FRED diodes in Twin Reverb

[dinkotom]

Hi all, so glad i found this forum!

I've modified SFTR to BF specs (incl. new transformers), but the amp still sounds too "spikey".
I've read long ago on Victoria amps page (though it's been deleted since) that putting FRED diodes in Twin Reverb will make it sound less "spikey"-can anyone comment on this?
Thanks.

[Andy Le Blanc]

Ive heard the same but havent tried it... I like a tube rectifier
Ive seen many HiFi projects that use FREDs to reduce switching noise
in a powersupply, transients that carry through the amp and effects the amps
sound stage and presentations
try them out and see..... wouldn't mind hearing about it...... welcome

[dinkotom]

Thanks, as soon as I can find them in my neck of woods I'll try them.

[tubetek]

Howdy dinktom-
If you can't find UF4007 in your area, try bypassing the 1N4007s with .01mfd 1000VDC ceramic caps (1 for each diode) Seems to work well in Fender amps I've built. Have fun!
tubetek

[jaysg]

Depends on what you mean by spikey. I swear by beam blockers, ymmv. I wish someone else would make them. There are lots of threads covering them here.

The FREDs are for eliminating some high frequency hash that can intermodulate with the audio. UF4007s are fine. I use them. Usually, when an amp manufacturer is talking about FREDs, they mean something in a T0-220 package.

DSEI12-12A-ND at digikey.com for example

[skyboltone]

Howdy dinktom-
If you can't find UF4007 in your area, try bypassing the 1N4007s with .01mfd 1000VDC ceramic caps (1 for each diode) Seems to work well in Fender amps I've built. Have fun!
tubetek

This is an old timey fix and I'm surprised it isn't used more.

I use both UF4007s and Fairchild stealth diodes. The fairchild ones come in a nice 1000volt double cathode single anode for full wave use. They are really dandy and small footprint. TO-220 but you only need one. I just built a bridge using 4 of the single diode package and they worked out well.

[dinkotom]

Thank you all for replies.
I already have these bypass caps, I left the bridge as it was - does that mean that FREDs won't do any difference?
Anyway, if I want to put these DSEI12-12A-ND, do I just solder them in the same places, without any other changes to the bridge?
EDIT:
Ah, and I also found this thread:
http://music-electronics-forum.com/show ... php?t=2990

[jaysg]

Ha! I forgot about Ken Gilbert...lots of people had heated discussions with him. I use them because they can't hurt and I don't have to squeeze my nickels. Also, Rick Erickson felt that the 1N4007s weren't really fast enough in the plate protection position and that the UFs were.

If you get a 1200V part, I believe you can replace the 6 diodes with two FREDs. (All the SF schematics I can find have the 6 diode configuration instead of a 4 diode bridge.) If you use UF4007's, you could actually just use 4 of those instead of 6. Whatever those ugly things were, they weren't 1000V parts.

[titanicslim]

Depends on what you mean by spikey. I swear by beam blockers, ymmv. I wish someone else would make them. There are lots of threads covering them here.

I've often wondered if such a thing should be so hard to make. Although I've never had an amp that I felt required them, I'm sure I would give it a try before I bought any. Maybe even a foam wedge or cone fastened to the inside of the grill. Or how about a solid grill with vents? By the way, I've recently seen photos of this type of thing on speakers in an old hi-fi. Perhaps on this forum?

Anyhow, back to FREDs
I don't want to hijack threads.

Dave

[skyboltone]

Ha! I forgot about Ken Gilbert...lots of people had heated discussions with him. I use them because they can't hurt and I don't have to squeeze my nickels. Also, Rick Erickson felt that the 1N4007s weren't really fast enough in the plate protection position and that the UFs were.

If you get a 1200V part, I believe you can replace the 6 diodes with two FREDs. (All the SF schematics I can find have the 6 diode configuration instead of a 4 diode bridge.) If you use UF4007's, you could actually just use 4 of those instead of 6. Whatever those ugly things were, they weren't 1000V parts.

I've always thought that we stack 1n4007s not for voltage protection but because there's a heck of a current spike when we first load the caps. The freds are 8 amp devices most of them with humongous momentary current specs. The UF4007s are still a 1 amp device.

[Analog Assassin]

Would there be any advantage to using a uf diode in the bias supply?

[jelle]

Yep,

The switching noise reaches the preamp via the PT into the heater supply into the cathodes of the preamp...

I do not know how big the effect is compared to the HV diodes.

Jelle

[drhulsey]

... I've often wondered if such a thing should be so hard to make...

They are easy to make with speaker dust covers or with PVC (there is a nice dome on a 4" pipe cap– cut away everything but the domed end) on a thin aluminum strap across the speaker.

[Andy Le Blanc]

you can glue or pin a section off a styrofoam ball to the inside of your grill
no sense spendin more than $.99.....

[dartanion]

You could always do the ghetto blocker method: put duct tape crosses over the grill cloth centered on each dust cap!