160v tube PSU

[amptramp]

I have two receivers, an H. H. Scott 340B (late schematic) and a Trio KW-55 that use DC only for the heaters in the phono preamp stage.  This stage deals with signals on the order of millivolts.  If you use AC, there is some 60 Hz that gets into the signal.  If you use DC, you get no 60 Hz but rectified, filtered DC will have 120 Hz, 180 Hz, 240 Hz etc. harmonics that are more audible.  If you use a guitar amp with limited response below 82 Hz (the lowest guitar note), you may be better off with AC.

[Hatredman]

I still think this would be way simpler if you just use the one transformer you mentioned originally with the 6.3 and "160v" secondaries.

I second that. Why use a hot resistor (and its problems) when you can use the proper solution?


--
Scarlett Johansson uses a Burst Box with her Telecaster.

[thermionix]

I have two receivers, an H. H. Scott 340B (late schematic) and a Trio KW-55 that use DC only for the heaters in the phono preamp stage.  This stage deals with signals on the order of millivolts.  If you use AC, there is some 60 Hz that gets into the signal.  If you use DC, you get no 60 Hz but rectified, filtered DC will have 120 Hz, 180 Hz, 240 Hz etc. harmonics that are more audible.  If you use a guitar amp with limited response below 82 Hz (the lowest guitar note), you may be better off with AC.

My home stereo is a 1962 HH Scott 222(A), just an integrated amplifier not a receiver.  The preamp uses four 12AX7s (two for phono only, two for everything).  The preamp tubes are heated with DC that is pulled from the cathodes of the EL84 power tubes, making the preamp heaters K resistors also.  There are other resistors is series (IIRC) and bypass caps in parallel with that.  It is quiet as can be, you can barely hear a hiss with it cranked all the way up and your ear in the speaker.  I worked an old Danelectro guitar amp once that did that too.  Pretty cool, DC without rectification.  Not a single solid state component in the whole amp.  Not really relevant to this thread, but still a slick idea IMO.

[PRR]

> preamp tubes are heated with DC ...It is quiet as can be, you can barely hear a hiss

DC heat avoids AC hum, not hiss.

The Scott 222 (if healthy) doesn't hiss much because it doesn't have any excess gain.

[thermionix]

DC heat avoids AC hum, not hiss.

Yeah I know.  That was my point.  No hum.

[amptramp]

I have two receivers, an H. H. Scott 340B (late schematic) and a Trio KW-55 that use DC only for the heaters in the phono preamp stage.  This stage deals with signals on the order of millivolts.  If you use AC, there is some 60 Hz that gets into the signal.  If you use DC, you get no 60 Hz but rectified, filtered DC will have 120 Hz, 180 Hz, 240 Hz etc. harmonics that are more audible.  If you use a guitar amp with limited response below 82 Hz (the lowest guitar note), you may be better off with AC.

My home stereo is a 1962 HH Scott 222(A), just an integrated amplifier not a receiver.  The preamp uses four 12AX7s (two for phono only, two for everything).  The preamp tubes are heated with DC that is pulled from the cathodes of the EL84 power tubes, making the preamp heaters K resistors also.  There are other resistors is series (IIRC) and bypass caps in parallel with that.  It is quiet as can be, you can barely hear a hiss with it cranked all the way up and your ear in the speaker.  I worked an old Danelectro guitar amp once that did that too.  Pretty cool, DC without rectification.  Not a single solid state component in the whole amp.  Not really relevant to this thread, but still a slick idea IMO.

My Trio KW-55 is like that.  The four EL84/6BQ5 cathodes are connected together and taken to the series heaters of the two 12AX7's with an additional 330 ohm resistor from the cathodes to a tap and 270 ohms to ground.  The tap is the supply to the 6BQ5 grid resistors.  The cathode bypass is 40 µF.  It all sounds good!

[thermionix]

So, putting +DC on the 6BQ5 grids?  As in control grids?  Now I'm confused.  It's not the first time.

[PRR]

> putting +DC on the 6BQ5 grids?

The cathodes are two-12AX7-up, or +25V.

The 330:270 divider gives 11V up.

The grid-cathode of the 6BQ5 "feel" the difference, 14V.

[thermionix]

Figured it was basically that, K maintained xx volts positive relative to g1, but I've never seen it done like that before.

[HeavyFog]

On a side note I noticed that kingsley tube pedals take a lower voltage (12v on some models) and step it up to voltages suitable for tubes. Not entirely sure what's going on there but I do see a 10uH inductor and what I think is a power inductor. Either way it looks like no power transformers are used and it looks relatively simple. Maybe something similar to that could work great for getting high voltage for a tube from a low voltage source

[nonoxxx]

I live in France and how all the informations you said  can be applied for 220 V ? for example to get a 160 V rail for tubes ?

[amptramp]

On a side note I noticed that kingsley tube pedals take a lower voltage (12v on some models) and step it up to voltages suitable for tubes. Not entirely sure what's going on there but I do see a 10uH inductor and what I think is a power inductor. Either way it looks like no power transformers are used and it looks relatively simple. Maybe something similar to that could work great for getting high voltage for a tube from a low voltage source

They may be using a flyback supply that is probably the most efficient choice for power under 50 watts but above the levels you can get from a 7660-type switched capacitor supply.  This design pulls current through an inductor then opens the circuit so the voltage rises like the coil in an ignition system.  Feedback is used to regulate the voltage.  It is more efficient than switched capacitor and generates less electrical noise.