ST-70 Rebuild Thread

Doctor Hugocat wrote:I put the bias pots in just to fill the holes in the chassis: the plan is to temporarily get some vintage-looking knobs for cosmetic purposes and in the longer term buy your triode/pentode kit which will fill the holes AND do something useful!!

Might I suggest twin volume pots? Separate pots also give you balance control ...

Tune wrote:Hi any progress?

Thanks for asking Tune! I've been waiting for a new power transformer to arrive from the excellent Dynakitparts. In the meantime, here's a pic of my newly-built VTA board in the chassis:

sKIZo, that's a nice idea about the volume pots........food for thought.......Thanks!

I note your Visa card is close at hand!!

audiobill wrote:I note your Visa card is close at hand!!

Yeah, it tries to hide when it sees me get another project!!

It's been a while since my last update.....I got the new transformer from the excellent Dynakit Parts: Thanks Kevin!! I also bought new tube sockets for all the old ones except the frnt 'bias' sockets. I've been seeing so many posts about problems with older sockets that it seemed to make sense.

I bolted in the new power transformer and the output transformers tonight: here's the result!



Next job: carry on the build according to the original Dynaco build manual until I get to hooking up the VTA board. More soon!

Excellent! Keep the updates coming

Today I took advantage of some holiday time to strip and prep the cover for painting.

I flatted back the mesh part, but used paint stripper on the sides. I was unsure whether to flat or strip it, but I'm glad I used the paint stripper: under the old paint was a bunch of rust. Next up: paint with black satin (semi-gloss).

Are you really going to use the cover and hide the beauty of the tubes?

Tubes4ever wrote:Are you really going to use the cover and hide the beauty of the tubes?

LOL probably not! But I'm a bit of a sad case and wouldn't feel I'd done a complete job unless I'd refinished the cover as well

Totally understand

It'a been a bit quiet on the rebuild front here recently: I have an arm injury which can make it difficult for me to work on it, but here's a pic of most recent progress. In total, there's probably only aabout 3-5 hours work left: audio in, bias sockets, NFB, a couple grounds, power cord and a few other small things. Hopefully I can get back to work on it soon.

Hi,

Been awhile any updates?

Tune

Tune wrote:Hi,

Been awhile any updates?

Tune

Hi Tune -

Thanks for asking!! Now moving house, putting another brake on progress

I did get a NOS RCA rectifier tube from a friend of mine though: he was carrying a box of tubes and I jokingly asked if he fancied trading one rectifier tube for a bunch of vintage tubes I got from a Hammond organ amp (I'm a Hammond player). He pulled one out of the box and we're both damn pleased with the trade!! He needed the 12AX7s for one of his guitar amps.

Hopefully I'll be moved in soon and I'm gonna start up again. Of course, now I'm in the position which I hate, where I've lost track of what I still have to do on the project (thus exponentially increasing the chances I'll mess something up).

Hey Guys - So I'm restarting this dinosaur thread: I'm eventually taking up this project again after months of delay. I just put in the grounds from the speaker terminals.

I only have a few more hours to put in until it blows up....I mean powers up. I stil have to the following:

Wire in the bias sockets
Wire in the B+, NFB and ground to the VTA board
Wire in the input jacks
Check everything a thousand times

I borrowed a tube tester and tested most of the tubes: everything tested good. It wasn't able to test the power tubes though.

I'll post more pics when I can. Looking forward to getting this on the road!!

An update: I've now completed the following:

Bias socket wiring
Input jacks
NFB
B+ and grounds to PCB

All I have to do now is tighten up the (non-functioning) mono switch and attach a power cable. Then it's off to the electronics store for some 3a slow-blow fuses. Then it';s power-up time!

Any interest in seeing a progress pic?

"All I have to do now is tighten up the (non-functioning) mono switch and attach a power cable. Then it's off to the electronics store for some 3a slow-blow fuses. Then it';s power-up time!

Any interest in seeing a progress pic?"


Absolutely!
I've been in here occasionally to see when you're up and running, Lol. I've been working out an issue with mine that never gets solved ( minor humming) so I can enjoy your successes instead!

p.s. restored a '54 Hammond C2 last year for keyboarding #3 son who has it now back in college town looking for friends with vans.....bought the organ for $11.00 plus tax on a municipal auction site, Winner!  Now just needs a trek II setup....

4MarkNY wrote:"All I have to do now is tighten up the (non-functioning) mono switch and attach a power cable. Then it's off to the electronics store for some 3a slow-blow fuses. Then it';s power-up time!

Any interest in seeing a progress pic?"


Absolutely!
I've been in here occasionally to see when you're up and running, Lol. I've been working out an issue with mine that never gets solved ( minor humming) so I can enjoy your successes instead!

p.s. restored a '54 Hammond C2 last year for keyboarding #3 son who has it now back in college town looking for friends with vans.....bought the organ for $11.00 plus tax on a municipal auction site, Winner!  Now just needs a trek II setup....

Thanks Mark! Unfortunately my success has turned to temporary failure: for some reason I have a major issue which I'm trying to route through:

https://dynacotubeaudio.forumotion.com/t3204-another-problem-with-my-st-70-build-rectifier-tube-flashed-and-now-dead-right-rear-tube-any-ideas

Here's a pic anyhow!!

I'm a Hammond player myself: the C2 is a great organ and you'll be pleased with the Trek percussion. What's he using for a Leslie? At last there's ONE company who IMHO have cracked the digital Leslie sound: the Neo Ventilator. I literally couldn't believe it when I first heard one.