805 MonoBlock SE Amp Kit?

[mpuman]

316a, thanks for the opinions. There is nothing in the Chinese amp that we have any interest in, as most are cap coupled, and obviously the iron is the major impediment.

Yea, 20 watts is 'only' -3db down ... and 10w only -6db ... but hey some of us like the big tubes, high voltages and challenges

The design actually is real simple and basic - just like the old times (other than CCS). The chassis will provide the HS for the CCS that will be done on a PCB that we just might supply as an assembled unit to eliminate any real hassle (we have auto insertion and wave soldering equ in-house).

I am not reinventing the wheel, just making some minor refinements and packaging it up as a kit. Once some kits are out, my guess is that some of the guys will try their tweaks and make even more improvements. I don't think it will be that much of a money pit - that's what hobbies are. Can't wait to get the final specs & pricing from the domestic xfmr mfgs - that is where the magic (and costs) are.

We are not considering offering any real time support. A blog, FAQ, User Group and such. After all, these kits are geared and sold to serious hobbyist that know how to solder, follow simple diagrams, pictures, and directions.

BTW: I have spec's all power xfmrs to have dual pri for you guys that have 240v power.

[316a]

Originally Posted by mpuman

316a, thanks for the opinions. There is nothing in the Chinese amp that we have any interest in, as most are cap coupled, and obviously the iron is the major impediment.

I find that unlikely , I have only seen 805 amps with DC coupled cathode follower drivers , or in the case of Shishido , an inverting interstage . There are various Mingda etc designs on the web which could be used as a reference . These use either a 2A3/300B or 6L6 variant DC coupled cathode follower driver . Have you seen the impedence a valve in A2 presents the driver ? That would make for a huge coupling cap and I would presume this would sound pretty awful . Also with cap coupling , how are you going to bias the 805 ? If you've seen some cap-coupled 805 designs I would be interested to see how it's done...

I am not reinventing the wheel, just making some minor refinements and packaging it up as a kit. Once some kits are out, my guess is that some of the guys will try their tweaks and make even more improvements. I don't think it will be that much of a money pit - that's what hobbies are. Can't wait to get the final specs & pricing from the domestic xfmr mfgs - that is where the magic (and costs) are.

I don't want to put you off but have you built such an amp yet ? I would strongly suggest building a prototype first . I am in no way an expert , but I build power amps all the time and struggled with A2 . I built several A2 amps with 3C24 , 15E and 826 but the big one used a HK54 output stage with 7236 cathode follower drivers and 809 input stage (a DHT with mu of 40) . It had low gain , requiring a linestage and even with feedback , the bass was poor in comparison to a 300B amp . It was huge , too big for a box and had two HT supplies , one AC and two DC filament supplies per channel . The HK54 had to have DC filaments , which took a lot of tweaking to find a decent sounding supply . To top things off I found that the output transformer has to be very special , what I had to hand was not up to scratch . Mids and top end was very good but I just couldn't live with the flabby bass . I would advise looking in to having the output transformer wound with a cathode feedback winding and run the rest of the amp open loop . In terms of price Sowter quoted in excess of £280 per piece for what I wanted . Alternatively try plate to grid feedback with a standard transformer

We are not considering offering any real time support. A blog, FAQ, User Group and such. After all, these kits are geared and sold to serious hobbyist that know how to solder, follow simple diagrams, pictures, and directions.

...rather you than me It's unlikely you'll be able to tell if the buyers are experienced or not , have a look at some of the kit builders' forums such as Bottlehead and you'll see what I mean . Good luck !

316A

[mpuman]

316a, you are not putting me off. Although I have not designed nor built any valve gear for quite a long time, by no way are we newbies. With dozens of products out there in commercial use, we are aware of the problems and pit falls of design & production. Of course we are doing a proto - actually a testbed as we call it. As I stated earlier, it will allow easy testing and modifications of mainly the iron. Once we are satisfied with the design, then we will have the chassis done and final BOM, manual, and pre-builds by a couple guys to catch any issues. Then the kit of parts would be ready. Although a valve product is 'new' to us, the design plan has been time proven here many times.

