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Old 9th February 2013, 02:20 PM   #11
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ranhaber:

To tie-off the unused transformer taps, I just soldered them to an unused lug on a terminal strip so they don't touch anything. They are not used. If you use the XPWR131, you'll have a least one set of HV taps to tie off, as well as a filament center tap.

The 10H choke is an excellent choice, the DC resistance of the choke has an effect on your final B+ voltage. If you are curious about the B+, download Duncan Amps PSUDII and model it, it's very easy to use. You can adjust the B+ somewhat (if required) by the choice of the first cap in the PS. You just need to be close to your target voltages, tubes have a little wiggle-room as long as you do not exceed their max dissipation ratings.

The TSE uses the 6.3 volt tap to power the 5V regulator for the 5V (or 2.5V) filaments. The regulator requires some voltage "head room" to operate (ie if the supply voltage to the reg gets too close to 5V it cannot regulate properly). That's why the 6.3V tap is used. That extra voltage times current equals excess heat that needs to get dissipated in a heat sink.

Some 300B's use more current than others, so the ones that draw more current will run the regulator hotter. You'll want a good sized heat sink one the regulator; the cooler it runs the happier it'll be.

The regulator heat sinks are in the lower right corner of the picture. Bigger is better, in my build, the components are on the bottom of the PCB and I am a bit limited for space.
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Last edited by boywonder; 9th February 2013 at 02:25 PM.
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Old 9th February 2013, 09:18 PM   #12
rknize is offline rknize  United States
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1) Just cover the end of the wire with some electrical tape or heat shrink tubing and tuck it away somewhere. As boywonder said, you can also attach it to an unused terminal somewhere. In the end, they will not be part of the circuit.

2) I used a Hammond 193J, IIRC, which has a 82 ohm DCR. Your's has a 75 ohm DCR. The DCR (DC resistance) of the choke has a part in the final B+ voltage of the filter. George's design specs a 150 ohm resistor if you are not using a choke. So a choke tends to make your B+ a little higher unless its DCR is 150 ohm. It just so happens that the Triad Magnetics C-14X has a 150 ohm DCR and is also quite cheap. A lot of people use the C-14X in SSE, TSE, and SPP builds. You can see the Hammond behind the Edcor XPWR131:

Click the image to open in full size.

3) I will post it on my site when I get a chance and give you a link. I get asked for that a lot.

As for the output tube heaters, it's as boywonder said. George's design uses a linear regulator IC to supply a very quiet 5V to the 300B heaters (2.5V in the case of 45s). Such IC's have what's called a drop-out voltage, which is the lowest voltage between the IC's input and output under which it can operate. This particular IC has an unusually low drop out voltage, which works well in terms of efficiency. The heat sink that George specifies for this application had 45s in mind. 300Bs draw much more current, which causes the regulator to dissipate more heat. It will shut itself down if it overheats. Thus the need for a larger heat sink in most applications.

Last edited by rknize; 9th February 2013 at 09:20 PM.
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Old 9th February 2013, 09:24 PM   #13
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Thanks you all for your detailed answers :-D
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Old 14th February 2013, 03:10 AM   #14
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Ranhaber: Here is a basic PSUD model for your Tubelab SE power supply.

Once you have this circuit in PSUD, you can modify cap values, resistor values, choke values, etc. and see what B+ and ripple voltage you end up with. The smaller the ripple voltage, the better. However, you will find that it won't go to zero with practical capacitor values.

I modeled this with your proposed 360-0-360 transformer, and you can see that the B+ is around 440V, a little high.

Several assumptions were made here; the DC resistance of both the Edcor Transformer and choke are guesses. If the DCR for these parts is lower, the resulting B+ will be higher than shown....and higher DCR=lower B+

Here is a brief overview of setting up and using PSUDII:

Each stage/section of the schematic can be modified by right-clicking on that stage/section.

Each component value can be modified by right-clicking on the component.

Start by right-clicking on the transformer section and select vacuum tube full wave.

right-click on the capacitor section and insert an LC filter

right click on the 5K load section and change to constant current

Then right-click on individual components to change their values, and select V(I1) and click simulate to see the voltage at the constant current load.

The 164ma constant current load is (70ma x 2) for your 300B's + (12ma x 2) for the 5842's. I've neglected the current though the mosfet followers for simplicity. These results should get you in the ballpark.

