I am not a tube person, so all of this is helpful. I think the artificial CT is worth the try as I already have the xformer rather than buy another one at this time
My original question is still where have any builders of this version of Jack's board connected the heater 6.3vac. Just a clue!!
Thanks
David
My original question is still where have any builders of this version of Jack's board connected the heater 6.3vac. Just a clue!!
Thanks
David
Then look up the heater pins of the tube in the data sheet and using the ohms range on the DMM check to which connection points they go. Done!
Jan
A little late to this conversation and it looks like the problem is solved. Just to answer the question, I soldered the heater wires directly to the bottom of the tube socket on the 6SN7. I believe that was done by another builder earlier in the thread. I used a wire to wire, 2 pin connector near the transformer so that I could have the heater wires tightly twisted near the Impasse board and still disconnect the board when needed.
Of course, Jan is correct. Anywhere on the circuit will work and checking continuity is the right way to confirm.
I also recommend checking the heater voltage across the tubes when you get to the point of powering and testing. Between the higher mains voltage at my home and Hammond transformer, I found that the heater voltage was out of spec for the 6SN7 tube. I added a 0.47R wirewound resistor in series to get everything back to normal. Of course, you will need to check your own power supply because it will be different from mine.
For others looking for a transformer in the US, the Hammond 290CX is a replacement transformer for electric guitar amps, so it's available. It has a center tapped 6.3V circuit.
Jac
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Unfortunately I don't have the board to hand but I have a vague recollection that the heater wires may have soldered in inside one of the tube sockets from underneath. By looking at the data sheet for the tubes you should be able to easily trace the pcb tracks to the pads for the heater. They also connect to the non connected together pins of c106 c107
Drpro, I am not a tube guy either but years of building SS gear failed to give me that open soundstage and illusion of live music from speakers.
Tubes are cheap, 12AX7 or 6922 are a few bucks each and can literally pound SS VAS stages or preamps into the ground. My final amp stage is Mosfet SS but a tube stage preamp is now required to get that final smoothness into the system. one or two tube stages are plenty more can make the system sound mushy and compressed.
my setup = opamp > volume > 6922 tube stage > tone stack > ss power amp
Tubes are cheap, 12AX7 or 6922 are a few bucks each and can literally pound SS VAS stages or preamps into the ground. My final amp stage is Mosfet SS but a tube stage preamp is now required to get that final smoothness into the system. one or two tube stages are plenty more can make the system sound mushy and compressed.
my setup = opamp > volume > 6922 tube stage > tone stack > ss power amp
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Dave, Jan words steered me where to look. Jack did put two pads on the bottom of the board, from there wider traces carry the filament amps. The tube socket above covers those holes when viewed from the component side, plus they are not labeled.
So I am either going to try the resistor ground or just order another xformer with CT filament.
So I am either going to try the resistor ground or just order another xformer with CT filament.
Thanks everyone for their kind words. The very nice folks at Mouser even though more than 30 days since I ordered the transformer lacking CT filament power, sent me a RMA and once they have it will credit my account. So I went ahead and ordered a 290CX based on Jac's suggestion.
Tnx
David
Tnx
David
So I have the 290CX in hand. Working with the PS board, while grandkids wrap packages. Getting 331vdc out. From my reading R102 and R101 values were chosen for the Allied transformer that is no longer available, so it seems I need to change those values to hopefully come closer to the desired 350vdc output.
Also on Jack's board right next to the +350 output pads there is a space for a resistor label R1. I haven't found that resistor in either schematic or parts listing. Any suggestions.
Tnx
Also on Jack's board right next to the +350 output pads there is a space for a resistor label R1. I haven't found that resistor in either schematic or parts listing. Any suggestions.
Tnx
Hi David,
The Hammond 290CX and the Allied 6K3VG are both 650VCT, but the 290CX is 5X as sturdy (207mA vs 40mA). The Allied's primary is rated at 115VAC where the 290CX is rated ad at 120VAC. I suspect it can be a combination of the main and the 5VAC difference to cause the 19VDC difference.
Try removing R1 and R2, but that will only give you a few volts. Also try bumping the c1 to 2uF from 1uF. Do you have the PS schematic? If not, please let me know.
Thanks,
The Hammond 290CX and the Allied 6K3VG are both 650VCT, but the 290CX is 5X as sturdy (207mA vs 40mA). The Allied's primary is rated at 115VAC where the 290CX is rated ad at 120VAC. I suspect it can be a combination of the main and the 5VAC difference to cause the 19VDC difference.
Try removing R1 and R2, but that will only give you a few volts. Also try bumping the c1 to 2uF from 1uF. Do you have the PS schematic? If not, please let me know.
Thanks,
Hi David,
With SS rectification, you should be seeing something around 460 VDC, a little less. I finally looked at the schematic and see it uses solid state rectifiers.
Personally, I would use SS diodes with some series resistance (mainly to reduce peak charging currents) like Stuart did, but with resistors in series with the rectifier. They are very effective in dropping the B+ you'll see. They also greatly reduce hot switching current spikes. So a lot of good in that plan with no downsides that I can see or have ever heard / measured.
Keeping C1 low also greatly aides in reducing switching transients. By low, I mean less than the 50 uF, much lower. 2 uF should bring up your B+ some too.
Enjoy your Christmas and I wish you success with your preamp.
-Chris
With SS rectification, you should be seeing something around 460 VDC, a little less. I finally looked at the schematic and see it uses solid state rectifiers.
Personally, I would use SS diodes with some series resistance (mainly to reduce peak charging currents) like Stuart did, but with resistors in series with the rectifier. They are very effective in dropping the B+ you'll see. They also greatly reduce hot switching current spikes. So a lot of good in that plan with no downsides that I can see or have ever heard / measured.
Keeping C1 low also greatly aides in reducing switching transients. By low, I mean less than the 50 uF, much lower. 2 uF should bring up your B+ some too.
Enjoy your Christmas and I wish you success with your preamp.
-Chris