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AUDIO FORUMS >> Replacement Tubes >> Rectifiers in Decware amps. A design flaw?
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Message started by Deep Structure on 02/03/22 at 00:27:51

Title: Rectifiers in Decware amps. A design flaw?
Post by Deep Structure on 02/03/22 at 00:27:51

There seems to be a design flaw in many Decware amps: The use of a 47mf capacitor downstream from rectifiers that cannot handle that much capacitance. Thus the 247b, supplied with the amp, is rated at only 4mf (!) and the 5U4G, more recently supplied, is rated at 40mf. The 5Y3GT offered for sale by Decware is rated for 20mf. This explains why my SE-34I.5 eats rectifiers of all types and I'm not the only one with the problem. They work fine for 3 months, then they arc for a few months and then they fail often taking out a fuse. As a result I cannot consider this amp reliable and it's getting expensive to constantly replace rectifiers that fail anyway.
Steve suggested I find older rectifiers that may work, but if you cannot use commonly available tubes then there is a problem that is less than consumer friendly. One individual suggested that the issue could be solved by replacing the 1st cap with a 22mf one. Does anyone have an opinion about this? How would the sound be affected? Of course another increasingly attractive option is to sell the amp and look for something that both sounds as good and is reliable.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by Archie on 02/03/22 at 00:37:01

Quote:

This explains why my SE-34I.5 eats rectifiers of all types and I'm not the only one with the problem.

I've loosely followed your problem with your Rachael but I don't remember seeing anyone else post about having this problem. Can you back this up? It's a pretty strong statement that this is a "design flaw" given the thousands of amps Steve makes this way. He seems to know his business. I've never had a rectifier failure but I don't have a Rachael either.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by CAJames on 02/03/22 at 02:20:04

FWIW here is a post from Steve a while back regarding rectifiers that lines up with my opinion was well (emphasis added by me). Spoiler alert, I'd steer well clear of current production rectifiers.

Quote:

Re: Roll Rachael Roll
Reply #13 - 06/23/20 at 06:08:32
Some great feedback regarding quality tubes...

The beauty of a tube amp is that you can change the tubes. You can change the tubes when they grow tired and lazy sounding over time... or you can change the tubes when you grow bored or just want to take a different seat in the music hall so that you can hear the music from a different perspective. So this leads to tube rolling which leads to brands and types... and here is some of what I know that you should know:

Current production vs. New Old Stock. In my experience the only consistently solid tubes on the market today come from Russia. Brands like Mullard, Tungsol, Electro Harmonix, Sovtek, Svetlana. The rights to these brand names have been acquired over the years by New Sensor Corp in the USA, who is predominately a tube supplier for the music industry / guitar amps. They own or partially own factories in Russia.

Decware purchases it's Russian tubes direct from Russia in bulk with the exception of the larger output tubes (EL34/KT66/KT88) which are current production branded tubes imported into the USA. All of the the Russian tubes that we purchase direct from Russia are N.O.S. Russian Military Grade tubes. Many of them have Gold grids, thick glass, high G ratings for missile use, and longer life, in some cases 10,000 hours. These are ultra-hi-end tubes in disguise and have always been. To hear how good these tubes are you have to install an American New Old Stock rectifier tube.

My experience with Boutique Chinese brands is mixed. The sound is good, the reliability and or consistency is ridiculous. I have been purchasing samples of these fancy tubes as they come out over the past many years and I have an entire collection of crippled tubes. Even KT88's that cost $1600 a quad drifted out of usable tolerance within days and had to be replaced.

New Old Stock is the real deal. Those who like to push the envelope of what is possible with their amplifier will often go down this path with no regrets. For one thing, the tubes not only sound better, but often last longer, in some cases like with rectifier tubes up to 10 times longer.

Rectifiers are a subject all in their own. Russian rectifiers are acceptable, everything else is a no-go from a reliability standpoint with some rare exceptions that are very pricey. My advise to all Decware amplifier owners is to find yourself a New Old Stock 5U4 or a 5R4 that has never been used and comes in it's original un-molested box. Consider the current production rectifier tube we ship with the amp the best sounding and most attractive option that will last long enough for you to find a real N.O.S. replacement.

Finding N.O.S. tubes is easy, even on eBay there are millions. Since you only need one or two you will have more to choose from than you know what to do with. Finding quantity of these tubes is another story. If Decware could secure reliable inventory of 1000's of N.O.S. rectifiers, it is an investment we would gladly make but in 25 years is has yet to happen. Because we can't find N.O.S. tubes in large quantities, even batches of 100 would be gone in less than 30 days, we feel there is no point in even trying.

For the customer it is easy, just find a N.O.S. 5U4 tube on eBay that is unused, and in it's original box for $40 and it could easily last for 10 years or more and sound better the entire time.

