Best Power Tranny for ST70

knowledge base for the classic Dynaco ST70

Best Power Tranny for ST70

Postby justinsweber » Tue May 05, 2009 1:04 pm

Im looking at building a beefed up version of the ST70. Build 1 already that incorperates alot of upgrades but I went with Triode Trannys the whole way.

I want to try Hammond 1650N Outputs... But how about an OVER BUILT/OVER SPEC Power Tranny? Sugestions and Sources?

Thanx

Justin
justinsweber
 
Posts: 188
Joined: Sat Sep 20, 2008 7:16 pm
Location: Long Beach, CA

Postby TerrySmith » Tue May 05, 2009 1:48 pm

The Triode or Dynakit replacement is way better than stock, should be exactly what you need.
T. Smith
User avatar
TerrySmith
KT88
 
Posts: 973
Joined: Sat Jan 31, 2004 12:51 pm
Location: Maryville TN

Postby justinsweber » Tue May 05, 2009 4:54 pm

I want a power tranny that is over built and allows for use of KT88s. The Triode vs is beefer, but I wanted even bigger. Some have gone to torodal type... any part numbers or other others? Something really big from hammond. Maybe a P-T278CX Secondary: 400-0-400 V, 465 mA
Filament winding: 6.3 V, 6 A CT.
justinsweber
 
Posts: 188
Joined: Sat Sep 20, 2008 7:16 pm
Location: Long Beach, CA

Postby Slartibartfast » Tue May 05, 2009 5:17 pm

If you go with Hammond, I would go with the 300 series. They have a 120v primary. The 200 series are only 115v. It will run a lot cooler...
User avatar
Slartibartfast
KT88
 
Posts: 458
Joined: Sun Apr 15, 2007 9:40 pm
Location: Columbia S.C.

Postby justinsweber » Tue May 05, 2009 5:49 pm

any sugestion on a specific model?

I want to be able to use almost any rectifer ... and just have it over built.
justinsweber
 
Posts: 188
Joined: Sat Sep 20, 2008 7:16 pm
Location: Long Beach, CA

Postby kheper » Tue May 05, 2009 7:44 pm

justinsweber wrote:any sugestion on a specific model?

I want to be able to use almost any rectifer ... and just have it over built.


Antec toroids are "over built" (whatever that means).

Below, the transformer has 400V x 2 secondaries with 500 ma per secondary. You could series the secondaries at 400-0-400 for a FW rectifier or parallel the secondaries for a FWB rectifier. You'll get about +565V from either configuration.

At 54 bucks, what a deal.

It also has (2) 70 volt bias taps. The 2 taps can be put through a FWB for about -100V bias voltage. Pretty cool.

When I get some funds, I will get one for a stereo SE 813 amp in triode mode. I am going to use it with a voltage doubler. With a doubler, you can tap off half of the voltage to run the drive circuity. This avoids dropping the full B+ with resistors.

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0192771510
User avatar
kheper
KT88
 
Posts: 1252
Joined: Wed Dec 21, 2005 10:14 pm
Location: Philly, PA

Postby ajsons » Wed May 06, 2009 7:37 pm

Has anybody tried this toroidal xfmr from Toroid Corp of Maryland? .75A on the secondary HV looks really hefty for an ST70.

http://www.toroid.com/standard_transfor ... s_tube.htm
ajsons
 
Posts: 6
Joined: Wed May 06, 2009 12:40 pm

Postby WA4SWJ » Thu May 07, 2009 5:19 am

Yes and it barely gets warm driving this amp:

Image

It's a very beefy transformer.

Regards,
Ed Long
User avatar
WA4SWJ
KT88
 
Posts: 650
Joined: Mon Dec 27, 2004 8:39 pm
Location: Belleview, FL

Postby ajsons » Thu May 07, 2009 6:51 am

Ed,
That's exactly the setup/layout I have in mind, but with the power section on the left side of the chassis. Got the same diy driver board, too.

Can you describe what you used for rectifiers and regulation circuit?
Last edited by ajsons on Thu May 07, 2009 11:34 am, edited 1 time in total.
ajsons
 
Posts: 6
Joined: Wed May 06, 2009 12:40 pm

Postby WA4SWJ » Thu May 07, 2009 7:24 am

Well, I used a couple of 1N5408's in a full wave rectifier. I'll have to look under it to remember what else I did. It's been a while since I built this amp. BTW - it is an excellent sounding amp. The output tubes are JJ KT-77's.

I'll look at it this evening and maybe I can post some more pics for you to look at of the underside.

Regards,
Ed Long
User avatar
WA4SWJ
KT88
 
Posts: 650
Joined: Mon Dec 27, 2004 8:39 pm
Location: Belleview, FL

Postby ajsons » Thu May 07, 2009 2:43 pm

Ed,
I will really appreciate that, 'cause it will make doing this project it a lot easier for me.
ajsons
 
Posts: 6
Joined: Wed May 06, 2009 12:40 pm

Postby WA4SWJ » Thu May 07, 2009 5:12 pm

OK,

Here are some underside shots of the amp. Kind of messy, but it works very well. I hope you can see what I did. The power supply is at the upper right of the pictures. I just mounted two 1N5408 diodes right to the first cap section wired to the HV secondary of the transformer and then went to a ST-70 style choke. Then through a couple of resistors and caps and that's it. I believe the resistors are the same values as used in the original ST-70 - but they are new. Just to the left of the main power supply mounted on a terminal strip is the bias rectifier and filter for the fixed bias supply. It's a full wave bridge.

Image

Image

My intent is not to jack this thread, but the transformer in question is the Toroid of Maryland device. No problems at all and as I said earlier, it barely gets warm after running for hours in the amp.

Let me know if you have more questions. Wish I had made this a little more pretty. No hum and those output toroids make for a great amp. They are Amplimo units.

Regards,
Ed Long
User avatar
WA4SWJ
KT88
 
Posts: 650
Joined: Mon Dec 27, 2004 8:39 pm
Location: Belleview, FL

Postby ajsons » Thu May 07, 2009 7:53 pm

Thank you very much, Ed.
Those pictures really help.
I'm new to this forum, but I got a lot of help already
ajsons
 
Posts: 6
Joined: Wed May 06, 2009 12:40 pm


Return to st70

Who is online

Users browsing this forum: No registered users and 18 guests