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previous: Tony Taliaferro Your right, the change is for the p... -- 11/16/1997 12:18 PM

Re: Silverface champ

11/17/1997 8:37 AM
Bruce	Re: Silverface champ This is just a clarification comment not a critique: I think the zener is in series FROM ZERO volts (which is chassis grounded) not shunted to ground. The zener is connected at the center tap of the power transformer (zero volt reference point) in series to chassis ground. In other words the center tap is held above chassis ground by the reverse biased diode. I think that is different then shunting the B+ to ground like a zener regulator. If you shunted B+ to ground through the 63V zener, wouldn't you have a 63V powr supply? The largest wattage zener diode I have easily found is from Mouser at about $10.00. It is a 63V at 50 watt zener. I have used this trick a few times with good results. It does NOT really drop the voltage the whole 63 volts, but more like around 40-45 volts. Also it does get very warm and needs a good solid hunk of chassis to act as a heat sink. Think of it this way... drop 50 volts with 100ma of current passing through the device is equal to only about 5 watts. More current more heat though. I have drawn a few hundred ma through the 50 watt zener with no damage. So a champ drawing much less current then that ought to be able to use a smaller wattage zener. I have been able to take a 530V B+ power supply down to a very useable value with this trick and run a number of 50 watt amps this way. To date I have never had a 50 watt zener diode failure. If you are building an amp from scratch, it is cheaper and easier to buy the correct power supply transformer in the first place. If you are stuck with what you have.... use it! Bruce

11/17/1997 8:37 AM

Bruce

Re: Silverface champ

This is just a clarification comment not a critique:

I think the zener is in series FROM ZERO volts (which is chassis grounded) not shunted to ground.
The zener is connected at the center tap of the power transformer (zero volt reference point) in series to chassis ground. In other words the center tap is held above chassis ground by the reverse biased diode.
I think that is different then shunting the B+ to ground like a zener regulator.
If you shunted B+ to ground through the 63V zener, wouldn't you have a 63V powr supply?
The largest wattage zener diode I have easily
found is from Mouser at about $10.00.
It is a 63V at 50 watt zener.

I have used this trick a few times with good results.
It does NOT really drop the voltage the whole 63 volts, but more like around 40-45 volts.
Also it does get very warm and needs a good solid hunk of chassis to act as a heat sink.

Think of it this way... drop 50 volts with
100ma of current passing through the device is equal to only about 5 watts. More current more heat though.
I have drawn a few hundred ma through the 50 watt zener with no damage.
So a champ drawing much less current then that ought to be able to use a smaller wattage zener.

I have been able to take a 530V B+ power supply down to a very useable value with this trick and run a number of 50 watt amps this way. To date I have never had a 50 watt zener diode failure.
If you are building an amp from scratch, it is cheaper and easier to buy the correct power supply transformer in the first place.
If you are stuck with what you have.... use it!
Bruce

Replies:

M.Romasco Go with the 50w zener like Bruce sa... -- 11/17/1997 10:26 AM
Tony Taliaferro Thanks for the clarification Bruce.... -- 11/17/1997 4:45 PM