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Western Electric SE 300b amp


captainbeefheart

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On 12/3/2021 at 1:05 PM, grindstone said:

Thank you for investigating and taking time to organize and post results.  And, BTW, I didn't figure anything out--any credit is due our benefactor Mr. Broskie (who can make my head hurt at least twice with every entry he posts). 

 

I am currently working on the model in LTSpice, the trick is the resistor values to get the best performance. With limited time to do this it may take me a few more days to find the time to go back and fine tune the circuit, after I will post the details for anyone wanting to try and build the circuit. It may even be fun to use a more standard, less expensive tube like say a triode wired EL34 tube which we will be able to at least double the power output. E.g. Anyone can build an inexpensive SET amp that puts out 10 watts per channel and uses inexpensive toroidal output transformers AC coupled. No DC current in the output transformer means we can get the inductance we need without the extra inter-winding capacitance and high leakage inductance. The output transformer can be a $15 Antek transformer and still get a very wide bandwidth.

 

I think anyone wanting to get into SET amps would be thrilled at the prospect of a 10 watt output power and a price tag of ~$300 total depending on chassis selection. I prefer a steel chassis with a nice finish paint, two tone design with the transformer bells painted a complementary color to the chassis. My latest favorite color scheme are both BMW colors, a Metallic Blue for the Chassis with a complementary Mineral Metallic white. I purchased both these colors at NAPA mixed in a spray can, they have two cans per color, one is the metallic base and the other being the actual color. Then topped off with a nice clear coat. I spent $100 on just these paints alone and I have a lot left in the cans so my next several projects are going to be using these colors.

 

My wife has an X5 with the MIneral Metallic white color which is where I got the inspiration, my good friend has the blue color on his M3. He painted his spare rims with the Mineral white Metallic color,  the  blue and white just looked so lovely together I made my mind up that was going to be my next color scheme for projects.

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OH SIDE NOTE!!

 

I found out the driver tube for the new Western Electric 91E amplifier is a 12AT7.

 

I was a little unimpressed by this selection but I can see why they went with this selection; Relatively high mu, low rp and the ability to run some decent current through them and have them take it with their 2.5 watt plate dissipation rating, the 12AX7 is only rated for 1 watt for example. They are in current production and NOS variants are not through the roof expensive.

 

Plenty of small power sections use a 12AT7, the famous Fender reverb circuit uses the 12AT7 with both sections in parallel as a single ended transformer coupled tank driver power amp, the tank input impedance is 8 ohms and the tube drives it just fine good for about 1 watt of power into the tank. Should be good driver for a 300b.

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  • 1 month later...
On 11/24/2021 at 7:16 AM, Curious_George said:

I’ve never designed or built a parafeed, but they do have great potential from the lack of DC gap. The audiophool guys will cringe at the thought of a coupling cap though!

I have.  In short, the benefits FAR out-weigh any negative elements you may be perceiving associated with that capacitor.  More than that, some of the the most capable designers I have known will enthusiastically opt for parafeed (which is sort of a lazy way of referring to its more descriptive 'parallel-feed') over the conventional air-gapped SE OPT.  One of the very best sounding amplifiers I ever built was one such design -- called the Horus 2A3 (designed by a very capable guy - Jean Francois Lessard).  While it was based on some of the work and research done by Gordon Rankin (Wavelength Audio), Dan Schmalle (Bottlehead -- or, some of you, as I, might also remember him from Electronic Tonalities) , and others, I came up with some quite good-sounding modifications to better suit my own priorities, tastes, etc.  Nevertheless, I could not have done any of that work without the roadwork of the others mentioned.  My abilities pale in comparison. 

 

It's about as close as one can get without going altogether OPT-Less, which can be staggeringly good sounding...in my opinion.  I don't cringe too much at a decent coupling cap.  Many extremely good products make use of them.  Note that a large plate choke is also needed in the finals stage.

 

If you've never built one, I STRONGLY encourage you to give it a shot.  I sold mine, and that most definitely was one of my dumbest 'audiophool' mistakes.  It was the design that got me addicted to extremely high impedance grid chokes over the more common, dust-cheap grid leak (for those of you know what I'm blabbing about....). Quality iron is key in such a design.

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23 hours ago, erik2A3 said:

I have.  In short, the benefits FAR out-weigh any negative elements you may be perceiving associated with that capacitor.  More than that, some of the the most capable designers I have known will enthusiastically opt for parafeed (which is sort of a lazy way of referring to its more descriptive 'parallel-feed') over the conventional air-gapped SE OPT.  One of the very best sounding amplifiers I ever built was one such design -- called the Horus 2A3 (designed by a very capable guy - Jean Francois Lessard).  While it was based on some of the work and research done by Gordon Rankin (Wavelength Audio), Dan Schmalle (Bottlehead -- or, some of you, as I, might also remember him from Electronic Tonalities) , and others, I came up with some quite good-sounding modifications to better suit my own priorities, tastes, etc.  Nevertheless, I could not have done any of that work without the roadwork of the others mentioned.  My abilities pale in comparison. 

