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Hello folks,

On my Mark III stereo build, I'm using and Antek 400v 200 ma toroid, SDS cap boards and Poseidon driver boards. When I look at the connections, Poseidon wants 330v (J) and 430v (K).

Using the Duncan Amps PS Designer, I run the values (both stock and SDS), and the voltages at all B+ points on the four filter caps are way too high (SDS), or way too low except for first stage plate voltage (Stock).

Question: Does it make any sense to use a big dropping resistor on the AC or DC side of the 5AR4/GZ34? And, secondly, to adjust the voltages at the other test points can a resistor be placed in series before or after a choke?

Using PS designer, I was able to work the voltages perfectly, but not without a supplemental resistance in series with the 1.5H 55ohm choke.

Ideas and help would be appreciated on the concepts. Thereafter, I'll try to run the values again and let you know what I find.

Thanks as always,

Chris

Run the PSU II but use a 5U4 rectifier instead of the 5AR4. If that isnt close pick another rectifier tube with similar current and voltage ratings. The 5AR4 has a very low forward voltage drop.

mesherm wrote:Run the PSU II but use a 5U4 rectifier instead of the 5AR4. If that isnt close pick another rectifier tube with similar current and voltage ratings. The 5AR4 has a very low forward voltage drop.

Thanks, I always seem to overlook the simple approach first. I'll check it out.

Appreciate it, as always.

Chris

ChrisK wrote:

mesherm wrote:Run the PSU II but use a 5U4 rectifier instead of the 5AR4. If that isnt close pick another rectifier tube with similar current and voltage ratings. The 5AR4 has a very low forward voltage drop.

This was the perfect solution. The 5U4GB has a voltage drop of about 50V whith 400V going in. When I plugged it into the simulation, everything fell into place: 480V at the first stage, 445V second stage and 430 at the third stage. A dropping resistor will bring the 445V down to spec at around 430. Everything fits nicely within the tube datasheet parameters.

Anyone else that wants to try the 5U4 series needs to be aware that the filament requires 3A instead of the usual 2A for the 5AR4/GZ34. Also the first input cap should not exceed 40uF.

Thanks again Mike...even though now I'll need a couple of new heater transformers and tubes. It's worth it to me just for the simplicity of it.

Best,

Chris

Hello all,

Does anyone have any information about the milliamp value to be used for a Poseidon board to calculate the value of a drop down resistor?

My B+ supply will be 450V, but I need to get that down to around 430V. Normally, I could just adjust the value of the RC filter section, but this one's an LC.

Thanks,

Chris

Well the PI will draw about 8 ma and the VA will draw about 2 to 3 ma so try a 2000 ohm resistor and a 10 to 20 uf cap. I usually start with a higher resistance since adding another in parallel is easier than clipping the old one out. 2K should be very close for one monoblock.
Another trick would be to use a 20 volt 5 watt zener.

mesherm wrote:Well the PI will draw about 8 ma and the VA will draw about 2 to 3 ma so try a 2000 ohm resistor and a 10 to 20 uf cap. I usually start with a higher resistance since adding another in parallel is easier than clipping the old one out. 2K should be very close for one monoblock.
Another trick would be to use a 20 volt 5 watt zener.

Thanks for the help! That's a much lower demand than I would have thought.

Thanks for the tip about series resistors, I'd start with a value on the high side also just to protect my stuff. I might just breadboard a bit before soldering just to make sure.

OTH, the Zener makes a lot of sense too. Haven't used them before but this would be a good time to learn.

As always, I appreciate your advice.

Chris