please check my work

[gary h]

Hi all,

I've finally got all my Aikido line stage parts together. Most of the circuit connections are automatic given JB's design and parts but before connecting the PS together on my desktop and testing voltages, etc. I was hoping some of you might be kind enough to look over the attached schematic. I expect there might be both glaring mistakes and possible changes worth making before going forward.

Questions:

1. I've read in discussions that I should not connect the filament supply CTs to ground. I gather this is because the 5AR4 will prefer this. True? Is this a longevity issue?

2. Do I need to add caps and/or resistors before either high or low voltage go to the 5AR4? If so what values?

3. I plan on putting a fuse before each transformer. Their VAs are 147 and 43. Will I be ok with a 3.2A and 1A fuse respecively?

4. I have insulated crimp connectors, wire nuts, non conductive work surface. Any other precautions recommended for the test run?

Thanks for the help.

gary

[DougL]

1. I've read in discussions that I should not connect the filament supply CTs to ground. I gather this is because the 5AR4 will prefer this. True? Is this a longevity issue?

Its more of a Don't ground your B+ kind of issue. If you grounded the CT of the 5AR4 heater, it would short 300v RMS to ground through the DC and AC "resistance" of the 5 Volt transformer. At least until the 5AR4 melted.

2. Do I need to add caps and/or resistors before either high or low voltage go to the 5AR4? If so what values?

Probably you will need to add resisters to the 5V legs to bring the voltage at the 5AR4 to 5 V. Best done by measuring to see if its higher than desired. This is a longevity thing.

Your voltages looked high. So I ran PSUD. Simply guessed on DCR . 80R for 5H and 60R for 2.6H.

I got 260V at the point you labeled B+ assuming 40 ma total current draw of an Aikido 6SN7. The Q and step response looked good. Ripple looked to be about 9 mV. Overall it looks like you get it.

[HollowState]

Originally posted by DougL

Probably you will need to add resisters to the 5V legs to bring the voltage at the 5AR4 to 5 V. Best done by measuring to see if its higher than desired. This is a longevity thing.

Actually the transformer rectifier voltage is depicted wrong. The 5V winding is just a regular center taped one. Not 5V either side but 2.5V.

[gary h]

Hi guys,

thanks for the replies.

Indeed I mislabled the 5AR4 heater supply, it's 2.5V per rail.

Attached is the PSUD2 model I ran. I'm probably making a mistake with the initial voltage. This will probably change when loaded, right?

So what is the safest way of dealing with the CT leads? Just cap them and tuck them out of the way?

gary

[gary h]

The spec sheet on the 6SN7s gives max plate dissipation for both plates at 7.5W. Does this mean I should make the 150 Ohm resistor in the B+ filter section a 30W for the 4 tubes? This seems a bit big. Am I calculating this correctly?

gary

[HollowState]

Originally posted by gary h
The spec sheet on the 6SN7s gives max plate dissipation for both plates at 7.5W. Does this mean I should make the 150 Ohm resistor in the B+ filter section a 30W for the 4 tubes? This seems a bit big. Am I calculating this correctly?
gary

Nope, The wattage of the 150 ohm resistor in the power supply is determined by the voltage drop across it times the current through it. (P=EI) I estimate less then a watt dissipation, so a 5 watt WW is plenty. Just simple ohms law stuff. The plate dissipation of the tubes is somewhat removed from this since you won't (or shouldn't) be maxing them out and the voltage drop across them is much greater. But it's the same formula as above.

[Tweeker]

No, you are not.

Current^2*R=Power.
If 4 tubes are drawing 7.5w each with 295V B+:
.102^2*150=1.5
1.5 watts dissipated, use at least a 5 watt resistor.

[gary h]

Thanks guys,

I ordered a 5W resistor and probably figured this out before but I find myself second guessing everything now.

I'm still having trouble understanding when and when not to connect the transformer CTs to ground. If I don't connect the 300V CT to ground won't I then get 600V across the 5AR4 plates?

[Tweeker]

The high tension transformer is indeed grounded at center tap, this is the winding the plates connect to.

The filament transformer is NOT grounded, this is where B+ is drawn from. Often from the center tap.

You have it correct as diagrammed.

[HollowState]

You'll have 600 volts across the plates either way. But you must ground the CT otherwise you'll have an open circuit. NOT true for the filament winding. Don't ground that.