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Everything posted by captainbeefheart

  1. This does allow one to use lower voltage rated power supply caps, basically rated to working voltages or slightly above. This simplifies the power supply because most common filter value electrolytics are under 500v. Tons of 350v even 450v choices, slims down quite a bit around 500v. With a 400v B+ and using an indirectly heated rectifier you can get away with one 450v cap, using SS rectifiers or directly heated tubes you end needing at least a 600v supply. BUT if the amp is ever turned on without power tubes you will get these voltages even with a 5AR4. I had universal power supply boards made up that can be configured a number of ways and it is setup for series caps with balance resistors. I use two 350v caps in series for most amps giving a 700v rating for worst case scenario no load condition. I can see why the 5AR4/GZ43 is more popular for Class AB amps as they have lower impedance vs the more common indirectly heated rectifier tubes like 5U4 or 5R4Y but I build Class A amps and so load stays consistent enough where you will not get any rectifier induced voltage drop compression with a higher impedance rectifier. I scored a ton of NOS NIB 5931 rectifier tubes a long time ago and have been using them pretty much exclusively because they just won't die, they are very rugged and robust, they seem to handle more capacitance without shortening their life. Two of my amps I have 100uF as the reservoir capacitor and it's been going on almost 20 years with the same 5931 in them.
  2. That would only effect the woofer circuit, like if you wanted to cut less mids from the woofer not the other way around like you want. If you want less bass in the squawker try lowering the 13uF capacitor to a 10uF.
  3. Which tube rectifier are you going with? I mostly use directly heated types and use the 5v winding center tap to feed B+ to the first filter. GZ34/5AR4 are overrated
  4. Both channels rail voltages should match, when they say +/-15% that accounts for fluctuating line power but the two channels should be very close to the same voltages. The fact the left channel is 2v higher than the right tells me that the left channel isn't conducting current, which jives with why you have no voltage across the emitter resistor and also why when you power it down the voltage doesn't drain away, with no load the voltage will not drain the caps down quickly. I know this isn't what you want to hear but if you do not know what you are doing you will most likely just waste a bunch of time and do more damage, no offense. How are you testing the transistors and how did you determine "they are so far out of spec"? Transistors work or they don't, that's it period, they do not have declining emissions like tubes. Their hfe or "beta" is the same throughout it's life varying only to input bias and base junction temperature. BTW if you end up wanting help with it I am in the Boston area.
  5. Thanks! Has anyone heard or built one of these "steered current" amps? When I have time I will make a simulation, I am very curious if the distortion profile is push pull or single ended.
  6. They are made by "sonicraft". I was playing around with the simulation and it looks like an ESR of 1 ohm might be audible as that's where you start to see an any added attenuation. My speakers sound great with the stock capacitors and the last time I checked the ESR the 2uF caps were not above 1 ohm for frequencies of interest. They did increase as frequency was reduced down near 100Hz but that won't effect the sound so I didn't replace them. I too question the difference of .01 ESR for a polypropylene vs .1 ESR polyester can be audible. It could possibly help dampen at extremely high frequencies where the reactance of the caps are so low the ESR comes actually comes into play.
  7. I remember an old console amp I salvaged a couple years back that was a single ended EL84 output and it had a strange bump in the bass region even after the tone control and RIAA eq were removed. All that was left was 6EU7 preamp stage (no cathode bypass cap) and the EL84 output which was bypassed with a 30uF capacitor placing the -3db around 50Hz. The coupling stage -3db was around 30Hz. It had global feedback, I don't remember how much but there was a filter network at the feedback junction on the 6EU7 cathode which looked to boost the low end so the bump on the output made sense to me at the time but I wish I analyzed it a little more. I gave it to a friend that wanted to try tubes but had no money.
  8. Don't forget about the 13uF cap, at 1kHz it is 12 ohms. If you are looking at the crossover reduction of -3.35db the capacitor is also attenuating the input signal.
  9. Sounds like low frequency instability where rolling the bass off with a smaller cathode bypass capacitor lowers the gain enough of the low frequencies to keep it flat.
  10. Hopefully this helps better. Input voltage is 10v (20db). We need the whole winding to be 44mH, each 4 inductors are yes 1/16 of the total inductance because of the squared function. Once you get past -6db you need to halve the next inductor (so divide by 4 again) to get just a -3db past the -6db making the -9db. That is the tricky part to make the exact model work for each tap. I left them all at 2.8mH because I got my tap I needed for the model (-3db) and the whole winding would be modeled correctly at 44mH. If I needed the next tap down would also be correct at -6db. For this to make more sense for you and everyone else I am showing the model with the other -9db and -12db inductance values for the model to work exactly how it would in real life. Starting at the top (20db), each tap going down will lower it -3db, so 17db, 14db, 11db, 8db. In the pictures, the graph is named at the top for which tap we are viewing.
