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captainbeefheart

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  1. Still unboxing things from our move and I am on to my audio stuff. We had to prioritize getting rid of a lot of other things to downsize before the move but now I need the awful task of figuring out what should stay and what should go for audio stuff. I only have one phono preamplifier that uses two 12AX7 tubes. Many moons ago lots of equipment used the 12AX7 and I always preferred European tubes, mainly Telefunken so I have the most of those. I also tinker and like to make amplifiers, I get the itch to make something every few years or so but I don't ever see myself making anything with a 12AX7 in it ever. I do like my phono preamp but I have far too many to be considered spares for an amp that might need new 12AX7 tubes every decade or two. I really dig that there are a lot of tube users on this platform so I figured I would throw it out there if anyone on here might be interested. I have about 25 that can go, planning to keep 15 or so for the future.
  2. I think you meant to say make it a true parallel filter -- and get the tweeter leg in front of the 13uF. The 13uF doesn't touch the signal going to the tweeter, it and the mid-horn driver now appear in parallel with the whole tweeter and woofer circuits, like most crossovers. My theory is profit, why waste a high pass filter when it's already there, just add upon it with filters with a higher roll-off frequency.
  3. Which is why a while back when radial electrolytics became the king of the hill where all the best caps are radial and axial took a back seat I made a universal board that takes advantage of increasing improvement in radial capacitors where they can be wired in series for high voltage ratings. I am surprised to see so many builders still using axial electrolytic capacitors, the choices are slim, ratings not so great, and the price is more than double!! Another wonderful rectifier is NOS Russian 5C3S which is similar to the 5U4G, the filament of the 5C3S looks amazing when powered up, much different vs the 5U4G.
  4. 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.
  5. 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.
  6. 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
  7. 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.
  8. 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.
  9. 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.
  10. 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.
  11. 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.
  12. 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.
  13. 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.
  14. 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 😜
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