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Oddwatt Push Pull Tube Amplifier Projects
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Author:  ian99 [ 29 Dec 2008, 00:17 ]
Post subject:  Re: Ming Da MC34B 6P3 / 6L6 Tube Amplifier

Hmmm, I went ahead and the result is excellent. I only modified the power amplifier section, the 6N2 and 6N1 valves are still being used to drive the output valves, but only the first half of each 6N1 phase splitter is being used. Any doubts I initially had about this unusual and simple circuit are completely dead and buried, from initial listening there is now deep bass I had not heard before and the clarity at all frequencies is improved. Very, very nice. Thanks Bruce.

Will post some pics later.

Author:  ian99 [ 29 Dec 2008, 07:58 ]
Post subject:  Re: Ming Da MC34B 6P3 / 6L6 Tube Amplifier

An example of a heatsink for the LM317 that is on the small side, it works, but is pushing it. Some pics:
Image
Image
Image
Image
I will make something more substantial when I get back to work.

Bruce, I am not sure that cathode bypassing of the LM317 regulator is not possible:
http://www.glass-ware.com/tubecircuits/ ... ing_2.html

Ian.

Author:  Gio [ 29 Dec 2008, 18:26 ]
Post subject:  Re: Ming Da MC34B 6P3 / 6L6 Tube Amplifier

Hi Ian, glad that worked out for you. How did you mount the potentiometer to the chassis?
Cheers,
Gio

Author:  ian99 [ 29 Dec 2008, 19:04 ]
Post subject:  Re: Ming Da MC34B 6P3 / 6L6 Tube Amplifier

Gio, I used some non-acidic silicone (Dow Corning 3145RTV Gray) which holds the pot nicely but can also be removed without breaking things, if required.

Author:  gofar99 [ 30 Dec 2008, 15:13 ]
Post subject:  Re: Ming Da MC34B 6P3 / 6L6 Tube Amplifier

Hi Ian, Bypassing the cathode on one of the self inverting output stages defeats the inverting process as the second tube gets its drive essentially through the cathode. On a conventional amp with the phase inversion done earlier and each tube driven in a typical fashion it may be possible to use a bypass cap across the 317. I can not determine exactly what the implications would be of such an arrangement. More gain probably, distortion ?, would it still be fully class A ?, I don't believe there would be any harm in trying it. Let us know if you do.

Good listening
Bruce

Author:  mwhouston [ 30 Dec 2008, 16:24 ]
Post subject:  Re: DIY KT88 Tube Amplifier Monoblock

gofar99 wrote:
Second photo

Bruce,
Just took another look at your monos. Yes they sure do look good. What do you think is your best build so far for this configuration? I'm still waiting parts from Edcor before I can start me SEs.

Author:  ian99 [ 31 Dec 2008, 06:29 ]
Post subject:  Re: Ming Da MC34B 6P3 / 6L6 Tube Amplifier

gofar99 wrote:
Hi Ian, Bypassing the cathode on one of the self inverting output stages defeats the inverting process as the second tube gets its drive essentially through the cathode.

Bruce, I'm a newbie so I don't really know much. I did try a 1uF cap across the 10 ohm resistor since the LM317 datasheet says it will improve transient response (as a voltage regulator, but maybe not as a current regulator). The result was not good, a bit less clarity, less deep bass, and a bit less gain. So I'll leave the experimenting at that. I reckon this is your baby so you know best. Probably the best thing I can do is order a couple of 5751's and make it a complete OddWatt conversion :) The new Svetlana's are selling for a reasonable price.

Thanks,
Ian.

Author:  gofar99 [ 08 Jan 2009, 18:08 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi Ian, There are a number of good 5751s out there. The tube type is a good nine pin sub for the octal 12/6SL7s. I have had good results with Russian made ones. If anyone out there tries some of the premium or NOS ones, I'd like to hear what their impressions are.

The protype pair of amps now has around 500-600 hours on them with about 60% of the time with the JJ KT77s and the rest with the Gold Lion KT88s. I like the sound of both although they do sound different. The 88s are more "gutsy" (good high tech term there!) and the 77s seem more refined. No problems with the amps. If anyone is trying to build them out there and can't find the thermal delay "tubes" make a post here. I have a new alternate circuit you can try using a 6H6 dual diode tube in place of the 6NO30. A single transistor circuit is also available for those who have need of it. As a last resort you can always use a B+ switch.

Good Listening
Bruce

Author:  billnchristy [ 08 Jan 2009, 19:48 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

I used to use GE Triple mica black plate 5-star 5751s (whew thats a mouthful) in my Onix SP3 and they were a wonderful tube. Very detailed but with a warm, smooth sound. They were a hair better than Mullard CV4024s.

My first 5751s were Sovteks and they were ok, especially for the price, better than stock Chinese ax7s, more detailed, more full sounding but not anywhere near the level of the GEs.

Author:  CrazzyAbtTubes [ 20 Jan 2009, 11:49 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hey there Bruce, if you don't mind I would like to see that 6H6 timer circuit as I have 3 brand new ones made by Rogers and have nothing better to do with them.

I am slowly collecting the parts for my williamson build, I have all the transformers and about 50% of the components needed to build this beast. I ordered a couple of LM317HV To-3 regulators for the CCS, so I should have no problems using KT66's, 88's and 77's, but the first tubes to be used are my 6L6WGC's made by Sylvania.

The only bad thing about this build is its mass, I may need a pickup truck just to transport this thing, but I will be satisfied with it as long as it works well and sounds well, I will compare it to my true williamson amplifier after it is built.

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