Tractrix horns with the BMS 4524L high frequency compression drivers
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Back loaded horn loudspeaker based on FOSTEX FE206 full range drivers. 
811A Tube amp DIY project. This direct heated triode design uses the Svetlana SV811-3 Tube. 
807 single ended tube amps
Submitted by costas sarris on Sat, 06/09/2008 - 01:22.
DIY tube 807 amplifier by costas sarris
In the summer of 2002 I decided to build a pair of mono block parallel single ended DIY tube amps, using the 807 tube. Actually, that was my third DIY tube amplifier project. It all started with my decision to use the less known tube 807 , a tetrode whose features and sounds I was well aware of, from a specific DIY project (with one tube per channel wired in triode) made by Christos Spathopoulos. Christos’ tube 807 amp played very smoothly in the whole spectrum (perhaps the best sound I had heard until then ) but, unfortunately, it lacked power.
After we discussed my idea with Giannis and Christos Spathopoulos we focused to build a tube amp with two parallel 807's per channel in a cathode follower connection, wired in tetrode - class A, using negative voltage in screen, based to the characteristics according to RCA and SCT...
My Parallel single ended 807 vacuum tube amplifiers at a glance :
- two 807 tubes / channel (parallel single ended)
- two independent power supply stages per Channel
- full tube rectifiers PSU
- pure class A
- No feedback
- two independent lines for tube 807 biasing
- CNC chassis design
- hand made output transformers P&K audio
For nearly two months Christos and I worked designing the amp -- having in mind to solve two major problems. First, it was my idea to build the power supply using tubes as rectifiers, and the second concerned the bias circuit for the final tubes. Finally, we decided to use two independent lines for powering the system (using GZ34 for the drivers and 5U4G for the power stage). We also built the Bias circuit, based on two SPECTROL 22K micro potentiometers for adjusting the bias (one for each tube ). Each tube 807 is biased at -15.5 volt (grid). Plate voltage is about 505 volts, and screen voltage is 228 Volts. Find the 807 tube amp schematic in amp schematics pages and the 807 tube data in tube data pages.And the Power Supply Unit schematic. The use of a NOS pair of RCA 807s tubes improved the clearness a lot instead of the westing house 807s I used before. The driving section uses the 12ΑΤ7 (general electric) (one per channel) and the pre-amp is the well known PV10A Conrad Johnson. I have to mentioned that Christos Spathopoulos triode SE807 amp was a derivative work based on RH807 by Alex Kitic costas sarris
807 Tube amplifier building
Next step was to construct the chassis. I designed the chassis in auto cad and my friend Gregory (who has a CNC) did the whole work. The whole construction is hard wired with the one exception of a small board for the power supply capacitors. All of the most critical path of amplifiers have been wired using silver-Teflon cables (especially the high voltage paths).Driving - pre amp
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Nice work ! congratulations.
Nice work ! congratulations.
πολυ καλό
πολυ καλό
Hi ! very nice amplifier,
Hi !
very nice amplifier, thank you for the inspiration.
What's the blue glow ? is it the tubes or did you
incorporate a blue LED ?
Cheers,
Mark
Thank you Mark ! Blue glow
Thank you Mark !
Blue glow is from the tubes (working with 505 volt !)
regards
costas
Hi, Could the builder of
Hi,
Could the builder of this amp email me I am a producer and looking for a very cool amp to feature in a TV program. I can be reached at scott@twistedlimemedia.com
Hi ! Already send you an
Hi ! Already send you an e-mail. Check your inbox.
costas
They run hot :-) Good job !
They run hot :-)
Good job !
Can you please explain 5 Ohm
Can you please explain 5 Ohm cathode resistor on 807 tubes? Normally it is 250 - 400 Ohm.
In auto biasing the tube yes
In auto biasing the tube yes you have right, (usually is 250 - 300 ohms), but here we have a direct -15.5 volts to the grid for biasing the tube, so we need only a small resistor for dropping about 250 mV from cathode.
you can take a look here see the section about tetrode connection (single ended)
Biasing the tube using direct negative voltage in grid helps for matching the tubes works the same.
costas
Hi Costas! Thank you for
Hi Costas!