As an amplifier designer, it is possible to create circuits that baby the rectifier tube by limiting inrush current, using smaller capacitors, running higher voltages with a choke and so on. Correctly done, this can make a Chinese rectifier tube last the full rated 500 hours or more. The problem with this is that it changes the sound quality of the amplifier well outside what we find acceptable. So, we have to make a choice, do we design tube amplifiers to baby the crappie rectifier tubes being made today, or do we design amplifiers to use REAL tubes. Of course the answer has to be REAL tubes, because we make real amps.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by funch on 02/03/22 at 04:01:01

I use the 10uF value of this one as my first cap after the rectifier tube.

https://www.tubesandmore.com/products/capacitor-ft-500v-type-axial-lead

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by CAJames on 02/03/22 at 14:12:58

Quote:

Posted by: funch Posted on: Today at 04:01:01
I use the 10uF value of this one as my first cap after the rectifier tube.

In what amp?

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by JOMAN on 02/03/22 at 19:13:07

I'm not so sure that the niche specialty segment of audio could be considered as being "consumer friendly". It is not targeted to the mainstream segment, rather to the few that will go to great lengths to achieve real music in their homes and there's a lot of trial and error associated with that.

If you do not think that is the case then consider the time and money that some will spend on fuses, cables, connectors and so on. Based on the Steve's post it's pretty clear that using a 47uF cap is a design choice to achieve a very targeted end result and not a design flaw.

My UFO25 went through 2 Sophia Aqua 274B in one year! Others have had better success with the same rectifier. I did not blame the design of the UFO25, it's doing extremely well with the NOS rectifiers that are now in it.

Yes, I have limited my choice of rectifier as a result. That's the "price" that I choose to accept and pay to get the results that Steve talks about. I would not be critical of anyone that chose not to do what I do.

Just in case, I'm not implying that anyone is being critical just saying it's a matter of choice and we all have our preferences.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by Showme on 02/03/22 at 22:49:24

That’s a bummer on those Sophia 274B’s. Painful. I’ve been fortunate and mine is going on 3 years and sounds marvelous to my ears at least.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by Deep Structure on 02/04/22 at 01:30:28

I was asked to back up my claim about rectifier failure in Decware amps. There are other forums on Decware amps other than the Decware site. For instance there is one on Facebook devoted to the Rachel and you will find many descriptions of the problem there among other sites. You can also find such descriptions in reviews of rectifier tubes on the web sites of several tube merchants. It is far from uncommon problem and I'll stand by that. But my own experience is enough for me. A rectifier twice a year is getting expensive and a hassle to say the least. Admittedly I have yet to try expensive NOS rectifiers which seem difficult to come by in Canada.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by CAJames on 02/04/22 at 01:41:03

Quote:

Posted by: Deep Structure Posted on: Today at 01:30:28
...Admittedly I have yet to try expensive NOS rectifiers which seem difficult to come by in Canada.

I know for sure that NOS rectifiers don't have to be expensive, and I'd be surprised if they are much harder to come by in Canada than in the USA. Here is a helpful thread about buying (inexpensive) NOS rectifiers:

https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1605822949

OTOH, there is nothing wrong with going solid state if vacuum tubes aren't your thing.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by Doug on 02/04/22 at 01:46:37

I also have a Sophia 274B Aqua that is nearly 4 years old and it still makes beautiful music. Its first couple of years were spent in a Torii Jr, and the last couple in my CSP3 with 25th mods. A 2nd Sophia 274B Aqua left with the Torii Jr when I sold it. That tube was well over a year old, used daily, and never showed any signs of weakness. Having said that, I will likely try a NOS rectifier in my CSP3 some time later this year.

Rectifier tubes have been a pain in my neck for much of my 35+ years of using tube amps. I had a pair of big Cary 2a3 mono blocks that gobbled up rectifier tubes in the same manner that Deep Structure has described. After approximately 10 years of this foolishness, I sent the amps back to Cary for some minor modifications to alleviate the problem. A month later, and with my wallet $700 lighter, there was no difference at all! The amps continued to burn up rectifier tubes AND 2a3 tubes, which were not cheap! I used all types of NOS rectifiers, and if I recall, those big old gray base potato mashers seemed to last longer than others. Cary claimed the amps were functioning perfectly. A few years later I sold them specifically because of the frequent tube blowing issue. And that’s when I bought my first Decware amp.

I feel your pain Deep Structure. Maybe you should pack up the amp, send it to Steve, and get confirmation that it is in proper operating condition. I wish you the best.

Doug

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by funch on 02/04/22 at 03:42:42

Oops! I see that I forgot to paste the link for the 'cap in my post above. Corrected. I use these in my SE84 clone headphone amp. These were the brand/type that were in my SE84UFO.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by JOMAN on 02/04/22 at 05:43:55

I live in Canada and NOS rectifiers are no harder to get here than anywhere else. NOS rectifiers can be hard to get because the stocks are being depleted. I haven't looked for rectifiers in two or three years and hopefully will not have to for a long time to come.

