Mercury Power Supply Design - Checking for Efficacy

[Paully]

Gave up the mercury rectifiers, just too much trouble.  Modelling on PSUD a Pi filter with the following parameters to feed a 45 amp with 76 drivers and a voltage regulator with a GZ33.  Planning on a rail for each driver tube and output tube, which is hard to model on PSUD but essentially the first cap totals to 50u for all rails combined.  Going to use a 475-0-475 transformer (need about 425V out on each rail for what we are planning.  The CLC filter for each 45 is 15u/20H(181 ohms)/20u.  For the 76 it is 10u/10H(270 ohms)/20u.  PSUD doesn't seem to have any issues with what we have done for warnings.  Anyone see a problem such as too taxing on the rectifier, etc...?  Any thoughts are welcome.

[Grainger49]

Anyone trying to check this with PSUD II will need to use a 50uF cap for the first cap in the string.  Without that the instantaneous current will be too high.  I figured that was only a little cheat.

To clarify there are 2 rails/filters for the output tubes and two rails/filters for the driver tubes

We are hoping that the 76 will have enough voltage swing to get the 45s to a comfortable volume (note not to clipping) with Paully's speakers, 100dB+ sensitivity.  He doesn't listen loud at all.  We do not ever want the 45s to produce maximum power.

[ALEXZ]

According to GZ33 datasheet C max = 60uF. Also with 475+475  and capacitor  input  it will be around 465v DC on the first cap.   Looks like HT for 45 is OK.  10H choke probably is not enough for 76 to filter properly. You may need to enlarge capacitors and add load to get more current through the choke.  
Here is the datasheet http://www.r-type.org/pdfs/gz33.pdf
BTW,  why 4 HTs ?
HTH
Alex

[Paully]

The plan is a choke for each rail so we have 4 chokes (2 for each 45 and 2 for each 76).  Does that explain the 4 HT (I am drawing a blank on HT, sorry)?  We will do a lead off 15u cap for each 45 and a 10u for each 76 (total of 50u leaving us well under the 60u total).  Do you think bumping it up to 20H on each 76 would be enough?  We can certainly bump the end capacitors to get more smoothing on each rail as well, I don't think that would hurt anything.  I will go try that on PSUD.  Thanks!

[ALEXZ]

Ok. Let's talk about one amplifier. I presume we are talking about 2x mono,right ?
So, you have one full wave rectifier (correct?),capacitor loaded ( that is the cap. With max value 60uF). What's next ? L-C-L-C where first half of the filter loaded by 45 and 2nd by 76 ? Or parallel lL-C for 45 and L-C for 76 ?

[Grainger49]

Alex,

This is a stereo amplifier.

There will be one power transformer for the B+ (500V-0-500V) feeding a single GZ33 (dual rectifier).  That will feed four filters, driver and output tubes, right and left channels dual mono after the rectifiers.  This is an old Bottlehead trick of PDMPS (pseudo dual mono power supply).

So when we talk about the 50uF that the rectifier "sees" it is the total of the four input caps.  Then each string will have a choke and a film cap to feed the voltage to the tubes.

Does this make sense???

[Paul Joppa]

Sorry I missed the switch - you are now looking an a CLC filter instead of LC or LCLC? That will increase the power supply voltage 35-40% - like, 600v or more from a 500v winding. That's a LOT, and way too much for 76s or 45s.

Am I missing something?

[ALEXZ]

Grainger,
Now I'm lost .... How rectifier " sees" four capacitors ? If rectifier is loaded by capacitor, it's one capacitor, never mind if it is made out of four parallel connected capacitors. If rectifier is loaded with LC, there are no capacitors at all, rectifier "sees" inductors first. Also, with regards to  dual mover supply (psudo or otherwise), I'm not clear why driver and output tube need to have separated filters.
Speaking of output voltage, "Typical operational conditions" for GZ33 shows with 500v AC and C load (from 8uF to 60uF) output voltage 479-493 v DC with 250 ma (!!!) current.
I not really comfortable making recommendations, i hope Paul will comment, but with 1000vCT transformer, the way to go is LCLC or LCRC for each side with additional R for bleeding.

