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805 SE stereo amp

R

Rob

Super Member
Banned
Well I've got most of the parts rounded up now for my proposed 30-35 w/ch stereo amp using the 805 transmitting triode in SE class-A. I made some hand rubbed walnut front and rear panels for the chassis today and started experimenting with suitable component layouts. This one best suits tube cooling, signal path, channel separation (reduced capacitive cross coupling between output tube plates), and physical isolation of 3B28 rectifiers to the amp circuits. On the front panel will be input jacks, two volume controls, master power switch and some sort of tube based Vu/power indicators. The chassis will be painted semi-gloss black or black powdercoated.

Does this get your mo-jo runnin' ? :)

Rob
 
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Sweet ! :boink:

Symmetry Rocks and makes trouble shooting the signal path easier.
 
I don't know nuttin' about tubes, but they shore are purty. Seriously it's really nice. I'd like to learn enough to build some kind of kit for a BR system someday.
Brad:beer:
 
Thanx fellas. Yes gonefishin, I did receive your private messages. Sorry if I didn't get back to you. I'm a schklay brain these daze. Powerful meds. :(

I'm getting closer to a circuit design. I asked a friend to help me find curves on an 805 and he found 'curves' on an 805 alright! :) She came from the Dr. Harvey "Gizmo" Rosenberg Triode-Guild Website.

Rob
 
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...and the winner is???????




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I am curious about the general circuit. Is the belled monster in the middle the PS? 4 rectifiers, 4 chokes,(or are 2 of those fil supplies?) 4 6SN7s or 6SL7s and your really big triodes? If this is so why 4 rectifiers? You going to use both sides of each of those driver tubes?
 
805 SE amp

Originally posted by Thatch_Ear
I am curious about the general circuit. Is the belled monster in the middle the PS? 4 rectifiers, 4 chokes,(or are 2 of those fil supplies?) 4 6SN7s or 6SL7s and your really big triodes? If this is so why 4 rectifiers? You going to use both sides of each of those driver tubes?
Click to expand...

Thatch_Ear

Do I have the pleasure of addressing the former Prime Minister of England? :)

Yes, the belled monster is the plate xfmer, no room for the three filament xfmers so those hide inside (I wasn't kidding when said 150 lbs!).
2 6SN7's, two 6V6's (now replaced possibly by 6080's), big toobz are 805's. Four rectifiers because full wave bridge. Yes, 4 chokes, 2 each side, a big one and a small one. I am close to pulling the rectifier tubes and associated 15 lb. high voltage insulated 3 winding filament xfmer and letting sanity prevail. SS will sound better (no emi radiation from the rectifier tubes), but won't look as 'retro'. That would free up chassis space for four 6080's as pass regulators though! :)

I'm after sound #1.000, looks #1.001. Besides good sound is automatically beautiful.

Rob
 
Gotchya:D I listened to some Conrad Johnson monoblocks that had if I remember correctly a 6SN7, 6CA7, 845 set up. I understand you have a very tricky and touchy circuit that you are building. Using SS diodes instead of hollow state will make things a lot easier when you build, but you won't be able to cook over it . Probably can read by the 805s though, so that will save the wear and tear on the light bulbs.;)
 
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What ever happened to this?

Going back through some old posts. I was wondering what ever happen to this project? Did it get shelved in the decision to build your mega multitube monobloc? Just wondering, I really llike the look of those 805's.
 
805 SE not dead

Wards,

I'm working on really limited R&D funds and have put my main thrust into loudspeaker development for the time being. This 805 amp still sits, pretty much as you see it in my lab awaiting my attention. I need output iron and possibly driver interstage iron to move forward on it....and the time. I agree those 805's look impressive.

Rob
 
Rob has an article in the mail that ought to get him frothing at the mouth over the 805s again.
You planning on winding your OPTs yourself Rob?
 
output iron

Originally posted by Thatch_Ear
Rob has an article in the mail that ought to get him frothing at the mouth over the 805s again.
You planning on winding your OPTs yourself Rob?
Click to expand...

