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First DIY tube amp
First DIY tube amp
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Old 13th June 2018, 04:46 PM   #11
guitarnerd is offline guitarnerd  Taiwan
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Good call, you're right C2 should connect the the anode of V1.
Yes, I'll look into LTP input stage and see how that goes. thx for the advise
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Old 13th June 2018, 04:50 PM   #12
jazbo8 is offline jazbo8
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First DIY tube amp
Quote:
Originally Posted by Sodacose View Post
See the well-documented AB input stages here for inspiration:
Do you mean even better documented than the Williamson amplifier?
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Old 13th June 2018, 05:15 PM   #13
azazello is offline azazello  Bulgaria
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Down side of speaker must be grounded. Between pot. R22 and ground must be res. 5-10 kohm against full openning of tube. The same and for R23...
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Old 14th June 2018, 12:30 AM   #14
kward is offline kward  United States
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To get 75 watts output in UL mode with KT88's, 6550's or equivalent, you'll need approximately 525V to 550V at the center taps of the output transformers with 4.3K to 5K primary impedance transformer and with 33% to 43% UL taps.

But the devil is in the details as they say. If this is your first attempt at scratch designing and building a power amp, I might suggest a simpler and lower wattage type for starters. I'm quite fond of my 6V6 amp that I re-engineered from a Motorola console. Twelve glorious watts!
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Old 14th June 2018, 09:02 AM   #15
hooman is offline hooman  Iran
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Quote:
Originally Posted by jazbo8 View Post
Do you mean even better documented than the Williamson amplifier?
hi
can explain about Williamson amplifier different to other pentode amps ?
nfb ?
pentode use ?
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Old 14th June 2018, 09:18 AM   #16
jazbo8 is offline jazbo8
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The Williamson amplifier is arguably the first "modern" tube amp design, first published in Wireless World back in 1947. Definitely pentode, as Williamson detested the "ultralinear" connection. There are literally hundreds of variants/clones of the Williamson amplifier since then, which you can find via a bit of Googling. Have fun!
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Old 14th June 2018, 11:24 AM   #17
hooman is offline hooman  Iran
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first audio project should be push pull and made by popular hifi tubes . dont use compectron and tv h out like el509.....transmitter tube .....dht tubes like 2a3....6b4g...vt25...300b..
but 6l6gc.....el34....6v6.....el84....6550...kt88...kt 66... ecl86.. are easy to use .never use ac transformer in place of output chock .tube rectifier is safe for beginners amps .
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Old 14th June 2018, 03:23 PM   #18
kodabmx is offline kodabmx  Canada
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I've built seven amps using Triad VPT series power transformers as OPTs, including a KT120 triode push pull that makes 45W, 5W class A limit. If you use individual bias controls in fixed bias, an automatic bias board like the ones Pavel sells at audioamp.eu or either CCS cathode biasing or a garter circuit, they work very well. They can tolerate a slight DC unbalance, too.

I would suggest for a first time build to use cathode biasing for the simplicity of it. You can always modify it for fixed bias at a later time.

The Acrosound 6L6 build was my first build, and it sounded great from the first power up. http://www.keith-snook.info/amplifie...%20Rebuild.pdf

If you build the above, I suggest separate biasing resistors (R14) for each output tube. Simply double the value of the single resistor to achieve the same bias point. Bypass each one with it's own capacitor. I prefer 330uF instead of 100uF.

Last edited by kodabmx; 14th June 2018 at 03:28 PM.
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Old 14th June 2018, 08:19 PM   #19
Sodacose is online now Sodacose  United States
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Quote:
Originally Posted by jazbo8 View Post
Do you mean even better documented than the Williamson amplifier?
Touche. But try asking Williamson for help if you don't understand something about his write up George, on the other hand, will probably chime in on this thread at some point if you ask him to or not!
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Old 15th June 2018, 04:46 AM   #20
jazbo8 is offline jazbo8
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Just joking... George's design is a truly modern take on the classic design.
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