Shunt Regulator with 45's?

[gstitt]

Is the Stereomour II Shunt Regulator upgrade compatible with a conversion to use 45's?

Greg

[Jamier]

I'm thinking not, as is. I'm sure PJ will eventually post the changes required to convert to 45s. The regulated B+ for 45s is lower than 2A3s, I believe.

Jamie

[Paul Joppa]

Is the Stereomour II Shunt Regulator upgrade compatible with a conversion to use 45's?

Greg

It should work equally well.

The kit regulates only the driver (same as Paramount/Kaiju). Thus the only change is less voltage at the input to the driver's C4S plate load. There is way more than enough compliance even at the 45 voltages, even in the worst-case scenario.

[gstitt]

Paul,

Great news. I don't know that I'll necessarily do the 45 conversion, but I'm thinking about getting a pair of EML 2A3 Mesh plates, and I've been trying some different 2A3 operating points with lowered dissipation. I'm currently running at 278 Volts Plate to Cathode and 44 ma current. That's getting pretty close to the same amount of B+ drop that the 45's would run, so figured if 45's would work then I'd be safe with my current 2A3 setup. Just got word that my Shunt Reg kit has shipped. Yippee!

Thanks,
Greg

[Paul Joppa]

Greg-

Excellent!

When I designed the Stereomour II I thought about several mods, making sure they would be possible. None of them have been tried out yet, and we are reluctant to give details until we have tried them and listened to them. But for information, here they are:

* stock 2A3 300v plate to cathode 50mA 4K output transformer

* 45 running 275v 36mA 4K (stock) OPT

* 2A3 as 45 275v 36mA 4K (stock) OPT

* lean 2A3 300v 40mA 4K (stock) OPT

* 2A3 with Kaiju or Magnequest iron 275v 55mA 3K OPT

* 2A3-40 with Kaiju or Magnequest iron 300v 60mA 3K OPT (dissipation 18 watts, exceeds standard 2A3 spec)

It will be at least 6 months before we get to testing these variants, and no advice will be available until then. I just wanted to put it out there that I have considered these possibilities and they should work OK.

[Jamier]

PJ,

Is the Magnequest iron you refer to currently available or would that be a custom item?

Jamie

[gstitt]

Paul,

Such a great design you came up with, and amazing that you also thought out such future possibilities for it. My amp has sounded wonderful from day one. I only decided to tinker because of the interest in the EML tubes and their need to be treated gently. Well, that and my inability, like so many around here, to leave well enough alone :^).

I look forward to thoughts on the future mods. My take on what I have done is that the lowered operating point in my system ( Omega Compact Alnico Monitors with single driver and 95 db efficiency listened to near field in a small room) brings a bit more bloom, ease and dynamics to the sound. I suppose that might be some added second harmonic?

Thanks again!
Greg

[Paul Joppa]

PJ,

Is the Magnequest iron you refer to currently available or would that be a custom item?

Jamie

You would have to check with Mike on availability. I had in mind the TFA-2004 parafeed output transformer and the EXO-003. The TFA would need new mounting holes and must go on top; the EXO-003 mounts below because of the exposed terminals at high voltage. As I said, we have not actually tried any of these yet, so I can't promise everything will fit.

There are some technical issues with the old BH-5/BH-6 combination in the Stereomour II, so I am not recommending them at this point.

[Jamier]

PJ,

          When you test the different Voltage/Current/OPT combinations, and should you approve them, will we be able to buy the Kaiju iron ( as though it was an aftermarket part) ? I have no personal experience with Magnequest products, and I do feel that BH OPTs are pretty damn good so I would be inclined to try a BH part first, most likely.

Jamie

   

[Paul Joppa]

... will we be able to buy the Kaiju iron ( as though it was an aftermarket part) ? ...   

I expect so, but whether, where, or when is up to Doc B. Those are the decisions which keep him in the corner office. Early days yet!

[Jamier]

PJ (and Greg),

      I get how to lower the voltage, but how do you lower the current on the 2A3? Greg is at 44mA, which could just be the normal current of his amp, but how would you get it down to 36 mA? Or up to 60mA? This thread made me realize that the C4S/SR regulates the driver but not the 2A3, which
I should have known after building 2 of these.

Jamie

       PS:


      So, I'm not trying to answer my own question, but if V=I*R then I guess the resistance of the chosen plate choke choke has something to do with it? Well I guess someone will tell me. I'm real interested in this topic.

Jamie

[gstitt]

Hi Jamie,

You are on the right track with V=I*R, but look to the values at the cathode of the 2A3. The current drawn though the 2A3 is determined by the value of the resistor from cathode to ground. Dropping the power supply voltage drops the voltage at both the plate and cathode. In my case the voltage at the 2A3 cathode dropped from the stock 60 volts to 54 volts. Keeping the stock cathode resistor (1200 ohms) and using I=V/R, the result for 54 volts is 45ma of current. I wanted to try using some Mills 12 watt resistors instead of the stock ones so I paralleled two 2.5K values which gives a resistance of 1250 ( I measured an actual 1240) ohms, which calculates closer to 44ma.

Greg

[Jamier]

Greg,

     Thanks for that information. In my ignorance of circuit theory I totally discounted the effect of those parallel resistors on that end of the schematic. What is the effect of the 220uF cap in parallel with those resistors? Also, what values did you use in the PS resistors to get your voltage down to 54V.Did you change both 130s (per side) or just one?

     Jamie

[gstitt]

Jamie,

I don't think the cathode bypass capacitor will affect the 2A3 operating point voltage and current. I changed both 2 watt 130 ohm power supply resistors to Mills 5 watt 620 ohm ones. That dropped the voltage at the 2A3 plate to ~332 volts and at the cathode to ~54, which gives ~278 volts from plate to cathode.

Greg

[Jamier]

Greg,

     Thanks for helping me understand this part of the SII circuit. I have been considering the JJ 2A3-40, and now,  considering PJ's modification list, I wonder if it would be at it's best if run at 60 mA and in combination with the EXO-003/TFA-2004. If That iron can be had, I'm gonna' find out.

Jamie