zener diode to decrease high voltage....

[jmaf]

I still dispute the 250mA figure per my post #35

Well now we know you were right

I guess the calculation should have been made based on the amplifier's nominal power consumption minus heaters, not on the audio wattage output.

Right. But the guy is cranking the amp. AFAIK zeners don't have a "nominal" rating like a slo blo fuse. So I added a little safety margin and called it ten watts. As for the five watt zeners, can you get those in the DO package?

You were right as well, Chuck, sorry I did not reply earlier - haven't been to the forum much lately. Don't know about TO packaging for 5 W zeners, a quick Mouser search should give us a pretty straightforward answer.

[jmaf]

play tested it just now....high volume/heavy playing caused the amp to go dead. fuses intact...looked at my diode chain: blown apart at one of the 'links'....hmmm

See the reply by Tom Philips, he was right. I replied in a hurry and the calculation should've been made based on consumption, not on audio output. I've done this several times in the past, it works a dandy(when you get the ratings right ).

One thing: the current charging that initial cap is the biggest high voltage pulsed DC current in the entire amp, I would place the zeners after the cap, as per my drawing, smoothed DC current is probably softer on the zeners(and I'm just guessing about this last part).

[trobbins]

If it's a leaded zener part then likely that its power dissipation rating is mainly via pcb conduction, and its free air dissipation rating is much lower. And if used in a string then derating needed may be even worse as there is less capability for conducted heat to escape.

[acorkos]

I would place the zeners after the cap, as per my drawing, smoothed DC current is probably softer on the zeners.

that's where i had them when the chain desoldered itself

[frus]

Am I wrong thinking that if you put the zener between center tap and ground (or bridge and ground in this case), it would also conduct the same pulsed current that charges the first reservoir cap?

[trobbins]

You're not wrong (ie. correct) - if you are just refering to the mains current pulses from the transformer. The cap also see's load current signals.

[Bruce / Mission Amps]

Quite a few years ago.. might even have posted this here 10-12 years ago.... I had a problem with a vintage AC30 that had been blowing up power tubes left and right.
Made for a 220vac or 110vac, running at 122vac it was crazy high B+ and the four EL84 power tubes were super hot!
I broke the center tap of the high voltage winding and used two or three 5 watt diodes to lower the B+.
They also got their respective leads hot enough to come unsoldered!!
I re-mounted them to a small term strip and used a couple pennies (two coins with two 1/16" holes drilled in them for the soldered-in diode leads) as big heat sink fins in between the diodes. Bingo!
It looked weird but it worked fine and the diodes never got that hot anymore either.
So, cheap fix for $2.02 in parts.

[trobbins]

Yes, I've seen punched out aluminium disks attached to olde SS diode packages (OA214) in the rectifier section for improved heatsinking.