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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 29 Sep 2009, 08:26 
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Joined: 29 Sep 2009, 07:50
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Location: Maribor -Slovenia -Europa
Hi !
I,m new here and will try to build for first ODDWATT with EL84. I have already 2 OT from two monoblocks 8k / 8 ohm, but without linear taps! I have also 2 PT with 300 V secondary and 130 ma and 6.3V 2.5A. I think to use PT as choke input to lower B+? For preamp tube
i think to use NOS GE 5751 - I have few here from my guitar amp project. Output tubes were EL84 JJ for first. How can i connect g2 to power supply with or without 100ohm / 2W on screen of el84 or have you another resistor value for version without UL taps?

What power can is common in such configuration.I think also about 6v6 from JJ .What B+ is optimal?

Thanks for first GSB


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PostPosted: 29 Sep 2009, 14:03 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, I don't see any big problems with what you plan to do. Send me a PM and I'll sort out the details with you. If you would rather, I have a project about to be posted that is rather similar to what I believe you have in mind. In some ways it is an improved version of the first project and uses the EL84 / 5751 combination. (project is called PoddWatt Stereo Amplifier).

Good listening
Bruce

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PostPosted: 07 Oct 2009, 15:29 
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Joined: 23 Sep 2009, 19:18
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Hi Bruce,
I started putting one of these together. I just got the driver stage assembled. I put in a 2.2v sine wave, and a 96v sine wave pops out the other side! Have any idea why the gain is so high? What sets the level of gain in this arrangement? This is my first experience with tubes, and I want to understand what is going on, so I hope you are OK with my many questions to come.

Thanks,
daneo


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PostPosted: 07 Oct 2009, 18:04 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi Everyone, Sort of an update. I have designed a companion tube line stage preamp for use with the Odd Blocks (and other power amps as well). It uses a pair of ECC802S tubes and has a gain of about 7 watch for a new thread on it in about a month or so when the project gets finalized and posted. In the mean time, i would be interested to hear of diy builds of the Odd Blocks and what tubes you used and how well they worked. I'm compiling a list of ones that work and more importantly ones that don't. So far, two have not worked, well EH KT88s (won't stay balanced - probably not their fault just a quirk of the circuitry) and Sovtek 6L6WXT (just didn't sound as good as others - but can deliver about 3-5 more watts output over the other 6L6GCs).

Good listening
Bruce

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PostPosted: 07 Oct 2009, 22:53 
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Location: Arizona, USA
Hi Daneo, Actually I can make a very good guess. In the circuit configuration used, the gain is around 40. Normally you would not need 2.2 volts of drive. The tubes depending on the types require between 10 volts drive (like EL84s) to about 35 volts drive (KT88s). So with a KT88 version the input would need to be about half a volt. A little excess gain is helpful for low output signal sources. The amps are designed to be able to use passive preamps (no gain) and direct output from various signal sources (like a CD player) directly if the source equipment has a volume control feature. One thing you can do if you want to control the gain is to substitute a 100K ohm volume control for the 100K ohm fixed resistor at the amp input. There are other ways,but all will IMHO degrade the sound quality.

Good listening
Bruce

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PostPosted: 22 Oct 2009, 13:52 
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Joined: 02 Sep 2008, 14:34
Posts: 527
Location: Rochester, NY
Hi Bruce,

Is there any chance you could post a top down pic of the PodWatt?

Alan

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Denon POA 2200 | Bottlehead Quickie with PJCCS | Integra CDC 3.1 | SOTA Sapphire-RG301-Grado Gold 1 | Soundwave Soliloquy Series I


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PostPosted: 22 Oct 2009, 14:23 
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Location: Arizona, USA
Hi, I'll check tonight to see if I have one. The amp is out on loan right now so if I don't already have one, I'll get one when it comes back.

Good listening
Bruce

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PostPosted: 26 Oct 2009, 01:04 
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Joined: 27 Dec 2008, 04:48
Posts: 25
Location: QLD, Australia
Hi Bruce,

Recently, I finally finished an Oddwatt conversion by building the SRPP section to drive the already-converted self-splitting output stage. I used the Chinese 6N2 tubes that the Chinese amp came with, these 6N2 aren't exactly the same as 6SL7 which is what you designed for but they are sounding really nice, another big improvement. I used the Oddwatt 225/KT77 schematic, and am running 6L6 Reflektor NOS tubes (AUD$30 delivered from ebay seller xryn). The only mishap was the power on LED blew after I tied the driver heater elements to 1/3 B+, the LED was originally tied to one side of the heaters and ground :)

At first I used triode mode, not too flash, tried pentode, small improvement, went to ultralinear and better again, then added the feedback and that did the trick. This amp has no special parts in it, a lot of cheap parts I would think, but my faith in valve amps has been restored, because the bass is tight and deep, the vocals are very clear, highs are excellent, great detail, great dynamics, really nice to listen to. I know what mediocre valve amps sound like, because I own four of them, sorry, only three now :) This one shines now. I am sure that using your recommended components including transformers could only make an amp that would be worth every single cent ever spent on it. In hindsight...if only... Well I have learnt from my mistakes and had fun (and spent money) making those mistakes. Thanks for a great design and I hope the kits sell well.

Ian.


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PostPosted: 26 Oct 2009, 11:00 
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Location: Arizona, USA
Hi Ian, There have been a number of conversions of other amps into Oddwatts. So far the vast majority worked right on the first try. I'm glad yours was in that group. The problem with the LED is foreseeable. Since there are really two separate sources of power and one is isolated from the ground, some confusion can occur. 6L6s are a good choice for general applications and seem to have a really great bottom end with many systems, if you prefer more detail, or your system is bottom heavy already, you can try KT77s. Here the price is virtually identical. Now all you have to do is build the companion amp, then there will only be two duds left.

Good listening
Bruce

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PostPosted: 31 Oct 2009, 23:06 
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Joined: 27 Oct 2009, 18:13
Posts: 4
I'm interested in building an OddWatt KT88 Tube Amplifier (ultimately a pair). Must one purchase the entire kit? For example, could the chassis be omitted from the kit since I would want to build a chassis of my own design?

Thanks in advance.


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