[Grainger49]

Paul,

We modeled this on PSUD II with a GZ33 rectifier and the 500V transformer.  We didn't get that high a voltage out at all.  We had started with a 375V transformer and had to keep increasing the voltage.

I think it would be best if I can somehow post the circuit from PSUD II.

Alex,

The four capacitors are the first caps of the CLC filter.  They are all across the rectifier's output so they sum to 50uF.  If we model with a 15uF cap the rectifier has too high an inrush current.  So we were modeling with the 50uF as the input cap.  I made no mention of an LC filter above.

Here is a link for the PDMPS on VoltSecond's site to catch you up:

http://www.siteswithstyle.com/VoltSecond/PDMPS/pseudo_dual_mono_foreplay.html

I don't understand your emphasis on 250mA current, is it necessary to draw full current to get the 479-493V output?

There will be a ~0.5M ohm bleeder on each B+ leg.

[ALEXZ]

Not sure what  PSUD II shows. Did you design four separeted CLC filers with it ?  Anyway rectifier GZ33 with 50uf input and current much less then 250 ma will give you  from 1000vct transformer voutage higher then you need.  
250 ma is important to get voltage drop on internal resistance of rectifier. Lower current, smaller drop.
Put GZ33, 1000vct, 50uf and current of 2x76 +2x45 into PSUD and check what voltage you will get.
Bleeder resistir: 500k - it's  less  then 1 ma , won't help to much with rectifier/ filter load.

[Grainger49]

Since there are pairs of rails, one pair for drivers one pair for 45s, we only looked at two CLC filters, so we did cover all four.

So you are saying that we need more current drawn through the rectifier to get a lower voltage, right?

I'll try to post PSUD shots later today.

We are not looking for the bleeder to be part of the load, just a safety device.  Most Bottlehead equipment, maybe all, has a bleeder of 400k+ ohms.  It is simply for bleeding the PS dry when you turn it off.

[ALEXZ]

Grainger, just look at the first stage of the power supply. You have 2x500v AC, full wave rectifier loaded by 50uF capacitor. If you have no load and no losses in the rectifier, you will get ~700v DC on the capacitor. Now you're loading this PS with 4 tubes via LC filters. That's were current starts to play a role. All of the voltage drop will be on the rectifier (there are relatively  small voltage drop on the DC  impedance on a choke in CL filter, as opposite  to LC).
I downloaded this PSUD software. With 1000VCT/GZ33/47uF/3H/47uF/120ma load  PSUD shows 600v output.

[Grainger49]

Alex,

Thanks, I have decided, for some reason, PSUD is not computing properly on my computer.  When I "simulate" I can not read the scales, neither the left side or the bottom.  I see what you are saying.  The resulting voltage is too high.  And I'm with you, there is only a drop in voltage across the inductor if there is appreciable current.  Since there is not much current total here.  I would guess less than 100mA.  We wanted a Beefy power supply. 

Since I can't run PSUD well on my computer, what transformer voltage would you suggest for a 425V output?

Your trace is on the first cap and not after the inductor so I won't worry about the ripple.  How did it look on C2?  Was it smooth? 

BTW, how did you get a JPG of the screen???  I'm not much of a computer guy.  I'm old!

[ALEXZ]

Ok. Last thing first. Whatever screen is active, you press alt+contr+shift+print_screen and after that go to whatever image apps you like (Microsoft Paint will do) and paste into into apps (could use contr+v)
Control+shift+print screen will cupture entire screen, with ALT only wiindow "in-focus"

For 425vDC after gz33 with C input, gz33 datasheet shows 2x375v AC (750vCT).
I installed PSUD in the office. Will let you know what's data I can get from it tomorrow.

[Grainger49]

Thanks for it all!