nice work as usual.... i'm enjoying these. as for that high plate dissipation, take a look at what Fender has done in the Blues Jr. they can eat EL84's. i've cooled the bias down on a few of those amps in the past, in an effort to extend tube life.
10:23 Wouldn't it be better to assume that both the plate and screen grids are at 300 V, where the screen grid is? Since the screen grid is intended to make the behavior of the pentode essentially independent of the the plate voltage? Of course, the difference between 300 V and 325 V is not that big anyway. But I guess that the tube power would come closer to 12 W. I'm still wondering about that, though. This is 12 W at the bias point, right? If the tube is already at peak power dissipation at the bias point, what happens when you start to feed in some signal? Guess I might get to see that in the next lecture...
2:09 I wonder why they use two input tubes in parallel for the first amplification stage? They could have had a switch to switch between low and high input amplification, and saved a tube?
When an amplifier circuitry RC charging time and discharge time is EQUAL, what does this mean? that the voltage and current pass through easier, this is considered the resonance frequency or the gain is higher or lower because the amplifiers circuitry RC charging time and discharge time is EQUAL so the gain is higher or lower? I know when the RC charging time and discharge time is EQUAL the duty cycle is 50% using a square waveform. In guitar amplifiers power supplies the RC charging time is very short and the discharge time is very long so EE engineers will want a 5% charging time to 95% discharge time giving a duty cycle of 5/95 which is based on the RC duty cycle of the filter capacitor values and the power amplifiers LOAD as the load Resistor to get the RC duty cycle percentage.
If you think of a square wave going into a simple RC lowpass filter, you can think of it charging and discharging at the same rate since everything has the same R. But in something like a power supply, what's charging is very different that the rest of the amp which is discharging, so you can't really think of them equivalently.
My guess is that the higher plate wattage is because its an AB power amp. So the tube isnt on all the time. Werent most television class-A amps using combo triode/pentode tubes?
Re: the AB: I've heard people say that, but the thing I can't wrap my head around is this is current that is flowing and power being consumed even if you're not actually playing anything. I haven't looked at television designs, to be honest; I was just spitballing. ;)
@@Lantertronics Yeah, that makes sense. I was thinking of transistor amps. Someone in the comments mentioned he fixed the issue to save tube life. And I have friend that has done it ro his amp.
From what I understand, safety standards don't let you float the secondary -- there could be a problem, for instance, if there's a breakdown in insulation between the windings in the transformer.
nice work as usual.... i'm enjoying these.
as for that high plate dissipation, take a look at what Fender has done in the Blues Jr. they can eat EL84's. i've cooled the bias down on a few of those amps in the past, in an effort to extend tube life.
also... it might be interesting to do some actual real world bias testing of this circuit with a bias probe or such & compare your notes.
4:28 Tremolo is covered in one of the Kuehnel books and shipping to my country just got reinstated. I know what to do. ;)
10:23 Wouldn't it be better to assume that both the plate and screen grids are at 300 V, where the screen grid is? Since the screen grid is intended to make the behavior of the pentode essentially independent of the the plate voltage?
Of course, the difference between 300 V and 325 V is not that big anyway. But I guess that the tube power would come closer to 12 W.
I'm still wondering about that, though. This is 12 W at the bias point, right? If the tube is already at peak power dissipation at the bias point, what happens when you start to feed in some signal? Guess I might get to see that in the next lecture...
2:09 I wonder why they use two input tubes in parallel for the first amplification stage? They could have had a switch to switch between low and high input amplification, and saved a tube?
When an amplifier circuitry RC charging time and discharge time is EQUAL, what does this mean? that the voltage and current pass through easier, this is considered the resonance frequency or the gain is higher or lower because the amplifiers circuitry RC charging time and discharge time is EQUAL so the gain is higher or lower? I know when the RC charging time and discharge time is EQUAL the duty cycle is 50% using a square waveform. In guitar amplifiers power supplies the RC charging time is very short and the discharge time is very long so EE engineers will want a 5% charging time to 95% discharge time giving a duty cycle of 5/95 which is based on the RC duty cycle of the filter capacitor values and the power amplifiers LOAD as the load Resistor to get the RC duty cycle percentage.
If you think of a square wave going into a simple RC lowpass filter, you can think of it charging and discharging at the same rate since everything has the same R. But in something like a power supply, what's charging is very different that the rest of the amp which is discharging, so you can't really think of them equivalently.
My guess is that the higher plate wattage is because its an AB power amp. So the tube isnt on all the time. Werent most television class-A amps using combo triode/pentode tubes?
Re: the AB: I've heard people say that, but the thing I can't wrap my head around is this is current that is flowing and power being consumed even if you're not actually playing anything.
I haven't looked at television designs, to be honest; I was just spitballing. ;)
@@Lantertronics Yeah, that makes sense. I was thinking of transistor amps.
Someone in the comments mentioned he fixed the issue to save tube life. And I have friend that has done it ro his amp.
Since there is no NFB, why connect the OT to ground? Is it a UL thing?
From what I understand, safety standards don't let you float the secondary -- there could be a problem, for instance, if there's a breakdown in insulation between the windings in the transformer.
Shouldn't I_k be I_p @12:06? The plot says Anode current vs Anode Voltage i.e. I_p vs. V_pk? I might just be getting turned around...
Watch from 12:52... ;)
@@Lantertronics funny enough I paused it and drove home after commenting this 😅
@@locojose13 HAH!