Correct, but I don't think what Sy or MrCurwin are actually discussing "characteristic factor".
Yes, a little confusion. I think that normally Rp is the plate resistance with a bypassed cathode (or grid bias). The "triode characteristic factor" is the plate resistance with self bias - unbypassed cathode resistor (i.e., including degeneration by the cathode resistor).
The thread was discussing the Darius version of a LW amp, which is where the factor of 4 entered the discussion. Just wanted to clear that up.
Sheldon
Edit: This brings up the interesting possibility of partial bypass, via series resistors, with one bypassed, or a resistor in series with a diode type device. Might be a way to get the "triode factor" higher and still allow noise cancellation. Sim Goldenbeer?
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I have used NiHi Batteries to bias certain tubes in the past. Stellar results - running the amp keeps them charged. Any reason it wouldn't work here?
Ian
I could work, but only if the grid/common potential is large enough to allow some reasonable unbiased resistance. A smaller cathode resistor means a larger noise cancellation cap and larger noise cancellation signal. It would depend on the application, as to how well everything works together. It does open up the possibility to give more freedom in operating conditions of the input tube.
Sheldon
At low listening levels, the amp sounds very lively and agile, effervescent, NOT only when its pushed hard does it begin to sound good.
I have no idea WHY this is so, and I never worry too much about explaining all I hear. If I hear it, and its consistent, that is good enough for me to wanna make use of it.
Thanks for asking.
Cheers,
Jeff Medwin
Member
Joined 2009
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There are many options, I've simulated a dozen the past few days (a few really novel approaches!). One of them uses the other half of the 12AX7 as coupled-cathode (see my thread on 'a nice little valve amplifier'). There are more ways to skin this cat than I thought. BUT given that some people do hear sonic differences from changes in cathode bypass cap size type and composition it seems that simulating all these different approaches only confirms that they are feasible in principle, nothing to tell me if they will sound as good as what Darious has already created.
If you don't find out, or at least even try to find out why, you will never achieve anything but the first steps of progress towards transparent reproduction. By accident.
How can you know what it is that makes you like it? Perhaps at wasn't the µ of the tube at all?
Well, first thing to come to my mind is that higher volumes tend to sound better, because the way the human ear works. This is why it's very important to match sound pressure levels when doing comparison tests; because otherwise the loudest one always tends to win.
However, from your description, it would appear that you really like distortion.
Both
1) SE tube amp driven hard
2) high µ, high rp tube with grossly insufficient plate load
produce a lot of distortion. The first produces it at a high volume, the latter produces it even at low volumes.
I make amps, that generally sound their best at lower volumes (when using speakers), because they don't have a lot of power reserves; low or mid µ tubes are in no way required for this. If in your case they are, you should look into better designs. And begin by learning how they work.
"Transparent" is not the goal here. When you see phrases like "the amp sounds very lively and agile, effervescent," you have to start thinking about which effects you're chasing and aim toward that target.
This makes no sense in the bootstrapped follower topology, since there is a (nearly) constant current across the input tube anyways.
For the simple gain stage, there is also no tangible improvement with suitable input tubes such as the EC86, since there is also actually only a small variation in cathode current. It also shows in the simulation.
Of course. I didn't mean to imply otherwise. But some have follower aversion. Sorry I didn't make that it clear that I was only speaking to the non-follower application.
Sheldon
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I don't follow. Simple, as in no follower? If that's the case, no variation at the cathode - no variation at the plate.
Sheldon
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With simple I meant common cathode, sorry.
Of course there is some variation, it's just very little. We are using a high mu tube, we don't go do a full swing to avoid grid current, we are using a large plate resistor to raise the gain and drop B+, approaching ccs conditions. Hence, little variation in cathode current, and consequently little variation in cathode voltage even when using a plain resistor in the cathode. And hence, even smaller effect of a partial bypass or diode etc..
Of course there is a significant voltage swing at the plate. It does not require a current swing! CCS load would be the extreme case.
I agree. I should have specified that partial bypass would only be useful in the "simple" Darius version, i.e., input tube, output tube, no follower. I have found in trying a few examples with no bypassing (as per Darius), that getting everything lined up voltage wise, load line wise, with a "triode factor" greater than 4, and practical voltages, is a pretty tight window. Using partial bypassing might allow a wider range of input tubes and operating voltages. It's just a thought experiment at this point. I haven't actually modeled anything, even on paper. Soundwise, I have no idea.
