• 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.

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Each monoblock is 54Kg. I installed small wheels under the amplifier to move it easily :)
Topology: Auto biased 6N23P-EV direct coupled to fixed bias 300B-Interstage-GU48 (833)
IT and OPT made by AE (Holland)
All power transformers are torroidal.
All anode, bias and heater supplies are regulated.
Wood is natural African.
Steel chassis painted with electrostatic dust paint.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


http://www.youtube.com/watch?v=4B_6Qfw7vtI
 
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Electric Chair Amplifiers...a reminder of safety folks!

Hoyan,

Lovely amplifiers and the video sounds very good for just a cell phone camera.

I need to make a comment though of concern about building an 'electric chair' amplifier that has very lethal 1000 volts exposed and no warning sticker. The original builder and owner might be alone or very careful and have no pets, BUT, what happens after they are gone and the amps fall into the hands of a new owner who may not know the DANGER? I would never build an amp like this without a shield in place to keep inquisitive fingers away that would shut down the high voltage if the shield was removed.
 
rcavictim,
Yes, you are right. I will organise a plexiglass safety cover.
Thanks
Noyan

Noyan,

Sorry I misspelt your name. I copied it off the previous reply.

I bought one of the very early MingDa MC3008AB, 805 SET amp. S/N 10. :) Uses 300B as a cathode follower to drive an 805. PD on the 805 is 120 watts, full tube rating at 1050 VDC. Plate shows just barely perceptible color in the dark. The plate volts climbs to 1600 VDC before the drive appears if I do not manually delay switch the hi B+ switch. This is due to a choke input Hi B+ filter in a totally new power supply I made for this beast. I could have tamed the choke during no load with a big wirewound 200 watt power resistor bleeder but this amp makes enough heat as it is thank you very much! ;) I installed solid state relays in the primary sides of the various power xfmers and a 5 VDC power supply which is always live to run power through the chassis banana jacks that receive the banana jack pin fasteners used to secure the removable tube cage. My miniature toggle main power switch only has silent LV DC running though it too so no hum radiation to the audio circuits as the power switches are in the same location as the volume control. Remove the cage and the amp will not run. A jack shorting cable can be inserted in the banana jack receptacles on top of the chassis to restore operation by a technician if desired. A dress chrome rack handle could be made to drop into the cover jacks as well if I wanted to run the amp cover off and have it still look nice. They would be at chassis earth potential. Frankly I prefer the look of my amp with the tube shield cover on. My cats appreciate this too.

I'll post a picture of my creation if I can find the file. BTW it makes 45 watts RMS per channel and sounds very good to me. With near 100 dB sensitive speakers it doesn't work very hard. In a class-A the first watts are the cleanest.

Plexiglass may heat and warp. A metal perforated or wire mesh cage would not impede cooling air. In my highly modified amp there is a plexi top cover over the 805's present in the original factory design and it has deformed slightly during the first few hours use which stopped after I rebuilt it and installed a cooling blower.

RCA (not me, the other guys) says that at full ratings cooling air needs to be directed to the spot between the grid and plate terminals from a nozzle and blower to prevent failure of the seals. Other than this the tube is radiation cooled. Whatever you do for a tube box/cage you don't want to impede the cooling of these big hot tubes. Judging by the plate glow on your amp I'd say you are near full continuous PD ratings.

Regards,

rca
 
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