The Amp Garage

ok for the lifted heaters.. but with humdinger pot you can see that hum is depending of the heater construction in the tubes and for all the preamp, mixed tubes is variable.. you can see where is minimum on the turn That is, you're re-stating what I said: hum comes from lots of places, and you can ...

There is no half turn in transformer heater winding :lol: :lol: For heaters you need to make very low number of the turns, and all the time you start and finish the turn on the same place..also is easy to make 3.15-0-3.15 , you are winding actually full number very close to the voltage (not to deci...

I just think about the millions of top name amps that never fused the filaments. You're right about that. In fact, even the military (per my experience) didn't. It depends on your objectives. If you want to prevent certain losses, there are often technical ways to do that. If you're OK with sustain...

If you had engineered at Bell, they would have been wired right, and that 400Hz inverter squeal wouldn't be in the headsets. 🙂 Sadly, I didn't get to do that. I wound up at [a Major Computer Company] instead of NASA, where I wanted to go: they weren't hiring. Neither was Electro-Harmonix, which was...

It's not for the actual heater currents. It's in case the CT is grounded and one heater wire breaks or otherwise gets shorted to the chassis or signal ground. I've been doing this stuff since '65 and have never witnessed such a failure. Have you? This just sounds like one of those new age theoretic...

actually power rheostat 5W is the best, but R.G. is stating that we need veery precise resistors, lets hear from him why. You're trying to put words in my mouth again. What I actually said was: (1) And the heater center taps are sometimes not too accurate. A couple of resistors may well make a bett...

(1) And the heater center taps are sometimes not too accurate. A couple of resistors may well make a better center tap, with lower induced hum. Why do you think that the minimum hum is on the middle of very- too much precision- resistors ? Give us some technical reference and measurement. 8) Sure, ...

A hard CT requires two fuses, one on each end. That's twice you've said that recently. I think two fuses is redundant. The same filament current flows from top end of the filament winding through the filaments and back into the bottom end of the winding. No current flows into the center tap. It onl...

(1) And the heater center taps are sometimes not too accurate. A couple of resistors may well make a better center tap, with lower induced hum. (2) And using two resistors with a pot lets you tune the residual hum - assuming it's line frequency hum, not ripple. (3) And not tying the CT to ground mea...

We laced all wires in aircraft tailbooms but I don't want them closer than necessary in an amp. Yeah, as I said - you have to pick your wires to lace. Closer is better for low-impedance, high current lines that carry out-and-back currents. This keeps the magnetic field loop as small as possible. Fa...

This popped into my head on a reply to another thread, and I thought it might be interesting to others. I love the look of neatly laced cables. True, long runs of parallel wires are not the greatest wire dress style, but then NASA did OK with it on lots of shots. I think it's a great way to corral h...

Stevem and johnnyreece have already hit the basics. As a pure and only tangentially relative side trip, I am a cable lacing fanatic. I love the look of neatly bundled and continuous-line laced cable work. Granted, running every single wire parallel is not necessarily the best cable dress :? but it l...

The note "stud" for mounting bothered me, but the math says that the preamp uses about 30ma. A 500mW or 1W zener would be fine. The 7912 would work and would be a superior supply for the preamp, much more noise rejection. You could even put a diode in its ground lead and get it up to -12.6 or so for...

Twisting works by the electromagnetic fields confining themselves to between the wires, and by both wires being almost exactly the same-but-opposite by external fields. This is a differential-voltage/current thing. Running the wires near the chassis works on the common mode stuff. That is, if there ...

That's interesting. Why do I never see it that way on schematics? I don't know. I can assure you that it's true, and that many people are surprised by it. It's true of all series strings of whatever components. As long as you don't tap into the series string in the middle, the order makes no differ...