Appropriate diode rectifier

a fine line between stupid and clever

Appropriate diode rectifier

Postby dhuebert » Tue Jan 02, 2007 11:02 am

I am building a bass amp with 4 KT88s using hammond 278CX transformer. Can anyone recommend a good sand rectifier for this? I notice the eiclone uses UF5408 but it is only rated for 3A, Would this be enough for what I want to do?

Don
User avatar
dhuebert
KT88
 
Posts: 820
Joined: Thu May 01, 2003 9:26 am
Location: Winnipeg Manitoba Canada

Postby erichayes » Tue Jan 02, 2007 12:29 pm

Hi All,

Don, I use UF5408s in series with no EQ resistors in all my amps--2 per leg in the 1773, and 3 per in the bigger stuff--and have never had a failure in 8 years. The only caveat is that all my power supplies are choke input. They don't break a sweat running 475 volts at 300 mA continuous in the 100 watt monoblocks using KT88s.
Eric in the Jefferson State
erichayes
KT88
 
Posts: 987
Joined: Fri Jan 23, 2004 9:01 pm
Location: McKinleyville CA

Postby dhuebert » Tue Jan 02, 2007 3:26 pm

So you're telling me you put 2 5408 in series on each side? OK

What I've been doing for power supplies is to put a 1 ohm 10W reistor into the first cap, taking B+ from that and then a choke into the second cap and the rest of the filtration. The reason I do it this way is: B+ goes into push-pull and dosen't need all that much filtering and I want a low Rs to deliver those big sharp rise-time currents a bass guitar will demand. Whereas the screen grids want stable clean power as do the single-ended front ends. This also keeps dissipation in the choke low so I can use a smaller one. The big resistor is to keep inrush currents under control during the charge phase.

http://www.diytube.com/forumpix/power_supply.jpg



Don
User avatar
dhuebert
KT88
 
Posts: 820
Joined: Thu May 01, 2003 9:26 am
Location: Winnipeg Manitoba Canada

Postby erichayes » Tue Jan 02, 2007 7:27 pm

Hi All,

I'd use three per side, given that it's a cap input filter. In my experience, most PN junctions in rectifiers get punctured by voltage spikes rather than excessive current. The 5408 is rated at 150 amps for a single shot, and you're only going to kick its ass for a tenth of a second or so at turn-on.

I buy 5408s in quantity, so my cost is about a quarter per diode. But even in single lots, I'd figure the extra buck for the additional diodes is a pretty cheap insurance premium.
Eric in the Jefferson State
erichayes
KT88
 
Posts: 987
Joined: Fri Jan 23, 2004 9:01 pm
Location: McKinleyville CA


Return to guitar amps

Who is online

Users browsing this forum: No registered users and 1 guest