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Yep @Bass trap, please tell and show us more.

@RickRycroft, just put some low or medium strength loctite thread locking compound on the nut closest to the motor. Make sure you screw the nut into the correct position after applying compound. You'll never have to think about it again.

Oh yeah, air caps are for treble only, and then really only with line level filters.

Filter caps I purchased in bulk multiple values from a US firm (0.001uF-0.68uF), but I was after a particular breed of polypropylene and foil high voltage capacitor (valve amps). They averaged something like $5 each and I spent a few hundred dollars all up, But I can mix and match and change to my hearts desire. The pF level air caps are modern production from a mob called OrenElliot. They are not inexpensive but you should shield them. Lucas Cant of Black-Art Audio wound and shielded my inductors to my specifications. He hated doing them because it is an iterative process. When an inductor is wound its values are pretty close but not quite perfect so he leaves a few taps up and down in say 1% intervals. Then they are potted into a steel and mumetal sarcophagus and the inductance values change again, and you just have to hope that they don't change so much that all the taps are outside the target range, otherwise it is back to the start to wind another inductor. Inductors are imperfect beasts, and are expensive and take up a lot of room in a build. Buy an unshielded inductor and shield it yourself and you will most likely change its inductance. Regarding measurement of inductors, capacitors, resistors, I use this meter. EDIT: Brian, you can parallel resistors to trim to exact values if you require. It's easy to calculate and measure. Air caps of course are adjustable within their range...you just have to measure them out of the circuit.

Yeah @BioBrian, that's the 4th order high pass filter set at 10khz. How to calculate them....that's easy. I have the "Electronic Filter Design Handbook" and I took the equations for calculating that particular "CLCL T High Pass Filter with unequal terminations - Fourth Order Butterworth - Infinite Termination" (simple when you say it like that haha) from within its pages and put it in an Excel spreadsheet, which also includes all the other types of much simpler filters that I have employed: low pass RC; high pass RL; bandpass RCL; low pass RRC; and the high pass coupling capacitor filter. Subtractive filters only. With those larger shielded inductors in the photo 1.241H and 0.298H are also two air capacitors set at 346pF and 490pf (yes picofarad). The filter is loaded by a 30k ladder type LPad. Do not fear the inductor...the inductor is good... capacitor is bad...reduce or eliminate the capacitor. EDIT: I should add that the caps used in my other passive line level filters range from 0.0047uF to 0.068uF with the large low passing at 78Hz. Tiny little suckers.

@A9X, yeah the bits add up. I have a 4th order highpass set at 10kHz using two air-caps and two inductors. It takes lots of space. ...like twice as much space as all the filters for the other five channels. 3rd or 4th order RC filters take next to no room. The caps are tiny and the resistors only need to be quarter-watters.

It's pretty simple Brian, you jam the filter at the input of the amplifier where the voltages are much smaller, let's say 2V max (4V in my case) and use the input impedance of the amplifier as the load for the filter rather than the reactive impedance of a speaker level crossover network and transducers. Then you direct connect your transducer to the amplifier. It keeps the filter component values much smaller, so tiny caps and inductors. In some circumstances you may even be able to build part of the filter into the amplifier itself. For example an interstage coupling capacitor can be sized such that it creates a first order high pass filter at the desired frequency. Couple that with a low pass filter before the amplifier and you have a bandpass filter. I've not yet read your thread Brian but the speaker photos on the front page look excellent.

Oops! Short circuit in the safety circuit. Safety circuits only work when you wire them up appropriately and what you see below is the result of a correctly wired circuit...well sort of, the ring connector on a connecting wire from a 450V 8,200uF capacitor was carelessly touching a hold down screw that was close by and managed to dump the capacitor to protective earth once the amp was turned off. There was a loud snap, a little bit of a welded bolt and some pcb trace that thought things were a bit hot. Talk about an inconvenient spot in the amp for repairs. It took most of a day to wrangle the board out, remove the components, solder them to a new pcb, and reinstall it and everything else that had to be removed to get to it. But before I dug into the amp I traced out the schematic of the good amplifier that I have been listening to for a couple of months now (which took a bit over a day) so that it might be easier to find the fault and the cause of the problem. So that is more than half of my Easter break that I had set aside to get this second DSET operational...bugger! Oh well.

I'll take all the brahms, Buckner, dvorak, britten please.

I'll take all the brahms, Buckner, Debussy,Copland,elgar,rimsky korsikov. Will pm.

Oops...just noticed that the filament of the 45 is 2.5V, not 4V as I mentioned above. Either way, it is doable. The circuit will determine what anode voltage you require and you should be able to drop 400V to whatever you require using a resistor, just so long as your transformer is able to supply the necessary current.

Looking at this again, 400V is could be too low for B+ and you will probably need about 55-60mA current from that winding...I don't know if you've got it or not. Knocking the 6.3VAC down to 4VAC/DC is trivial but you will have hum unless you (a) use AC heating from a separate transformer or (b) go for DC heating with something like a Coleman Regulator.

What you do is start with a high voltage and then filter it with inductors, capacitors and resistors ending up at the required voltage for the tube. For example, for my 45/2A3/YO186/RE604 amplifier the B+ from the transformer is 455VAC which is rectified with Cree Schottky's then an LCLCR filter which leaves 405VDC at the anode of the power tube. Your tech friend should know this...the final resistor sets the voltage B+ voltage. If for the driver tube you need to reduce that voltage then just use a RCR filter to drop to (in my case) 140V for the 6E6P.

400V for B+ should be fine, assuming it is capable of providing enough current. Being a DHT, under all circumstances I would run a separate transformer for the heater especially if you use AC heating (which I do).

Here you go. Of course I've not heard it or any of its variants, but it should be very good. Which circuit you actually have built depends on how you are going to use the amplifier. In my case I have a 2.5V/4V DHT circuit for my midrange channel only so can get away with a direct coupled circuit because it does not have to handle bass. The result is stellar. Being single ended, the output transformer should match both the speaker load that it is driving and the load required for the 45 tube which happens to be the same for both the 2A3 and 45's...so worry most about getting the best output transformer for your particular job which is where you should sink most of your $$$. The OPT is the biggest determinant of sound in the entire circuit so get it right. The multi-tube 45/2A3 circuits are just as perfectly capable as a specialised circuit for either valve so certainly do not look past them.