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ampage archive
Vintage threads from the first ten years
5 volt 12ax7 supply?
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 6/2/1999 1:36 PM |
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phil  |
5 volt 12ax7 supply? I don't use the 5 volt rectifier tap on my transformers... could I use this to power my 12ax7 preamps? Has anyone tried to put a full-wave bridge and filter caps on a 5-volt tap? Thanks! |
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| 6/2/1999 3:35 PM |
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| R.G. |
If you want to run it regulated, you'll probably have to run it into a doubler to get enough headroom, then drop it through a regulator or resistor. 5Vrms= 7.07V peak - 2(0.7V)= 5.67Vdc, maybe OK for 12AX7 filament, as that's 6.3V 10% low, so it's probably OK in the normal line case, and a 5V winding may be wound a bit high, so it could be OK if you don't insist on regulating. |
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| 6/2/1999 10:55 PM |
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| Bruce |
I hate to say it but I've done it a few times myself (unregulated) and I couldn't hear the slightest difference in anything. Here's something else scarey...I used an aftermarket 10 watt SE OT in a blown up SF Champ but used a 6L6 in it with a solid state rectifier and then moved the 6L6 onto the unused 5v line and left the 12AX7 on the regular 6v line and that worked OK too. Plus it sounded very cool. Bruce |
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| 6/4/1999 7:31 AM |
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| John Martin |
Some of the old "hi-fi" amps had lower than normal heater voltages. I have an old Harmon Kardon amp that is running very low voltage on the preamp tube heaters. Its supposed to cut down the noise without the extra expense of using a DC supply. I thought it was defective at first, until I read about this practice. Sounds just fine. One of the few using 6V6 outputs. JM |
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