Royer MXL2001 build cont'd

[Migs 31]

https://www.gyraf.dk/gy_pd/g9/g9pd.htm

Thanks Kron,
I saw that one too. Just that Kev's one looked a bit simpler (less parts count).
As for noise on the power line?!? Guess I have to build and try ?

M

 

[Khron]

I only meant to validate the principle. Kev's one does indeed contain only one stage of passive filtering (as opposed to Jakob's regulated and protected one), so you may or may not want to add some of your own.

 

[Migs 31]

I only meant to validate the principle. Kev's one does indeed contain only one stage of passive filtering (as opposed to Jakob's regulated and protected one), so you may or may not want to add some of your own.

Yeah, I got your idea.
Kev referred to Jakob in his post too.

I was thinking that one (or a variation) or go for the Dave Royer multipler (Quad in my case) But I can see diverging opinions and even a bit of opposition in some members concerning multipliers. I get it.
In any case thanks for you quick reply/input.
M

 

[Khron]

I guess it depends mainly on choice. Do you wanna try to use what you have at hand in your parts bin NOW, be it a second (suitable) transformer, or diodes & caps? Or do you wanna order parts for either path?

"Same-same, only different" - AvE

And/or "it's how you use it"

 

[rock soderstrom]

Yes. He does do that. But he told me that he went with the wall wart and voltage multiplier because he didn't want any possibility of liability, and specifying a UL-approved wall wart, at least according to him, got him around that.

Terry, I believe you. I would still advise against it because of the lack of PE. This is possible with a fully encapsulated enclosure, but not with a microphone, as you have a free-standing metal housing. In the event of a fault, B+ can be applied to the body and no protective mechanism will be triggered.

And, as we saw in doorunrun's video, audio frequency noise was not a significant problem.

This is independent of the safety issue.
I must say I was surprised how clean the Royer Tripler PSU of doorunrun is!

Here is my PCB design of the Royer tripler, I modified a few things, mostly to work with my existing parts and have some ripple filter reserve for other mic projects as well. I have divided up the thermal load in the heater circuit a little more. @doorunrun , do your 5W resistors get very hot?



When I've tested the PCB I'll post it here and make the design available.

 

[doorunrun]

@doorunrun , do your 5W resistors get very hot?

rock,
No, not too bad. But, I'm glad the PC power supply enclosure has all that ventilation. I will try taking some readings. The 5840 tube draws ~150mA, so for a 100R resistor that'll be ~2.25W.

 

[rock soderstrom]

rock,
No, not too bad. But, I'm glad the PC power supply enclosure has all that ventilation. I try taking some readings. The 5840 tube draws ~150mA, so for a 100R resistor that'll be ~2.25W.

Thanks!

Are these 5W or 10W types? I can't really tell from the photos.The idea was to distribute the heat a little better so that my electrolytic capacitors are not cooked

They are also relatively large and would have been difficult to fit on my circuit board.

I have also installed bleeder resistors for B+ and filament. It seems that some User had problems without it in the past.

 

[doorunrun]

These are 5W wirewound resistors.
I put my DMM's temperature probe directly on the 110R resistor (the physically larger of the two) and measure ~75C or 168F degrees. This was after the supply had been turned on for about 10 minutes.

I haven't installed a bleeder resistor, but it's a good idea especially for B+. If the mic stays attached to the power supply the filament voltage will drop pretty quickly when power is shut off.

 

[rock soderstrom]

These are 5W wirewound resistors.
I put my DMM's temperature probe directly on the 110R resistor (the physically larger of the two) and measure ~75C or 168F degrees. This was after the supply had been turned on for about 10 minutes.

Okay, that's already nice and warm! If the electrolytic capacitors are in close proximity, as in my case, they are already negatively affected.

I haven't installed a bleeder resistor, but it's a good idea especially for B+. If the mic stays attached to the power supply the filament voltage will drop pretty quickly when power is shut off.

Yep, the problem was apparently (in a user report from the past) that the mic was unplugged immediately after use and then there were serious problems when it was plugged back in after a certain time. I can't find the forum post that described this at the moment, but I think B+ bleeder is basically a good thing.

The bleeder for the heater voltage is actually the series resistor for the status LED.

 

[doorunrun]

Okay, that's already nice and warm! If the electrolytic capacitors are in close proximity, as in my case, they are already negatively affected.

Holding one's hand above the case you wouldn't think it's that hot. Those resistors are rated for 155C max.
I have them elevated off the PC board; always a good idea.

I see what you mean about the electrolytics. I'll dangle the probe closer to one of them.

Addendum: Measuring temperature near the first electrolytic I'm getting 29C or 80F.

 

[Tubetec]

Ive tried the step-up-down transformer thing , with smaller transformers ,
and they tend to get quite hot ,
Smaller transformers have poorer regulation and more losses , placed back to back as we can see the losses become even more serious ,
Kev is driving a 6V transformer with a 9V winding and still not making anywhere near the full voltage a proper 230v secondary would give ,
the other thing is the losses , the energy has to go somewhere and most likely it ends up causing current spikes which make noise harder to filter .

With the back to back arrangement ,you also have a possible see-saw interaction between the two rails , depending on what current is being drawn .

If your running off 230V mains ,do yourself and your tube projects a favour ,
re-purpose a 220/110v 20VA shaver socket as a HT transformer ,
It can get you a very well passively filtered HT in the region of 300 or 150v ,
series resistances adjusted to suit the individual circuit needs ,
Currents in the region of 15-20 mA , it will supply without even breaking a sweat .

The nice thing about using the shaver socket is its has to pass proper safety approval to be allowed to be sold , it comes set up for a really good PE bond to the enclosure .
All you need to do is add a fuse , three core mains cable and assuming everything in your mains installation is upto to spec is as safe as it can possibly be .

Theres a lot to be said for seperate HT/LT transformers ,
I dont trust the insulation on toroids with HT/LT windings ,
An old fashioned mulitwinding E-I power transformer for tube gear ,if its properly made , employs a winding geometry that sheilds and insulates HT and LT windings from one another , I dont see how thats even possible with a toroid . The adjacent windings in a toroid are heavily capacitively coupled , that would seem to me to be leaving the door wide open to all kinds of mains bourne garbage ,as well as possible unwanted interactions between HT/LT lines .

 

[rock soderstrom]

I have them elevated off the PC board; always a good idea.

+1

Addendum: Measuring temperature near the first electrolytic I'm getting 29C or 80F.

That’s almost nothing. I guess this will not affect the lifetime of the electrolytic capacitors in any negative way. Air is a pretty good thermal isolater! I would have expected more temperature on the capacitor surface, I am positively surprised.

 

[Tubetec]

Something you notice in really good tube mic power supplies ,
they use chassis mounted HT dropper resistors , that way a lot of the heat is conducted away via the metalwork .
The modern metal clad wirewound power resistors are a good equivalent but require more deck space to mount .