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Old 12th July 2010, 03:24 PM   #1
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Default Another kt88 Monoblock Builders Thread

The idea for this thread is to go over the design characteristics and parts lists for a modified oddwatt kt88 Push-pull monoblock. The mono-block will be used to drive two high efficiency drivers wired in parallel on the 4ohm output. Most notably, improved capacitors will be used. Improved output transformers are currently being researched and may be used. Also to be provided are labeled diagrams and parts lists. Solen caps will be upgraded to auricaps. Electrolytics will be upgraded to sprague atoms. The heater reactifier will be replaced with 5A Stth506d fast response diodes. Resistors will be replaced with KOA SPR series carbon film. Tubes will be genalex gold lion or cryo winged-C. Bleeder caps to try will be mundorf Hg/Au & Hg/oil, russian k40 PIO, Auricap, Sonicap Platinum / Teflon, Audience Aura-T Teflon. .33uf/450-700V Completely new, and possibly ill-advised, I will be trying a quick-connect system for the push-pull (bleeder) capacitor that allows the loading of different capacitor that have been loaded into cartridges (oddwatt's kt88 monoblock uses a .33uf/630V Russian PIO cap here). The use of mini-banana clips (gold plated copper) will achieve this. Those that like to tinker should like that feature. However, I am unsure as to the best design for the cartridges. Originally, I wanted to cast them in clear resins with the capacitors embedded. However, I am worried that the resin will insulate the capacitors, increase running heat, and accelerate failure. SO: I have a question. Does current / voltage across this component produce that much heat? I'll keep updates coming on the build.
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Old 12th July 2010, 06:07 PM   #2
Loren42 is offline Loren42  United States
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Bruce's OddWatt is a great design. Upgrading some of the components may not be a bad idea, but my position on those upgrades is that you can quickly run into diminished returns.

Any cap that passes a signal is a good candidate for a quality component. Beyond that, I think that you will not get that much for the extra investment.

I use the Edcor transformers for my Class AB KT88 build and have nothing but good things to say about them. They are hand wound in the USA at a reasonable price.

I would be interested in hearing what design changes or modifications you have in mind with the actual circuit. Perhaps you could post your intended schematic.

Also, Bruce is a great guy to work with and you might contact him with your proposals to see what he thinks.
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Old 12th July 2010, 07:06 PM   #3
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When going for HIFI or the top end of anything, you eventually end up making your mountain by piling up small stones near the top. Diminishing returns indeed, but returns non-the-less. Power Supply: The resistors are going to be spec'd out as the Kiwame equivalents (search kiwame and Koa SPR carbon film series:they are supposedly the same thing) this means that each capacitor will be overrated (2W) for the application. It's an added cost but may sound better. These are available from Mouser's Electronics. Power capacitors will be a mix of Sprague Atom 100uf/450V from tubes&more or boiaudioworks $11 Upgrade to obligato psu caps @$30ea may happen later. Small PSU caps will be Auricap 0.1uf/600V (Vitamin-Q's may be used if I fell in the mood) & 2.2uf/400V (400v may be pushing it, i'm a little worried and may use the spec'd solen here). The heater 10000uf cap I may go exotic if I can get a cerafine 63V, I will. Otherwise I may use a Nichicon Super from PercyAudio. The 47uf will be solen poly's at 630V from percy audio. I will keep the 0.1uf RIFA's in place. Rectification is still in the works as I'm having Bruce look over the non-standard voltage drops for ultra fast rect-diodes. So far, I'm liking the MUR150G 1A@1.25V/500V/75ns for the Hi-test PS rectification and the STTH506D fast switching diodes (stth5r06d 5A@2.9V/600V/40ns digikey 497-2746-5-ND)(STTH5L06RL 5a@1.3V/600V/95ns DK: 497-5231-1-ND) for the heater rectification. These however, will be subject to change. The FBR I am thinking can be replaced with 4 single diodes from the 5A range: Bruce is also looking over that option. I'll keep you updated. Suggestions and warnings are welcomed. James
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Old 25th November 2011, 02:58 PM   #4
PWR RYD is offline PWR RYD  United States
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James,

Did you finish this amp? If so how does it sound?

Thanks,

Craig
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