PRS MT-15 Choke
- Thread starter 2dadz
- Start date
D
Deleted member 5962
Guest
Someone here did that a couple years ago and loved the results. Can’t remember who it was but maybe they’ll chime in.
A choke provides better AC ripple rejection, but there is something about the screen voltage saging that makes an amp more of a pleasure to play when the power amp is driven hard.
BrianC
more toys than talent
I added a choke to my Marshall JVM 210H - for me it improved the tone a lot
Rule of thumb - modern metal resistor, more classic rock choke
Rule of thumb - modern metal resistor, more classic rock choke
D
Deleted member 5962
Guest
Right. Maybe I read something extra into your post. I thought you may have been inferring that playing with the screen resistor could bring the sag in sooner… giving one of the advantages of cranking an amp up, to those who may not be able to crank it up as much… sometimes I let my mind run wild with these kinds of ideas.
A screen resistor does bring the sag on sooner. It also reduces clean power because the voltage drop across the resistor increases as the current drawn through the screen supply in the pi filter increases. A choke has a DC resistance, but unless a manufacturer really cheapened a build, usually has a DC resistance of 250 Ohms are less.
That’s a gross overstatement. I saw someone make that claim of TGP. It goes against engineering principles. The only way a choke is better for sag is if the choke has a higher DC resistance (DCR) the resistor it replaces. If you want to experience the effect of having a large value resistor in place of a choke in the pi filter, play an one of the old Mesa Studio .22s. The advantage to having a choke instead of a resistor in the power supply pi filter Is that it reduces hum better than a resistor.
Last edited:
The choke voodoo that is being pushed on TGP is up there with carbon comp resistor and capacitor voodoo. Carbon comp resistors are noisy and any two caps with a specific marked capacitance that result in a difference in tone have different measured values. There are days that I thank my father for beating this nonsense out of my head as a young engineer. He worked in the standards laboratory at a major defense electronics company; therefore, he was no stranger to measurement.
The amp that I am giving away uses all metal film and metal oxide resistors. If I had used carbon comp resistors the hiss produced by the EF86 would be be significantly higher. Carbon film resistors are a compromise. The reality is that carbon comps were used because that was all that was available and different caps could make a difference because they were high tolerance components at that point in time, which means that caps could measure as much as 20% off from their marked values.
The amp that I am giving away uses all metal film and metal oxide resistors. If I had used carbon comp resistors the hiss produced by the EF86 would be be significantly higher. Carbon film resistors are a compromise. The reality is that carbon comps were used because that was all that was available and different caps could make a difference because they were high tolerance components at that point in time, which means that caps could measure as much as 20% off from their marked values.
Last edited:
Here is a video of Glen Kuykendall talking about the his Trainwreck Express:
Unlike a lot of Express videos, Glen's amp is not a clone. It is an original Trainwreck Express that was built by Ken Fischer, so it is a good reference. Ken was no stranger to using chokes in a guitar amp. He worked for Ampeg and his Liverpool amp uses a choke; therefore, the use of a resistor in the PI filter on the Express was definitely a design decision. The Express owes its bloom to the use of a resistor instead of a choke. An Express has a plate voltage of around 400VDC, but it only produces 35 Watts of power. That is because the screen voltage is moving around with respect to current draw much more than it would with a choke. Ideally, one wants to hold the screen voltage rock solid while the plate current moves around for maximum clean output power.
Unlike a lot of Express videos, Glen's amp is not a clone. It is an original Trainwreck Express that was built by Ken Fischer, so it is a good reference. Ken was no stranger to using chokes in a guitar amp. He worked for Ampeg and his Liverpool amp uses a choke; therefore, the use of a resistor in the PI filter on the Express was definitely a design decision. The Express owes its bloom to the use of a resistor instead of a choke. An Express has a plate voltage of around 400VDC, but it only produces 35 Watts of power. That is because the screen voltage is moving around with respect to current draw much more than it would with a choke. Ideally, one wants to hold the screen voltage rock solid while the plate current moves around for maximum clean output power.
Last edited:
Similar threads
