintage hammond.

STANCOR Williamson Ultra-Linear Amps

These mono Williamson amplifiers are based on the Stancor Ultra-Linear schematic. However, the output tube selection differs slightly from the original. I opted for 1625s, which are the 12V heater military version of the 807 tube. The amplifiers deliver approximately 30 watts before exceeding 1% distortion.

The Williamson design is known for its instability if not implemented correctly. Therefore, numerous hours were spent fine-tuning feedback capacitor and resistor choices, as well as various other small adjustments, to ensure stability while maintaining the 20dB of negative feedback. The power supply section is my own design. It utilizes a 5AR4 tube, which produces approximately 460V B+ voltage. Since the amplifiers are cathode-biased, the plate voltage is around 410V, which exceeds the triode limit specified in the data sheet. However, these tubes are tough and can handle the extra voltage.

We are just slightly over 100% plate dissipation, The cathode current is set to approximately 62mA per tube, I added a cathode current balance pot and a AC drive balace pot. I plan to adjust the bias in the future. The ultimate test was whether the new Hammond output transformers had the bandwidth required for the Williamson design and they passed. The result was an exceptional pair of amplifiers. I will include the final square wave testing results.

20 hz

1 khz leading edge

1 Khz

10 khz

"Little Jewel" 807 (1625) SE Stereo Amplifier

David Beard at ElPaso TubeAmps designed this amplifier and he is one of the most trustworthy guys I have interacted with when it comes to vacuum tube amplifiers and how thorough he is about testing and tweaking his creations, he is always just an excellent man to talk to.

This amplifier runs a pair of RCA black plate 6SN7 as drivers and in my version 1625s as outputs instead of 807s, B+ is around 405V. The reason I went with 1625s is I have about 75 NOS ones on hand with sockets and far less 807s. It produces about 3.5W of power and sounds fantastic. The output transformers are custom wound from Marko at Delatsch Electronics in Poland https://delatsch.com. The power transformer I used was from a 1950s Rockola jukebox and for the rectifier tube a coke bottle Soviet black plate 5C3S. Marko has David's schematic hosted on his website.

3.5W does not sound like a lot of power but connected to speakers like the efficient Klipsch Cornwall 3 (102dB 1w/m) it is more than enough.

5 watt single ended 6N1P/EL34

Here is another singled ended amp we have built running a sinlge dual triode 6N1P and a pair o EL34s. It is running a 5AR4 tube rectifier.

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