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Tube rectified PSU
Tube rectified PSU
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Old 27th June 2020, 03:49 AM   #31
trobbins is offline trobbins  Australia
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You may also want to read through the other recent post in this sub-forum that is using an 83 rectifier - well in fact that OP has used a few 83's now, so well worth appreciating how easily and quickly this type of rectifier tube can fail.

Link: Help please: Bias and hum
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Old 27th June 2020, 06:08 AM   #32
Brian28 is offline Brian28
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Originally Posted by HollowState View Post
You should not run the supply unloaded because the provided voltage output will be substantially higher and will stress the supply's filter capacitors. But you can simulate the amplifier's load with a suitable power resistor. Simple ohm's law (#7) will give you the value once you determine the desired voltage and current. Unfortunately this requires other calculations, or good estimates.

However if you have the various transformers for the supply, you could make a temporary setup to power and test an 866. A 2.5 volt filament transformer will light the tube. Give it a full sixty seconds or more to heat up. You will notice the tube becoming cloudy from the mercury vapor build up. This is normal. Connect a plate supply transformer to form a half wave rectifier using the tube. You don't need high voltage for this test. 20 to 40 volts will work well. And no filter caps are necessary for this.

If you don't know what a half wave rectifier circuit is, you probably shouldn't be doing any of this.

Connect a suitable power resistor across the output (cathode to ground), depending on the voltage you will be testing with, to consume one (1) ampere of current. (Example: for 25 volts use 25 ohms at 25 watts, or more) The tube will turn blue in color and get hot. Carefully watch the tube's plate for signs of a blistering coating and peeling or flaking. If none of this happens after a couple of minuets, you're good to go. If it does flake off there may be a flash or pop if the residue gets between the cathode and plate. The round cylinder below the plate is connected to the cathode that's inside. You could even go for more then one amp if you're limited in available parts. A variac in the plate supply transformer is a good idea. If you don't have a 5 amp variac or better, you should have one if you're going to work with tube amps.

Actually I forgot about the 15 volt tube drop so you'll want to use a little higher voltage source. Say about 50 volts.
Thank you very much ..very clear and understood ..🙏 As for the Sulphur .. I use it in the garden .. I was unaware of its possible use with Valve Amps though 😂
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Old 27th June 2020, 06:08 AM   #33
astouffer is offline astouffer  United States
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Starting at page 65 is a very detailed explanation of mercury vapor tubes including the filter design. http://www.tubebooks.org/tubedata/tt4.pdf
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Old 27th June 2020, 06:12 AM   #34
Brian28 is offline Brian28
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Originally Posted by astouffer View Post
Starting at page 65 is a very detailed explanation of mercury vapor tubes including the filter design. http://www.tubebooks.org/tubedata/tt4.pdf
Oh thatís a good book 📚. Many thanks ..
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Old 27th June 2020, 06:19 AM   #35
Brian28 is offline Brian28
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Thanks guys ...for your help with this project .. believe me ...I’m well aware of H&S issues , and I don’t go ploughing into any projects without getting a much better understanding of what I’m doing . I’m never going to be a an amp designer , but would like to gain the confidence to understand the schematic and build safely ...
Your help in my learning curve is very much appreciated.. Brian
 

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