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Hi All
Just finished a 801A amp, something I have been planning to do for few years and finally got to it.
Initial impressions - clean tops and mids, and the lows are nice and tight. J&K audio xformers give this tight sound to the lows. I will be installing their nano-crystal 5K o/p transformers in my 811A replacing my James sometime in the next few months.
- Filament supplies for 801A's are Guido Supplies
- Bias supply is using Pete Millet's bias supply boards
- Input and driver tubes are 6EW7 dissimilar dual triodes in one tube perfect for this application
- First stage is cap coupled using Duelunds
- Second stage is 2:1 stepdown Lundhal IT, which should be good for brief A2 transitions
Power transformer is custom Heyboer. Initially I started with 2 X 6AU4's for full wave rectification, messed up in the drilling for the octal openings and opted for using UF4007's for rectification and a single 6AU4 for slow start on
Next amp in line - as of now, the plan is a 2 stage amp using 12GN7 as the gain stage and using mosfet source follower to drive 211 grid.
cheers
ganti
Follow Ups:
Comments to improve this amp :(1) You do not want to use electrolytics, nor any single cap, as an Rk bypass. The electrolytic Rk is IN the SE audio circuit, every cap is.
(2) You would do better to get rid of the 0.22 uF coupling cap, and use about three small gauge pure silver wires, as a Direct Couple of the two stages. Its superior coupling, compared to your use of a Dueland cap.
(3) You need to have the RCA jacks located in the front of the amp, so the lead length to the input tube is SHORT, and not effected by under-chassis fields. Suggest under two inches, doubled-up silver wire.
(4) The use of a 10 HY choke, with a "whopping" 130 ohms of DCR, is "anti-good" audio. The 801A, or any good DHT, is a " direct access to the music" device, and so, chokes need to be 20 Ohms MAXIMUM, or less. This is "rule number one" in building a superior SET power supply.
(5) Have a choke as the first element "seen" by the rectifier tube, not a cap. Choke can ( and should ) be " non-critical " in inductance.
(6) Have the output and power transformers' cores face the vacuum tube, NOT the open winding as you have them positioned. Turn trannies 90 degrees.
(7) Your driver tube seems to be a bit too far away from the output tube, and the output tube is crowded by the output transformer's close proximity.
Nice looking.
Jeff Medwin
Edits: 04/16/16
Nice job!!! Looks like a good circuit. The 10 family sounds really good, my favorite is the 842.
Congrats! Hope you enjoyed the wine as well... I built a line preamp based on that tube (and 10Y), it's very "clean" sound. Good luck with your 211 project.
... I love the sound of all the type 10 variants.. they all seem to have that clear sweet quality.
Enjoy your new amp. Let us know of any changes in build or more importantly in sound !
Have fun!
Willie
You have any 801A variants you don't mind parting with?
Sorry Geo, ..I only have one real 801A. I do have pairs of 10's, 10Y's and VT-25's.
All I use in my DC Universal DHT stereo amp.
Don't give up searching Geo there are probably more out there!
Have fun
Willie
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Have Fun and Enjoy the Music
"Still Working the Problem"
the801 need the load to be 10k at last, better 14k ,there is a proper LL opt ....
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