My first project.

knowledge base for the classic Dynaco ST70

My first project.

Postby MrMiele » Tue Feb 08, 2011 11:11 pm

Hello guys!
Long time visitor, finally registered today.
I want to build ST70 amplifier and of course have lots of questions. I know how to solder and good with mechanical/electrical staff.
I like Dynaco ST70 amp. kits selling online, but I don't like original chassis.
Wanderring if some one ever use Hammond chassis.
Need help with tubes too.. I like clear, warm and reach sound and heard KT88 output tubes will be good choice. Also what tubes you can recommend for driver board (will use Shannon’s new ST-70 driver board).
Thanks an advance!
MrMiele
 
Posts: 26
Joined: Tue Feb 08, 2011 5:59 pm
Location: Los Angeles, CA

Postby TomMcNally » Wed Feb 09, 2011 9:32 am

Hi and welcome to diytube!

I build a lot of amps on Hammond chassis ...

see: http://tmamps.com

I built an ST-70 clone with a diytube board on one of Yaeger's
chassis ... here: http://www.yaegeraudio.com/enclosures.tpl
It's heavy duty steel with aluminum top and bottom panels.
This used recycled Heathkit AA-100 transformers.


Image
Image[/url]
User avatar
TomMcNally
Darling du Jour
 
Posts: 2729
Joined: Sat Nov 19, 2005 2:19 pm
Location: Northfield, NJ

Postby DeathRex » Wed Feb 09, 2011 10:07 am

Seems to be the tubes of choice are the KT88 and KT77. Opinions very greatly on output tubes, or even tubes in general, but I doubt anyone will have anything bad to say about the KT88 or KT77.
To use 4 X KT88 in a ST70 you're going to need a hella power supply. About 120ma B+ more than a ST-70.
At first I wanted to be a ET. Now I are one.
User avatar
DeathRex
KT88
 
Posts: 1014
Joined: Wed Nov 18, 2009 8:13 pm
Location: Cortez, CO

Postby mesherm » Wed Feb 09, 2011 2:29 pm

Wecome. I am not a big fan of JJ brand tubes anymore so I can't recommend them.
Shannon's driver board will drive KT88's or any similar pentode or beam tetrode with no problems. I would start with a quad of EH EL34s and see how you like them. They are not expensive and of decent quaility.
As for driver board tubes, a typical sub for the 12AX7 is a 5751. The phase splitter subs can be the 12AT7, 5814A, 5963, 5965, or even 12BH7A if you have sufficent filament power.
I'm not that far away from you here in Burbank. When you get the amp built send me an email as I have lots of tubes and just about all the above dual triode NOS tubes and could lend them to you for tube rolling until you find your favorite combination.
Mike's N-1 Rule: When looking for N number of components to finish a job, you have a 95% chance of only finding N-1 of them.
User avatar
mesherm
KT88
 
Posts: 1232
Joined: Fri Aug 27, 2004 10:33 pm
Location: Alvin Texas

Postby MrMiele » Wed Feb 09, 2011 6:58 pm

Thanks everyone for greetings!
Can't decide between two casses, Hammond or this one I have found on eBay.
Regarding tubes:
According wiring diagram, driver board needs thee tubes (1) 12AX7 and (2) 12AU7 or 12AT7. So wich ones should I get, were and what brand?

Next step will be order from Mouser Electronics. And I want to upgrade C1, C2, and C7-C10 capacitors like in Wardsweb build.
Also I found discontinued LM334Z on eBay...
Thanks again!
MrMiele
 
Posts: 26
Joined: Tue Feb 08, 2011 5:59 pm
Location: Los Angeles, CA

Postby mesherm » Thu Feb 10, 2011 1:41 pm

http://www.tubesandmore.com/
http://www.tubedepot.com/?gclid=CP6AttGn_qYCFRhzgwodJDk5Zw
http://thetubestore.com/
http://angela.com/
http://www.eurotubes.com/

Here are some of the better links for tubes and supplies.
As to what kind of tubes, it is kind of a subjective thing.
There are always those that prefer the sound of new old stock tubes and even individual brands. The Telefunken 12AX7 is usually the most expensive of the 12AX7 types although most any NOS 12AX7 commands a high price. They are still a favorite tube with the guitar guys. There are only a small number of factories making tubes so even though you see new issue Mullards, Tung-Sol, and Gold Lion brands chances are they were made in the same factories with different levels of quality control.
Electro-Harmonix (EH) is a relatively consistant tube for a reasonable price so I would recommend EH for your 12AX7 and 12AU7/12AT7.
Its hard to be completely objective about the sound of different tubes since everyones hearing is so subjective. Be warned though, vacuum tubes can be addictive. I was a solid state Heathkit fan until I built a sub $200 vacuum tube amp. Now my tiny apartment is filled with tubes and amplifiers.
Mike's N-1 Rule: When looking for N number of components to finish a job, you have a 95% chance of only finding N-1 of them.
User avatar
mesherm
KT88
 
