Hi,
Here's PSUD2:
PSUD2
Power supply Designer modelling.
Runs native on Windows, Works perfectly with Wine on GNU/Linux platforms.
It's highly recommended - both to check the effect of Choke and caps on Ripple voltage, plus you can also see the current draw in the transformer.
Transformer current should be carefully inspected, because changing the value of the cap for the rectifier will increase the peak pulse current in the rectifier/trafo, and higher peaks mean that the rms current is higher (crest-factor effect). Higher rms current means more stress, which the old transformer may not withstand. Also, the higher effective load means there's less power for the speaker.
With PSUD2, you can simply model all this in a few seconds. Next, try all the values of C you have in mind, add chokes, etc.
Maybe a choke of something like 1 to 2 Henry, 600mA rated would be a starting point for a choke (will be quite large, but they are no use in the main circuit unless they can take the current).
For a rough estimate of the dc supply current check out the Tung-Sol 6L6GC data sheet.
for 450V B+, and 55W output power (single pair), the dc current is 210mA in the anodes. so, allowing for the screens and the preamp, three pairs of 6L6s may take as much as 750mA for 180W out, using higher B+.
It's an unusually high current - may make the choice of chokes smaller than other power levels.
for 450V B+, and 55W output power (single pair), the dc current is 210mA in the anodes. so, allowing for the screens and the preamp, three pairs of 6L6s may take as much as 750mA for 180W out, using higher B+.
It's an unusually high current - may make the choice of chokes smaller than other power levels.
I'm starting to wish I'd removed the entire power supply, and put it in a second chassis mounted on the bottom of the cabinet. That would allow very sensible layout, move the power transformer field and power wiring etc. farther away from any sensitive circuits, allow me to mount decent screw-post electrolytic filter caps via clamp mounts, mount multiple chokes, have short wires all around the bridge rectifier, allow me to experiment with power supply seperately from the real amp circuit, and leave lots of room in the main chassis for new features (tetrode/ultralinear/triode mode switch, 1/3 power switch, voltage drop switch, seperate bias pots), put a heatsink on the bridge rectifier, and keep both chassis cooler. A power relay could even keep the 120 V out of the amp chassis if I wanted. I could add a 110/220 switch and universal cord socket, some line MOVs. And it wouldn't be quite so top-heavy anymore. It would certainly keep the power tubes cooler with the transformer out of the way of airflow to those two last tubes, and keep the power transformer cooler without the power tubes radiating heat directly onto it. I just wish I'd made that decision earlier and made an even taller cabinet shaped more like the tall "Showman With Reverb" cabinet to maximize the benefits.
Plus there's the preams/splitter and not 'choking' off the necessary supply of current to replenish and maintain good regulation. I was thinking 700 ma to 1A conservatively derated to do no harm, if possible. For 1H that's do-able, but if I want 10H and low Dc resistance, it's starting to approach the size of a toaster. Which is why the mfgrs don't throw in a 20-pound $100 choke when there are cheaper lighter options.
No lie. I found only one. It's only 1.35H 1.1amp and 20 pounds. But there are a LOT of 500ma chokes with much more inductance. Maybe I should consider parallel inductors, but I would think there would be ringing issues which might require damping resistors. I'd make seperate parallel supplies for pairs of output tubes, but it gets complicated and I want the B++ down-ladder from the B+ so if B+ does sag B++ will sag too, and never cause a grid to go more + than plate, so B++ would hang off only one B+ if I had multiple B+. So I'd rather use parallel inductors. There's no easy way around the weight, as a certain amount current requires a certain amount of iron.
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OK I bought the huge 20-pound choke. Now both my bigger guitar amps will be the only ones on the block with filter chokes for the full B+ rail. Yikes what have I done. I'm waiting to inspect & measure it. I don't know its DC resistance, but it's got to be pretty low or it would have more inductance; its got to be wound with pretty thick-guage wire. It's sure got a lot of iron, so the 1.1 amp rating is no lie! That will handle 550 watts. It's certainly got way morethan enough surface area to dissipate any heat from resistance or doing its job.
Oh now I know I'm a nerd. I've been playing with that PSU designer 2 four hours and having a real blast. Often I get unexpected results and have to investigate and learn something.
But I have no clue what the real resistance of mhy capacitors is...I assume that the ESR but I have no idea what a typical real value is. I guess I should dig in a catalog.
And my transformer source resistance...I'm working that backwards from the behavior I want, so this is not much of a real simulation.
As suspected, nothing beats adding another filter stage for getting rid of ripple.
But I have no clue what the real resistance of mhy capacitors is...I assume that the ESR but I have no idea what a typical real value is. I guess I should dig in a catalog.
And my transformer source resistance...I'm working that backwards from the behavior I want, so this is not much of a real simulation.
As suspected, nothing beats adding another filter stage for getting rid of ripple.
As a noise filter on the wall-power? How did you choose that value? Is it related to the primary inductance at all?
I'm glad that you're enjoying PSUD2! It really does save a lot of guesswork.
For normal 220uF 400V caps,assume 0.7 to 1 ohm (yes, ESR is the data-sheet value).
