I have a choke that I would like to install on my combo amp, and was hoping anybody could chime in for me on any do's and don'ts.. I'm not very experienced with tube circuits and want to do this right! Any advice would be greatly appreciated.
Firstly would I be correct in saying this replaces the big series power resistor that comes after the standby switch, on the B+ line?? So its just a matter of taking that out and installing the choke in its place with no importance to orientation like a resistor?
The main thing I'm concerned with is that my amplifier is a pcb design, and there is no physical space on the board to put it.. There is however plenty of space on the chassis I could bolt it on, and I was thinkng I could just feed the wires through a hole and then connect it to the 2 points via spade connectors... My main question is if this is ok feeding about 18 inches of choke wire to the pcb like this, could this cause any problems with regard to picking up hum or stray currents?? Lastly is it important where I physically mount the choke and would I be correct in saying NOT near the power transformer??
Thanks so much and look forward to hearing from you
No particular way around. An HT choke works as well 'backwards' as it does 'forwards'.
And yep, in a PP amp, it usually replaces the first resistor (between the plate supply and the screen supply filter cap nodes), and only needs to be rated for peak screen and pre-amp current.
If it's for a 'whole-of-supply' CLC filter (such as is beneficial for cancelling out ripple hum in a single-ended amp), then it goes between the rectifier and the plate supply filter cap. But the choke then needs to be DC-rated to take the peak current seen by the amp (i.e. it needs to be rated for the same peak current as the PT's high-tension winding)
Is this for your Marshall DSL401? If so replace R32 (470Ω/5W) with the choke. Mount the choke near the PT, OT, or power tubes. Don't mount it near the preamp tubes or other sensitive low level signal circuits.
Thanks guys, Sluckey you legend thanks! Yep its for the DSL401, I got a classictone part they recommended for the DSL series amps.. So I got you its the big white 5W resistor.. I was about to put it near the V1 tube so I'll stay away from there.. Is there any benefit to twisting the two wires from the choke like a twisted pair cable, or is it not so critical??
Ok tubeswell brilliant so any angle and orientation is not a problem thats awesome, ill leave it at a right angle i think..
Look at a Marshall 1987 chassis for how it's mounted there and no problems. It's on the preamp side of the OT facing the end of the chassis. That should be close enough for your short run.
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