What criteria is used to determine the choke ratings on a new amp build?
Either a 50 watt or 100 watt. I understand the current ratings are crucial so as not to burn out the windings. It is the inductance relationship to the sound I'm uncertain on.
For example Train Wreck vs. Dumble clean channel would be the amp examples in question...
silverfox.
Which Choke
Moderators: pompeiisneaks, Colossal
Re: Which Choke
Information on calculating sufficient inductance for a CLC filter can be found here: http://www.valvewizard.co.uk/smoothing.html
The choke needs to be dc-rated to handle the peak DC draw likely to be seen though it. For your average 50W-100W marshall, a 50 to 90mA-rated choke in a CLC filter between the plate and screen supply nodes is sufficient (because you're only supplying the screens and pre-amp from that point in the power supply rail).
If you're talking about a vintage tweed fender amp where the CLC is a 'whole-of-supply' filter (i.e. including supplying the plates), then the HT choke needs to be rated at least as high as the power transformer's HT winding (i.e. 180-200mA for a 2 x 6L6 amp, or double that for a 5F8)
The choke needs to be dc-rated to handle the peak DC draw likely to be seen though it. For your average 50W-100W marshall, a 50 to 90mA-rated choke in a CLC filter between the plate and screen supply nodes is sufficient (because you're only supplying the screens and pre-amp from that point in the power supply rail).
If you're talking about a vintage tweed fender amp where the CLC is a 'whole-of-supply' filter (i.e. including supplying the plates), then the HT choke needs to be rated at least as high as the power transformer's HT winding (i.e. 180-200mA for a 2 x 6L6 amp, or double that for a 5F8)
He who dies with the most tubes... wins
Re: Which Choke
Another key characteristic is choke resistance.
I suggest that it be fairly low (eg 100-200 ohms) for max power / big cleans, with the downside being potentially excessive screen grid dissipation when overdriven.
Whereas for amps intended to be overdriven, rather more resistance (eg 500 ohms - 1k) in the supply to the screen grid node can be beneficial in keeping screen grid dissipation in check, with the downside being a slightly reduced max power output.
Variables in the amp design that might also affect choise of choke resistance include the increased screen grid current draw of pentodes over beam tetrodes, 2 or 4 etc power tubes, and the actual value of the individual screen grid resistors used.
For low resistance chokes, resistors can be added in series to obtain the desired total resistance value.
I suggest that it be fairly low (eg 100-200 ohms) for max power / big cleans, with the downside being potentially excessive screen grid dissipation when overdriven.
Whereas for amps intended to be overdriven, rather more resistance (eg 500 ohms - 1k) in the supply to the screen grid node can be beneficial in keeping screen grid dissipation in check, with the downside being a slightly reduced max power output.
Variables in the amp design that might also affect choise of choke resistance include the increased screen grid current draw of pentodes over beam tetrodes, 2 or 4 etc power tubes, and the actual value of the individual screen grid resistors used.
For low resistance chokes, resistors can be added in series to obtain the desired total resistance value.
https://www.justgiving.com/page/5-in-5-for-charlie This is my step son and his family. He is running 5 marathons in 5 days to support the research into STXBP1, the genetic condition my grandson Charlie has. Please consider supporting him!