imo
Well-known member
Hello,
I am refurbishing an old Presto 3 channel mixer to use as a funky "character" pre for my friends studio. kind of a Christmas/bday kind of thing, so not wanting to spend any additional money. The topology is mixer/repro channel the mixer has: 26J7's, 6SL7GT, 6SN7GT. The repro channel mirrors this. Both sides have transformer ins and outs. There is an XLR after the mixer side that i could feed back into the repro side if i want to add another gain stage(using the repro volume to control it).
I have cleaned it up and recapped it and now i need to make a power supply for it. I am trying to use some parts i already have laying around. I have a PT that i was using in a guitar amp(AC15) that is in the ballpark. Plenty of heater current(6a) and enough current(150mA) for the HT. The B+ is a little high @ 330v. I am looking for the best ratio of elegance/frugality<g
If you look at the schematic you can see that there is already a ton of filtering within the circuit, so i was thinking a simple solid state rectified, into a choke, cap, resistor--Main thing is that i need to get it down from an anticipated 460v down to around 350 into circuit. The 6J7's are about 2.5mA class A, 6SL7 4.6mA, and 6SN7 9mA. I am assuming around 40mA total for both sections.
I have a couple of chokes laying around that will knock off a few volts, but still looking at 90 or so. With all the filtering downstream and it being a funky thing to begin with, would i be ok just kludging in a big 2-2.5k resistor in there, or would it be significantly better to split that up over a couple of filter sections(ie 2 5w 1k resistors)
Thanks for any help or ideas
Best
Ian
I am refurbishing an old Presto 3 channel mixer to use as a funky "character" pre for my friends studio. kind of a Christmas/bday kind of thing, so not wanting to spend any additional money. The topology is mixer/repro channel the mixer has: 26J7's, 6SL7GT, 6SN7GT. The repro channel mirrors this. Both sides have transformer ins and outs. There is an XLR after the mixer side that i could feed back into the repro side if i want to add another gain stage(using the repro volume to control it).
I have cleaned it up and recapped it and now i need to make a power supply for it. I am trying to use some parts i already have laying around. I have a PT that i was using in a guitar amp(AC15) that is in the ballpark. Plenty of heater current(6a) and enough current(150mA) for the HT. The B+ is a little high @ 330v. I am looking for the best ratio of elegance/frugality<g
If you look at the schematic you can see that there is already a ton of filtering within the circuit, so i was thinking a simple solid state rectified, into a choke, cap, resistor--Main thing is that i need to get it down from an anticipated 460v down to around 350 into circuit. The 6J7's are about 2.5mA class A, 6SL7 4.6mA, and 6SN7 9mA. I am assuming around 40mA total for both sections.
I have a couple of chokes laying around that will knock off a few volts, but still looking at 90 or so. With all the filtering downstream and it being a funky thing to begin with, would i be ok just kludging in a big 2-2.5k resistor in there, or would it be significantly better to split that up over a couple of filter sections(ie 2 5w 1k resistors)
Thanks for any help or ideas
Best
Ian