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    Fried rectifier solution

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    KT88

    Posts : 10
    Join date : 2011-08-12
    Location : Dubrovnik,Croatia

    Re: Fried rectifier solution

    Post by KT88 on Mon Aug 29, 2011 11:49 am

    There are ways and ways...one solution ( the best ),if your amp has semicondactors in it,would be o good ,enough strong UPS...but not any kind,only 100% online machine with double conversion what means that amp is always conected with battery so that no metter what hapens with input current,you have always stable 110 or 220 volts on output with almost perfect sinus vave..they are not cheap but your amp is protected from all spikes and overloads..in case of black out,you have always enough time - more or less about 20 minutes - to shut down your amp on regular basis.
    One more suggestion...when lighting,disconect everything from the wall..and...in case you have SS amp.,disconect loudspeaker cables from output terminals as well Exclamation

    sandy

    Posts : 36
    Join date : 2011-03-04
    Age : 54
    Location : Los Angeles, CA

    Re: Fried rectifier solution

    Post by sandy on Mon Aug 29, 2011 6:35 pm

    Would a proper selected MOV solve much of the transient voltage problem on the 120/240 AC side of
    things? Don't know how fast the transients are or how fast the MOV's react to them but they are in every reasonable UPS I'm guessing.

    One other device might solve some of the issues is an ONEAC (Isolation transformer), I have used them on computer gear in the past where they have problems with lightning, and other poor power deliver, not sure how they will work on Audio gear but they keep computer gear happy. Cheep on ebay, but a bit expensive to ship.

    For the brown out/momentary loss of power I think you can find a bunch of very simple circuits that solve that issue too.

    I do also like the Tube solution, simple and generally durable, and it's part of the heritage of the tube amps when you can use them. I have a Weber solid state rectifier in my ST120 and it's great, I'm not a audiophile but when I tried my ST120 with the JJ GZ34 for testing before swapping to the Weber made no difference to my simple ears. Also the Weber seems to run hot like a GZ34 (well not quite as hot).

    All good stuff, and good to be aware of the PIV ratings for solid state rectifiers which seems like a lot of folks just take the PIV for granted in looking at many power supplies spec'ed with 1N4007's or 1N5808's that have voltages much higher then the stock ST70's 360v.

    Great info everyone!

    Sandy

    KT88

    Posts : 10
    Join date : 2011-08-12
    Location : Dubrovnik,Croatia

    Re: Fried rectifier solution

    Post by KT88 on Tue Aug 30, 2011 11:16 am

    I had isolation transformer.The thing was strong 1kw and had 60 kg,was producing 60 db noise.Now I have UPS with 15 kg weight and I find it better because if you make recordings you can proceid even by black outs what we have here prety often,besides having UPS conected you have clean power as you get power from battery.Any way would be happy to have tube rectifier in power stage of my amp and not diodes.My friend has Bewitch tube amp with tube in power stage and has never problems with spikes and such things

    KT88

    Posts : 10
    Join date : 2011-08-12
    Location : Dubrovnik,Croatia

    Re: Fried rectifier solution

    Post by KT88 on Wed Aug 31, 2011 4:09 am

    Here is something more about spikes and their inpact on semiconductors....here is one tekst from Electrical Engineering .....Effects on Semiconductors
    Frequently, damage occurs when a high reverse voltage is
    applied to a nonconducting PN junction. The junction may
    avalanche at a small point due to the non-uniformity of the
    electric field. Also, excess leakage current can occur across the
    passivated junction between the terminations on the die
    surface. The current can create a low resistance channel that
    degrades the junction blocking voltage capability below the
    applied steady-state voltage. In the avalanche case, thermal
    runaway can occur because of localized heating building up to
    cause a melt-through which destroys the junction.
    If the base-emitter junction of a transistor is repetitively
    “avalanched” or “zenered” to a high current level by a reverse
    pulse, the forward current gain may be degraded. The
    triggering sensitivity of a thyristor can be reduced in the
    same manner by “zenering” the gate-cathode junction.
    Thyristors can also be damaged if turned on by a high
    voltage spike (forward breakover) under bias conditions that
    allow a rate of current increase (di/dt) beyond device
    capability. This will occur in virtually all practical circuits
    because the discharge of the RC dv/dt protection circuits will
    exceed device capability for di/dt and destroy the thyristor.