I did not buy expensive rectifiers in the early stages of rolling rectifiers. The ones that I started with cost $40.00 CAD - $60.00 CAD and had no trouble getting them. Next were the $100.00 - $150.00 CAD rectifiers. Then I tried the Sophia 274B at $200.00 CAD each. That IMO that is expensive but I did like what they did. Very good sound until the light shows.

That's when I decided to up the anti in order to try to get as good a result as with the Sophia or better with longevity. Ended up with the GZ34 Metal Base and haven't looked back. But these are very hard to find at a sane price, anywhere.

I think that Dougs suggestion is a very good one. Talk to Steve first then if he recommends it, send it back. I've done that with my ZRock2 and my CSP3. However doing that from Canada can be a pain. If you do that and haven't done it before I'll be glad to give you the benefit of my experience.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by JOMAN on 02/04/22 at 06:08:41

Here's another suggestion. I have some rectifiers that I'll never use. Planning to sell some. I'll give you a AWV Type 80 ST with an adapter if it will work in your Rachel, which it should or an AWV 5AS4 which is a %u4G variant. I think the Type 80 is NOS and the other used but built like the proverbial brick out house. Just pay for the shipping.

If your amp eats one of these, then definitely, talk to Steve and consider sending the Rachel back if he suggests that. You can PM me if you want.

I know the feeling and frustration when rectifier fails before it should and takes out fuses as a bonus.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by Tony on 02/04/22 at 15:50:05

That's what I call being supportive. [smiley=icqlite20.png]

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by spyder1 on 02/04/22 at 18:29:33

There is the Sylvania 5931, which is a ruggedized 5U4GB tube. This should be tried because of its longevity. They can be bought at surplussales.com, search {5U4WG, $35.00 each}.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by spyder1 on 02/04/22 at 19:02:50

IMO, other rugged rectifier tubes worth experimenting with are 6087 GE, and 6106 Bendix. These are 5Y3GT tube types. You can save $500 on the purchase of GZ34 Mullard Metal Base.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by Dana on 02/04/22 at 19:05:30

Going off the NOS bend. is the UX281 globe compatible with the UFO84?

UX281 = 81 not 80

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by CAJames on 02/04/22 at 19:21:17

Quote:

Posted by: Dana Posted on: Today at 19:05:30
Going off the NOS bend. is the UX281 globe compatible with the UFO84?

No. UX281 is 7.5 V filament. Also, it is only a half wave rectifier.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by Dana on 02/04/22 at 21:12:08

THANKS!
Must be why they're so cheap

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by Rivieraranch on 02/15/22 at 01:10:42

Grab a 5Z3 and use it with an adapter. they are cheaper than the 5U4G and electrically the same.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by My Name is Earl on 04/02/24 at 17:48:17

I have successfully used Type 80 and 280 with the appropriate adapter in my SE84UFO. I have found that they do sound better than the stock 274B that was shipped with the amp (and failed) and have had no issues with longevity or tripping the internal fuse.

So far I have preferred the RCA Radiotron UX-280s. A Majextic 280 that I have is almost as good and there are various 80s in ST glass that are excellent but not as satisfying as the 280 globe tubes. The same holds true for the 5Y3 types I’ve tried.

The globe/balloon 280s seem to deliver more energy and better dynamic range, better PRAT.

The best ST type 80 that I have encountered is a ‘50s Sylvania in ST glass. Others are close, but the Sylvania was the first 80 I acquired and it opened my eyes to the world of rectifiers.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by Sai on 04/02/24 at 20:48:54

Using NOSMullard 5AR4 (GZ34) fat base tubes. So far has about 800 hours on them on my Torii MK V. Still all sorted on that front so far…

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by chapsjon on 04/03/24 at 01:05:15

I can't speak to the rectifiers in Decware PP amps, but I have never had a rectifier fail.

I have an SE84C+ with over 2000 hours on a Russian winged 5U3c, a mini torii with at least 1200 hours on Mullard EZ81s, a CSP2+ with well over 800 hours on a Sylvania tall, black plate 5U4, and an SE84 UFO with at least 500 hours on a Mullard GZ32.

These were all NOS tubes, and my anecdotal experience is to recommend these as better sounding, less frustrating, and a better value than current production. If you are patient, you can pick them up pretty reasonably. I have limited experience with current production tubes, only using the Chinese rectifiers my SE84UFO and CSP2+ came with until I could with them out.

Title: Re: Rectifiers in Decware amps. A design flaw?
Post by Lon on 04/03/24 at 10:43:52

I know this thread was started over two years ago but I want to point out that the OP's mention that the 274B that the amp shipped with was NOT manufactured for a much lower 4mf but was a modern design electrically similar to a 5U4G.