Sheldon
Asano 2A3 kit
I'm planning to build a 2A3 DC amp, but don't want to do it from scratch. I saw that japanese society eifl ASANO-Amplifier propose a kit of Asano amp with magnequest OPT.
What do you guys think about this amp and about Magnequest transfo ? Hishimoto, Tango... would be better ?
NB : I'm listening classical music, in seek with true emotions with a fertin full range driver
I'm planning to build a 2A3 DC amp, but don't want to do it from scratch. I saw that japanese society eifl ASANO-Amplifier propose a kit of Asano amp with magnequest OPT.
What do you guys think about this amp and about Magnequest transfo ? Hishimoto, Tango... would be better ?
NB : I'm listening classical music, in seek with true emotions with a fertin full range driver
Nice looking amp at a pretty reasonable price for a kit of that quality. It also incorporates a version of the original L/W ripple cancellation method. I'd consider making R1 adjustable to fine tune the noise null.
Sheldon
Sheldon
Hello,
Which output transformer to use, despite what others will tell you, is truly of MINOR consequence compared to the ENTIRE design and execution of such an amp. The output transformer can be much less expensive, yet the entire amp will EASILY outperform another amp employing the three output types you are looking at !!
IMHO, you got it RIGHT doing a two stage DC amp !! It does NOT need to be a Loftin White implementation, what so ever, to achieve successful performance.
I would advise AGAINST doing the ASANO kit.
For the same expenditure, you can have an amp that will not have the "traditional" design mistakes inherent in most people's execution, and it will make you way way happy. Write to me privately, and I will be happy to serve you, with some guidance !!
What is the rated sensitivity of your speaker ?
Jeff Medwin
No it does not NEED to be a Loftin/White implementation - anymore than it NEEDS to be another implementation. Jeff, lighten up on the ONE TRUE religion. This is just a hobby.
Sheldon
Sheldon
That's true to a point, but not exactly my experience.
I have a pair of Tamura 5002 output transformers and have had them almost a decade. During that time I tried several different topologies, but never a two stage direct coupled front end. I used three stages with a wide assortment of tubes RC coupled. For instance a 5687 RC to a EL34 (T) RC to the 300Bs. I have always been disappointed with the sound and so the amp sat on a shelf for years.
In the interim I discovered the benefit of two stage amps and direct coupling using all Electra-Print iron (back when Jack made power transformers.) I listened to various combinations of front end tubes and output tubes and was always pleased with the sound. After experimenting with PP 6P14P "El Cheapos" for a while, I felt bad about my expensive output transformers in the basement unused, and decided to build something a bit different, so instead of driving the JJ 2A3-40s with a modern high transconductance triode connected pentode, to go back to the roots and use the 6K5GT which is a low transconductance triode with a mu of 70 (half of a 6SL7) and direct coupling. I know you are well acquainted with the concept.
To cut to the chase: this is by far the very best sound I have ever gotten with these transformers, but more to the point, it is the best sound I have gotten ever. Now the subtlety and clarity of this amp is astonishing and while I am sure the circuit contributes, I am also certain that the finesse and tiny details the amp reveals is a result of the amorphous core output transformer.
Hi Sheldon!!
I think you have a good mind, and I certainly respect you.
WE each have differing ( slightly ) sets of audio experiences, and, while you may consider it a hobby, I just turned 71, so, I wanna get what "I" know to be true out there, (been building with DHTs since 1982, mentored by Robert Fulton).
If I speak with zeal, honesty and passion, so be it. I will not change in my enthusiasm for things I directly have experienced. People all have a choice. I respectfully say, listen to all things, and choose well !!
On another note, I want to wish you a happy and healthy New Year!!
Jeff
Hi,
Nice post. Yes, a DC two stage will be better than ANY three stage amp, common sense, less is more.
You do not have to be tied to ElectraPrint for power transformers for DC amps, etc. Hammond makes a very varied line, almost any DC amp voltage and current you will need. I just replace their lead outs with double 12 AWG on the primary ( equals 9 AWG ) and single 12 AWG Mil Spec on the secondary, and it " flies ".
I LIKE the fact that you use a mu of 70 tube, it provides a "lively" presentation - and a mu of 100 is even more fun to experience. I use 1/2 a 12AX7 DCed into the grid of a Type 45 tube now, ALTEC speakers, with a really good power supply, and optimized wiring, and it is VERY satisfactory to me and my tastes.
Its a fun hobby, and fun to build and hear good stuff !!
Jeff Medwin
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