diytube.com

This is the '70 I got from click2media last fall. As with any vintage amp it was a total gut and rebuild. Parts reused were the transformers, chassis, fuse holder, bias pots, and speaker strips. The bias pots are date coded 60-07, so I imagine this puts it sold in late 1960 or early 1961.

Before pics:





Before and after polishing the chassis, took exactly one hour. It ain't perfect but presentable.





Driver circuit plate mostly built ready to install. Circuit is the HF-89 / Ike driver.

Time for assembly!

Power trans, new C24X choke, NOS russian tube sockets, driver plate, etc. The power trans is mounted on faucet washers, beveled on top flat on bottom, to cut down on noise.


Wiring it up, added the cap board, restuffed quad cap from previous thread. Power switch moved to front, no more burned arms! The original cloth insulation was stiff and a heat gun took care of that. Installed failsafe 100k resistors to bias pots, THANKS to GEEK for the idea!


10 ohm cathode resistors mounted to front test sockets.


Smoke test #1 using sacrificial JJ 5AR4 and leftover EL34's from a Music Reference RM9. I have since replaced the 5AR4 with UF5408 diodes mounted in an old metal tube and replaced the CL50 with a CL90, I was out of them but found one stashed away.

Very nice work indeed! Does the power switch up front cause any problems with hum?

Dave

Very cool indeed.

Does the power switch up front cause any problems with hum?

Nope, it's dead quiet! This is the third one I've done too.

The ST-70 I got from Click2Media was very clean. I had to do very little to it to get it running. It came with a new circuit board with the original 7199 circuit, but they put in 47ohm resistors where there should have been 47K. And I had to make a new can capacitor.

I have a set of Russian 6P3S-Es in it biased at 45ma, a Sino 5AR4 and, I think, 6GH8As. Power transformer is very happy.

I thought of seperate bias for each tube, but decided to just match the tubes. I got 12 6P3S-Es and 12 6P3Ss, matched them, picked 4 in the middle and put them in.

Very nice job Terry.

The HF-89 / Ike driver looks very easy to build.

Sal

I looked for the schematic and haven't found it yet.

I've been playing this thing hard for two weeks now and it has really opened up. After reading reviews and getting good advice on EL34's I decided to try the new Tung Sol EL34-B tubes, so far so good. Supposed to be a matched quad but one of them spiked up to 66ma then settled down to 45ma, Ill keep an eye on it. They sound really good and only been one hour!

In the past week I rolled in the 6CA7-EH quad with the glowing screens, those still sound really good. Then tried some Shuguang large EL34's that have TAD tested stickers and Marshall branding on the glass, these sound great too. On one of them the getter ring is very close to the G1 cooling fins so I won't use these on a daily basis, that could be disaster!

Terry- How do you compare the sound of the Ike driver to Shannon's board? As I'm sure you're quite aware, I'm using the Diytube board with your 6CG7 driver mod. I've compared it directly in A/B tests with an ST70 using the same Chong cap board and a VTA high gain driver, and I really like the sound of your board better. I'm curious if an all octal driver board is really a departure.

It sounds about the same as the Diy board, as it's virtually the same circuit, the difference being the CCS. I just wanted to try octals!

Seeing your ST70 up and running makes me want to get mine going! I got mine for $10 and haven't even checked it out yet. I sold the 7199's on ebay and stuck the Amperex GZ34's in my AC30, and have 4 used Mullard EL34's to play with from it, so a screaming deal for me. I've been letting it sit around untouched for 5 years now though (along with a Scott 299B) while I play with guitar amp projects. One of these days I hope to get to it! I've got the SDS Labs EF86/12AU7 board for it...I wonder how that will sound?

Anyway, just wanted to compliment you on your project...looking good!

Greg

Thanks for the complements! That is a deal for a '70, especially with the original tubes.

The SDS board is basically the stock 7199 circuit but laid out to use a EF86 / 12AU7 combo. Should sound better than stock since the EF86 is a better tube than the pentode section of a 7199.

Nice! Makes me want to try the same style of P2P wired IKE driver, but with Loctals, 2X 7N7 for the LTPIs, and 7F7 for the VA

I've gotten on a "loctal kick" lately. Maybe 'cuz I found an almost forgotten stash of them in the cellar...

7N7 is equivalent to 6SN7, and 7F7 is equiv to 6SL7.

(and 7C5 is equiv to 6V6GT)

/ed B in NC