# Need help on B+ output

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#### celestar32

Can anybody help to calculate what is my B+ output if the configuration is like this power supply circuit. How to get 435V output if this configuration is wrong.

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#### DF96

Look at the rectifier data sheet. Hopefully there will be a graph of output volts versus output current for various input voltages. Interpolate between the curves if 380V is not shown.

#### kevinkr

Paid Member
Consider using PSUD2 to figure this out. Free software you can get here:

PSUD2

You need to know your load current, and the more accurate your transformer model the better the results.

#### rayma

Can anybody help to calculate what is my B+ output if the configuration is like this
power supply circuit. How to get 435V output if this configuration is wrong.

You should be close, so I'd go ahead and breadboard it. Use a Variac if you have one.

#### famousmockingbird

Several pieces of information are missing.

380*1.4=532

You have a theoretical max voltage of 532.

Now you need to know the DC load current, the source resistance of the transformer secondary, the voltage drop across 5U4 vs load current provided in datasheet, and the DCR of the choke being used.

#### TNoll

You will need to know the dc resistance of the choke, too.

Rayma's advice is good. Breadboard it and use a power resistor for a dummy load which will draw the current your device will draw.

Two points, though:
Where is your bleeder resistor? You Need to have one. Its job is to discharge the filter caps so they don't hold high voltage and discharge through your body. It goes on the B+ line, after the last cap.

What's that cap doing across the switch? That's a leakage path, and will somewhat energized the transformer at all times. With the snubber (marked NL), which is a very good idea, you do not need anything else.

#### Eli Duttman

NL = neon lamp. It's a pilot light. The series resistor is a voltage dropper/current limiter.

The breadboard suggestion is spot on.

A 20 muF. cap. in the 1st position and a 100 muF. part in the reservoir position gives an option to use a "potato masher" 5R4, instead of a 5U4, should the rail be too tall. At the rated 250 mA., the forward drop in a 5R4 is a whopping 67 .

#### gabdx

at least if you knew how much mA to draw from the transformer, and sample transformers to simulate ratings (internal resistance etc)

#### TNoll

Thanks Eli, Neon lamp. I thought a snubber might be New Longevity for switch contacts.

The bleeder resistor can be 220k 2W (minimum) or, better, 2x 470k 2W in parallel.

The best simulation is a bread board.

#### celestar32

I tested it with this configuration. I got 315V on my B+ but the rectifier will red plating. The choke resistance is at 45ohms.

#### famousmockingbird

What is the voltage before the choke?

You must be pulling a lot of current. What is hooked up for a load (or what do you think is hooked up for a load)?

Deduct 315 from the voltage before the choke and divide by 45, and that is how much current you are pulling.

#### Eli Duttman

I tested it with this configuration. I got 315V on my B+ but the rectifier will red plating. The choke resistance is at 45ohms.

You are drawing more than the 250 mA. allowed with a 5U4GB. Other 5U4 variants allow only 225 mA. Increase the value of your "dummy" load, to hold the draw down.

Look at the 5U4GB data sheet. That 47 muF. 1st cap. is suspect.

Back in the day, all sorts of liberties were taken with published tube limits. Tubes were inexpensive and performance claims helped sales. Definitely adhere to published limits, until you accumulate experience. With experience, you will learn where small liberties can be taken. Beating the living guano out of your tubes is very bad for your bank balance.

#### BarG01

I tested it with this configuration. I got 315V on my B+ but the rectifier will red plating. The choke resistance is at 45ohms.

Hope you switched it off immediately!
http://frank.pocnet.net/sheets/127/5/5U4G.pdf
Look at this datasheet, if you had only 315V, you must have seriously overloaded the rectifier tube. Or the smoothing capacitor is defective.

#### celestar32

I also suspect the 1st cap value should be lower maybe 10uf or 15uf. Maybe the output transformer rated at 290V is ideal for this configuration.

#### famousmockingbird

I also suspect the 1st cap value should be lower maybe 10uf or 15uf.

That wouldn't cause the issues you are having. What is being presented to you is that the first cap is defective and not just sized incorrectly. I am willing to bet this is the case if you do not have any other load connected.

#### rayma

That wouldn't cause the issues you are having. What is being presented to you is that the first cap is defective
and not just sized incorrectly. I am willing to bet this is the case if you do nothave any other load connected.

Agreed, this is about the only possibility given correct wiring.

#### famousmockingbird

Just in case you don't know electrolytic caps are polarized, make sure you have them installed correctly and not backwards.

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