All Antek toroid ST-70, anyone tried it?

[zippy1540]

i'm looking at building an all antek toroid ST-70. has anyone had any experience with this? is it worth it or should i stick with the standard transformers?
the case i'm going to build from scratch, 14 years of aviation sheet metal work left me with the ability to build anything out of sheetmetal.

[DeathRex]

Since you're good with sheet metal, you can probably make a prettier amp than a ST-70.

[Quad]

Not Antek, but there are a few builds using toroid OPTs -

Mike Sherman's mini amp build (pics links broken)

http://www.diytube.com/phpBB2/viewtopic.php?t=1214

Ed Long's build -

http://www.diytube.com/phpBB2/viewtopic.php?t=2792

I built an amp using a VTA board and Trafomatic toroids,
and it sounds pretty fine to me.
Pics here -

http://picasaweb.google.com/prasadb/TubeAmp

EWBrown also has a similar amp, in progress -

http://www.diytube.com/phpBB2/viewtopic.php?t=1752

[kheper]

i'm looking at building an all antek toroid ST-70. has anyone had any experience with this? is it worth it or should i stick with the standard transformers?

The specs for the AT-040L are pretty similar to the A-470 and $30 cheaper.

http://www.antekinc.com/details.php?p=156

The specs for the AN-4TK360 are similar (but better) than the PA-060 and $50 cheaper.

http://www.antekinc.com/details.php?p=88

I'd go with the Anteks. Be unique and keep some dough in your pockets. The Anteks will deliver more audio output power, too. I'll bet you'll hit 40W/ch with that AN-4TK360 and diode rectification.

[zippy1540]

as of now i'm looking at using the DIYtube board with the triode electronics cap upgrade board, the Antek4t360 power transformer and AT-040L output transformers. if i use a tube rectifier then i'll need a 5v 2a filament transformer. i think it's now time to start collecting parts. i just have to sell some of my other stuff to pay for it.
anyone have any other suggestions for the wish list?
for a user friendly setup i'll incorporate a rotary selector switch for multiple inputs and keep all the connections in the back of the unit. once i get all the major parts i can start measuring for the chassis.

[kheper]

anyone have any other suggestions for the wish list?

Transformer covers if you are not making your own and if you are not going to hide them under the chassis.

http://www.antekinc.com/details.php?p=159

[TerrySmith]

One thing to note is the 4T360 transformer is capable of over 1000ma (1 ampere) of current on the 360v secondaries! I would strongly suggest NOT using a tube rectifier as it will live a very short life. Maybe some UF-5408 diodes should work, put them in an accessible area so it's easy to replace/upgrade them. Since you're going to use a cap-board, get the largest caps you can find, your limits are spacing and chassis height. The old style Triode board limits you to 25mm dia snap-in caps, I don't know about the new one.

[battradio]

I have used the Antec toroids a realy like them . Here is another cap board
http://www.classicvalve.ca/dynaco.html#ST70P

[kheper]

Good catch Terry Smith.

The Antek AN-4TK360 toroid when the windings are connected in series yields 720V@1000ma. Tube rectification is not a good idea with that much current available, unless you want to parallel 2 (5AR4) rectifiers.

With an SS, full-wave rectifier, the power supply will put out a theoretical 510Vdc.

6550 tubes are a better choice than EL-34s.

510V x .05A = 25.5W (too much for an EL-34 with a 25W max plate dissipation.)

510V x .055A = 28W (looks like about the sweet spot for 6650 tubes with its 35W max plate dissipation.)

You will have to adjust the idle bias low for EL-34 tubes (if running with an SS, full-wave rectifier). The ST-70 was designed to run an EL-34 tube at 425V B+ and 50ma idle bias. Even that spec is pushing 25W tubes.

[Geek]

One thing to note is the 4T360 transformer is capable of over 1000ma (1 ampere) of current on the 360v secondaries! I would strongly suggest NOT using a tube rectifier as it will live a very short life.

Here you go. Been running for over a year with no failure:

With an SS, full-wave rectifier, the power supply will put out a theoretical 510Vdc.

The board Mark mentions is rated up to 700VDC.

Though if you go can cap, the stock rating of 525VDC will be fine.

Cheers!

[20to20]

One thing to note is the 4T360 transformer is capable of over 1000ma (1 ampere) of current on the 360v secondaries! I would strongly suggest NOT using a tube rectifier as it will live a very short life.

Here you go. Been running for over a year with no failure:

With an SS, full-wave rectifier, the power supply will put out a theoretical 510Vdc.

Cheers!

On that SS rectifier you have two 75R current limiters. If those were used in a tube rectifier circuit there would be no worries about too much current available from the Antek. If you read the Antek specs you'll see it has 22R DCR on each secondary half which is only about 10R less that the original Dynaco PT. It also has about twice the primary DCR which also helps toward having enough DCR for a 5AR4. If the input capacitance is limited to the same 30uf as the original '70, there should be no worries abouth the current rating of the Antek. The total DCR of the Antek about 40R is nearly equal to the original PA060, (about 40R). With a choke and limited input capacitance all should be fine with the 5AR4.

The formula is ... one secondary half DCR, + [tranny turns ratio(squared) x the primary DCR].

For the Antek... 22 + [(3 squared) =9 x 1.9] = 40R

If your load is equal to or less than the original ST-70 design there should be no problem. If you reduce your choke, you'll have problems. If you add capacitance, you'll have problems.

You'll have another issue though with no bias tap. You'll have to go with cathode biasing. You won't be building an ST-70.

[tomlang]

Check again, I think that Antek power trans has a bias tap. And, even if it didn't, he could do the biasing circuit like on the Eiclone using a capacitor-resistor voltage divider off one side of the HV secondary.

[20to20]

Check again, I think that Antek power trans has a bias tap. And, even if it didn't, he could do the biasing circuit like on the Eiclone using a capacitor-resistor voltage divider off one side of the HV secondary.

When do you decide you are not actually building anything like the original?

Here's a link to the specs

http://www.antekinc.com/details.php?p=88

[Geek]

On that SS rectifier you have two 75R current limiters.

Ummm, no, not current limiters.... they simulate the drop at proper bias on a ST-70.

Cheers!

[20to20]

On that SS rectifier you have two 75R current limiters.

Ummm, no, not current limiters.... they simulate the drop at proper bias on a ST-70.

Cheers!

Geek,

Take a look at a 5AR4 data sheet that prescribes limiting resistors for varying amounts of input capacitance and choke and transformer DCR. It shows your resistors in series with the secondary before the rectifier and calls them current limiters.