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Here's my next project. It is an ePay find. The chassis is rusty as you can see, so I will glass bead and paint it.

That looks like a fun project Terry ! You're lucky that is is a kit version, so the tube sockets and stuff aren't riveted in, that makes it easier. You might want to try some of Ned's brass or nickel plated transformer ends - they really look great.

I was thinking just that, usind Ned's nickle plated covers.

My plan is to install the new RED Diy board, and paint the chassis with some gold to silver Chromalusion leftover that I have.

I also ordered some aluminum stock, 2"x .250", that I'll fab up an updated faceplate for the '70. I wonder how nice 6061-T6 alu will polish?

If you're feeling adventurous, you could scrap the center PCB, put a plate over the hole, and use the real estate for a big choke. Wire the PT in series for 720V, and use a 5AS4 or two with UF4007's on the negative legs (hybrid bridge) into the choke for around 620, 630V. Run the EL34's in pentode with a separate regulated screen supply, driven by a couple of 6CG7's or something, that you'd squeeze in to the right and left. Maybe a LTP followed by drivers? Plenty of gain for NFB use. Just my crazy imagination at work... :D

But... there is something to be said for the classic simplicity of the ST70 circuit as-is, or even with the Diytube board.

Who spinked cinnamon all over those photographs?

A diamond in the rough... Looks like the basis for a nice restoration / rebuild project! I'd replace just about everything except for the transformers, and chassis, (of course, they're the most valuable parts) and maybe keep the bias pots if they're still OK. The old tube sockets may be or not be OK, I generally replace them with new, and keep the old good ones around for experiments and prototypes.

I'm sure that Hafler and company never imagined, in their wildest dreams, that their amps would still be a "hot item" 40-50 years into the future Yellow_Light_Colorz_PDT_02

/ed B in NH

TerrySmith wrote:Here's my next project. It is an ePay find. The chassis is rusty as you can see, so I will glass bead and paint it.

Nice try, Terry. But you'll have to do better than that to dethrone me. Yellow_Light_Colorz_PDT_04

Here are the latest pics of my chassis. I didn't need to glass bead it, after sanding it with 180 grit, the rust was very minimal. Then I soaked it in some phosphoric acid to dissolve any remaining rust and give paint something to bite to. The first pic is the primer stage, the other is the finish. The Chromalusion paint was no good, so I went with wrinkle black. Makes the red board really stand out!

looks pretty cool! are the transformers going to get a similar sprucing up? polishing the black paint off and clear-coating the steel bells would be pretty neat to contrast with the chassis..

Soren, I ordered the nickle plated covers from Ned at Tubezone. That should look pretty cool. I will clean the transformer cores with a wire wheel at work tomorrow.

Hopefully next weekend we will see a finished '70!

i'm sure the finished product will be very nice to look at, and sound fine to boot. are you planning to stick it back up on the bay? i'm sure that it'd fetch a solid price, and besides, dynaco's are old hat now Yellow_Light_Colorz_PDT_07

Well today I stuffed the driver board and discovered I only have THREE .047 coupling caps. Yellow_Light_Colorz_PDT_21 Will there be any problems using .1uf @ 600v caps in their place?

The only other changes will be 6GU7's for the PI, and maybe a 5751 for the VA on the board. I'll be using a 30-80-40-20 cap from AES and most likely UF4007 diodes in place of the 5AR4, and a CL-80 inrush current limiter.

Since I cut & jumpered the PI heaters, I can use 6AU7, 7AU7, 6GU7, 6CG7, and possibly 6DJ8 types. The 6AU7's and 7AU7's are dirt cheap for NOS! Yellow_Light_Colorz_PDT_06

The 0.1µF caps should work just fine.

Well after many months it's finally finished! Here is what I changed:

40-80-30-20 quad cap.
Diy driver board, rev B build, cut&jumper PI tubes to use 6CG7, 6GU7, etc.
Inputs moved to rear, power switch to front.
UF4007 diodes hidden in gutted metal tube, socket is wired stock to use GZ34 if desired.
CL80 inrush limiter installed.

Nice tranny covers! What are they? Did you measure what the power on B+ surge is with the diodes? I always wondered.

Looks great, btw. Makes me want to grab my rustiest ST70 and do a 6B4G mod or something to it. Yellow_Light_Colorz_PDT_05