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Old 24th December 2009, 08:09 PM   #1
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Default New 300B JEL/Walton Builder's thread

The latest post on the KT88SE builder's thread diverging from the KT88 to the 300B:

"Jeff, since you are ready to build the 300B SE, start a new thread and I'll chime in as catch up to building it.

Questions:
1. Which JEL 300B SE amp are you going to build exactly?...
2. Monoblock or Stereo?...
3. What will be the Edcor TX and choke design values because I might still go with Walton's 300B because I only have matched NOS Sylvania 6SN7GTB's?...

Pending on the values, I am in for the Edcor design PTX and chokes - better choice than Hammond!

I have the Hammond iron for the SE KT88, and for me, it looks like junk - very thin and frail wiring. I've heard it's also prone to buzzing, noise in refined applications - so I am mounting them to the chassis plate with rubber washers and grommets for electromechanical isolation. However, there are those who are perfectly happy with Hammond. I'll see how it turns out...

I should have gone with Edcor in the first place even with their blue color and all, it's better spec'd too with 200ma instead of 175ma, which doesn't leave much for dynamics or headroom. Sensing that Hammond doesn't have a 200ma 375V PTX in their line up, all of a sudden, they've listed the 273BX as 201ma (1 ma better than Edcor) without any without any design change to the transformer. I emailed the HQ in Canada to be sure. Even their OPT are not spec'd 20-20khz, and bass is where it's at with OPT. I am with you, Jeff - EDCOR!

This is where I got my ASC motor run caps - inexpensive and they sell mounts too. I think the 47uF for the PSU is for an arbitrary value for polypropylene or electrolytic caps. I am using the 50uF ASC motor run caps as they are well within the 10% tolerance anyway. Here is the link:

ASC Capacitors - X386S-50-10-440 - Allied Electronics

They even have the 7.5uF ASC that Derrick was trying to find, and ended up using two 15uF...
"

88man,
I think I am going with the JEL monoblock DX design. The JEL will allow you to use your 6SN7GTB tubes in the driver position.....

I will state here what I mentioned before in the KT88 thread.

I have asked Edcor to design a replica of the Angela Universal power transformer as well as the chokes required for the JEL SE300B DX. I am going to pay the first design fees of $40 each part so after the design is finished subsequent DIYers can purchase these at regular cost. I am not yet sure what the final cost will be but judging from there comparable power transformers (and chokes not listed on their website) I imagine the power transformer will run between $95 and $110 USD, The Chokes will likely fall in the range of $25 to $45 each as well. I am not sure if the chokes will be open bracket or bell ended. Personally I like the open bracket as I prefer to mount underneath the chassis.

The OPT from Edcor that will work in this design sells for $83 each. So I figure for a monobock set of amps built with all Edcor iron you will be looking at about $500 give or take $50 either way depending on what the final prices will be.

Here are the links to the 2 websites most of the design will come from on this build:

300B Mk1 Tube Amplifier

And

SE300B classic and DX

More to come.....

Jeff
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Old 24th December 2009, 11:32 PM   #2
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Default T-Rex 300B

Maybe you all have seen this. Great article, nice power supply. Looks like a good candidate.

The T-Rex SET Amplifier -- A DIY Project Article By Dick Olsher And John Broskie
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Old 25th December 2009, 03:40 AM   #3
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Good to move the discussion in a separate thread.

Both approaches are very attractive, one is very simple and linear, the other more complicated.
I have to say that, at least in theory, the regulated PSU make sense as much as the CCS for the cathodes. This is actually one of the reason why I was also interested to the tubelab approach.
What I am not sure about the T-Rex, is that sound to me as "I want tubes and tubes only" approach. I have the feeling that tubes are great for amplification, but in other business, as regulation, solid state can be a better solution.

For what concern me I would like to go for a monoblock, hoping to keep the cost of the PSU reasonable.

Jeff what design of PSU do you want to go for ? 20 H/400mA that's a huge piece of iron !! Is this the choke you asked Edcor to produce ?

As OPT I think I will settle for the Hashimoto H-20-3.5U, I have the constrain that I need the 4 ohm tap, that Tango for example does not have it.

As I am a kind of gipsy, now I live in a 100V country, but sooner or later I will move again to a 220V country, so I would really approciate if I could find a power transformer that has these two input. The Angela replica you proposed, would be great for me, but I am not sure I can run 20 % down. Maybe Edcon could accomodate this in the custom design.

