SV811-3

[Cressy Snr]

OK,
I think this one deserves its own thread.
Our Ant was never going to do anything with Ed's old Aikido driven, SV811-3 single-ended amp bread board, so I have acquired it and intend to transplant it all into a box.

IMG_0261.jpeg (148 KiB) Viewed 5614 times

It works perfectly on the breadboard and sounds excellent, if a little bit hyper-detailed for my lo-fi tastes, so a bit of warmth needs finding from somewhere. It might be as simple as putting my little collection of old stock ECC83 and ECC82 valves to use in the Aikido front end. Once this weather cools down next week I'll try the old valves in the front end to see if that does the trick before I start tearing it down.

In the meantime I'm going to have to trace out and make copious notes around the subject of power supplies and the rest of the engine room of the amplifier. The audio circuit is simple, but the power supply sure as hell ain't, so we're going to have to be careful about what goes where and why.

[Cressy Snr]

The general idea is that if everything works out the way I want it to, the internal layout and external aesthetics will be based on this:

T_Mayer300B23.jpeg (80.91 KiB) Viewed 5652 times

[Cressy Snr]

As far as I can make out, given a cursory inspection, the amp looks to be a fixed bias design with the DH filaments fed from one Rod Coleman regulator per channel. The regs pick up their DC from a pair of SMPS power supplies, one per regulator.
The front end also looks to be fed from the Coleman regs. The HT supply is solid state rectified, and appears to be choke input, given the 600V transformer and the 500V HT on the power tubes.

There is also a pair of bias supplies providing negative volts to the power tube grids. That's as far as I've got at the moment.

That copious quantities of close-up photos will need to be taken of what goes to what and where goes without saying.
It needs careful examination and a full understanding of how it has been put together before I make any attempt to reproduce it in a box environment.

[Cressy Snr]

The panel is going to be called on quite a few times I think.

[Mike H]

Lurking.

[Dave the bass]

Are you sure it needs boxing up Steve?

It might lose its mojo!

[Cressy Snr]

Are you sure it needs boxing up Steve?

It might lose its mojo!

Don't have much choice in the matter Dave if I intend to actually use it in the house. It's too good to just leave it to gather dust.
It'll be my 'winter' amp

[Cressy Snr]

I've managed to get a few more details from Ed this afternoon via email, so in terms of the power and bias supplies I now have a better idea of what I'm dealing with. The SMPS powered Rod Coleman filament supplies are self-explanatory, so they shouldn't be that much of a problem.

[simon]

The front end also looks to be fed from the Coleman regs.

That would be a bit of a surprise I think. I wouldn't have anything attached to the reg than a single SV811. Definitely worth a separate heater supply for the Aikido.

I feel your boxing up pain BTW, I've had a few failed attempts at boxing up the GM70. Maybe one day...

[Cressy Snr]

That would be a bit of a surprise I think. I wouldn't have anything attached to the reg than a single SV811. Definitely worth a separate heater supply for the Aikido...

I traced the heater lines for the Aikido driver back, and yes they do get their DC from the Coleman regs. They will be getting their own supply. I have two Danbury 6.3V heater transformers, one of which will be just the ticket for that job. The 600V BLS transformer only has the one HT secondary, so it looks as if Ed had no alternative, due to a lack of room on the breadboard for any more transformers. I won’t have those restrictions with a Thomas Mayer type vertical stacked construction.
Gonna be a fair bit of Dexion involved with this one.

[simon]

The loop I keep going around is:
- weight too heavy for one box
- so build PS for HT and filaments in separate boxes so I can lift them
- now I need multipin connectors of suitable voltage relating. Which aren't cheap, or particularly easy to specify the correct parts.
- so build monoblocks - erk, only got the one HT transformer for output valves and one for drivers. So now I need to buy 4 HT trafos, and probably some more chokes.
- put it all back on the shelf and think about it again another day

You'll do far better than me I know.

[pre65]

Expense aside, monobloks are probably more sensible in several ways.

Using wheels is good if you only need to move short distances on one level.

For connecting sub assys of big (and heavy) amps I was a fan of using stainless M4 screws and nuts/washers mounted on Delrin, and attaching the wires with M4 solder tags. Spacing each pair at least 1" apart.

[Cressy Snr]

Much tracing, emailing and drawing later, we have some schematics:


Audio Circuit:

AikidoSV811-3AudioCct.png (61.59 KiB) Viewed 5359 times

Power Supply:

SV811-3PSU.png (46.64 KiB) Viewed 5359 times

Bias and Heaters:

Bias&Heaters.png (58.04 KiB) Viewed 5359 times

Edit:
I've missed the earth symbol off the bias supply drawing, but I really can't be arsed to change the drawing. We know where it should go. Let's just revel in the imperfection.

[Cressy Snr]

The intention is to put in a tube rectifier because I like the look of them; no other reason than that. This of course means that with the chosen high voltage 5R4GY, I will be around 50V short of HT. This puts the output stage HT at 450V, which is the book value off the data sheet for a 3 and a bit watt power output. I'd like to get used to this kind of project before I go hoiking the HT up for higher power.

This also means, that in the presence of the tube rectifier, Ed's original RC scheme for the last cap feeding the Aikido driver will be short of voltage, so a series gas tube has been put in to knock 150V off the 450V, which will keep the Aikido driver at 300V...ish.

I'm still umm-ing and ah-ing about the SMPS supplies to the Coleman regs and whether to keep them or revert to Ed's older scheme and feed the regs with a linear DC supply. I have a big 9V 300VA twin secondary toroidal transformer that could be used to make a supply to feed the regs with a 12V DC output per secondary to the regs.

[izzy wizzy]

I have a similar beast, just PP. I use 2mm plugs and sockets, shrouded 1000v rated for HT internally. Iec mains to join mains between chassis. So only 4 x 2mm and 1 iec between chassis.

I had smps feeding lehane regs and swapped it for rod's linear design. Smps won't be going back . Huge difference IMHO.

Mine are also stacked; audio on psu. Whole lot on casters.

Good luck!