Forums - 274B MOD?

EdGuY Seasoned Member Fact is just a solid opinion. Posts: 133	274B MOD? 04/05/17 at 09:20:28 Maybe some of you can help? I was wondering is there any 274B tube modifications for CSP2+ and Torii III amps?
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Rivieraranch Seasoned Member Posts: 2126	Re: 274B MOD? Reply #1 - 04/05/17 at 15:50:26 I think you could change the resistor somewhere. There was a thread about using the 274B with these amps and having problems at startup. But if you do that you change the way they are designed and then you could lose some of the unique characteristics of the sound.
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mark58 Seasoned Member Posts: 5647	Re: 274B MOD? Reply #2 - 04/05/17 at 16:04:27 I'm not a tech expert but I thought I read here that the Valve Art 274B was more like a 5U4G internally. I think I've got three sent with new Decware gear...CSP3, Taboo MK III and ZP3 I think. So maybe no mod needed? I'd ask Steve.
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Lon Seasoned Member "Love without guts is worthless!" Philip K. Dick Posts: 23459	Re: 274B MOD? Reply #3 - 04/05/17 at 16:06:14 Right, the Valve Art is safe to use, but it is NOT the same as other 274Bs which can cause problems or have a shortened life in a Decware amp.
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will

Seasoned Member

Posts: 2919

Re: 274B MOD?
Reply #4 - 04/05/17 at 16:47:03

It seems to be about the power supply cap values, by most reports new Valve Art/Shuguang 274Bs fine, but a different story with more traditional 274s. Here is a post Steve made some time ago.

Not an answer, but a pointer.

"Re: Safe rectifier roundup (Decware input pending)
Reply #1 - 07/05/12 at 11:38am Decware amps typically use between 33 ~ 47uf caps as the first section of the power supply filter after the rectifier tube.

In the case of the SE34I.3 the value is 47uf.

So far all the 274B's I've looked at ( and I haven't looked at all of them ) would like to see less than 10uf as the first section of the power supply filter. Going beyond the value could cause flashing upon startup. That said, many people ignore the warning and use it anyway, claiming the sound is worth the potentially short-lived tube.

Steve"

https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1341384562/1#1

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All Modified: PSA-P5>DIY Strip/Shunyata Defender>RevolutionMacMini/Amarra-KTE Singxer/Gustardx20pro/ZBIT/CSP3>OldChen 300B/845, Torii IV>Omega S-A-H-O monitors/SVS Micro3000>Pi PCs-DIY PCs, ICs, USB, I2S, Speaker-SR and aluminum w ball bearing feet

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EdGuY Seasoned Member Fact is just a solid opinion. Posts: 133	Re: 274B MOD? Reply #5 - 04/05/17 at 21:34:00 I thought there is a solution for that when I saw this: https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1409441941
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will

Seasoned Member

Posts: 2919

Re: 274B MOD?
Reply #6 - 04/06/17 at 01:39:58

I don't know details about modding for 274Bs, but have a few things that may help. The MKII post you linked is shown with 5U4G-STs, saying it can use 274B and 5AR4s also...Both my MKIV and CSP3 have 47uf caps in the power supply. Unless the MkII post is referring to the Valve Art 274Bs, based on Steve's post, standard 274Bs needing 10uf or less caps, this seems a long way off.

But, if that MKII was modded for the real 274Bs, the upgrade is listed with the usual Decware Hazen and attenuator upgrades, so it may well have been done at Decware....Even if not, Steve has tried and heard a lot of things in Torii development. I would call and ask.

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All Modified: PSA-P5>DIY Strip/Shunyata Defender>RevolutionMacMini/Amarra-KTE Singxer/Gustardx20pro/ZBIT/CSP3>OldChen 300B/845, Torii IV>Omega S-A-H-O monitors/SVS Micro3000>Pi PCs-DIY PCs, ICs, USB, I2S, Speaker-SR and aluminum w ball bearing feet

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