I'm working on an active tube DI, based on the Altec 1566A:
I had to sub out the power transformer, but the new one is fairly close to the one called out in the schematic: It puts out 120VAC at 93 mA, and the filament is 6.3VAC at 1A. I'm inexperienced at best, but I did follow the schematic and the connections etc. are all good.
The filament side is fine, a little high at 6.8VDC but that seems at least in the ballpark. The problem is the B+; even bumping R9 up to 9500ohms, the lowest voltages I can get are 345VDC at "2" and 240VDC or so at "1."
In short: HELP!!!!!!!!!!!
I'm assuming I'm going to need to introduce a regulator of some kind; I have a spare LM350 but I need a plan!
-Seth
I had to sub out the power transformer, but the new one is fairly close to the one called out in the schematic: It puts out 120VAC at 93 mA, and the filament is 6.3VAC at 1A. I'm inexperienced at best, but I did follow the schematic and the connections etc. are all good.
The filament side is fine, a little high at 6.8VDC but that seems at least in the ballpark. The problem is the B+; even bumping R9 up to 9500ohms, the lowest voltages I can get are 345VDC at "2" and 240VDC or so at "1."
In short: HELP!!!!!!!!!!!
I'm assuming I'm going to need to introduce a regulator of some kind; I have a spare LM350 but I need a plan!
-Seth
^^^^
Since it's a voltage doubler circuit:
2(120 * sqrt(2)))= 339.4Vdc
That's reasonable for this circuit. I wouldn't worry much about it since the load will pull the voltage down a bit, especially since RC filter sections are included for ripple filtration.
Since it's a voltage doubler circuit:
2(120 * sqrt(2)))= 339.4Vdc
That's reasonable for this circuit. I wouldn't worry much about it since the load will pull the voltage down a bit, especially since RC filter sections are included for ripple filtration.
The voltages shown on the schematic are what you should find with a load. If your measurements are without a load I expect all is well.
The voltage rating of C6 should be higher than the unloaded B+ voltage. If you use the common 350V capacitor, there is a risk. Go for 450V if you want to be in the safe area.
No, this is loaded!
Thanks for the replies gents; I should have specified: The voltages I'm getting are with tubes installed!
And thanks oshifis, the filter caps are F & Ts rated at 500 I believe....
Thanks for the replies gents; I should have specified: The voltages I'm getting are with tubes installed!
And thanks oshifis, the filter caps are F & Ts rated at 500 I believe....
Almost Forgot...
The "120VAC" transformer actually puts out 146VAC, a least unloaded. Is this so far off spec to be worthy of return or replacement? Still seems there's other issues at play here, but....
The "120VAC" transformer actually puts out 146VAC, a least unloaded. Is this so far off spec to be worthy of return or replacement? Still seems there's other issues at play here, but....
Hmm...no. I suppose it couldn't hurt. But either way, something seems real off here. Supposedly:
2(146 * sqrt(2))= 412Vdc
which is actually just about what I got with the PT unloaded.
I'm just trying to figure out if this transformer is going to work at all or if there's a way to lose 25V or so right off the bat....
-Seth
2(146 * sqrt(2))= 412Vdc
which is actually just about what I got with the PT unloaded.
I'm just trying to figure out if this transformer is going to work at all or if there's a way to lose 25V or so right off the bat....
-Seth
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