Thatch,

Probably not for this amp. Rolling your own output xfmers is very time consuming and subject to a learning curve where experience is valuable. To make a successful output transformer yourself may require you to make several transformers. Like automobile tires, output transformers are available off the shelf and can represent a bargain compared to trying to roll your own. Ohhhh bad pun. :)

Rob
 
Late but not forgotten

I have finally ordered a pair of SE output xfmers for my long time proposed 805 SE stereo power amp. The pictures I posted of a possible chasis layout are completely out the window at this point. Since my earlier posts on this project I have gone through a wild learning curve in the artistic development department and have some much more 'eye candy' type plans for this behemoth. I am now giving my amplifier designs an innovative signature Deco look.

Getting these transformers will now give me a nice indoor project to go with all the others now on the go for this winter. This amplifier may actually happen yet! :)
 
Re: Late but not forgotten

Originally posted by Rob
I have finally ordered a pair of SE output xfmers for my long time proposed 805 SE stereo power amp.
Click to expand...
Hey HEY, that's exciting! What did you decide on? I think I would go with Electra-Print for an SE transmitting triode. But there are many choices. Good going Rob!

I have on a shelf an unfinished project for 845 (or similar) tubes. I liked the idea of parallel feed, with a giant high-inductance plate choke to handle the plate current, and a relatively small ungapped output transformer, with a capacitor to keep the OPT DC-free. I built a dual 10vdc filament supply with two chokes per supply (one chassis, extremely low ripple), a chassis for the chokes and OPTs (Magnequest), a chassis just for the audio tubes, and another for the HV PS. I used 4 matching chassis bases, all narrow, and it's not quite as monstrous as it sounds. The idea was to avoid a hernia with 3 merely HEAVY chassis, rather than 1 unmanageable one.

I let the project go when my son was born, and 1000+ vdc didn't seem so important. Now I have a pair of deHavilland 845 SE amps, so I have the audio quality I was after, and it confirmed my love for the 845. So I thought maybe a much smaller, less powerful single-chassis amp...

So I recycled a PA amp chassis and built up a design running the 845 at lower voltage and current (more than a 300B, but not a lot more) and using 3K OPTs. I've heard this recipe before, and it's a winner. It is mostly built, with plate-choked 6550 for driver and 6SN7 before that. I used a full-wave bridge of damper diodes for B+... but I haven't finished wiring it anything but the power supply and filaments. It's very heavy, as I used a lot of chokes. I guess if I were starting it now I'd consider 813's...

I'll take pictures one of these days.

Tubino
 
Tubino,

That behemoth project you described sounded like a winner performance wise. Too bad you didn't finish it. Not the leanest design however. I'm glad you have found what you were after in the Dehavillands.

Regarding 813's, I had a pair of 'em and in the last move they got lost. I would like to try them as the circuit is simplicity itself and you'd end up with an amp resembling an overgrown SE 6BQ5. Might even sound as good as a SE 6BQ5 and that would be awesome!

The output iron I just ordered is from handwoundtransformers.com . It is far less costly than some of the SE alternatives and will enable me to at least proceed with this experiment. I just don't have $500.00 each to spend on output iron for this experiment. I'm fully taxed both timewise and financially on several other projects at the moment. These transformers are rated at 120 mA, 25 watts, 10K ohm primary, 4-8-16 secondary, 20 Hz - 45KHz. At 11 lbs they are a good chunk of iron and would be the size of the end belled plate transformer seen nested in the center rear on the chassis in the pictures I posted at the beginning of this thread. One interesting idea is that if I choose to try parallel coupling I can close the air gap in these, improving the bottom end, increasing L and use these as the ouput transformer without DC. Additionally, putting the 8 ohm load on the 16 ohm tap gives me a 5 K ohm plate load Z option.

My thoughts on parallel coupling are that it is an exciting alternative to the conventional transformer for SE circuits. I am using it with great success in my SET design using multi 6080's in parallel.

I've chosen to use the 805 only because I have about a dozen good pulls in stock. The 805 was designed for zero bias class-B use. If I were buying a tube new I'd probably choose the 845 as well. It has curves that better suit class-A operation. I am initially going to try the 805's in Class A-1 which makes the driver a lot easier to build. I don't need full 45 watt output potential from this bottle with a 25 watt output xfmer so this may be OK. I'll likely be running my tubes at max plate voltage rating because of the class A1 to get the power I need. The amp will be designed so curious fingers cannot find the high voltage, so no worry there. Like I said, this is an experiment. I love the learning curve and fun associated with such 'experiments'! :)
 
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