HF-89 clone?

[TerrySmith]

I'm finally getting around to this project, but I am still throwing around ideas.

The chassis is ordered, a 16x11x2" 12ga aluminum box from Dirty Dawg.I also had him bend the bottom cover up the sides so hopefully it will look like a king size '70 chassis. Pre-ordered my Antek 4TK-400 PT. I'll most likely be using the Diytube ST-70 driver board built to MK-3 specs since it will be a KT-88 / KT-120 amp. The circuit will be basically a stereo MK-3 in a single chassis.

The output transformers is where I need guidance, I'm looking at Edcor CXPP100's, but do I choose 4.2k primary or go with the 3.3k or 2.2k? Or is the A-431 Dynaco trans a better choice? KT-120 tubes will be used mainly but I like the option of a KT88 or 6550. FWIW, the Edcor 100's and the A-431 are the same physical size if that means anything.

I'm leaning toward a tube / transformer layout similar to the Eico HF-89 or possibly a Dyna ST-70 layout.

I welcome any ideas or opinions!

[battradio]

I would stay with 4.2K , the st70 i built with KT120 would do 90 watts before cliping , with shannons driver board and with st120 outputs that are 4.2 k , i would use the Edcors if you have the space .
viewtopic.php?f=6&t=5641

[Shannon Parks]

Yes, go with the 4.2K outputs. I've used the 4.3K Hammonds (1650Ns) with my Eiclones - a HF89 knock-off - and it's worked well. I hope to get the 100W Edcors for the next set of Ikes, too.

Shannon

[msmpe]

Sounds like an awesome project!

I've considered similar Mullard hi-watt clone, but in stereo mode the weight is a bit much. So my Mullard clone will be only around 30 w/c stereo - alot lighter - with Bogen (unity coupled) OPT. I actually have just about everything for this project - rebuild and mods to a Bogen AP60 - changing the 7591s to 6L6GB or KT66 - scrap all the tone/filter controls but keep the phono stage - may add an amplified pre-out for bi-amping connections.

But my dream is a pair of Williamson monoblocks (to cut the weight down) 6550/KT88 in UL and looking for about 60 w/c. First choice for OPT is of course the Edcor as value/cost is excellent. But a pair of ElectraPrint or Magnequest ($$) are worth dreaming about...

[TerrySmith]

Here's what I have so far, the 12ga chassis from Dirty Dawg, and the Antek 4TK400 toroid. The transformer in really big, measures about 5.25" at the widest point so finding a cover will be a challenge. Still waiting on the Edcor CXPP100 outputs before I start cutting the chassis.

[battradio]

Antek sells cases . http://www.antekinc.com/details.php?p=162

[Geek]

I dunno if his covers survived the fire, but Antek sells them.

An alternative is go to an east Indian store and checkout the shiny stainless bowls. Some are the perfect size and shape for toroids and cost a buck!

Cheers!

[mesherm]

I don't know how much trouble you want to go to for toroid covers but it is possible to make them yourself and even pot them. I used Speedy Metal to order the aluminum tube and the round solid discs. Then used the lathe at work to do some touch-up. I used epoxy putty to fill in the centers and provide an anchor for the center mounting bolt on the OPTs. The PT I drilled and tapped three 4-40 holes in the edge for mounting.
http://home.earthlink.net/~mikesherman/images/Toriod%20covers.JPG
http://home.earthlink.net/~mikesherman/images/toroid%20covers%202.JPG
http://home.earthlink.net/~mikesherman/images/toroid%20covers%203.JPG

[EWBrown]

Those covers look very nice, well made, much nicer,and more solid construction than the usual extruded sheet metal covers.

Some general advice for others who want to make their own toriod covers:

Just make sure that you don't inadvertently create a "shorted turn "when using a cover and mounting bolt. There should be no electrical continuity between the cover and the toroid's center mounting bolt, else a very low resistance shorted turn through the bolt, cover and chassis, could result. This would cause major problems, least of which would be repeated blowing out of the AC power line primary fuse.

/ed B

[mesherm]

Yeah when you have a complete circuit through the toroid center you basically have a soldering gun...
You can't see it in the photo but there is a 8-32 nylon threaded stand-off between the mounting bolt you see and the short bolt and metal plate under the toroid preventing a complete circuit.

[TerrySmith]

I remember those machined covers and would like to make my own, but if I brought them in to work and tried to leave with them I would get fired.

Here's a couple of ideas I came up with. one is a Fat Daddios 6" cake pan, all I will need to do is make a couple of angle brackets to attach is and paint it wrinkle black or a hammertone finish.

Another is an old PC power supply box, it has a place for the IEC connector and power switch. It will need a panel for the front and paint.

[Geek]

You did get your own pan, right?

I turned one of the wife's cake pans into a chassis once and did.. not.. hear.. the.. END of it!

Cheers!

[mesherm]

Before I decided to make my own I was considering water bowls made for Parrots as trannie covers.

http://www.windycityparrot.com/Parrot-Stainless-Steel-Replacement-Dish-20-oz-Medium_p_1066.html?gdftrk=gdfV23504_a_7c1354_a_7c4218_a_7c30311061002&gclid=CO-h_s_o_7UCFVSVMgodtmIABg

http://www.windycityparrot.com/Prevue-Pet-Select-Replacement-Parrot-Dish-8-oz-Shallow_p_1081.html

[tomlang]

Sunny the Sun Conure agrees!

[TerrySmith]

It looks like I'll be using the cake pan, didn't realize the Antek toroid was so big. I'm still waiting on my Edcor order, it's been 5 weeks now so they should arrive soon, and then I will see how it all fits.