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June 16, 2021, 03:13:28 AM

Author Topic: Zener string  (Read 88 times)

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Offline triode

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Zener string
« on: May 22, 2021, 09:29:27 PM »
Hi

Revisiting my Bottlehead manuals this weekend and I'm wondering what is the function of the zener string in Paramount (5 of them in series)?

Why Paramount has this? Stereomour and MonAmour don't have this (I don't have Kaiju so don't know if its also has the zener string)
What happened if this string omitted?

Just trying to learn and understand the circuit more...
Thanks in advance   

Offline Paul Joppa

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Re: Zener string
« Reply #1 on: May 23, 2021, 05:23:26 AM »
During startup, they prevent the driver plate voltage from rising too high before the shunt regulator begins functioning. Once the amp is running, the are out of the signal path. (They also prevent some collateral damage if an error has been made during construction.) What's being protected is the PNP power transistor in the C4S, which is rated for 375 volts maximum. Semiconductors, unlike tubes, have no sense of humor about high voltages. If we could get higher voltage rated transistors, we would not bother with them, and the other amps have lower voltages and less need for the protection.

The technical term for this kind of design is "kludge".
Paul Joppa

Offline triode

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Re: Zener string
« Reply #2 on: May 23, 2021, 09:21:15 AM »
Thanks Paul