High B+ using SS rectifier

[expat]

I greatly appreciate the actionable info, Abbey Road From Hell!
So, to try to understand Ohms Law better, I plugged those numbers into an Ohms Law calculator and also asked Ai, and I guess I did something wrong, but they both say I'd need a 1k (not a 100r) to drop 50v at 50mA.


R = V / I = 50V / 50×10-3A = 1000Ω
P = V×I = 50V×50×10-3A = 2.5W

 

[amplexus]

I don't knw why Amplexus mentioned that, because the oneon your schemo seems adequate to me.

I was speaking generally, and in reference to
The Fender circuits as the early 6V6 ones did not use them.

 

[abbey road d enfer]

I greatly appreciate the actionable info, Abbey Road From Hell!
So, to try to understand Ohms Law better, I plugged those numbers into an Ohms Law calculator and also asked Ai, and I guess I did something wrong, but they both say I'd need a 1k (not a 100r) to drop 50v at 50mA.


R = V / I = 50V / 50×10-3A = 1000Ω
P = V×I = 50V×50×10-3A = 2.5W

Correct!
So my recommandation becomes "You should order a selection of resistors of 220, 470 and 1000r so you can adjust on test."

 

[expat]

Ha, ok! Thank you.
I'll get the order together.

 

[Wavelength]

AR's "Acoustic suspension" type speakers was probably the worst thing that happened to audio in the 60's. Being grossly inefficient meant much more power was needed to drive them, along came higher power amps with less performance. A ten dB less efficient speaker needed 10dB more power, the old 15W now needed 150W, hopefully.
If you want a small poweramp you also need a very efficient speaker. Obviously, or not, music production has a different set of criteria than reproduction.

Actually the Hifi arena wanted more linear frequency response and therefore more feedback was applied to amps, transistors replaced tubes and so forth. Xovers were more eleborate and therefore ate more power as well.
Sealed speakers can sound real good if you use Aperiodic type vents especially for tube amps since the Fs of the driver cabinet can force the load upwards of 200 ohms. You send that into an 8 ohm terminal and back to the driving plate and you can kiss the power good by. Plus if you look at the power vs frequency, its log property therefore in the bass 70% of the power is required. All my sealed speakers are aperiodic which keeps the Z @Fs to a minimum and allows the amp to better drive the speaker cabinet. My 4x12 has two of the Scanspeak aperiodic vents in it.

 

[expat]

As I try to learn from advice (and not just follow it) I have a question - Abbey Road d'Enfer - you said I'm looking at 50ma of idle current - is that the right number? Earlier I added up the amperage from the tube array and it was 2.69 amps. Is that 'under load' at 2.69 and you're talking about when not under load? Just trying to get my head around what is going on here.
Also, I ordered up a slew of different value 10W resistors, I was found greatly lacking in that part of inventory. Should be here tomorrow.

 

[rock soderstrom]

As I try to learn from advice (and not just follow it) I have a question - Abbey Road d'Enfer - you said I'm looking at 50ma of idle current - is that the right number? Earlier I added up the amperage from the tube array and it was 2.69 amps. Is that 'under load' at 2.69 and you're talking about when not under load? Just trying to get my head around what is going on here.
Also, I ordered up a slew of different value 10W resistors, I was found greatly lacking in that part of inventory. Should be here tomorrow.

I am not Abbey but I can solve your confusion.

You are confusing two important parameters of tube circuits here (I think ChatGPT is not entirely innocent).

For tubes to be operated at all, they have to be heated. This current is called heating current and it is relatively high. For example, for a 6V6 power tube you need 0.45A, i.e. 450 milliamperes. A 12AX7 preamp tube requires slightly less, at 6.3V this is 0.3A. A fat power tube such as an EL34, for example, needs 1.5A per tube, so you can see that a powerful power amplifier can already add up to a few amps (and a lot of heat).

That is one side of the coin, the heating current ensures the basic functionality of the tube.