From Hashimoto I saw that there is the possibility to have the PT-220 with 220V, but I still did not understand if it is 220V only or it has different taps.

Let's see what comes out. This time I will build prototypes before assembling the chassis :-)

Merry Christmas,

Davide

P.S. In Japan this is a working day :-(
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Old 25th December 2009, 05:58 AM   #4
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The Edcor designs I have requested are for an exact replica of the Angela power transformer (universal). I have also asked for a 10H 125mA choke and a 8H 65mA choke. I am looking at the Deluxe version at the JEL website for the Monoblocks.

Yes, Edcor can make anything you wish for an additional fee of $40. This is the cheapest most reasonable company out there for design fees! You will still be able to benefit from the chokes I will have designed as I will have already paid the design fees for these.

I would bet you could get by using the 110V transformer at 100V without much compromise. You could also change some of the resistor values slightly too if needed.

Nikon, If you could find a few more of those rotary switches in Japan I would gladly pay you for your troubles in getting them to me, they look very nice, I have not seen anything comparable at Mouser, Digikey, or elsewhere I have looked. How much did they cost you in appx USD, do you recall?
Jeff
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Old 25th December 2009, 08:58 AM   #5
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The Angela is rated 120 V, so it meand that I would be 20% off, not 10 %. Playing with the primary voltage is annoying, as all the secondaries would be off, not only the HT. I had enought trouble with the PSU of the KT88, I don't want to go the same way. I'll ask edcor how much would be to ship to Japan, or will try to find a provider in Japan.
Just one question, what's the difference between a "good" power transformer and a bad one ?

I also already have a 3.5 KW step up-down transformer. Maybe I can just set it up nicely to have a 100 V source in Europe. They always say to to do it with power amplifiers, but I don'r really understand why. If the transformer is big enough. Somewhere outside your apartment there is a transformer.

Changing all the PTW in three years would be painful, especially with monoblocks :-(

BR,

Davide
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Old 25th December 2009, 12:46 PM   #6
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First of all, I do not want to offend anybody today or get into any ideological discussion .
But even I, not being an expert in tube technology at all, know that the idea of building a 300B amp with a cascaded 6sn7 is not clever any more. There is a lot of information right on this forum that tells you that if you do not believe me.
Any mu-stage, mu-follower, drd design, the already mentioned T-rex, or this one Gary Pimm's DIY audio pages will give you a lot more pleasure for the buck.
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Old 25th December 2009, 01:35 PM   #7
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Now this is a dizzying experience....... Gary Pimm's DIY audio pages
No thanks,
Jeff
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Old 25th December 2009, 01:40 PM   #8
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Jaap,
I don't think anybody here would be offended but to tell the truth, most of us (I think 3 or 4) involved in this new thread are fairly new to the hobby. I myself want to keep things simple rather than clever. The JEL and Walton (essentially the same basic circuit) are well tested and fairly easy to implement. Maybe a year or 2 from now I will be ready to try something a little more clever but for now I am still getting my feet wet with DHTs and would like to have fun putting something together I understand and is not too difficult to build. Thanks for the ideas though, I will certainly keep all these in mind for future adventures.
Merry Christmas,
Jeff
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Old 25th December 2009, 02:19 PM   #9
Jaap is offline Jaap  Netherlands
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Quote:
Originally Posted by jmillerdoc View Post
Jaap,
I don't think anybody here would be offended but to tell the truth, most of us (I think 3 or 4) involved in this new thread are fairly new to the hobby. I myself want to keep things simple rather than clever.
Merry Christmas,
Jeff
I reacted because because when i was still less expierenced than I am now I also started this hobby with the cascaded 6sn7 => 300B. I consider this now as a (expensive) mistake and hope that others can cut corners.
I now think that if you want to combine "simple and clever" you better start with the el84 (or russian equivalent). I also think now that most people are better off with a PP amp. For a starter one of the proven designs (tubelabs, pete millett, etc.) that provide a PCB is also a good idea, less mistakes and easy to build (not so easy to tweak). If you insist on SE look at the RH84. You can always built your 300B amp later

But I also realize that everybody has to find his own way through the tube jungle to the Sierra Nirvana

merry christmas
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Old 25th December 2009, 02:30 PM   #10
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Quote:
Originally Posted by jmillerdoc View Post
Now this is a dizzying experience....... Gary Pimm's DIY audio pages
No thanks,
Jeff

well 1000 volts of B+ is indeed too much for anybody with a family (including me), so this was not such a good suggestion I admit
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