I've looked at the Ming Da 805 mono blocks (MC3008). They cap couple from the 12AX7 to the 12AU7, then cap coupled to the 300b, then they direct couple the 300b to the 805. Straight DC heating of the valves by what looks like 25amp std bridges ... Personally I just don't like their design. Actually from the pix that I've seen, I don't like their assembly methods either, sloppy, too many parts, and looks like a semi-experienced hobbyist did it. They are supposed to be a commercial product? Maybe I saw old pix ...

We are planning to use the Shishido design with inverting interstage. Valve line up is 12AT7 (or 12AU7) direct coupled to a 6L6, then IITC interstage coupled to the 805. My domestic xfmr suppliers assure me that what they turn out is ex-Tango quality but at very reasonable cost. They still need to prove that to me, but I believe they will - as they have been doing so for decades. They will be customize for us.

In the coming week or so, I'll get around to posting the working sch /w changes as we go. Shishido was a very talented designer - simplistic to the max. I love looking at a clean finished product and wonder how something with so minimal parts can function so nicely ... then as you did deeper, you realize what elegance is!

Real easy to tell if a buyer has experience or not. The question asked? ... what kind of a soldering station do you have? I am sure that some might still sneak through, then they will have a boat anchor. The proper warning and such will be there. We are not attempting to be a 'Heath Kit' - just a supplier of a high quality kit of parts at an affordable price. My guess is if the product is well received, there might be a cottage industry for some of you guys to build for those that are not experienced ... or to rebuild the ones that got through the test!

[swb502]

Sir,

I wanted to know, why most of the 805 blocks I see range 20-40w but the Antique Sound Lab Explorer is putting out 50w. From poking around the internet it looks like 50w is the max a 805 can do. So I'm curious why you are aiming for 22w with an 805 to get the same as a 845 in your kit? I don't know much of anything about this stuff other then it seems like a good time to try kit building.

[mpuman]

swb502, we are doing a 50w with a 805 ... I think you are thinking about 845 that does 20w or so

[316a]

Originally Posted by mpuman

We are planning to use the Shishido design with inverting interstage. Valve line up is 12AT7 (or 12AU7) direct coupled to a 6L6, then IITC interstage coupled to the 805. My domestic xfmr suppliers assure me that what they turn out is ex-Tango quality but at very reasonable cost. They still need to prove that to me, but I believe they will - as they have been doing so for decades. They will be customize for us.!

The IIT is a tall order , I don't think you understand just how difficult these are to manufacture . Not only are the Tango's 1:0.8 in terms of turns ratio , which rules out wide bandwidth bifilar windings , but the secondary current offsets the primary current . My understanding in terms of winding geometry that these are very different to a standard interstage and also have a reduced gap . Whatever you will have wound will probably not have sufficient HF bandwidth for purpose . Probably better off using a DC coupled cathode follower or driving the cathode of the 805 using a standard IT

cheers

316A

[TugaTweaker]

The IIT i have is ISO/Tango make# S-2014 . I think their cost isn't very high concerning that it garantees a good final work . I paid near 300 euros with postage from Japan to Portugal .

Regards
tt

[mpuman]

Thanks TT & 316a. I am not going to design the transformers, the transformer guys are. I want to pick up a couple of S-2014 (I think they changed P/N) for references to check the others by. Most likely, I'll also pick up their outputs. I have EI and P cores in the works. The P core looks very promising - if they work as spec'd wow ...

TT, did you order from EIFL? Either the S-2014 is a special, or they changes the P/N. What OT did you order as the 10887 is long gone ...

Anyway, we are on a roll.

[TugaTweaker]

mpuman i think S-2014 is nowadays number .

regards
tt

[jazbo8]

Many schematics here.