 

It's about as close as one can get without going altogether OPT-Less, which can be staggeringly good sounding...in my opinion.  I don't cringe too much at a decent coupling cap.  Many extremely good products make use of them.  Note that a large plate choke is also needed in the finals stage.

 

If you've never built one, I STRONGLY encourage you to give it a shot.  I sold mine, and that most definitely was one of my dumbest 'audiophool' mistakes.  It was the design that got me addicted to extremely high impedance grid chokes over the more common, dust-cheap grid leak (for those of you know what I'm blabbing about....). Quality iron is key in such a design.


Capacitors are used so much in electronic circuitry that it’s hard to dismiss them as “horrible”. A few coupling caps in your preamp / amp are not going to make a difference when there are so many more upstream from recording to post processing, etc.
 

I’ve never been a capacitor-phob, but I do like to use good quality (not boutique) caps when I can. 
 

Anyway, I just may have mock-up a para-feed to see how it performs. It’s funny how some topologies although deemed better in a lot of areas, never make it to the mainstream and become popular, while other topologies that may seem less optimum find a popular following. 
 

Take solid-state for example, I prefer output stages that are “triples” to anything else. However a good Darlington output stage with modern high gain transistors can sound great and drive just about anything. 

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In parallel feed, a plate choke is used for B+ on the output valve.  The grid choke to which I referred is superior, in my view, to a grid leak resistor for a number of reasons, none of which I'm going to take the time to explain.  I did enough of that here 15 years ago.  Use your gyrator load;  I'm comfortable with my choice.

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A rather long and tiresome story.  They were truly incredible amplifiers, but, in short — and this is intentionally vague — the forum was very different back then.  My old avatar is Erik Mandaville, my name obviously.  You can probably check archives, card catalog, or whatever, and find images and text. I used to write ludicrously long posts....

 

They used extremely high quality parafeed transformers and grid chokes from MagneQuest, and I sold them for the price of parts alone.  Parallel-feed is a very old yet extremely good sounding topology in a well-designed circuit; and the Horus 2A3 mono blocks were/are most definitely an extraordinarily competent design.  I have no problem admitting errors when I make them, and selling those was not well-thought out.  Again, the Klipsch forum back then, as many of the longer-term members here will remember, was kind of like the old west with egos on horseback. ;)  I loved the grid chokes in that amp.

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21 hours ago, erik2A3 said:

Again, the Klipsch forum back then, as many of the longer-term members here will remember, was kind of like the old west with egos on horseback.

I remember the forum back then. It’s one of the reasons I was absent from the forum for so many years. DIYAudio is one of the worst forums for that behavior. Now, I’ll fire back a reply if needed and try to keep it “not personal”, but if pushed, I could care less about being banned from any forum. 

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On 1/9/2022 at 11:26 PM, erik2A3 said:

In parallel feed, a plate choke is used for B+ on the output valve.  The grid choke to which I referred is superior, in my view, to a grid leak resistor for a number of reasons, none of which I'm going to take the time to explain.  I did enough of that here 15 years ago.  Use your gyrator load;  I'm comfortable with my choice.

 

I was referring to the quote

 

On 1/9/2022 at 8:19 AM, erik2A3 said:

Note that a large plate choke is also needed in the finals stage.

 

My point was the word 'needed' isn't true because although you may prefer it you can load it anyway you want to, with a resistor if your B+ is high enough. Plate chokes are great but expensive and impedance changes with frequency where a gyrator load will in regard to AC be a much higher and more linear impedance across a much wider range of frequencies. The benefit of the choke is it can swing beyond the B+ by it's reactive nature so you don't need as high a B+. Technically they are similar, a gyrator is inverting a capacitance into an inductance (that can't store energy though) so with a gyrator you can reach a much higher AC impedance over a wider range of frequencies unless you have such a massive plate choke to reach the amount of inductance you can get from a gyrator that it would be outlandish really. A CCS is also popular because it will have a constant high impedance for an extremely wide frequency range and has better PSRR, but I still prefer the gyrator as it comes as close to a massive plate choke as possible without using an unrealistically large (and very expensive) plate choke.

 

Nothing about a grid choke was even mentioned. The benefit of the Grid choke is a very low DC impedance for the grid circuit, this is good for tubes that require low g1 resistance for stability purposes. I prefer A2 operation which is going to best any AC coupled output stage grid choke or not. 