Posts: 1232
Joined: Fri Aug 27, 2004 10:33 pm
Location: Alvin Texas

Postby MrMiele » Thu Feb 10, 2011 9:48 pm

mesherm, thank you for links.
How about russian tubes? Are they good?
MrMiele
 
Posts: 26
Joined: Tue Feb 08, 2011 5:59 pm
Location: Los Angeles, CA

Postby Geek » Thu Feb 10, 2011 9:56 pm

MrMiele wrote:How about russian tubes? Are they good?


I'd trade all my NOS for a nice quad of winged =C= Svetlana's ;)

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
User avatar
Geek
KT88
 
Posts: 3585
Joined: Sun Oct 21, 2007 3:01 am
Location: Chilliwack, British Columbia

Postby MrMiele » Thu Feb 10, 2011 9:57 pm

..my wife's name is Svetlana :)
MrMiele
 
Posts: 26
Joined: Tue Feb 08, 2011 5:59 pm
Location: Los Angeles, CA

Postby EWBrown » Thu Feb 10, 2011 10:18 pm

I'd trade all my NOS for a nice quad of winged =C= Svetlana's ;)



I've found Winged C Svetlana EL34s and 6550Cs to be very nice sounding, indeed [:) The Gold S versions aren't too shabby, either...

Most of my older Russian 6C4C / 6S4S are marked with a black winged C emblem, these are the twin plate version, of late 1950s or early 1960s vintage, which are very faithful replicas of our 6B4Gs.

/ed B
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !

Postby MrMiele » Thu Feb 10, 2011 11:26 pm

Thank you guys!
Will order EL34 Winged =C= matched quad ($145).
Can some one explain why they have to be matched?
MrMiele
 
Posts: 26
Joined: Tue Feb 08, 2011 5:59 pm
Location: Los Angeles, CA

Postby Geek » Fri Feb 11, 2011 3:49 am

MrMiele wrote:..my wife's name is Svetlana :)


I have a mate in Lithuania with a wife of that name too. He's a tube geek and I told him it was a good omen! ;)


Can some one explain why they have to be matched?


In systems with a shared cathode resistor, or shared fixed bias, matched means both tubes will pull the same amount of current. Mismatched can cause one tube to hog current and if the mismatch is large enough, the resulting DC imbalance in a PP output will saturate the output transformer.

In a system with independent bias on each tube, a balance control, or individual cathode bias resistors, matching is moot.

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
User avatar
Geek
KT88
 
Posts: 3585
Joined: Sun Oct 21, 2007 3:01 am
Location: Chilliwack, British Columbia

Postby TerrySmith » Fri Feb 11, 2011 12:01 pm

Here's an amp I built years ago on a Par-Metal 12x12x2 case flipped upside down. http://diytube.com/phpBB2/viewtopic.php?t=1256

This would probably be a great chassis for a '70. The bottom (now top plate) is really thick. If you order one be sure to tell them no vents or holes in the bottom!
T. Smith
User avatar
TerrySmith
KT88
 
Posts: 973
Joined: Sat Jan 31, 2004 12:51 pm
Location: Maryville TN

Postby MrMiele » Mon Feb 14, 2011 12:19 am

I have question regarding Big bias circuit.
Can I use this Trimmer Resistor?
..and how many jacks for bias test points on ST70?
Thank you!!
MrMiele
 
Posts: 26
Joined: Tue Feb 08, 2011 5:59 pm
Location: Los Angeles, CA

Postby TomMcNally » Mon Feb 14, 2011 1:22 am

Those small trim pots go on the diytube ST-70 driver board,
and are used to balance the bias. The large chassis mounted
pots (as in the original ST-70) set the bias, then you balance
the bias with the on board trimmers. You should have 4 test
points. I just adjusted the amp shown in the pictures above.
The exact procedure is in the manual.
User avatar
TomMcNally
Darling du Jour
 
Posts: 2729
Joined: Sat Nov 19, 2005 2:19 pm
Location: Northfield, NJ

Next

Return to st70

Who is online

Users browsing this forum: No registered users and 14 guests