Hand built 6V6 - 6N2P stereo amplifier with built in phono preamp

Description

1950's replica 6V6/6N2P Audio Amplifier
This device is completely hand made by a Ham Radio operator with 50 years of experience building everything from antique radio stations for museums, to moon bounce transmittters to laboratory equipment to vacuum tube audio amplifiers.   The wiring is all point – to – point such as as done in the 30’s and 40’s [see picture and schematic - with my amps you will know exactly what you are getting] . As you can see the circuit  is simple and robust. It is a variant of audio amplifier designs for the 6V6 amplifier tube that have been in use since the mid 1940’s with the advent of the 12AX7 dual triode driver/preamp tube and the more robust Russian version - the 6N2P.   Cabinet is poplar and oak.  Panel is copper anodized aluminum.
This amplifier was bench and sound tested for power supply ripple and hum   - it is dead quiet with zero signal.  Frequency response is typical of circuits using the 6V6.  Using an oscilloscope, signal generator and an 8 ohm dummy load resistor,  low frequency roll-off was found to start at 100Hz and cut off at 20Hz.  High frequency roll off starts at 20K Hz.  This amplifier will produce an undistorted  4 watts per channel, and can even drive a set of 15 inch Panasonic CS-V9910 speakers.
60's vintage "Rooski Tubski's"  are included with this amplifier.  A wide variety of 6V6 variants should work with this amplifier.  Results will vary with the tubes.  The 12AX7 family of tubes will also work, but the filament connections at the tube socket will need to be rewired - a trivial job.
These tubes have been [and continue to be] in production since the 40’s.  They can be easily and relatively cheaply had  on Etsy or eBay.
This design incorporates a phono-preamp stage for use by those who have a turntable for vinyl disks.
No additional external phono-preamp is needed – you already have one.
The phono-line switch must be placed in the “phono” position to activate this preamp which is the first half of each 6N2P.  I think there is something cosmic about listening to Count Basie or Duke Ellington or Benny Goodman disks on “hifi” equipment that would have available at the time the original disks were pressed.  And not just music from the classical and  old swing kings...this rig  is a killer rock and roll amplifier too.
All other inputs [CD, tuner, iPod, etc] are made thru the “line” plugs and the phono-line switch must be in the “line” position.  Be certain to attach the turntable ground wire to the black "G" plug on the amp or the turntable will inject hum into the amplifier.
To operate the amplifier, put the tubes [2x 6N2P, 2x 6V6 [6h6 Russian], 2x OB2] in their respective sockets.   The OB2 gas-discharge regulator tubes are supposed to glow purple.  They function to provide precise control over the preamp [6N2P] plate voltage  under different load conditions.   They also look really cool in the dark [see picture]!   Once the tubes are in, hook up the speakers  - you will probably need to solder RCA male plugs to your speaker leads.
Set the phono-line switch appropriately.   Next, turn her on and enjoy recorded music as it was supposed to be heard in 1956!  A note of caution – make sure to set the volume controls to zero at the end of a listening session.  This way, if you plug your headphones in and forget that you were trying to blow the windows out with the speakers during the last session, you won’t destroy your hearing by mistake.
Here are a few words  I need to impart for safety reasons.  The power supply in this amplifier produces about 300 volts.  Needless to say, this can kill you if you are incautious enough to poke around underneath while it is plugged in. If you have experience working with vacuum tube equipment you will find this amplifier easy to modify to your personal taste [bias resistors, coupling capacitors, etc]. These circuits are extremely robust and components are unlikely to fail.  However, if a component like a tube DOES fail it could blow the fuse found inside the amp.  In the event of a failure [amp plugged in, switch on but no pilot light], switch the amplifier off, unplug it and WAIT 5 MINUTES BEFORE REMOVING THE BOTTOM COVER.  Find and replace the 1 amp fuse.
The exposed tubes are part of the “romance” of operating this sort of audio equipment.  Kind of like a mini-fireplace that plays really good music! But stuff happens – dropping/spilling things on the tubes while the amplifier is on will probably produce dramatic effects.  In this event, switch the amplifier off , yank the plug, clean up the mess and replace the tubes and [probably] the fuse.
Folks seem to like these amps - here are a couple examples:
New message from:
tgood1958
(259
)
Rick the amplifier is outstanding! I am really pleased with it and it drives my 94 spl open baffle speakers perfectly. I am using it with both my MC tube phono stage and with the built in MM 12ax7 phono stage. Both sound terrific! I try to buy made in the USA in the hopes of promoting cottage industries like audio and this exceeded all my expectations. It blows me away!
Thank you again and feel free to put the above into any of your future listings.
New message from:
cjon9705
(133
)
Thank you Rick. The tube amp sounds really nice on my Beyerdynamic DT990 Pro 250ohm headphones. I’m actually starting to build amplifiers with my daughter. I went to school for Electrical Engineering, but ended up in software after school. I’m really enjoying getting back into electronics. I’m starting with solid state class a circuitry, but will try my hand at some tube amplification and pre-amplification in the future. Really nice to have this tube amp as a reference from someone with a lot more experience.