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PA060 filament current?

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Posted on March 22, 2020 at 07:20:09
zacster
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Posts: 2179
Location: NYC
Joined: November 22, 2003
 I was looking around for the filament current rating on the 6.3v taps of the PA-060 power transformer, and I read somewhere that it is 3a, but that the upgrade transformers available are 5a to give some headroom and to run cooler. But just looking at the data sheets for the EL34 and 7199, the total draw is 3.45a, which exceeds the 3a spec. Is that spec incorrect? Or how did it get away with it in an original ST-70?

 

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"I read somewhere that it is 3a", posted on March 27, 2020 at 06:01:27
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007
 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.

 

RE: "I read somewhere that it is 3a", posted on March 27, 2020 at 06:58:44
zacster
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Posts: 2179
Location: NYC
Joined: November 22, 2003
 That's an interesting read. One thing I noted was the filament voltage of 6.8vac with house AC of 122v. That's exactly what I have in mine, and was my second concern. I was going to put mine on my Variac and reduce that voltage to 6.3 and see what the AC measures then. I like how he defends the original circuit, but my experience was that it sounded very "tubey".

I'm already pushing the transformer, using a 4 tube driver board, and also pushing that by replacing a 6DJ8 with a 6N6P. That almost triples the draw from the driver. My power tubes make up for that, the EL34 draw 1.5a but the 6B4G only draw 1a. It all works and has been for 10 years now so I'm not concerned, just as he said.

Thanks for posting.

 

"a 4 tube driver board", posted on March 27, 2020 at 08:10:43
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007
 When I wrote my reply this morning I nearly wrote "three or four tube", but didn't. I should have.

Your experience of using a stock PA-060 in a circuit demanding that much current for that many years without failure is impressive. Most, if not all vintage tube gear could benefit from the use of a bucking transformer, another project on my long list. Meanwhile, like you, I use a variac to dial the amps back to 120 VAC or less.

I had Hayboer Transformers (link below) build me a "higher current capability" PA-060 when I converted one of my ST-70s to a three tube (12AU7) driver board, but I never had an issue with the stock transformer getting too hot, so I never got the urge to install it.

I'm glad you liked the article. Dave Gillespie is very "objective", especially in his public comments, so his defending the stock circuit is very much based on his measurements.

While I don't disagree with you regarding the "very tubey" sound of the stock ST-70, the above mentioned 12AU7 circuit I have in one of my ST-70s sounds too "solid statey" to me. More so than my actual solid state First Watt F1J amp, in fact. Yes, it became more detailed, and the bass tightened up, but it lost some of its subjective musicality and fun factor.

 

RE: "a 4 tube driver board", posted on March 27, 2020 at 10:55:59
zacster
Audiophile

Posts: 2179
Location: NYC
Joined: November 22, 2003
 Yea, that 4 tube board is the Curcio premium board. 4x6DJ8/6922, except that I substitute the 6N6P for the driver tube. The other 6DJ8 is phase splitter. I've always assumed Joe knew how far you could push this transformer since he sold this board.

It's funny, I always assumed Joe Curcio was some grumpy old guy that did this in retirement, but then he took a job with Apple and dropped all this? Is that the story? Another grumpy old guy wants to know.

 

"Is that the story?", posted on March 28, 2020 at 06:56:45
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007
 You know more than a few of us, it seems. Joe going to Apple was news to me. I had no idea what happened to him and was saying he was "Missing In Action". I don't know if he still sponsors this forum, but I would assume not, not if he's not selling anything.

If that's the case, I'm very grateful that Rod (the owner and caretaker of Audio Asylum) has kept the Dynaco Doctor doors open. Between posts by Joe, the late Bill Thomas, Uncle Ned (formerly of Triode Electronics) and some others, this forum is the best treasure trove of Dynaco information I've ever found. I hope it never goes away.

 

RE: "Is that the story?", posted on March 28, 2020 at 18:10:32
zacster
Audiophile

Posts: 2179
Location: NYC
Joined: November 22, 2003
 https://www.signalhire.com/profiles/joe-curcio%27s-email/5376611

But I also saw on another page that he left Apple in 2017. His last post here was in 2015.

And yes, it is great that we can still access this forum, and the website is still up with the technical manuals.

 

Nearly five years for Joe, posted on March 30, 2020 at 06:28:06
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007
 And nine years since Bill Thomas' last post.

Damn.

What's that old line? "Life is like a roll of toilet paper. The closer it gets to the end, the faster it goes"

 

There were a minimum of three different power transformers..., posted on April 28, 2020 at 07:21:56
viridian
 ...used in Dynaco ST70 amps, a large stack cloth lead, a short stack cloth lead, and a short stack plastic lead. I believe the later was Japanese sourced and the two former of American manufacture. Even though I believe that all three are rated at 3A the large stack runs cooler than the others in my testing. Sorry, no hard figures as I just use my hand (no jokes, please).

 

RE: There were a minimum of three different power transformers..., posted on April 28, 2020 at 09:14:27
zacster
Audiophile

Posts: 2179
Location: NYC
Joined: November 22, 2003
 Mine is the short stack cloth lead variety. I gave up on the mod I was trying to do in any case. I'll buy a new power transformer and build a completely new amp if I ever do anything.

 

Best of luck with that. Nt, posted on April 28, 2020 at 09:54:53
viridian
 Nt

 

RE: There were a minimum of three different power transformers..., posted on March 5, 2021 at 18:41:34
Mushroom Soup
Audiophile

Posts: 310
Location: Western New York State
Joined: November 1, 2003
 I think maybe I heard of a larger stack transformer was made because the filament current wasn't really adequate on the original transformers. I would love to find one with a lower impedance B+ but that's probably just dreamin'.

 

RE: Nearly five years for Joe, posted on January 18, 2024 at 06:23:02
understudy
Audiophile

Posts: 9
Location: northeast
Joined: January 12, 2024
 I heard that saying the first time last week, then find it in print scrolling this old thread. Life is weird.

 

RE: PA060 filament current?, posted on January 18, 2024 at 06:30:48
understudy
Audiophile

Posts: 9
Location: northeast
Joined: January 12, 2024
 Would putting a small 6.3VAC 1A filament transformer in parallel with the same output on the PT help? Those are about the same size as the choke. You might even be able to get it under the chassis if the choke rotated 90° and moved over 1/2".

(understood this thread is 4YO)

 

Yes, weird...and short. Enjoy it while we can! (nt), posted on January 18, 2024 at 07:52:20
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007

 

RE: Yes, weird...and short. Enjoy it while we can! (nt), posted on January 18, 2024 at 09:13:06
understudy
Audiophile

Posts: 9
Location: northeast
Joined: January 12, 2024
 For tomorrow.....

 

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