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    RESOLVED - Rectifier sparked, fuse blew. Both replaced. But Now, one channel is 'out'

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    Tubes4ever

    Posts : 110
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    Location : Star, Idaho

    Re: RESOLVED - Rectifier sparked, fuse blew. Both replaced. But Now, one channel is 'out'

    Post by Tubes4ever on Sun Dec 24, 2017 3:02 pm

    GreggW wrote:Should've mentioned I did the yellow sheet diode modification. Not sure if it contributes to the life of the 5V3a. Time will tell. (I built a tube guitar amp from a kit and did the yellow sheet mod to it also.)

    Gregg, I doubt that it helps the 5V3A any. Very robust tube as opposed to the 5ar4. But it can't hurt.
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    10-E-C

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    Re: RESOLVED - Rectifier sparked, fuse blew. Both replaced. But Now, one channel is 'out'

    Post by 10-E-C on Sun Dec 24, 2017 7:41 pm

    Tubes4ever wrote:
    GreggW wrote:Should've mentioned I did the yellow sheet diode modification. Not sure if it contributes to the life of the 5V3a. Time will tell. (I built a tube guitar amp from a kit and did the yellow sheet mod to it also.)

    Gregg, I doubt that it helps the 5V3A any.  Very robust tube as opposed to the 5ar4.  But it can't hurt.

    Today marks the 3 anniversary of my M125s build, I play them almost daily over the past 3 years. I didn't do the yellow sheet mod, I just bought Mullard GZ37s, but I do use a variac set at 118vac and a manual reset ground fault breaker which has saved me a few times over the years. In the 3 years of operation my bias has never changed, no hiccups or anything. I'm looking for another 3 years of service.

    TM
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    deepee99

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    Re: RESOLVED - Rectifier sparked, fuse blew. Both replaced. But Now, one channel is 'out'

    Post by deepee99 on Mon Dec 25, 2017 8:28 am

    10-E-C wrote:
    Tubes4ever wrote:
    GreggW wrote:Should've mentioned I did the yellow sheet diode modification. Not sure if it contributes to the life of the 5V3a. Time will tell. (I built a tube guitar amp from a kit and did the yellow sheet mod to it also.)

    Gregg, I doubt that it helps the 5V3A any.  Very robust tube as opposed to the 5ar4.  But it can't hurt.

    Today marks the 3 anniversary of my M125s build, I play them almost daily over the past 3 years. I didn't do the yellow sheet mod, I just bought Mullard GZ37s, but I do use a variac set at 118vac and a manual reset ground fault breaker which has saved me a few times over the years. In the 3 years of operation my bias has never changed, no hiccups or anything. I'm looking for another 3 years of  service.

    TM
    Hey Terry,
    Congrats on 3 years of cool runnings, and merry Christmas. The M-125s are the Russian tanks of the Dynaco inventory.
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    Bob Latino
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    Re: RESOLVED - Rectifier sparked, fuse blew. Both replaced. But Now, one channel is 'out'

    Post by Bob Latino on Mon Dec 25, 2017 11:46 am

    10-E-C wrote:

    Today marks the 3 anniversary of my M125s build, I play them almost daily over the past 3 years. I didn't do the yellow sheet mod, I just bought Mullard GZ37s, but I do use a variac set at 118vac and a manual reset ground fault breaker which has saved me a few times over the years. In the 3 years of operation my bias has never changed, no hiccups or anything. I'm looking for another 3 years of  service.

    TM

    I still use almost every day the original two prototype M-125 amps that were built in 2010. I don't know how many thousand hours they have on them ? I have changed out the tubes twice now even though the amps seemed to be running well. Believe it or not the two original fuses are still in these amps ? I have the two amps plugged into a power strip with a circuit breaker and that is plugged into a Shockshield GFCI. (See link below) Nothing else is plugged into this outlet. In Massachusetts here we have had a number of ice and snow storms and I have lost power a number of times during these storms. You have to manually reset the GFCI. If the power goes through a quick ON/OFF/ON, the amps will stay off unless you manually reset the GFCI. Rectifiers especially do not like to be "short cycled".

    The VTA amps and preamps are "overbuilt" with quality parts. Most tube amp troubles come from tubes that have gone bad. Some newbie tube amp users do not realize that tubes are "consumables" They have a finite life span and all will eventually die or be worn to the point where they will noticeably affect the sound quality of your amp or preamp. Link below on the long term durability of the VTA amps ..

    Shockshield GFCI

    Long term durability of VTA amps.

    Bob
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    j beede

    Posts : 425
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    Location : California

    Re: RESOLVED - Rectifier sparked, fuse blew. Both replaced. But Now, one channel is 'out'

    Post by j beede on Mon Dec 25, 2017 5:07 pm

    ...what Bob said.