    sandy

    Posts : 36
    Join date : 2011-03-04
    Age : 54
    Location : Los Angeles, CA

    Re: Fried rectifier solution

    Post by sandy on Wed Aug 31, 2011 12:45 pm

    KT88 wrote:I had isolation transformer.The thing was strong 1kw and had 60 kg,was producing 60 db noise.Now I have UPS with 15 kg weight and I find it better because if you make recordings you can proceid even by black outs what we have here prety often,besides having UPS conected you have clean power as you get power from battery.Any way would be happy to have tube rectifier in power stage of my amp and not diodes.My friend has Bewitch tube amp with tube in power stage and has never problems with spikes and such things

    To be sure the Oneac is not just an isolation transformer, and not sure the trouble you had with one being noisy, but never had an issue where they are audible cheep insurance when all said and done.

    Lot's of ways to skin the cat Smile

    Sandy

    merlot

    Posts : 22
    Join date : 2008-12-22

    Re: Fried rectifier solution

    Post by merlot on Wed Aug 31, 2011 2:33 pm

    I'm rebuilding my WZ68s. I've got the diodes and resistors but can't find a source for the thermistor... I figure I might as well rebuild them from scratch to be safe. Has anyone found a source for it?

    Thanks.

    Luddite

    Posts : 235
    Join date : 2009-02-04
    Age : 66
    Location : Texas

    Re: Fried rectifier solution

    Post by Luddite on Wed Aug 31, 2011 4:36 pm

    merlot wrote:I'm rebuilding my WZ68s. I've got the diodes and resistors but can't find a source for the thermistor... I figure I might as well rebuild them from scratch to be safe. Has anyone found a source for it?

    Thanks.

    I don't know what value you need, but Dynakitparts.com has these in stock at $2.25 each:

    CL-80 (47 ohms) 3.0 amps max.
    CL-90 (120 ohms) 2.0 amps max.

    Best Regards,
    Charlie

    merlot

    Posts : 22
    Join date : 2008-12-22

    Re: Fried rectifier solution

    Post by merlot on Thu Sep 01, 2011 8:36 pm

    Thanks Charlie,

    It is difficult to read. The part number looks like NTC 100D-11. The "D" is hard to discern. Others on this site have identified it similarly. I think it might be 100 ohms. I've spent a lot of time in various sites looking for it, but have been unsuccessful. I'm thinking I should ask Weber.... May be they'll sell me some...


    merlot

    Posts : 22
    Join date : 2008-12-22

    Re: Fried rectifier solution

    Post by merlot on Sat Sep 03, 2011 10:44 am

    Weber will indeed sell me some. I just ordered them. They are on the Weber site under diodes.

    KT88

    Posts : 10
    Join date : 2011-08-12
    Location : Dubrovnik,Croatia

    Re: Fried rectifier solution

    Post by KT88 on Fri Sep 23, 2011 8:10 am

    Bob Latino wrote:I believe that the Weber's do use two of the 1N4007 diodes. These are 1000 volt rated but only at 1 amp. The 1N5408 diodes are also 1000 volt rated but at 3 amps. The 1N4007 won't stand up as well to the severe power spikes that Baddog has mentioned in his post. If you have power spikes up to 138 volts (!) as Baddog does at times in Costa Rica you can expect issues with your rectifiers either tube or solid state. Personally, I have used the same Weber WZ68 in my own ST-120 here for over 2 years with no issues. My voltage is always in the 119 - 120 volt range and I don't ever remember any voltage spikes. IMHO Weber should probably make the Copper caps with 1N5408 diodes. The cost difference is very little. Diodes are very inexpensive. In quantity you can get the 1N4007 for 2 or 3 cents each and the 1N5408 for maybe 7 cents each. It would cost pennies for Weber to make the Copper caps a little more resistant to severe voltage spikes.

    Bob


    Well...the amp came now from service and the sound is again good old sound that I know...and what was???...yes...the rectifie diodes IN5408...but now swaped with UF5408...I was on many forums out there but nobody mentioned the diodes in power stage..so many people told me to change output tubes or corect bias...the others where thinking that power transformer is damaged...some of them even that I might not hearing well...but nobody mentioned diodes...and they are the only semiconductors in the amp...and just semicondactors are very sensible on transient spikes..well...anyhow...I have my amp again sounding great

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