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mpuman 4th January 2011 10:36 PM

805 MonoBlock SE Amp Kit?
I have been lurking for a while. As a recovering audiophile from the past, I am convinced that I want to do a monoblock based upon the 805 to restart my interest. Have been designing and mfg all sorts of electronics for several decades, so experience I have plenty of.

With contacts and suppliers in Taiwan, HK, China, & the US, for just about everything, I have no real issue of putting it together other than if I should and of what design / features.

The production side of me sez, if I'm going to do 2x units, why not do 30x or so to start. The design that I am leaning to is based upon Bauanleitung fuer einen 805-Verstaerker, von Ronald Koridon - really like the concept - but in monoblocks. Thinking of canning the B+ silicone in favor of valve rectifier.

The reason for the thread is to get some idea if there is any interest in the future kit. No, I don't know the price yet - as it is only in planning, but I am sure it will not be cheap - but will be reasonable. The iron is very pricey as you guys know. My guess it might be 4-6 months until ready to ship.

Right now I am working with some well known and not so well known trany mfg to get some ideas. It is really interesting, one of my 'normal' domestic suppliers used to source the Acrosound back in the day ...

Open to all suggestions and patter - perhaps it will get all of us that are interested in this style of amp an easier and better way to put it together - or on the other hand, it might kill the project!

TugaTweaker 5th January 2011 12:08 AM

805 MonoBlock SE Amp Kit?
I have done it in monoblocks . The 805 is a really good sounding tube, I have three NOS american makes RCA ,United , and less known CEI . Difficult tasks in this Nobu Shishido schematic is to replace the rare and costly WE437A and achieve a clean 3.25A 10v supply and solve hum. I was obliged to buy the very effective GuidoTent heater supply make. Replace the IITC interstage specially wounded by Tango, it is nearly impossible. I started with a russian driver the 6H45pi sounds good but it oscilates easily and my task for now is to change it for the Shishido's 12AU7 and or 12AT7 version , or maybe 6SL7. I think the idea of a kit is a good one but i am sure will be costly aimed for diehard tubesound lovers .


singa 5th January 2011 07:39 AM

Hi mpuman,
Perhaps this project may be too much to chew on.I don't mean
to be sarcastic but like you say putting our heads together can make
for an achievable one.

1. Shishido's circuit may put off the pure single ended guys because it has
feedback from an extra coil at the output.It has an interstage and
high power rating of the output transformer which make it expensive.

2. It is operating the 805 at positive grid voltage vs conventional
single ended.The plus point is more power to drive inefficient high end

3. There is another implimentation by Hirokuni Michimori at the 2008
European triode festival which he called Regulator Drive which does not
use interstage ( a saving) but still using a feedback coil at output.
This is more feasible at lower cost but still you need custom wind output.

ETF2008 Michimori

Single-ended triode Amps using zero-bias transmitting tubes

Check out the 838 circuit. at low anode B+ so easy on component choice.

So it boils down to standard single ended or much more power with
positive grid and feedback.

Then there is the question of anode cap on top or new one below socket.Will
you implement both for flexibility?

I know I can't afford this so count me out,hope this helps.If you really want to
do it it can be done but what of sound quality?.Shishido died in 1998.Maybe
Michimori can help with the transformer.

Do you have gridstopper resistor 50-220 ohm at the grid
of 6C45? that should stop oscillations?

If you use tube regulator then only one type 5R4 is feasible,I know there are russian tubes but you want people to have easy replacement and unfortunately 5R4 is NOS so no current production tubes.

JLH 5th January 2011 11:29 AM

Keep the cathode feedback on the output transformer - this is the best sounding type of feedback for zero/positive bias transmitting triodes. Get rid of the interstage transformer and use a FET follower and bipolar power supply with a CCS in the -B supply. (aka Tubelab's Power Drive circuit) Try to DC couple the first and second amplification stages and then cap couple to the FET. Don't even think about using the crappy 6C45Pi. There is no reason why you can't use current production 6SN7/12AU7/6SL7/12AT7/6V6 etc. and get good results. I would stay with solid state rectification, you don't want a tube rectifier choking the dynamics of your amplifier.

mpuman 5th January 2011 04:25 PM

Hi guys,

Thanks for the input - it all helps with my decision.