On the other hand, there is the high-voltage operating tension, usually several hundred volts, which is often referred to as B+. Only relatively low currents flow here due to the high voltages.

Let's take your amplifier, the 6V6 will require the largest amount of current, roughly between 35mA and 50mA. This is divided between the anode current and the screen grid current when connected as a pentode, more details can be found in the relevant data sheets. The current consumption of the preamplifier tubes is almost negligible in comparison. A 12AX7 requires just over 1mA per triode system, which is almost nothing compared to the power tube.

So now you understand the mA specification from Abbey, he was talking about the B+ voltage and the total amount of current required there. This is important in your case, because this affects your "too much voltage" problem, because the series resistors that are supposed to reduce this, do it according to Ohm's law. The current of the B+ voltage is important for that, not the heating voltage!

 

[rock soderstrom]

Is that 'under load' at 2.69 and you're talking about when not under load?

Under load was meant in this thread, when the tubes are plugged in (and heated), then a current flows in the B+ circuit and your power supply goes down a bit with the B+ voltage under this load and a corresponding voltage drops across the series resistors (can be calculated, Ohms Law again). If no current flows (no tubes plugged in), no voltage will drop across these resistors, your power supply is also not loaded, ergo your B+ idle voltage reaches its maximum.

 

[expat]

You are confusing two important parameters of tube circuits here (I think ChatGPT is not entirely innocent).

For tubes to be operated at all, they have to be heated. This current is called heating current and it is relatively high. For example, for a 6V6 power tube you need 0.45A, i.e. 450 milliamperes. A 12AX7 preamp tube requires slightly less, at 6.3V this is 0.3A. A fat power tube such as an EL34, for example, needs 1.5A per tube, so you can see that a powerful power amplifier can already add up to a few amps (and a lot of heat).

Hey Rock, thanks for your input.

So, ChatGPT had nothing to do with it, fyi, I reference it, I don't rely on it. My estimate of amps for the tubes seems to be pretty close to what you just said for your tube lineup - 2.65 amps in my case. I believe I made that estimate from referencing the original tube datasheets about 10 yrs ago when i started this old thing.

My question is, how did Abbey come up with the 50ma idle current value, and why is that the value upon which I want to estimate my resistor's value if I'm about to plug tubes into it?

 

[abbey road d enfer]

My question is, how did Abbey come up with the 50ma idle current value, and why is that the value upon which I want to estimate my resistor's value if I'm about to plug tubes into it?

Check the 6V6 datasheet.

 

[rock soderstrom]

My estimate of amps for the tubes seems to be pretty close to what you just said for your tube lineup - 2.65 amps in my case. I believe I made that estimate from referencing the original tube datasheets about 10 yrs ago when i started this old thing.

But unfortunately it is wrong, the tubes in your amp need 0.45A (6V6)+0.3A(12AX7)+0.3A(6AT6)= 1.05A heating current!

In addition, this has nothing to do with B+ and the amount of current that flows there. You've got it wrong, I tried to explain it to you, but I didn't succeed

 

[expat]

Hey Rock,
I'm a small-brained person, and I really appreciate your patience. I dig the difference between heater current and plate current on that basic level, i think my feeble mind is just getting a little overwhelmed.

Hey Abbey,
So I checked it and I find that you were completely wrong about 50ma - it's 49.5ma!!
So since we are talking about cutting the B+ (not the heaters, thanks Rock), how is it correct to base our resistor value on only the plate current of the 6v6, when this resistor will be effecting all of the tubes? Does this mean that "if we get it right for the 6v6 then we get it right for the other tubes, too?"

 

[abbey road d enfer]

So I checked it and I find that you were completely wrong about 50ma - it's 49.5ma!!
So since we are talking about cutting the B+ (not the heaters, thanks Rock), how is it correct to base our resistor value on only the plate current of the 6v6, when this resistor will be effecting all of the tubes?

