Driver Board for the ST-70 Using Common Mode Feedback PI

[Geek]

Beauuuuutiful!

You had the chassis powdercoated yourself, or buy one like that?

Cheers!

[nyazzip]

my bet is bead/sand blasted. looks good. i have been lusting after a sandblasting setup for years but it would be hard to justify the thousand dollar compressor needed to operate one. plus all that compressed air in a fatboy sized tank would make me nervous

edit: ok i take that bet back upon further examination. still looks good though

[Slartibartfast]

my bet is bead/sand blasted. looks good. i have been lusting after a sandblasting setup for years but it would be hard to justify the thousand dollar compressor needed to operate one. plus all that compressed air in a fatboy sized tank would make me nervous

edit: ok i take that bet back upon further examination. still looks good though

How much air do you need? An 80 gallon compressor is less than $500. There is nothing to fear from a tank of compressed air. I have worked in some places that had 30 year old tanks.

[tomlang]

Sanded, not sand-blasted, (Shaken, not Stirred?) then primed with self-etching primer, then top coated with Rust Oleum hammertone gray. All applied via rattle-can.

And now ***Drum Roll Please*** the finished amp!

First I want to thank Gregg for offering such a wonderful ST70 driver board. I just completed it and I absolutely love it. I have had a VTA board in the past (unfortunately no A-B comparo) but this one has detail far and above and best of all controls the woofers on my Heathkit AS-101 (Altecs) the best I have heard yet on them regardless of amp. Currently I am running 20 ohms NFB. I have not yet adjusted the pots on the board either, they are set at midpoint.

I am running it with an Aikido preamp (no tone controls, folks, and I dare say, hardly now needed!).

The heatsinks on the transistors (that I mounted under the board) are running barely warm so I will just pop some hole plugs in the front holes.

[TerrySmith]

VERY NICE! I like hammertone paint and wrinkle finish paint. Rust-oleum also makes red hammertone but nobody carries it.

Are those Mullard XF1's original to that amp?

[tomlang]

I've seen hammertone brown, I'm not sure but maybe a couple different colors of brown?

The Mullards and the OPT's are original. What exactly is an XF1? They do sound nice, even though they test good, but not great. I can see a very light DYNACO on one or two of them, they came with an amp as a set I think they have always been together and are probably 40-50 years old.

[MashBill]

Very nice! Congrats on a great build and thanks for sharing.

I have always liked silver hammertone paint. I also like those Neutrik RCA jacks. They are all I use anymore.

How about a view of the bottom? I'm curious how "crowded" it is under there.

Bill

[Quad]

Very nice! The gray color looks perfect.

Gregg, in a future rev, it would be great if those heat-sinked
transistors could be shifted a closer towards the input
jacks, so the ST70 front-socket holes are clear.

[Geek]

A lovely amp indeed, Tom!

I never could get hammertone to look that good. Mind you, 85% humidity is considered a dry day where I live.

Thank you for the review ^_^

Gregg, in a future rev, it would be great if those heat-sinked
transistors could be shifted a closer towards the input
jacks, so the ST70 front-socket holes are clear.

They are supposed to go on top, not the bottom. Tom was just being creative here ;-)

Cheers!

[Geek]

Anyone else got theirs done? :-)

I'm contemplating making a kit out of this, given how many parts there are....

Cheers!

[tomlang]

I soldered up another board but haven't fired it up yet. Once again, I put the transistors with the heatsinks underneath as it makes it look much cleaner IMHO. I haven't had any problems with the first board running it like this even with the big front unused socket holes in the chassis plugged.

I also recess the board 3/8" on standoffs which 1. Looks better as the PCB tube sockets are level with the chassis, 2. Allows cooling air to circulate.

[Ty_Bower]

What exactly is an XF1?

This guy is an Xf3. Zoom in on the photo, and look near the base of the tube. It's printed upside down for whatever reason.

[Geek]

Very cool, Tom!

You've come up with a great plan:-)

What exactly is an XF1?

This guy is an Xf3. Zoom in on the photo, and look near the base of the tube. It's printed upside down for whatever reason.

It's a tube code for type. I only have Philips codes here and aren't correct for that one, as an "XF" is showing to be a 12DJ8, LOL!

BTW - that's a Mullard Blackburn made tube you have.

Cheers!

[tomlang]

Super 6BG6GA's, Edcor 6600 ohm OPT's, Triad 800VAC CT power trans, 530 VDC on plates and screens.

Geek Octal Board, Geek Cap Board.

The 6BG6GA's require nearly -60 vdc bias for 45 mA.

IEC power cord, chassis safety ground config.

[Geek]

Absolutely GORGEOUS!!!!

Cheers!