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[email protected] johnnhelen4@gmail.com is offline
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Default B Field collapse

On Monday, June 26, 2017 at 5:04:33 AM UTC-4, Xtrchessreal wrote:
While researching ignitors on gas arc tube lamps I read about how the magnetic field collapses when the circuit is basically opened as the AC input signal falls to zero and it causes a spike in the secondary as high as 2500-3000 Volt range for 150w to 400w lamps. I know the spike in a ballast is designed for the lamp to start. I should say the lamp is designed to take advantage of the spike.

SO:

A spike must happen to a tube push pull amp as well though perhaps not that high in voltage, I don't know.

I got to thinkin'. The Power Transformer, if opened while standby is closed, could do some real damage to the amp, right? If a spike like that is released across the rectifier and filter caps, the inductor, and the power tubes...I don't have testing experience in this so here is the question.

Q1 What happens to the amp as this spike works its way through a basic amp; e.g. http://drtube.com/schematics/marshall/2204u.gif

Part1: Assume a proper speaker is connected.
Part2: Assume without a speaker connected.

Slightly different note:
I've noticed that when I open the standby preparing the amp to be shut down after playing for a while that I can hear my guitar chord at lower volume and fades within a few moments through the speakers. This is a different discharging scenario since the standby is open no spike from the PT can pass.

Q2 What is contributing to the discharging of the amp, providing enough energy to the amp for the signal to still be heard for a few seconds? The heaters are still hot so is the amp dissipating the coils and caps stored energy only? Or is there stored energy in the hot tubes as well? Provided there is an input signal.

X


Not to worry, do the following. Connect a 1000 PIV SI diode such as a 1N4007 so that its anode side is connected to the common lead (ground), the cathode lead to the load side of the B+. Any energy stored in the LCL filter network will be safely dissipated when the standby is set to OFF. Wish I could show you on a schematic. What make & Model is the amp? It might be in Aspens book.

Cheers to all, John L Stewart