Akai Roberts Tube Monoblock to Plexi 8 Guitar Amp Conversion

Here are some more time-lapse videos of one of my builds. This one is of me building one of my original designs, an 8 watt, single ended, Plexi style guitar amp out of an Akai Roberts tube monoblock amp from one of their 60's reel to reel decks. I did the teardown, desoldering, and cleanup of the donor chassis in a previous blog. This set of videos has me taking all the parts, both new, and refurbished, to build the amp.

In this first video you can see the parts all laid out on my bench. I am wiring up all the heaters and ground wires directly to the tube sockets.



In this second video I am installing the tag strip board, wiring up some of it, and then stuffing the custom painted faceplate with parts. The blue tape is to protect the paint job during the rest of assembly.



In this third video I am installing the faceplate, wiring it up, and installing some parts directly to the tube sockets.



In this fourth and final video I am finishing up this amp: wiring up the rest of the tag strip, controls, and tube sockets. All that is left now is knobs, tubes and a power cord and it is ready to test! I will be recording this amp over the weekend and posting samples soon. Oh yeah, and the schematic, as promised. I add a 25uf-25 volt electrolytic cap across the 820R resistor in the cathode follower (pre-EQ) for more bass if it will be used with a bass guitar, but otherwise this is the schem.

Tablebeast TB-PLX1 8 Watt Akai Roberts Monoblock Conversion, the Plexi8:

This amp is made reusing the chassis, choke, and transformers of an Akai / Roberts tube reel to reel monoblock. I also reuse, once refurbished: a few resistors, the tag board strip, some jacks, the meter, tube sockets and retainers, various screws and hardware. But all of the wiring, coupling caps, electrolytic caps, pots, knobs, some jacks, power switch, fuse block, and paint is new. The pictured case is made out of the original wood tape machine case sliced and reworked. The rubber feet and rear plate is also original Akai / Roberts. I can get the donor amps for $50 to $100 each currently plus shipping that also ranges whether I have someone send the whole thing or not. The tape transport is sacrificed to the metal recyclers for about $3. If anyone ever needs any transport parts let me know. I hate tossing them, but am forced to every once in a while when they pile up too much. This is all of the summer of 2012, so who knows where costs will go, but I add about $35 worth or parts. So, it is easy to get it done completely for under $150 and even under a hundred if you're lucky! All in with case building and all it is about 16 hours of labor for me, so expect twice that for a novice. But anyone could possibly build this as it is not difficult. Taking it apart really gives you a good idea of how to put it back  together. I have improved greatly on the strength and rigidity of my soldering, parts mounting technique. They just kind of flooded everything and stuck parts and wiring in the blobs. This has held up surprisingly well, but cold solder joints are more likely, especially with a slightly flexible tag strip board. I mount all my parts directly to the tag and then wrap my wiring around it all and crimp it tight making a full mechanical connection before a single drop of solder hits it. Luckily, because of the quickey way the original Akai builder made most of these units they are much easier they are to take apart. My finished mod would be a real beeotch to take apart completely compared to the original way it was built. It will still be easy to service of course, small repairs are no problem, but the way I build it, unless something smashes the board, it should work forever. Call my building style brick shithouse for lack of a better term, they are lightweight tanks. Maybe in 35 years you have to replace the electrolytic caps and of course tubes will come and go, but the finished product is like a sexy Japanese sports car of an amp. I keep the made-in-Japan tubes stuffed int here as much as I can help it as they just sound right! I've always been a sucker for an old Datsun, so I have a fond appreciation for Japanese engineering of the post war era. They were so far ahead of us for so long and held out longer before everyone started "value engineering" everything. Anyway, long story short: you can build a sweet amp cheap and have it last forever!