You can reduce the value of the first cap to reduce B+. Below about 8uf or so the B+ will begin to drop.
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Old 18th February 2013, 02:36 PM   #15
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More questions:

1) If i'm puting small cap like 6uF and mesure the voltage, i get big osillations, allmost 490V, is it OK? if yes do i have to pick a cap with 500V?

2) If i'm going to put a motor run cap in parallel to C5, what is the recomended value for C5 and the motor cap? which type shell i buy?

3) One of George modificationwas ...
"My personal preference is to use a high quality electrolytic on the board, and connect an external (off board, mounted in the cabinet) paper in oil capacitor directly between the output transformer and the filament of the output tube."
connect the electrolytic cap to where? T2-2,T3-2 to ground?

Thanks
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Old 18th February 2013, 03:08 PM   #16
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ranhaber:

Where are you putting the small 6uf cap? At C1 in PSUD (C4 on the TSE schematic)? At around this value (and lower uf) or so, it should start to decrease the B+ voltage. I'm not exactly following your first question........if your oscillations are 490V, you've got a model problem......

For C5, the bigger the better as far as ripple voltage goes, same with the motor run. IIRC, I'm running a 220uf Panasonic TS-HB or TS-UP electrolytic and a 100uf motor run. The 100uf motor run (paper/oil) cap is BIG.

George's comments pertain to locating the parallel motor run cap as close to the load as possible. Looking at the schematic, if you connect it to the top of the 10R resistor (R18/R29) and to the ground side of the filament, you are still in parallel with C5. Apparently, the 10R resistor won't affect this cap's operation if you tie one side of the cap to the bottom of the 10R resistor, which I think is what George is suggesting.

The idea here is that the motor run/PIO cap has very low ESR, and by having that close to the load it's able to provide the instantaneous current when needed for transients like bass drum whacks, etc.

BTW, paralleling 2 caps adds their capacitance, so if you are paralleling say a 220uf and a 100uf in PSUD, just make C2 320uf in the model.

As far as power supply cap voltage goes, multiply your transformer secondary by the square root of 2 (1.41) to get your max possible DC voltage. Most high voltage caps suitable for power supply use are typically rated for 50V higher than nominal voltage for short duration.

So for a 330V transformer 330V x 1.41=465 use 450 or 500V rated caps, and for a 360V rated transformer you'll definitely need 500V rated caps as the transient start-up voltage is can be as high as 507V.

For affordable high voltage low ESR caps look at panasonic TS-HB (450V), TS-UP (500V-getting hard to find in stock), and Cornell Dublier caps. There are also JJ brand HV (500V) caps, the same folks that make tubes. There are a fair number of other HV cap manufacturers as well.

Last edited by boywonder; 18th February 2013 at 03:12 PM.
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Old 19th February 2013, 04:27 PM   #17
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1) Do you have a choke in your model?

3) The SSE PCB has terminals for an off-board capacitor, which most builders use to attach a film capacitor of some sort. The TSE PCB does not have these terminals, so you have to wire the off-board cap in yourself. That is the film cap George is talking about and it goes in parallel with C5. I also have a 220uF for C5 (as well as for C2 in my SSE), as it fits in the PCB perfectly. I don't think I have an off-board cap on my TSE right now, but the SSE has a 90uF motor run cap IIRC.
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Old 19th February 2013, 06:52 PM   #18
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Rknize:
1) yes i'm using Edcor choke 10H 75ohm. And yes i'm talking on C4.

Boywonder:
I see that if i put a low value, 6.8uf, i can lower the voltage to 400V but... I also see in PSUD that i get very big oscillations on c1V.
What can be my model problem?
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Old 19th February 2013, 07:28 PM   #19
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There is no problem. That is completely normal for a Pi filter. It's partly why you want a 500V cap there. What matters is the final result: C2V.
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Old 19th February 2013, 07:29 PM   #20
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Quote:
Originally Posted by ranhaber View Post
Boywonder:
I see that if i put a low value, 6.8uf, i can lower the voltage to 400V but... I also see in PSUD that i get very big oscillations on c1V.
What can be my model problem?
Big oscillations at C1 are normal, as you are just beginning the filtering. I only look at the voltage at the constant current load(s).

As you add RC or LC stages, notice that the ripple voltage drops after each stage. Adding stages also increases output impedance. So, everything is a compromise.

Is the Edcor 10H/200ma choke DCR actually 75 ohm? I could not find the DCR value at Edcor's website. Do you know the secondary resistance of the power transformer from either end to the CT?
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