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Great!  Sort of a matter of semantics, I would say.  I'm familiar with gyrator loads, and I suspect I'm just sort of a more traditional sort of builder.  I'm of course also very familiar with CCS active loads, which you probably know can be achieved a few different ways.  I've used them in two or three preamps I've built over the years

 

What you're explaining is really not a benefit to me, if that's what was intended.  I'm actually pretty well-versed on this - and I will be the first to admit that the more I've learned, the more I've also learned about how much I don't know, as well as what I prefer.  Hopefully you are the same in that way.

 

Use your gyrator; I'll stick with the hefty choke.  Plus!  that big anode choke is much heavier, which we know just adds to the cool factor, and thus subsequently automatically improves sonics.  Wink.

 

Grid Chokes:  I'll choose them over a resistor, which in my view -- and to use your words -- is technically inferior to the ubiquitous grid leak resistor.  It was really just mentioned because not many builders that I know of use them...a few do, and I had to learn about them myself way back when.  And you're right.  There isn't anything wrong with preferring one thing over another.  Again, I am comprehensively aware of their function and how they operate, although I'm sure there are others here that enjoy techno-jargon.  Building for me is often an intuitive sort of thing, within reason and observation of operating parameters.  Designing is something of an art to and for me, and most often has to do with extensive experimentation and listening comparisons -- and, good grief, not the quest for ultimate linearity.  Build the way you wish and enjoy the process.  That's what this is about.

 

And YET again, a plate choke (or your gyrator if that's what you prefer - even though I don't care for them) is absolutely needed in a parallel-fed (LOL) output final stage.

 

Good?  Good.

 

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7 minutes ago, erik2A3 said:

Great!  Sort of a matter of semantics, I would say.  I'm familiar with gyrator loads, and I suspect I'm just sort of a more traditional sort of builder.  I'm of course also very familiar with CCS active loads, which you probably know can be achieved a few different ways.  I've used them in two or three preamps I've built over the years

 

What you're explaining is really not a benefit to me, if that's what was intended.  I'm actually pretty well-versed on this - and I will be the first to admit that the more I've learned, the more I've also learned about how much I don't know, as well as what I prefer.  Hopefully you are the same in that way.

 

Use your gyrator; I'll stick with the hefty choke.  Plus!  that big anode choke is much heavier, which we know just adds to the cool factor, and thus subsequently automatically improves sonics.  Wink.

 

Grid Chokes:  I'll choose them over a resistor, which in my view -- and to use your words -- is technically inferior to the ubiquitous grid leak resistor.  It was really just mentioned because not many builders that I know of use them...a few do, and I had to learn about them myself way back when.  And you're right.  There isn't anything wrong with preferring one thing over another.  Again, I am comprehensively aware of their function and how they operate, although I'm sure there are others here that enjoy techno-jargon.  Building for me is often an intuitive sort of thing, within reason and observation of operating parameters.  Designing is something of an art to and for me, and most often has to do with extensive experimentation and listening comparisons -- and, good grief, not the quest for ultimate linearity.  Build the way you wish and enjoy the process.  That's what this is about.

 

And YET again, a plate choke (or your gyrator if that's what you prefer - even though I don't care for them) is absolutely needed in a parallel-fed (LOL) output final stage.

 

Good?  Good.

 

 

I just wanted folks to know that they don't necessarily need a large plate choke going with a parafeed amp as that may scare some away due to costs and size. I only wanted to mention that you can use any other means of loading the plate, all with their own unique pros and cons, there are trade offs to everything. Anyone reading your original quote might take it as they can only go parafeed by using a plate choke, which is untrue.

 

Plate chokes and gyrators are actually very similar as they both present an inductive load, with a real inductor that can store energy you can get away with a lower B+. In other fields where I needed a large inductance value for filters and in no way possible use a real inductor because of size and cost is where a gyrator is handy so long as you don't need the energy storage aspect. Now the downside is  I need higher B+ with a gyrator BUT I can achieve a much larger inductance value compared to your actual real choke. And let's face it here, you would chose a choke with the highest possible inductance possible if you can correct? It's in this regard the gyrator is great, small footprint, inexpensive, and huge inductance values that we look for in a large plate choke. I am in no way trying to tell anyone what to use, I am merely pointing out pros and cons to each choice and more importantly, if you are interested in parafeed circuits you have options on output stage loading and are not stuck with a plate choke as the only option.

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15 hours ago, captainbeefheart said:

I am in no way trying to tell anyone what to use, I am merely pointing out pros and cons to each choice and more importantly, if you are interested in parafeed circuits you have options on output stage loading and are not stuck with a plate choke as the only option.

I do like and prefer your choice of words and tone here.  Well said.

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