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807 monoblocks

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PSE 807 monoblocks is my latest project . I decided to build this pair of monoblocks in the summer of 2002.

An externally hosted image should be here but it was not working when we last tested it.


It was my decision to use the less known 807 tube, a tetrode whose features and sounds i was well aware of, from a specific diy project (with one tube per channel ) made by Christos Spathopoulos.

kato_opsi_807.jpg


The whole construction is hard wired with the only exception of small board for the power supply capacitors. All the most critical path of amplifier have been wired using silver-teflon cables (especially the high voltage paths).

Image_sasi.jpg


The use of a NOS pair of RCA 807s tubes has improved a lot the clearness instead of the Westing House 807s i used before. The driving section uses the 12ΑΤ7 and the pre amp is the PV10A conrad-johnson.

find out more here : http://sarris.info/main/en/pset807

costas
 
Nice looking amplifier! I have always had a nice warm corner in my heart reserved for the 807, as of now I have 16 NOS and growing over time... at least as they remain somewhat "undiscovered" and cheap. Out of curiosity what kind of power are you getting out of it?

Cheers

James
 
Odd, never thought of the 807 as undiscovered... my Dad used them in his power amplifier back in the 1950's. I would agree that the Westinghouse versions weren't that great... usually made in Canada and the plate cap had a spline pattern on it.

One thing to look for on NOS versions... the internal structure on the earlier ones had ceramic supports top and bottom... later manufacturing changes deleted these, so even with NOS versions there are some better than others.

In short, the 807 is a nice tube, but they suffer from fragile screens and can have a short life if the screens are pushed a bit too hard. Nice work on the amp.... I also use AutoCad for schematic and chassis layout.

Regards, KM
 
thanks !
this amp works in a tetrode connection (about -15.5 Volts in Grid ) and according to my estimations it has about 16 -18 watt output power.
These babies sounds really pretty ! (clear voices and excellent mid - freq tone ! ) I combine them within a pair of a BL horn speakers and i enjoy every minute of listening !

costas
 
kmaier said:
In short, the 807 is a nice tube, but they suffer from fragile screens and can have a short life if the screens are pushed a bit too hard. Nice work on the amp.... I also use AutoCad for schematic and chassis layout.

Regards, KM

i agree. that was a problem with Westinghouse and some pairs of CVC (Chelmer valve). Now i m using two pairs of NOS RCA 807 and i have no problems.


costas
 
I guess undiscovered wasn't really the correct word choice, you are right about that. Though they sound just as good or better the 6L6 types and 6550 types seem to steal all the lime-light. There isn't an abundance of DIYer's or pro companies that use them in their designs. Thankfully due to this, and the fact that they where made by the boat load, the price has been kept low. I am afraid though that as 6L6's reach up to $100 plus a pair or more the 807's will slowly start to rise in price as well.

Cheers

James
 
JPeitzman said:
I guess undiscovered wasn't really the correct word choice, you are right about that. Though they sound just as good or better the 6L6 types and 6550 types seem to steal all the lime-light. There isn't an abundance of DIYer's or pro companies that use them in their designs. Thankfully due to this, and the fact that they where made by the boat load, the price has been kept low. I am afraid though that as 6L6's reach up to $100 plus a pair or more the 807's will slowly start to rise in price as well.

Cheers

James


Thats right ! and i have to quote that : As i m listening tubes during last two decades i noticed that manufactures chose classic audio tubes ( EL34, 6550, KT88 etc) for their designs. Don't forget that 807 is a classic power output tube designed for transmitters...
It is difficult to make a design using this tube as an AF output. ( these designs suffer from noise produced by heaters, or from a careless design in power supply... ). Using of chocks or interstage transformers solve these problems but increases cost ( e.g WAVAC) and make the whole construction more complicated.
I think that this is the reason that remain "undiscovered.."

regards
costas

P.S. perhaps they produce the most smoothly and sweet mid - freq i ever heard !
;)
 
sarrisk said:
Don't forget that 807 is a classic power output tube designed for transmitters...

The 807 is a 6L6 in a different bottle. At the time, RF designers still liked the old style 5-pin base, as opposed to the newer octal. Same internals, same specs, but the 807 has a higher voltage rating due to the top cap plate connection that won't work with the 6L6 (socket pin-to-pin flashover) and it's a good deal more convenient in that you can build your output circuits on top of the chassis, and the input circuitry beneath it. That doesn't really matter since the best audio Q-Points occur at the lower plate voltages anyway.

Doesn't matter what it was originally designed for. The 1624 was originally designed as an RF final for mobile xmtrs, but it also has some brag-worthy audio specs: THD= 2.0%, and better than a whole bunch of audio finals. Same deal with 6BQ6GTB horizontal derflection PAs: those sound as good as any of the best audio pents.

It is difficult to make a design using this tube as an AF output. ( these designs suffer from noise produced by heaters, or from a careless design in power supply... ). Using of chocks or interstage transformers solve these problems but increases cost ( e.g WAVAC) and make the whole construction more complicated.
I think that this is the reason that remain "undiscovered.."

Not really. You just have to work within its limitations. Since the 807/6L6 likes to make higher order harmonics, you need to add some local NFB to linearize it. The developer of the type, O. Schade, recognized this, and recommended feeding back 10% of the plate voltage to the grids. I followed that recommendation when doing an 807 design, and he definitely knew what he was talking about. Include active screen voltage regulation and they sound just fabulous.
 
Miles Prower said:

Not really. You just have to work within its limitations. Since the 807/6L6 likes to make higher order harmonics, you need to add some local NFB to linearize it. The developer of the type, O. Schade, recognized this, and recommended feeding back 10% of the plate voltage to the grids. I followed that recommendation when doing an 807 design, and he definitely knew what he was talking about. Include active screen voltage regulation and they sound just fabulous.

Sure. That was i meant saying "careless psu design.." . I heard about NFB but i didn't knew the exact percent of feedback ! Thanks for the ifno ! ;)

regards
costas

(meet me at my DIY web page : http://sarris.info )
 
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