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Audio and Video Talk
Valves / Vacuum Tubes
Having tube preamp Transformer wound questions
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<blockquote data-quote="handsome" data-source="post: 946776" data-attributes="member: 772"><p>Aha. Then 200V will probably do - 200mA is absurd. As a thumbsuck both channels of that preamp will draw about 4mA! So you can spec 200V@50mA. Since its a phonostage you will need a quiet power supply - are you planning on using a choke in the PSU? i strongly recommend regulated DC heaters (1x LM317T+resistors+capacitors+some stripboard is not expensive) because it is a phonostage, so spec 9V@2A minimum. Look at getting an isolation transformer (220V:220V) plus a 9V 2A/3A transformer, these are off-the-shelf items so total cost could be cheaper than the R600 you have been quoted? Also think of your layout, phonostages are susceptible to interference so if you planning on a single chassis you will need space between transformers and circuit.</p><p></p><p>12AX7s don't make great line drivers (cathode followers) as they can only do a one or two milliamps standing current - this design has the cathode follower doing ~0.5mA. I would substitute a 12AU7 for V3 and run it at >5mA (change R7 to 18k-27k) you need some current to drive the capacitance of cables plus the input of your pre. </p><p></p><p>Don't let any of the above put you off. Building valve amps/preamps is a lot of fun and surprisingly simple. I built my first valve phonostage on two pieces of off-cut aluminium (pre and psu) and used them like that for 4 years then over about 6 years i put boxes around them, removable connecting cable, mute delay, regulated HT, changed the cathode follower three times, ditto the PSU....you get the picture. They do look like crap though so a bit of planning will get you something that looks and sounds good.</p></blockquote><p></p>
[QUOTE="handsome, post: 946776, member: 772"] Aha. Then 200V will probably do - 200mA is absurd. As a thumbsuck both channels of that preamp will draw about 4mA! So you can spec 200V@50mA. Since its a phonostage you will need a quiet power supply - are you planning on using a choke in the PSU? i strongly recommend regulated DC heaters (1x LM317T+resistors+capacitors+some stripboard is not expensive) because it is a phonostage, so spec 9V@2A minimum. Look at getting an isolation transformer (220V:220V) plus a 9V 2A/3A transformer, these are off-the-shelf items so total cost could be cheaper than the R600 you have been quoted? Also think of your layout, phonostages are susceptible to interference so if you planning on a single chassis you will need space between transformers and circuit. 12AX7s don't make great line drivers (cathode followers) as they can only do a one or two milliamps standing current - this design has the cathode follower doing ~0.5mA. I would substitute a 12AU7 for V3 and run it at >5mA (change R7 to 18k-27k) you need some current to drive the capacitance of cables plus the input of your pre. Don't let any of the above put you off. Building valve amps/preamps is a lot of fun and surprisingly simple. I built my first valve phonostage on two pieces of off-cut aluminium (pre and psu) and used them like that for 4 years then over about 6 years i put boxes around them, removable connecting cable, mute delay, regulated HT, changed the cathode follower three times, ditto the PSU....you get the picture. They do look like crap though so a bit of planning will get you something that looks and sounds good. [/QUOTE]
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Audio and Video Talk
Valves / Vacuum Tubes
Having tube preamp Transformer wound questions
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