FRED

[cedricb]

Hi,

I'm just wondering if D1 and D2 can be replaced by FRED http://ixdev.ixys.com/DataSheet/93021.pdf ?
Any real advantage in term of the rectifier for the ST35 circuit?


Regards,
Ced.

[WA4SWJ]

Hi Ced,

Should work just fine.

Regards,

[DerekVa]

Yup - they work great. I'm running them in both my ST-35 amps.

-D

[WA4SWJ]

Don't cha just love em???!!!!

[EWBrown]

Almost any modern-era 1000V / 1A or greater rectifier will be better than the original ones in the ST35s. UF4007s would be a good choice, and FREDs would be great!

Mid-60s silicon technology was still in its infancy, as compared to now.

/ed B

[Vince]

Ed, I hate to ask a question this fundamental, but the FRED data sheet in the post above shows 30 Amp capability. A 1N0007 is a 1 amp device.
Which one would you use,ignoring cost, to replace selenium rectifiers in older units you plan to keep?

Thanks for your patience, Vince

[EWBrown]

The 1N4007s & UF4007s are more than adequate for the original ST35s, and are a LOT more capable, and rugged than the original silicon rectifiers. Which had lower voltage and current ratings, they were closer to running on the razor's edge.

The 1 amp / 1000V rating provides a very good safety margin for the PA-774 and the rest of the PSU components.

One mod I would put in, is to replace the 50 ohm resistor in the CRC chain, with a C354 choke, it can fit on top of the chassis in the "empty space", as can one of teh Cyrus Chong cap boards, which would replace or supplement the original multisection can cap.

I hhave two very clean and one slightly "tired" looking ST35 carcii all slated for refurbishing, with new PC boards, the Chong cap boards, and C354s, and individual 400 ohm cathode resistors and bypass caps for teh 6BQ5s, in the near future. I have all the boards assembled and ready to install. Those units will eventually be available on Pre-Bay then e-pay. Just need some time and to locate just which of many boxes they are hiding in...

The 30A rated FREDs would devinitely be an "overkill", and the minimal benefits gained would not be worth the additional expense.

There are smaller FREDs (or HEXFREDs) with 6A, 1600PIV ratings, THose would be better applied to serious powered PPP amps.

I would recommend using FREDs or other heavy-duty rectifiers with the heftier ANTEK power toroids, especially the 400VA units, as these could easily fry smaller rectifiers.

HTH

/ed B

[nyazzip]

i think you guys need to start hyping up the superior soundstage and grainless 3D imaging that only a selenium rectifier can deliver, so i can sell the one i have in my PAS2 for big bucks on ebay in a couple years

[EWBrown]

Way I see it, DC is DC is DC, once you get beyond the last cap in the CLCRC string, and strip off most of the ripple, , it doesn't really matter if the DC was rectified via silly-con, selenium, tubes or even a dynamotor (though the latter will have its own unique, self-generated sound, somewhere between the SPL of a Hoover vacuum cleaner, and a MiG-15 taking off, in which case any ripple or other noises suddenly become rather irrelevant).

Seleniums are really good for stinking out a room, when they fail...

/ed