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AUDIO FORUMS >> General Discussion and Support >> 274B MOD?
https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1491380428

Message started by EdGuY on 04/05/17 at 09:20:28

Title: 274B MOD?
Post by EdGuY on 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?

Title: Re: 274B MOD?
Post by Rivieraranch on 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.

Title: Re: 274B MOD?
Post by mark58 on 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.

Title: Re: 274B MOD?
Post by Lon on 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.

Title: Re: 274B MOD?
Post by will on 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

Title: Re: 274B MOD?
Post by EdGuY on 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

Title: Re: 274B MOD?
Post by will on 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.