    I have been running my MkIIIs for 5 years with the same pair of Sovtek 5AR4. I had one Sovtek 6550 fail two years ago. I buy output tubes as matched sextets for this reason.

    -Yellow sheet diodes, yes.
    -Series thermistors, yes (if using solid state rectification)
    -Short-cycling--NO, never
    -Variac, bucking transformer, Furman, etc. Only for bench operation for me.
    -Tube rolling; I keep it to a minimum for a variety of reasons

    I have re-built, repaired, updated, and modified many Dynaco amps of "unknown origin" and have encountered plenty of poor workmanship and sometimes unimaginable wiring errors. Why Dynaco/VTA amps are selected (apparently) as first time DIY projects I do not know. I am sure that Bob deals with this on a daily basis. He is a very patient man!

    Merry Christmas
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    Dynalover

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    Re: RESOLVED - Rectifier sparked, fuse blew. Both replaced. But Now, one channel is 'out'

    Post by Dynalover on Wed Dec 27, 2017 12:14 am

    j beede wrote:It's not going into a Leak Stereo 20 so a fake GZ34 should be fine.


    The existence of this thread alone shows why they are not!! They just aren't worth the risk or the hassle, and once they go Roman Candle nobody has saved any money (except maybe Sovtek I guess.)
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    Dynalover

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    Re: RESOLVED - Rectifier sparked, fuse blew. Both replaced. But Now, one channel is 'out'

    Post by Dynalover on Wed Dec 27, 2017 12:19 am

    PeterCapo wrote:If not already done, consider the "yellow sheet diode mod:" http://dynacotubeaudio.forumotion.com/t1006-tube-rectifier-diode-mod

    So, why not just remove the tube rectifier altogether? LOL!
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    PeterCapo

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    Re: RESOLVED - Rectifier sparked, fuse blew. Both replaced. But Now, one channel is 'out'

    Post by PeterCapo on Wed Dec 27, 2017 12:20 am

    While I cannot speak from personal experience, I have read posts from others who have said that with the yellow sheet diode mod, the Sovtek is a viable choice.

    The newer Tung Sol and GL are said to be better and are still relatively affordable.

    Dynalover wrote:
    PeterCapo wrote:If not already done, consider the "yellow sheet diode mod:" http://dynacotubeaudio.forumotion.com/t1006-tube-rectifier-diode-mod

    So, why not just remove the tube rectifier altogether? LOL!

    Simply because someone may prefer the "yellow sheet diode mod" plus rectifier tube for his or her own reasons.  While I cannot speak for anyone else, someone may prefer the sound quality a tube rectifier imparts.  Or, maybe for some the additional glow from one more tube adds to the delight of a tube amp.
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    j beede

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    Location : California

    Re: RESOLVED - Rectifier sparked, fuse blew. Both replaced. But Now, one channel is 'out'

    Post by j beede on Wed Dec 27, 2017 1:41 am

    Speaking from personal experience... The yellow sheet mod raises the effective PIV of the 5AR4, it does not replace the 5AR4. Simply bypassing the 5AR4 with 1N4007 or 1N5408 puts the HT caps at risk in some Dynaco designs, e.g. the MkIII. The forward voltage drop of the 5AR4 is desirable/necessary in some tube circuits. Bypassing the 5AR4 with silicon diodes also eliminates the HT time delay feature built into the 5AR4 which some (most) prefer to retain.

    I suggest that retaining the 5AR4 after the yellow sheet mod is neither cosmetic nor euphonic.
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    Tubes4ever

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    Location : Star, Idaho

    Re: RESOLVED - Rectifier sparked, fuse blew. Both replaced. But Now, one channel is 'out'

    Post by Tubes4ever on Wed Dec 27, 2017 11:47 am

    j beede wrote:Speaking from personal experience... The yellow sheet mod raises the effective PIV of the 5AR4, it does not replace the 5AR4. Simply bypassing the 5AR4 with 1N4007 or 1N5408 puts the HT caps at risk in some Dynaco designs, e.g. the MkIII. The forward voltage drop of the 5AR4 is desirable/necessary in some tube circuits. Bypassing the 5AR4 with silicon diodes also eliminates the HT time delay feature built into the 5AR4 which some (most) prefer to retain.

    I suggest that retaining the 5AR4 after the yellow sheet mod is neither cosmetic nor euphonic.

    Replacing the 5ar4 with silicon diodes will cause the caps on the VTA board to experience about 25 volts beyond their maximum voltage rating every time you turn on the amp until the tubes come up and start conducting. I know because I've measured the effect.

    So keep the rectifier tube. Plus its a tube amp. More tubes glowing is a good thing.

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    Re: RESOLVED - Rectifier sparked, fuse blew. Both replaced. But Now, one channel is 'out'

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