  11. The discussion about the different tweeter network values led to a simulation of the entire network which led to a question about the simulation. A little sidetracked but in my opinion a good sidetracked, some folks want a better understanding of the entire filter network and the autoformer is often misunderstood. We can steer this train back to the tweeter you watch 😜
  12. Yes same thing different math to show it. BUT, we need the individual values of each "inductor" So the halfway tap (0-3) we have each side totaling 11mH giving a total winding inductance of 42mH. 11/4=2.75mH ^^^This would be cutting the halfway points in half again down to a value of 2.75mH each "inductor", I just used 2.8mH instead of 2.75mH because that is what the actual autoformer measures because the total winding inductance is closer to 43mH-44mH.
  13. editing- I am trying to do other work while I think of this and I am old!!! 👴 Once I finish up I will help dissect and explain the exact individual inductances and not the total inductance between each tap(1-5) to tap 0. With 10vac at input, across pins 0 and 5, you will get 10vac or 0db attenuation if you take the output from pin 5. Each tap down 4,3,2,1 are increments of -3db. We want to put into the simulator each of those individual inductance values.
  14. Let's simplify the model between inductance and turns. Let's say the total inductance of the entire winding is 44mH to make math easy If you place a center tap it would be half the turns ratio, but each side of the center tap is not 22mH like you would think, they would be 11mH because of the squared function.
  15. Basically if you want to increase by 3db it is roughly 1.41, so that is the turns ratio. The inductance/impedance ratio is a squared function or 1.98 Look at it backwards; 2.8mH * 1.98= 5.4mH 5.4mH*1.98=10.9mH 10.9mH*1.98-21.73mH 21.73mH*1.98=43mH
  16. I messed up and forgot a tap, I only have 4 inductors, I will add the fifth. It still dropped -3db but the total inductance is only 21mH in my model and with the next tap will be 42mH.
  17. The autoformer total inductance is 42mH Each tap is reduced by -3db Inductance is a squared function Inductance going from -3db onward would roughly halve looking at it from first tap to each attenuation tap; -3db= 21mH -6db=10.5mH -9db=5mH -12db=2.5mH But you don't write it in this way, each tap needs to be it's own inductance value, not the value from first tap to each individual tap like as i listed above.
  18. I have my all my directives listed away from the schematic to clean things up including the K I place the DCR in the inductance model, it just isn't seen on screen
  19. First is Tiz's values Second is stock values Third sim Changed scale up to 20kHz max
  20. Ask and ye shall receive First image is values posted by tizman: 2.2uF/160uH/6.8uF Second is the stock values: 2uF/245uH/2uF
  21. I have the AA network in LTSpice, I can easily show what happens by changing the values.
  22. Somehow you misquoted something Tizman said as something I said. Is there anyway to correct this.
  23. Bingo dead on. Amplifiers definitely need good measurements to a certain degree but there are ones not listed in the reviews or sales literature. For example reactive load instability problems giving rise to ringing or overload recovery dynamics. Measurements are taken on resistive loads while we need them to drive reactive loads. Besides performance I mentioned people like to own things that you purchase once and never have to purchase another one again, I am one. Made in America products designed for long service life and sustainability. This does not need to come at a huge price tag, there is a grossness of bling bling in the audio world and yes bias of spending huge bucks where some cheap small amp does 98% of what it does. I am a little more zen in my approach, I like hand made sustainable devices. I have salvaged so many parts I can easily make many very nice amplifiers on a beer budget. Price isn't everything, I am not attacking this because of the price, in fact I personally endorse it and say it's amazing really and perfect for the vast majority of people. Then there are weirdo's like me that just do things differently. More importantly, I have heard so many amplifiers in my life and poured over the technical objective facts along with the subjective personal experiences that I know there are minor differences between topologies that just won't show up on resistive load testing but show up in the real world with reactive loads and human beings pushing things further than they should. Yes there should always be adequate headroom, but that just isn't the case many times. Many measurements show normal operating conditions but we know someone somewhere will push it harder than they should and here are where topologies will sound way different even though the specs show the same on a resistive load under normal operating conditions; e.g. <max power. People clip from transients far more often than you care to think.
  24. Totally awesome as you know this is a throwaway item once it fails on you. The repair to purchase ratio isn't worth fixing. I really enjoy American made things that will last decades, even generations. For anyone that doesn't really care about perfecting the first watt or two in regard to imaging and sound stage then these amps are just a no brainer really. I mean seriously the vast majority of the consumers want clean transparent reproduction as easy and cheaply as possible, especially with such a small footprint makes decor easy these amps just kill the competition. It's the niche market where tailoring the perfect soundscapes for your listening pleasure that may not get into these as much because let's be honest, the specs they provided aren't equal to great sound, they are a guideline but not the end all so for some ears, rooms, or speakers these units will not satisfy all. It really is the perfect amp for about 90% of the consumers.
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