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Posting new threads at the site has been fixed.
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| Romy the Cat's
personal site dedicated to advanced audio and evolved music reproduction
techniques
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Hello Romy, Been a long time since I've been on the fora... too much real work, too much travel. Still, nice to see this particular thread resurrected. I'm interested to see if you have revisited the 45 since more than a year ago. I still run my 45 ...
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Agreed, not really knocking it, but I've used a similar/same input/driver on the 300B and the results were not satisfactory in my view. I think the view of using premium and exotic parts got started years ago... where people wrote that due to the si...
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I looked at the schematic for Herb's 300B SET many years ago. It's been copied and slightly modified by many.... personally, I would not use it for a 300B amp... then again I probably wouldn't use it for a 2A3 or 45 either (I think my input/driver d...
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A most interesting post... and I can see how things get altered based on incremental changes to resolve one issue only to find another down the road, which is often disguised by components which simply don't perform in a pure manner. I've not heard ...
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Romy, I don't think we're in any major disagreement. It's clear you have a good operating point and performance indicates this as well. I did a "normalized" model of this with the 2A3 and 45 and it specs well. All I'm suggesting is that all early an...
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Hi Romy, The final ratings on later ST-style glass 45s was 10 watts on the plate and 300 volts cathode to plate max. Recommended bias current is between 34-36ma max. Short answer... I prefer no more than 34ma on the 45 cathode. It's a coated cathode...
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Paul, Everyone has their personal favorite on the 45... I have several RCAs... still prefer the Sylvania over them. Also, I've never seen a 45 with anything but a black plate. RCA did make black plate 2A3 tubes which are more rare than their gray pl...
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Romy, I have a very large collection of 45 triodes.... many brands and varying internal construction. From my humble viewpoint, here's some personal findings on the various types:- Globe 45 tubes... these are the earliest, mostly from RCA. There are...
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One of the reasons I no longer use a tube tester. They make a measurement at a specific target operating point(s). You don't really know what it is, so what are the chances they will be close to your actual circuit operating point? So choosing a clo...
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Romy, et al, I got rid of my tube tester a few decades ago... yet I still need to match sets of tubes for equipment. When you consider many SE designs with no feedback loops, you need to match "sets" of tubes to get matched performance between ampli...
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Paul, Some good valid points... yes, they've gotten much better over the years, no doubt to technology improvements. A good example is Mallory CGS caps made in the 80's versus new ones. The newer ones are much lighter physically (same p/n), hence th...
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Romy, I have to admit that there are as many differences in film caps as there are in electrolytic caps. You can find varying opinions for and against both based on brand, type and usage. As noted, large value film caps get (physically) large so you...
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Romy, No easy drawing program available this second (traveling for 3 weeks) but I can send you a simple schematic in PDF if you like via email. In any case, to adapt what you have already have to the split biasing, just remove the cathode bias resis...
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I like having a center-tapped filament winding for flexibility. First, you can use a traditional approach on hum balance (what you have now) or use a slightly different approach. I use the center-tap as a fixed DC balance (cathode bias resistor solo...
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Yes, a dedicated filament for each DHT output tube is best. I would suggest getting one with a center-tapped secondary.... gives you some options. Regards, KM...
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Romy, I have some (strong) opinions on DHTs concerning filament supplies versus specific tube types. For virtually ANY 45 triode, AC is my preferred option. Still, not all 45 triodes will be acceptable for my use, hence weeding thru many of them to ...
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A typical switching supply does not evenly load the input (sinewave) power source and can create some dirt on the AC line (Paul's "backwash" statement??). Depending on many variables, the amount of contamination the switching supply could contribute...
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Paul, et al, I tend to agree that many DHTs can have a fair amount of AC hum output from an AC filament. In general, I've not found any tricks (like humbucking chokes) to make any significant difference. Ideally, a perfectly balanced AC filament "sh...
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From my view, I would add a dedicated filament transformer for the DHT. It's clean, simple and a known performer. I'd also be inclined to drop the support of a 6A and stick to a 2A3 only. Alternately, if you have no need for a center-tap on the DHT ...
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Hmmmm, not sure what to say in this case. From a higher view (and do correct me if I am wrong), you seem to have a general dislike for Fostex drivers. I can also sympathize that some of them are hard to listen to. In any case, you bought an exp...
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Romy, Any updates on this? Regards, KM...
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Options are limited here... looking at the schematic, you're sorta pinned in by the biasing topology used. One typical method would be to use a resistor divider network at the input grid to the 6E6P. Problem is, this results in a huge bias offset. By...
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Well, ultimately dropping the signal driving level to the 2A3 is the best approach for reasons already noted. If you can get a closer idea to how much you really need to drop, the simplest approach is having a custom IT wound with the correct r...
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Romy, As you pointed out, if the input circuitry and driver operating points are fixed, your only options are to lose it via coupling or the output stage. Maybe split them, i.e. use a 1:0.5 ratio on the inter-stage transformer and you coul...
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A slightly lower filament voltage is okay for a coated filament (not for a Thoriated-Tungsten filament however). There was some testing done some time ago on this and findings indicated an increase in tube life and lowered distortion. I just don't re...
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Romy, That gets you where you want.. good transfer curve, low distortion and about 2.7-watts output. 2A3 should last a long time. One question and one comment:Question: the 0.75 ohm resistors in the filament lines on the 2A3. Is it your in...
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Agreed.... ditch the choke... you don't need any additional decoupling. One last model shows the following assuming a 350 volt supply and a 6K load.Useing a 1.21K cathode resistor, it works best to minimize distortion and balances the transfer charac...
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Romy, As you're planning to run a 6K load, you can run less current without the transfer curve suffering as much. So, another shot at some numbers.... rather than use a RC setup to drop the voltage, Hammond (not my favorite) make an open f...
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Romy, I did some models using a 400V supply and a 6K OPT load. It's easy to get 4 watts output in this configuration, but using a 2K cathode resistor results in higher distortion and a weak transfer curve. Plate dissipation is around 11 wa...
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Romy, Yes.... in a city or congested neighborhood what is available as a ground can vary substantially. I keep referring to my own situation (sorry about that). Your points about a congested city and the power grid ground, etc. would be co...
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