HF-89 clone finished!

[TerrySmith]

Or is it a super sized ST-70? I guess it's mostly similar to two Mark 3's on a common power supply. It doesn't really matter because they all have a similar circuit.

I chose this layout because the power transformer is larger than expected. The chassis is painted with color changing paint that I forgot I had, it looks green or gold depending which way you look at it.

The build is basically like building a ST-70. The board is stuffed with MK-3 components, power supply is old style SDS cap board, caps equal 90uf-choke-195uf-3.3k-75uf-68k-75uf @ 700v.

As for the chokes there's two 1H 240ma Hammond 158SA chokes MADE IN CANADA- not China like the Triad C24X! Mouser has them and their the same price also.

[battradio]

Looks very nice but how does it sound , try some 12BH7's in place of the au7's let us know if they make any difference .

[tomlang]

Very very nice. What Edcors are those? Where are the NTC thermisters in the circuit, i.e. primary or secondary?

[Brik]

Great idea and beautiful amplifier!

[mesherm]

Fancy paint job!! I like the look of the offset power tubes. Impressive looking from the front. Did you pot the PT or just cover it?

[Geek]

Love that colour scheme!

[TerrySmith]

Well the 12BH7's do sound better than the 5814's that were in there. I have to say it sounds really good, just like my Mark 3's! At first it did sound kinda tinny, but I had a badly worn set of KT-88's in there for initial power up, and doing the routine voltage checks revealed voltages to the driver board were WAY off and has been corrected. For now I "borrowed" the Tung Sol 6550 tubes from my Mk-3s until I get the KT-120s.

The Edcors are CXPP100-MS-4.2K, they are the same size as the Dynaco A431 Mark 3 transformers. And they are heavy! The two CL-90's are in the primary side, one per primary winding.

I did not pot the PT, that's just the 6" diameter cake pan covering it. Hopefully Antek will have the transformer covers one day.

[Blair]

Beautiful work Terry!!

[DeathRex]

Nice, very nice. And I just love the look of the 6550s. I'll be eagerly waiting for a 6550 KT120 test.

[TerrySmith]

Well I got the KT-120's in and what a difference! The biggest difference is the bottom end, bass is more powerful and well defined. Right now I have them biased at 80ma each and they're not breaking a sweat.

[Shannon Parks]

In semi-famous website parlance, LIKE! Metal flake would look nice, too, on the tranny covers.

Shannon

[TerrySmith]

Thanks for the compliments!

This color looks silver - gold in the can, but you have to spray it over a black basecoat for the best effect. This is actually the second try, first I sprayed it over silver base and looked terrible and washed it all off and started over.

I'm really liking the KT-120's, wonder how they would sound in a super ULtra Clementine, maybe with CXSE-25 for the outputs?

[Shannon Parks]

I'm really liking the KT-120's, wonder how they would sound in a super ULtra Clementine, maybe with CXSE-25 for the outputs?

Dunno, but I have some KT120s and my Edcor 100W ready for testing shortly. I'll post any tuning notes.

Shannon

[coolhandjjl]

Very nice looking amp!

[mesherm]

You said you have two chokes installed. Did you parallel them to connect to the SDS cap board?
Those KT-120s are some serious lookin puppies for sure. An ST-70 with supercharger running nitromethane. Have you done any measurements of power output?