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Vintage threads from the first ten years
Tube Preamp Box *Power supply?*
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 5/9/1999 9:06 PM |
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| Jim L. | Tube Preamp Box *Power supply?* I would like to build one of the preamp boxes from the Ampage schematic database, maybe a JCM800 preamp. Can someone help me out with a powersupply? I would like it to fit inside a stomp box, I know R.G Keen has posted some schematic's on the W-20 and Alembic boxes but the power supply sections on all are not detailed. Thanks, great page here! Jim |
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| 5/10/1999 7:55 AM |
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R.G.  |
It's very difficult to get a real tube power supply into a stomp box. The combination of high input impedances, high gain, and magnetic noise in close proximity make for big hum problems. That's one reason I didn't post a great amount of detail on the power supplies. You can't get the custom transformers the W-20 and Alembic used. You can get a two-12AX7 transformer from Stancor, the P8714, but you'll need to build your box around it as it will not fit the standard stomp boxes. You can also use two 120:12VAC transformers back to back to get the high voltage plus filament. The key here is that you have to sacrifice either space or money. Space for a bigger box or more accessible transformer versus money for a special transformer. |
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| 5/10/1999 8:51 AM |
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| Jim L. | Hey R.G I certainly would like to build one of these boxes, wether I will have to pay for a custom transformer or perhaps make the box larger to accomidate the transformer. I haven't dealt alot with tube preamps, Could you tell me what diodes to use for the recifier? Thanks, I will be checking out Stancor... Jim L. |
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| 5/10/1999 8:59 AM |
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| R.G. |
If you're willing to make the box bigger, a whole range of possibilities open up. The simplest way to power them is to use two transformers. Get at least one dual primary 120/240 to 12VAC one and one 120VAC to 12VAC one. Use the 120VAC to 12VAC one to power the filaments of the tubes and the nominal secondary of the 120/240VAC to 12VAC one. That gives you 240VAC on the nominal primary of the second tranformer. Then use a diode bridge to get appx. 350Vdc. The diodes can be 1N4007's, cheap and readily available. Filter caps will be in the 10uF to 22uF range, use one or two Pi section filters. |
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| 5/10/1999 9:29 AM |
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| Jim L. | Thanks AGain! I'll be scouting out the parts for this sucker.... |
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| 5/10/1999 8:42 PM |
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| Steve M. |
for RG: suitable PT? RG, I got thise cute little PT from Allied a while back, PN: 6K27VF. It is a 125v @15mA and has a 6.3v winding @600mA. Unloaded it puts out about 140v, and with a FWDB it puts out about 198v. Would this be suitable for a tube preamp pedal? I was thinking of using it for one. BTW it is about the size of a Fender reverb driver OT. TIA, Steve |
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| 5/11/1999 1:35 AM |
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| Jim L. | I have been searching the web for a small/medium sized transformer, any suggestions? Steves little tranny sounds cool,..any thoughts? Jim |
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