Transformer primary and secondary wiring query.

Thread Starter

danbest1130

Joined Sep 25, 2019
6
what is the purpose of the primary and secondary coils of the microwave transformers here being wired together? and how is this done?


Screen Shot 2019-07-27 at 12.15.27 pm.png
 
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ericgibbs

Joined Jan 29, 2010
9,354
hi dan,
Welcome to AAC.
Your Thread is Closed pending a Moderation check.
E

Thread Re-Opened.

Please indicate the Voltage sources. are they direct local Mains voltage inputs.?
 
Last edited:

KeithWalker

Joined Jul 10, 2017
603
what is the purpose of the primary and secondary coils of the microwave transformers here being wired together? and how is this done?


View attachment 186966
The primaries and the secondaries are wired in parallel. I can only assume that the designer did not have a single transformer that would supply enough current to drive the circuit. This is a very badly designed and drawn circuit.
The secondaries of the transformers should NOT be connected directly to the mains supply as shown. . THAT IS VERY DANGEROUS !
They should be connected instead to the circuit ground to give the correct reference for the high voltage supply. The suppressor grid should be at the same potential as the cathode.
 

TeeKay6

Joined Apr 20, 2019
565
Another question, but what do the dots between the two diode components mean?
@danbest1130
My guess is that the dots mean other diodes are inserted there. The 10A10 diode is rated for Vr=1KV and--as best I can read the schematic--the TS needs a rating greater than 2KV (the 2 10A10's shown). However, there is nothing shown to force voltage sharing along the string of diodes...one diode may shoulder much of the burden...not good.
 

MisterBill2

Joined Jan 23, 2018
4,889
The purpose is incorrect, the result will be a terrible electrical shock when you grab it to attempt to put out the fire! The circuit shows putting two non-identical transformers in parallel with a capacitor directly across them. This circuit is dangerous even just on paper!
 

Reloadron

Joined Jan 15, 2015
4,909
This is likely what the circuit should look like. The circuit as drawn uses a Russian Made GU-81 vacuum tube and the link I just posted uses a pair in parallel while the crude drawing reflects a single tube. The GU-81M 700W 50MHz pentode is used in self-excited oscillation and power amplification circuits of RF equipment, it is simply a high power tube which over the years have fallen from grace. All vacuum tubes, well almost all, relied on a high plate voltage. The transformers are configured in a boot design which will merely provide a higher output voltage and are a pair of Microwave Oven Transformers. The circuit is actually driven by a Variac but using a Variac is not necessary. The circuit amounts to a vacuum (valve) tube type Tesla coil.

The design is pretty common. So is it dangerous? Yes, it can be but so can using an electric hair drier in a shower. Anything involving high voltage at high currents can without a doubt make you dead. Amazing so many of us survived the era of vacuum tubes and high voltage B+ power supplies. Would I suggest an amateur build anything like this? Nope. There is nothing inherently wrong with working with high voltage and high current as long as those working with it understand what they have in front of them.

Ron
 

MisterBill2

Joined Jan 23, 2018
4,889
This is likely what the circuit should look like. The circuit as drawn uses a Russian Made GU-81 vacuum tube and the link I just posted uses a pair in parallel while the crude drawing reflects a single tube. The GU-81M 700W 50MHz pentode is used in self-excited oscillation and power amplification circuits of RF equipment, it is simply a high power tube which over the years have fallen from grace. All vacuum tubes, well almost all, relied on a high plate voltage. The transformers are configured in a boot design which will merely provide a higher output voltage and are a pair of Microwave Oven Transformers. The circuit is actually driven by a Variac but using a Variac is not necessary. The circuit amounts to a vacuum (valve) tube type Tesla coil.

The design is pretty common. So is it dangerous? Yes, it can be but so can using an electric hair drier in a shower. Anything involving high voltage at high currents can without a doubt make you dead. Amazing so many of us survived the era of vacuum tubes and high voltage B+ power supplies. Would I suggest an amateur build anything like this? Nope. There is nothing inherently wrong with working with high voltage and high current as long as those working with it understand what they have in front of them.

Ron
Presuming that the microwave oven high voltage transformers are 500 watt devices, is a 1000 watt Tesla coil REASONABLE?? I really do not think so. And my comment about the danger is exclusively about tying the AC mains into the secondary circuit, which is a VERY POOR CHOICE, by the way. AND tying two non-identical transformers like that will certainly provide some circulating currents limited only by the transformer resistance.
Thus it is not wise for those without a fair amount of understanding and insight to be doing things that certainly are not good designs. It has nothing to do with the tube, the problem is in the power supply area. THAT is where the fire would start. AND, since most oven transformers do have one end of the secondary fairly solidly tied to the frame, the shock hazard would be real. Tying a high voltage supply winding to the mains is asking for problems.
 

Reloadron

Joined Jan 15, 2015
4,909
Presuming that the microwave oven high voltage transformers are 500 watt devices, is a 1000 watt Tesla coil REASONABLE?? I really do not think so. And my comment about the danger is exclusively about tying the AC mains into the secondary circuit, which is a VERY POOR CHOICE, by the way. AND tying two non-identical transformers like that will certainly provide some circulating currents limited only by the transformer resistance.
Thus it is not wise for those without a fair amount of understanding and insight to be doing things that certainly are not good designs. It has nothing to do with the tube, the problem is in the power supply area. THAT is where the fire would start. AND, since most oven transformers do have one end of the secondary fairly solidly tied to the frame, the shock hazard would be real. Tying a high voltage supply winding to the mains is asking for problems.
All I did was provide a clear readable link to what amounts to the same circuit originally posted. I also covered the danger. The fact that you disagree with tying a primary and secondary opf a transformer together for a boost function is something you can take up with the author of the article. It's a simple transformer boost circuit and its use is not all that rare. You figure it will catch fire then take it to the guy who authored the circuit. Nobody else took the time to research the circuit and all I did was provide some explanation and a link. I also said my view of building the circuit.

Ron
 
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