The current drawn by the other tubes is less than 1mA, so whether the total current is 50.5 or 51.5 mA doesn't change much.
You must remember that the mains voltage may vary by as much as +/-10%.
BTW, the official symbol for milliamperes is mA.

Does this mean that "if we get it right for the 6v6 then we get it right for the other tubes, too?"

Yes.

 

[amplexus]

Hey Rock,
I'm a small-brained person, and I really appreciate your patience. I dig the difference between heater current and plate current on that basic level, i think my feeble mind is just getting a little overwhelmed.

As I mentioned before- you are feeling overwhelmed because you haven’t got a good basic understanding of how a tube functions. And you will probably continue to be confused (and not be able to filter out incorrect information from sources like chatGPT) until you do.

One big basic thing that should help: don’t think about a tube (esp a power pentode/tetrode) as one single component with one fixed property.

For example- a 6V6 as we are talking about here is a type of Beam Power Pentode. It has 5 “parts” inside that are involved in making it work, each with a connection (or two) to the outside world, and some internal connections to other bits that make it function in a specific way.

When this tube is in operation there is current flowing in all 5 of these parts at varying magnitudes. The current flowing in the control grid is minuscule usually in the sub mA range, for example, and the current flowing in the heaters is comparatively massive at one half Amp. The plate and screen grids also have current flowing in them on the order of a couple mA to a few dozen mA.

We have some control over these currents-within limits- based on how we design the surrounding circuit. That allows us to dial in - again within limits- how the tube will perform for a given application.

In operation some of these currents fluctuate- usually in relation to each other- some don’t.

But your ability to design or modify tube circuits will depend on your understanding of these various currents and where/why/how they work inside the tube. Your difficulty understanding some of the information here will be GREATLY improved by learning a few of the basics of vacuum tube theory and operation.

 

[expat]

Hey Abbey - mA indeed, thanks. And good to know that getting the 6v6 right means the others are inline too. I was just kidding about the mA's being off by so little!

Hey Amplexus, thanks for the advice and info. I do actually understand the majority of what you outlined, but for sure I have a great deal to learn, so I appreciate everyone's time in explaining it. I've thrown myself into this project like its the deep end and I need to learn how to swim better.

My being overwhelmed was more a reference to the 20 different projects I am bouncing around right now. Aside from this amp, I have had my gear in storage for 14 years, so now I am replacing batteries and cleaning keybeds of 9 synths, rebuilding the PS on a tube amp conversion, rebuilding a PS for my Soundcraft 600, upgrading the console and cleaning faders, fixing the black glue problem of the KRK's, fixing the red glue of the JD-800 keys, mod'ing my 8-track recorders with direct outs, etc. I love it all, but it's a lot! I've started a list of priorities to help me thru it, and this amp here is at the top. So, I'll take a breath and try to be more focused!

Also, just to be clear, I'm not using Ai for anything other than the occasional question - I'm certainly not making any decisions based on it. It's wrong as much as humans are, after all!

 

[expat]

Got the 2k 10watt resistor delivered and am popping it in now. Will report back.

Also, I've got these 5 and 10ohm NTC thermistors here and it seems its a good idea to add one for the in-rush current. Would this be in series before the fuse? On the description it says it should be used in parallel, which I don't get how it could even be useful that way in this use case.

 

[Cqwet Dbdfte]

Got the 2k 10watt resistor delivered and am popping it in now. Will report back.

Also, I've got these 5 and 10ohm NTC thermistors here and it seems its a good idea to add one for the in-rush current. Would this be in series before the fuse? On the description it says it should be used in parallel, which I don't get how it could even be useful that way in this use case.

...in series. I prefer breakers to fuses.

 

[expat]

Hey CD, thanks. So, in series just before the fuse?

 

[Cqwet Dbdfte]

Yes, either.
Also, use double pole switches for AC mains.

 

[expat]

Installed the 2k 10w resistor (big old sucker!).

Now getting:

472v on Pin 3 of 6v6 (plate).

Also checked the volts on the heaters, getting 3.5v on either heater winding.