Everyone, let's just agree that there is no physical anode resistor with most "power" tubes (but yes, there is a resistance via that transformer and the load/speaker). So what? How does that change anything with idea of matching tubes by temperature? It's just not a great way to find tubes with similar mu/rp/DC-bias/etc. when these parameters can be measured directly without too much hassle.
Of course you have to know the input voltage limits of the meter you use but puting the (-) common lead of most meters on B+ is no more risky than the (+) lead on B+. It's actually the way to get a reading on the plate signal swing if you use a signal generator to drive the amp with a frequency low enough (60 - 400Hz) that the meter can read accurately. The B+ becomes 0v to the meter and the swing voltage is the difference. It's about the only way to get a reading on an output plate because most scopes and scope probes have a fairly low max input voltage limit on the order of 350 DCV + ACV. The 10x switch doesn't protect the probes above their limit.
Puting the (-) lead on B+ is also how you would read the voltage drop across a cap input/choke in the PS to see if it's good and get the load current through the rectifier. You must have done that a few times in your experience, yes? Saves time doing the math from 2 readings.
Last edited:
I do sometimes. Last time was with an LTP, which has a CCS tail on the cathode.
Oh my... what a brilliant new idea of pairing tubes. I agree with Pirinha's idea.
So the idea of pairing tubes based on temperature sounds just like pairing resistors by temperature. I wouldn't say it's impossible, but if I have a meter that measures, why bother?
Let's be honest. How do you define a resistor? Surely it can't be "the manufacturer's brochure calls it a resistor" or "it's axial shaped with two leads" right? For me a resistor is just a thing that when current flows through it, (1) the voltage across it rises proportionally with the current rise with no phase shift (2) the energy consumed is transferred into heat. In this sense the plate is a perfect resistor. Strap a triode like a diode, and you get a resistor! You can even insert an additional resistor between grid and cathode and now the tube behaves like another resistor μ times larger, even dissipating the same heat! How wonderful it is!
So the idea of pairing tubes based on temperature sounds just like pairing resistors by temperature. I wouldn't say it's impossible, but if I have a meter that measures, why bother?
And, what current amp manufacture uses that circuit? Also note the high 800 volts
"And, what current amp manufacture uses that circuit?"
Replace the anode "load" resistor with choke or with CCS.
Isn't familiar the layout?
Replace the anode "load" resistor with choke or with CCS.
Isn't familiar the layout?
Wrong. Take an 6550. With Ua 400V, Ia 85mA and a 3k load impedance/resistance you get 20W output power. Your B+ would have to be 755V.
Last edited:
Resistance is a kind or type of impedance. Other kinds of impedance would be capacitance and inductance (coils of insulated wire). An impedance can be one or a combination of these 3 types of component. In short, resistance is a subset of impedance types.
Impedance is a specific subset of resistance. It is frequency dependent with a frequency > 0Hz. If the resistance at frequency of 0Hz is meant it is DCR.
For an ideal fixed resistor impedance is flat and the same as DCR. And exception would be non ideal resistors like wire wounds where the inductance of the coiled wire figures in at higher frequencies.
For an ideal fixed resistor impedance is flat and the same as DCR. And exception would be non ideal resistors like wire wounds where the inductance of the coiled wire figures in at higher frequencies.
Interesting idea. But what was the problem with conventional matching method?
You say you used to match them by temperature. How do you do it now?
Thank you.
Last edited:
The load line for the output tube(s) becomes an ellipse for a reactive load, rather than a straight line when resistive.
The biggest difference is that the current and voltage are in-phase for a resistor.
The magnitude of the resistance is constant with frequency (to a first approximation).
Resistors dissipate power.
The magnitude of the L or C impedance is not constant with frequency.
In an inductor, for a sine wave the current lags the voltage by 90 degrees (a quarter cycle).
In a capacitor, for a sine wave the current leads the voltage by 90 degrees (a quarter cycle).
L or C do not dissipate power (to a first approximation), because V and I differ by 90 degrees.
A general impedance can be any kind of combination of any number of R, L, and C.
Complex crossovers can stress the amplifier more than one would think.
https://www.stereophile.com/reference/707heavy/index.html
Most people here on the forum actually build there own amps....
I have myself in the last 20 years have built somewhere around 30 different tube amps, from s.e. To p.p to parafeed, and with b+ from 300v. To 750v.
And I have not used temperatures to match the tubes either😉
This thread feels like watching a dog trying to catch it's own tail🙄
"This thread feels like watching a dog trying to catch it's own tail🙄"
This thread is trolling bs started by a troll who does the same thing in all threads started be that person. An @admin / @Moderator should shut all that nonsense down.
This thread is trolling bs started by a troll who does the same thing in all threads started be that person. An @admin / @Moderator should shut all that nonsense down.
Tubesaregreat, it does seem to appear that quite a number of your posts feel somewhat confrontational, if not sometimes borderline rude.
Even though I am a bit older and have decades of experience in building amplifiers, I still learn quite a bit from some of the very experienced members on this forum. There is such a wealth of knowledge here, it’s fantastic, and very helpful.
If one is open to constructive discourse, that is……
Even though I am a bit older and have decades of experience in building amplifiers, I still learn quite a bit from some of the very experienced members on this forum. There is such a wealth of knowledge here, it’s fantastic, and very helpful.
If one is open to constructive discourse, that is……