Royer Mod PSU Troubles

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sethinspain

Active member
Joined
Dec 18, 2011
Messages
36
Happy holidays gdiyers,

I've been steadily working on a MXL 2001 giving it the royer mod and was enjoying the process until the past 48 hours more-or-less.  I have searched quite a bit and can't seem to find the same problem so either this is blatantly obvious and I am missing something here or there is a problem thread and I haven't yet found it...

I'm having problem with the heater voltage rail on my PSU.  Unfortunately, there is no schem available outside of the Tape Op issue, but I put a link to a photo below.

With no load, the heater rail I have runs at 36Vdc, this is I guess normal. However, if I plug in my mic after running the PSU with no load, the voltage fries the 5840 sylvania tube filament.

The problem is that no one else seems to have stated this problem. Granted, I could make an effort to always plug the mic in first before I plug in and turn on the PSU to avoid the caps getting to 36V under no load, but that seems like a headache and as if the purpose is defeated here. Did Royer really design this thing so that you had to always have the mic plugged in first without turning it on?

I have fried 3, yes 3, 5840 tubes because of this error. I always start my PSU to check voltages and make sure everything is kosher, then turn off, then plug in mic, then turn on again. Luckily, last time I had the sleeve off of the mic still and saw the results with my own eyes; a very bright blue flash and then reading open between pin 3 and 6 on my DMM. I wasn't sure what was happening before then.

Here is my solution to try and combat this: I put in a 6z2 zener diode right before the connection between the corresponding XLR pin that carries heater voltage and after the last resistor in the heater rail, and it dropped the voltage unloaded to a whopping 4.3V, and with the mic plugged in to a ridiculous 2.7V. I thought this would be my solution but to no avail.

All I wanted to do here was give myself a bit of protection just in case in a session someone flipped on the power switch without plugging in the mic. I wanted to do this without having to totaly redesign the PSU (which I am not capable of doing, I'm still green at electronics). I also have 7z5 diodes but my local electronics store only carries 6z8 (ideal here) at 10 watts and for 5 euros a piece (I live in Spain).

I don't see an available schematic but here is a photo of what my PSU looks like to try and give you an idea. It uses a tripler to get the B+ between 93-100V and then uses a 100R and 82R in series (5 watters here) to drop the voltage down to a usable 6V +/-.

http://www.google.es/imgres?q=royer+mod+mxl+2001+psu+schematic&um=1&hl=en&sa=N&tbo=d&biw=1024&bih=677&tbm=isch&tbnid=w5UxNcURD2I50M:&imgrefurl=http://messageboard.tapeop.com/viewtopic.php%3Fprintertopic%3D1%26t%3D53130%26postdays%3D0%26postorder%3Dasc%26start%3D0 %26fini sh_rel %3D-10000&docid=Bc9jSsouOP-VVM&imgurl=http://www.organissimo.org/pub/603s/royer603s5.jpg&w=600&h=619&ei=fEzpUIbYFaS80QW224GgAw&zoom=1&iact=hc&vpx=4&vpy=172&dur=1809&hovh=228&hovw=221&tx=93&ty=121&sig=115708942658352515364&page=1&tbnh=147&tbnw=154&start=0&ndsp=23&ved=1t:429,r:6,s:0,i:106

So, is there anyway around this to stop frying my tubes or is it that I must keep the mic plugged in after the caps have fully discharged and THEN turn on the PSU?

Thanks in advance.
Seth
 
sethinspain said:
I'm having problem with the heater voltage rail on my PSU.  Unfortunately, there is no schem available outside of the Tape Op issue, but I put a link to a photo below.
As you made the mike & PSU, you must have a circuit.

If you have no circuit, you have no idea what you've made so we have a problem figuring that out too.  :eek:
 
You should always connect a tube mic before you turn on its PSU and it could be a good idea to let the mic stay connected a while after shutting off as well. Especially if you intend to poke around!  ;)

 

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If you use the PSU that Sredna posted, ALWAYS connect the mike before switch on.  The last 3m3 cap will charge to 35V and zap the heater if you plug the mike in later.

Here's an easy mod to the Heater supply which will probably make it safe to hot plug.  Change 2 resistors and add 1.
 

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Ricardo and Anders are on the money as usual.

It has been a few years now since I built this circuit, but on some occasions I used a 7805 or 7806 regulator off the 35V supply to protect the tube.

You are still dropping 30V so quite a bit of heat is generated - it will need a heat sink on it, or attach to the PSU chassis.

I put a big resistor between 35V and the regulator to reduce the voltage. I have 220 ohms in my head, but it was a long time ago. Your mains transformer will be different so trial and error time!

Those tubes are all still working after 6 or 8 years (which is more than can be said for some of the toroidal transformers).

Cheers!

Stewart
 
Built the same power supply for a 5840 tube. In order to protect the microphone, a 200k !/4 watt resistor was installed from B+ to gnd. & a 20k 1?4 watt from Filament + to gnd.

This will bleed down the voltages very quickly after the power has been turned off & avert any future tragedies. The 82 ohm 5 watt resistor can be followed by a 6 volt regulator & will eliminate any chance of exceedeing the tubes heater spec. should you plug into a circuit that is running more than 121vac.
 

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