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slimecity 25th September 2012 10:32 PM

Vintage Tehnics amp rectifier replacement
Hi there,

I have a set of technics amplifiers that I am restoring - an SU-9011 preamp (which has a fried power supply, thats the next job!) and currently I am working on the matching SE-9021 power amplifier. The power amplifier is working fine and sounds quite good.

I have replaced all electrolytics in this amp, and also the ceramic (where I could find equivalent values). My next move is the rectifier diodes – I have replaced these in the past with other great vintage amplifiers with huge success (especially when substituting with “MUR” series diodes). I want to double-check proposed replacement diodes with you guys.

There are 4 x SVD-S3V20 primary rectifier diodes. The site lists an equivalent for these as the NTE156A. I have gone off these specifications for the NTE156A to find an equivalent in New Zealand, the IN5408.

Following the above diodes on the PCB, there are 2 x SVD-RA1Z diodes. The site lists an equivalent for these as the NTE552. I have gone off these specifications for the NTE552 to find an equivalent in New Zealand, the MUR160.

Do any of the above proposed equivalents ring any alarm bells for anyone? Would my proposed replacements suffice? I am a bit worried as I cant find the original spec sheet for the actual SVD-S3V20 or SVD-RA1Z diodes anywhere on the net, so I hope that my approach seems sound.

Cheers in advance for your help! Simon.

DUG 26th September 2012 12:22 AM

It would have been more informative to list the characteristics of the diodes you want to replace so that we don't have to re-do all of the research that you have done.

average forward current
max peak current (or 1/4 cycle surge current)
normal, fast or schottky
and package would be also helpful

equal or exceed and you should be fine.

Ian Finch 26th September 2012 02:40 AM

The diode you quote is a standard 3.5 amp axial leaded silicon rectifier diode and, for preamp duty, will likely be overkill as it is the same as the main power diodes on an old Yamaha 50W integrated amplifier that I have here for repair. 1N5404-8 will be fine as a substitutes and probably all you can buy locally in a similar package anyway.

If you want to substitute soft recovery diodes, their package is usually similar to T0220 transistors for anything over 1 amp rating. IIRC 4 amp ratings are about the smallest rating above this. However, this is not a power amplifier and you might want to consider whether it will be better to snub the existing diodes with small, 100nF caps or simply rely on the effectiveness of the regulators which are not present on amplifiers, hence the justification for using soft-recovery diodes there.

I haven't found too many relics that benefit from this sort of mod, whilst there are so many over-riding noise problems dominating the sound. Technics product was noticeably quieter when it hit the market, mid-70s, so perhaps you will get some improvement in the power amplifier.

slimecity 26th September 2012 02:57 AM

Thanks for your replies guys. sorry my post isnt that clear, at this stage I am working on subbing and upgrading components in the power amp, which is working fine, however based on great results i have had in the past, i want to upgrade rectifier diodes. From your reply Ian, it seems that my proposed replacements will be fine. However my only query is WRT to the IN5408 - this differs from the NTE recommended replacemetn (the NTE156A) in one respect - the Max forward voltage on the NTE part is 1.2V, whereas the IN5408 has a value of 1.0v for this figure. In all other respects, all other voltage and current specs are identical. Is this a worry? cheers!

Ian Finch 26th September 2012 03:14 AM

'Seems I've confused the issue of what you have in front of you. If you have increased electrolytic size or ripple rating in the amplifier, you'll need larger power diodes than the type fitted. A small 10 amp bridge would likely be fine unless you have been silly but otherwise as above with the appropriate 4-6 amp rating. On-semi have only a couple of readily available types in their MURxxx range. Your Search Results | element14 Australia | Results

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