"I read somewhere that it is 3a"

Posted by 1973shovel (A) on March 27, 2020 at 06:01:27

In Reply to: PA060 filament current? posted by zacster on March 22, 2020 at 07:20:09:

I've read a few posts which casually mention 3 amps, but never seen an actual Dynaco specification.

Below is a link to baseline testing of a stock Dynaco ST-70. Scroll down to "The Power Supply" where the power transformer is discussed. Here's an excerpt:

"The case against the power transformer centers on its current capacity, and the temperature it operates at. However, it still allows its individual per channel power output level to be achieved across the entire audio bandwidth, even permitting it within the majority of the audio bandwidth with both channels driven. So its current capacity is hardly of the grossly inadequate grade that some give it."

Also noted in the article is that there wasn't a high power transformer failure rate in the ST-70. So, while the 5A filament rating is better (especially with alternative input stages which add an extra tube), the original transformer was not unacceptable for the stock circuit.

ST-70 Testing (Open in New Window)

This post is made possible by the generous support of people like you and our sponsors:

Follow Ups Full Thread

Topic - PA060 filament current? - zacster 07:20:09 03/22/20 (15)

RE: PA060 filament current? - understudy 06:30:48 01/18/24 (0)

There were a minimum of three different power transformers... - viridian 07:21:56 04/28/20 (3)

RE: There were a minimum of three different power transformers... - Mushroom Soup 18:41:34 03/05/21 (0)

RE: There were a minimum of three different power transformers... - zacster 09:14:27 04/28/20 (1)

Best of luck with that. Nt - viridian 09:54:53 04/28/20 (0)

"I read somewhere that it is 3a" - 1973shovel 06:01:27 03/27/20 (9)

RE: "I read somewhere that it is 3a" - zacster 06:58:44 03/27/20 (8)

"a 4 tube driver board" - 1973shovel 08:10:43 03/27/20 (7)

RE: "a 4 tube driver board" - zacster 10:55:59 03/27/20 (6)

"Is that the story?" - 1973shovel 06:56:45 03/28/20 (5)

RE: "Is that the story?" - zacster 18:10:32 03/28/20 (4)

Nearly five years for Joe - 1973shovel 06:28:06 03/30/20 (3)

RE: Nearly five years for Joe - understudy 06:23:02 01/18/24 (2)

Yes, weird...and short. Enjoy it while we can! (nt) - 1973shovel 07:52:20 01/18/24 (1)

RE: Yes, weird...and short. Enjoy it while we can! (nt) - understudy 09:13:06 01/18/24 (0)

Follow Ups

"I read somewhere that it is 3a" - 1973shovel 06:01:27 03/27/20 (9)

RE: "I read somewhere that it is 3a" - zacster 06:58:44 03/27/20 (8)

"a 4 tube driver board" - 1973shovel 08:10:43 03/27/20 (7)

RE: "a 4 tube driver board" - zacster 10:55:59 03/27/20 (6)

"Is that the story?" - 1973shovel 06:56:45 03/28/20 (5)

RE: "Is that the story?" - zacster 18:10:32 03/28/20 (4)

Nearly five years for Joe - 1973shovel 06:28:06 03/30/20 (3)

RE: Nearly five years for Joe - understudy 06:23:02 01/18/24 (2)

Yes, weird...and short. Enjoy it while we can! (nt) - 1973shovel 07:52:20 01/18/24 (1)

RE: Yes, weird...and short. Enjoy it while we can! (nt) - understudy 09:13:06 01/18/24 (0)

"I read somewhere that it is 3a"

Post a Message!