TugaTweaker, I too was thinking of replacing the WE437A with a 6C45, but JLH's comments (and others) kind of led me away from that and looking at some of the alternatives that are suggested. Do you have any of Shishido's 12AU7, 12AT7, 6SL7 version designs? I have heard that if you drive the 6C45 harder >10ma, it starts to be very nice.

I too was considering a Constant Current Heater supply for the 805 for the same reasons that Tent observed - I think it is the way to go - you have confirmed it. What do you think of DC or CC supplies for the drivers? I was figuring on DC.

Since you have built the 805, please explain further: "Replace the IITC interstage specially wounded by Tango, it is nearly impossible" - yes, ex-Tango is gone, but someone, somewhere must have the real specs. As I found, basically is a 1:.08 ratio around 2K5:2K as I recall - OK, 'special winding, etc. Seems to me a very wide band toroid might be a solution - but then again ... BTW, your amp pix looks very nice!

Singa, I looked at Michimori's designs and like some of his ideas, but I have issues with cap coupling ... it opens up all the tonal issues of it. Also, they are much more complex than Shishido's. I don't know, but seem to me simpler is better. An old friend of mine (almost around when tubes were invented) when I mentioned what I was thinking about, told me he did an OTL amp based upon regulators ...

As for the feedback, one of the things that Koridon to the design was lower it. Also could go the way of Cary in the 805 series by putting a pot /w switch to control the FB. That way even the pure Class A guys might be happier.

JLH, OK, you probably are correct about the HV supply, that was one of the things I was juggling with. I will stay with the diodes. The FET follower is a sound technical solution to the interstage, but then too, more complex, cap coupling, and more parts.

As I said before, the big cost is the iron - what I am trying to do is lower the cost of the iron by quantity and design. I want to stick pretty much to a 'classic style'.

Well, a conversation has started - perhaps others will join in and offer their 2 worth. Open to other SE designs, in the 30-50 watt range.

TugaTweaker 5th January 2011 11:07 PM

Mpuman ,thanks for finding my amp nice . I will post here the Shishido's 12au7 alone and 12AU7&12at7 switchable schematic versions , this one delivers 50W rms. The interstage Tango, now ISO, was sold to me by the nice people at EIFL Japan. It is wounded in special way that cancels DC at secondary winding, provided by the IITC design. Explanation can be found at product description of Wavac805 amp at their website . The feedback at 805 tube extends bandwith i think and I like it .To me , besides power the most important goal of this amp is that there are no caps at all in signal way , and that can be heard !!! And we know how much we need to pay for the nice teflon caps or for other best caps !

TugaTweaker 5th January 2011 11:19 PM

I find it ! MJ????? - ?????


mpuman 6th January 2011 03:42 PM

Thanks TugaTweaker for the link. I really like Shishido's 12AU7/12AT7 version.

Too bad that the links to MJ articles are images and not actual text, as I do not read Japanese and the translators need characters. Have you ever taken a look at: MJ????? - ????? - neat, but I surely do not like the feedback cap nor the 22w. I will have to search more of MJ ... sure is a lot of good looking stuff for us.

As I do not have Shishido's papers, do you or anyone else have his notes on the IITC design? The descriptions that I see are rather vague and not geared for an engineer or something that I can spec a part with.

I am making some headway on the transformers.

TugaTweaker 6th January 2011 09:56 PM

Sorry i don't have the book . The second link provided by singa at third post in this thread has it explained by Michimori Hirokuni .
I use the google toolbar translation , it's very helpful and quick .


mpuman 6th January 2011 11:20 PM

I too use google translate - works pretty good.

What about C Core & R Core transformers? Seem to be from a technical side a no-brainer as they are inherently gapped - but from the subjective side - how do they sound? Much lighter in weight and cost? Has anyone actually tried them & listened side by side? If they sound the same, sure would lighten the load both in weight and cost!

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