• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

"Dirt Cheap SE" 6BM8 spud amp

chrish

Member
2003-10-20 2:43 pm
Sydney
Just letting guys know that Eli Duttman (of 'El Cheapo' fame) is helping to design a low cost Single ended amp using 6BM8 dual triode/pentode tubes and the Edcor XSE15-8-5K ($20) output transformers based on an old Mullard design. Jim McShane is putting together a parts package so that optimal components can be purchased from one supplier to save on shipping costs (and the hassle of finding where to get the different parts).

The design is just about finalised. It looks like it will be an interesting project. Here is a link to the discussion on the audiophile talk forum:

http://www.audiophiletalk.com/cgi-bin/yabb2/YaBB.pl?num=1202342808/0

Those looking for a low cost entry in to tubes, or a second office/bedroom system should check it out.

Thanks Jim and Eli,

Chris
 

chrish

Member
2003-10-20 2:43 pm
Sydney
I have just completed this little amp. It is in a 10" * 6" * 2" Hammond chassis. Valves were found at a movie prop warehouse, about to be thrown out. One is a Mullard (Australia) and the other a National (Matsushita Japan), both NIB.

This little amp only puts out a couple of watts, but really sounds great. I have used Russian K40Y-9 0.1uF coupling caps, rest of resistors are just standard stuff. Power supply is a cheap Chinese R style transformer, dual 230 volt 0.05A outputs and dual 6.3 volt 0.8A secondaries, just enough to run these two 6BM8 valves. Ran the two 230 volts in series to make 460 volt centre tapped full wave RRSF snubber filter, inrush current limiter then rectified with UF4007 diodes. Dual can JJ 100+100 uF and 100 mA 15H choke ($8) finish the power supply. Output transformers are Edcor XSE15-8-5K ($20 each).

This thing sounds pretty remarkable considering it was done on the cheap! No hiss at all, no buzz and no hum! If it put out more than 2 watts I would be happy to have it in my main system! Once I have finished playing with it, it will be for my son to be matched with his computer and a pair of Fostex FE87Es in standard bass reflex boxes (have been built, but still to be sanded and painted).

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