Thank you for your fast answer! I get it now... By further research I found construction similarities to RH807 by Alexandar Kitic (12at7, Rfb and other component values). Can you estimate RH807 wattage, since there is no any data that can be found?
What is your estimate or measured RMS wattage for your amp? Datasheets also say 10% THD for 807 tetrode grid-biased construction, which is probably hearable at higher volumes? Also is there schematic for your dual tube power supply available?
Regards,
Damir
I know the RH807 for many
I know the RH807 for many years now and i had listen an amp with this exactly design, before start constructing my 807 and i was really impressed.
Actually my design is similar to RH807, but there is a big difference between my 807 SE and RH807, regarding the topology. In RH807 the tube is auto biased and connected as a triode (anode and screen strapped ) ( that means low distortion and low power ), while in my design connected as a tetrode for achieving more power output and also using a direct negative voltage to grid. Αcording to my estimations my amps wattage it is no more than 17 - 18 Watt while a triode design can supply only 3 - 8 Watts depending the plate voltage and the tube.
Talking about THD the answer is yes, this design ( according to datasheets ) distort more, but having in mind that all SET designs distort to some degree some times "how it sounds" have greater importance than the data sheet curves.
Besides that, i choose to build a 2 X 807 parallel SE amp for having enough power to drive the speakers (a BL horn with full range drivers ) without running the amp to the edge where the THD is greater.
And at last I have to say that I am from those who like this sweet tube amp harmonic distortion !
costas
Very nice work. Good
Very nice work. Good looking, too. I've always had a soft spot for the 807 tube, probably since the first good gear I ever had included a PP 807 power amp my dad built during the Hi-Fi boom of the 50's (single-channel in those days).
I will be building a pair of them as soon as I can start assembling the components. Thanks for the design, and for providing the impetus to get going on the project I've been looking for.
Thanks for your reply and
Thanks for your reply and for your comments ,
If you have any questions regarding this specific project don't hesitate to ask
costas
Hi Costas, Great looking
Hi Costas,
Great looking amp!
I am thinking of building a 807SE to drive my open baffle speakers. What voltage do you have to drive them at to get the blue effect, or do they always look like that when running?
looks really cool.
many Thanks
Ian
Ian, plate voltage is 500
Ian, plate voltage is 500 Volts. The blue effect is always look like in the photo (it is more visible using westingHouse 807 tubes ) and it is more impressive and visible when the listening room has low lighting.
the schematic is here http://sarris.info/main/807schematics
costas
Beautiful amplifier, Costas.
Beautiful amplifier, Costas. I've been looking around for quite a while for one to build, and your's is definitely a serious consideration. Just curious about your transformers. What did you use for your power transformer? I bet you use 240 mains in Greece, and I want to see if there is a comparable model for 120 here in the states.
Best Regards,
Jim
Jim, here in Greece we use
Jim,
here in Greece we use 220V mains. The power transformers in this project are custom made, ordered in a local laboratory. The data for the transformers are as follows :
T3 (secondary ) = 600-0-600 volt 250mA
T2 (secondary ) = 5V 3A
T7 (secondary ) = 280-0-280 volt 150mA (Im not sure - Ι have to check it again - Its been a long time since their construction !)
T6 (secondary ) = 5V 3A
T1 (primary) = 220V (if you are in US I suppose this must be 110V or 120V for Canada)
the link for the PSU is here http://sarris.info/main/807-se-tube-psu-schematic
if you need any help contact me via the contact page or post your question here
costas
Costas, congratulations on a
Costas,
congratulations on a fantastic job. I'm seriously considering building them. I was given some NOS RCA's over 10 years ago and am getting itchy to bring them to life. What are your thoughts on modifying your circuit to 4x 807 parallel SE in triode mode?
Craig, I think It is a very
Craig,
I think It is a very good idea to build a 4X807 parallel SE. If you connect the 807's in triode you have a big advantage regarding the THD which in triode mode (for the 807) is less than in tetrode mode !
Proceed and let me know if you need any help.
costas
Hello Costas, it is really
Hello Costas,
it is really meaningful, that the tubes work with 500V? Can you say something to the longevity of the tubes with 500V operating? Thanks for your reply.
But it´s really a nice project.
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