For the transformer resistances, just measure primary (do this by measuring at the mains plug. The mains lead is checked at the same time, even if it's 0.1 ohm - and you can also be sure it is not powered). Measure the secondary ohms with a meter, too.
The resistance for PSUD2 is the "secondary-referred" resistance:
R = Rs + (Rp x (N^2))
because the primary resistance is added when factored by the square of N (turns ratio).
So for 120V input, 360V output (N=1/3, looking backward)
R = Rs + Rp/9
Choke sounds very good!
For normal 220uF 400V caps,assume 0.7 to 1 ohm (yes, ESR is the data-sheet value).
For the transformer resistances, just measure primary (do this by measuring at the mains plug. The mains lead is checked at the same time, even if it's 0.1 ohm - and you can also be sure it is not powered). Measure the secondary ohms with a meter, too.
The resistance for PSUD2 is the "secondary-referred" resistance:
R = Rs + (Rp x (N^2))
because the primary resistance is added when factored by the square of N (turns ratio).
So for 120V input, 360V output (N=1/3, looking backward)
R = Rs + Rp/9
Choke sounds very good!
I've got to digest that for a while...this is the cap from cathode to ground in parallel with the resistor from cathode to ground? The super twin uses a 750 mfd there on the first stage; that's pretty big.
I expected to see a stopper cap from grid to ground, but there are no caps anywhere from input jack to grid on the first stage. This is not like my old Alembic Fender-style circuit.
Check out the wiring of the input jacks; classy little mute of the first stage when nothing's plugged in. It doesn't mjute via grounding the input to the first stage, nor does plugging into just one bypass the gain-splitting resistors for summing two inputs; no, when nothing is plugged in it grounds the input to the second stage so any noise from the first stage is also turned off. That's kind of classy, and if I get rid of all output stage hum it would work. Heck, I'm going to change one of those 33K series input resistors for a Mesa-boogie style lower like 1K or even none at all, and have one hot input and one less hot; I don't have a stereo guitar or share an amp, so why would I want to waste any sensitiity to mix two identical inputs? Might as well see which loads a particular individual pickup better.
Yes, 750uF is big - and it's there to reduce hum from heater pickup, as described. You can use a high-quality 1000uF 6.3V cap there. Please don't use higher voltage rating - the working voltage is only 1-2V. The cap will polarise faster and better, and leak less, when the working voltage is a good portion of the rated voltage.
The cap stoppers were used to control instability in some Fenders (Riveras, especially) where the wiring was so badly laid out that oscillation was assured.
Talking of oscillation - take care when reducing stoppers. The Boogies I have looked at use ferrite beads on the grids, where the stopper is omitted. These play the same role. The first stage stopper (68K in classic circuits) is a good value for most purposes. I believe that Boogie used zero so that really high-output pickups can overdrive V1 (gain set HIGH, master volume set LOW). A special kind of dirty sound. For clean sound, the stability will be more important.
The cap stoppers were used to control instability in some Fenders (Riveras, especially) where the wiring was so badly laid out that oscillation was assured.
Talking of oscillation - take care when reducing stoppers. The Boogies I have looked at use ferrite beads on the grids, where the stopper is omitted. These play the same role. The first stage stopper (68K in classic circuits) is a good value for most purposes. I believe that Boogie used zero so that really high-output pickups can overdrive V1 (gain set HIGH, master volume set LOW). A special kind of dirty sound. For clean sound, the stability will be more important.
Why just the screens? It looks like an FET capacitance multiplier will handle the full current of the B+ for the output tubes, even on these huge amps.
I imagine this is similar to the London Power QuietSupply kit for high-voltage tube amps:
Tube Amp Mods - - QS-HV - Quiet Supply for High-Voltage Tube Amps
The kit is $60 compared to about $20 for the parts; a bit expensive but the printed circuit sure does make it difficult to get anything wrong and it saves $100 worth of shopping time. It still saves a TON of money on big caps.
If I was still intending a pi filter consisting of cap/inductor/capwbypasscap what would be the advantages or disadvantages of using a cpaacitance multiplier on the first cap rung on the ladder versus the second cap rung on the ladder?
It looks like the kit uses just 4 22uf caps, but of course it is a capacitance multiplier LOL.
Except for the very low level stages, DC heater power isn't necessary, unless you're using DH finals, and you'd like to keep DH finals out of a guitar amp. The delicate filaments don't stand up well to the abuse most guitar amps get at the hands of roadies. For most audio applications with indirectly heated cathodes, AC heater power works very well.
Most hum problems in audio amps come from poor lay-outs and/or poor grounding that lets the DC returns build up AC ripple voltages. For guitar amps, hum is also possible due to deliberately undersized power supplies -- the price you pay for compression and "sustain" caused by poor voltage regulation.
You can also get hum problems by means of magnetic coupling between a PTX and OPT, or a ripple choke and the OPT. A steel chassis can also encourage magnetic coupling. Usually, hum from ripple will have a frequency double the line frequency, and mag-coupled hum will be equal to the line frequency.
If you can o'scope, hum waveforms that look jagged and sawtooth-like are recharging pulses, and sinusoidal or near sinusoidal hum waveforms at the line frequency are mag-coupled.
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