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    New Production CE Quad Cap Reliability (?)

    danmartinic
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    Post by danmartinic on Sat Apr 25, 2020 8:13 pm

    Hello!

    About five years ago, I installed a new CE 30/20/20/20 525v quad cap. It has now failed: brown residue is coming out of the half-moon 30uf terminal and two of the four terminals show nothing on my DMM's capacitor scale.

    I am a little surprised given that these are made in USA on original equipment. At the time, I replaced what appeared to be an original quad cap! At least 15 years old in my ownership.

    Could something else be causing this failure?
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    Post by danmartinic on Sat Apr 25, 2020 9:25 pm

    Instead of the questionable new quad can cap, could I use four 30uf 600v Axial Caps instead? EDIT: found 30uf 600v and 22uf 600v small size axial caps

    Just tie all the negative leads together?
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    Post by PeterCapo on Sun Apr 26, 2020 8:37 pm

    Which amplifier is it in? Some amps push it harder than others. And, if your AC mains runs high, it could cause increased voltage on the quad cap to the point that it failed.
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    Post by danmartinic on Sun Apr 26, 2020 8:41 pm

    Dynaco ST70. All original except for power supply caps (the other 2 50ufs) I replaced aprox 5 years ago along with the now-failed CE quad cap
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    Post by danmartinic on Sun Apr 26, 2020 8:50 pm

    New Production CE Quad Cap Reliability (?) 1db2a810
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    Post by danmartinic on Sun Apr 26, 2020 8:51 pm

    ST70 good up to 125V, no?

    5 year old CE Quad

    New Production CE Quad Cap Reliability (?) 5c94f410

    New Production CE Quad Cap Reliability (?) Aee49010


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    Post by danmartinic on Sun Apr 26, 2020 9:01 pm

    New Production CE Quad Cap Reliability (?) A0716810

    Triangle 20uf tap reads fine but 30uf tap no bueno...

    New Production CE Quad Cap Reliability (?) 45200710
    New Production CE Quad Cap Reliability (?) 11d41c10
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    Post by danmartinic on Sun Apr 26, 2020 9:15 pm

    Forgot that I am using a Mullard GZ37 / CV378 rectifier tube. However, my understanding is this would if anything reduce the voltage on the quad caps?
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    Post by PeterCapo on Sun Apr 26, 2020 9:50 pm

    A quad cap should last longer than five years in an original Stereo 70.  You could try the discrete electrolytics with the higher voltage rating.  However, "all original" means your amp is anywhere from forty to sixty years old.  It may be that your Stereo 70 needs some kind of repair or other restoration.  I'd like to suggest the following diagnostic procedures.

    The first thing to do is to take regular readings of your AC mains for a while.  Ideally, you'd want to measure and record your AC mains at different times of day for several days.  Your image shows your mains at a single point in time.  If you are fortunate, it will stay that way.  However, it can wander.  If it were to go much higher, it could be a problem.  Yes, the original Stereo 70 was warrantied up to 125VAC.  But, I haven't taken readings in a while and don't recall what kind of wiggle room there might be, if any.  Depending on what you find after taking readings of your AC mains over several days, you should think about installing a CL80 thermistor in series with your Stereo 70's power transformer primary.

    Then, in the owner's manual there is a chart of reference voltages on the same page as the schematic for the power supply: https://www.dynakitparts.com/wp-content/uploads/Dyna-ST70.pdf  You'd need to take readings in your Stereo 70 at the places indicated in the voltage chart and compare your readings to the values in the chart.

    Regarding your images, what's up with the resistors strung together at the quad cap?  A good approach is to just go through the entire manual step-by-step and put the amplifier back to the original configuration exactly as described in the original manual.  This could eliminate problems.  Also, some of those connections look like they could use some more solder.  The original Dynaco circuit design works very well and does not need to be changed, but due to sheer old age it may need to be put in proper order.

    I looked at a datasheet for the GZ37 but could not find the spec for voltage drop.  The only rectifier tube that Dynaco specified for normal, regular operation is the 5AR4/GZ34.  The manual mentions that 5U4 can be used temporarily.  But that's it.  The current production Gold Lion 5AR4/GZ34 should provide good service.  But, again, the amp needs to be in proper operating condition.

    I trust that that you know how to safely perform testing and troubleshooting procedures.  Here's an article that talks about safely working on this sort of amplifier - this article is a starting point, and I'd recommend you look further for more information on safe work practices: https://www.aikenamps.com/index.php/safety-tips-for-working-on-tube-amplifiers
    danmartinic
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    Post by danmartinic on Sun Apr 26, 2020 10:07 pm

    Thank you for the info.. very helpful. I will certainly perform the checks you and the manual recommend, including the house AC. And yes, I am a novice tech, basically only using the soldering iron sparingly when something goes wrong (I've always thought less is more when it comes to solder?).

    I have a small stash of passive electronics parts. When I last fixed my ST70 and installed this quad cap, I measured a little deviation on a few resistors so I made up similar values from what I have on hand. My understanding is 2 resistors in series can be used to makeup a replacement value.

    Thanks also for the general practices article; I can always use reminders, In a few days, I'll report back what I observe
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    Post by PeterCapo on Sun Apr 26, 2020 10:15 pm

    If you are missing anything, Mouser and Digikey are good sources for resistors. Original values and ratings likely to be available in 1% metal film.
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    Post by PeterCapo on Sun Apr 26, 2020 10:16 pm

    Solder is a "just right" thing.  Neither too little nor too much.
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    Post by PeterCapo on Mon Apr 27, 2020 9:12 am

    Just a few additional thoughts... make sure you have a 3A fuse in the fuse holder, nothing higher.

    With the quad cap half dead, your readings will be off.  But, in order to get meaningful readings at all, a 5AR4/GZ34 tube rectifier needs to be in use.  You could try a less expensive Sovtek 5AR4 just for testing purposes.  I'd avoid Chinese 5AR4, not because it won't work reasonably well, but because most Chinese octal base tubes I've see have pins that are splayed-out and/or have bulbous solder on the ends of the pins.  Splayed pins and/or bulbous solder deform socket contacts, and this can cause problems.

    Replacing the quad cap should be fine, but there's a question as to what caused it to fail in the first place.  You should be able to have a quad cap last a good while.  I am still thinking that going through each assembly step in the manual while referencing the pictorial wiring diagrams would be a good way to make sure the amp is in its proper configuration with the correct parts.  This could eliminate some problems.
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    Post by shermanaudio on Wed Apr 29, 2020 7:51 am

    I can share my experiences with CE Metal Can Caps since 2005.

    My results are mixed, using the CE Metal Can Caps, especially on some Amps.

    So I stopped using them in Amps that operate the first Section of the Cap close to the rated DC voltage.

    These CE caps seem to work fine in applications that don't suffer from AC Transformer Voltage Boost.

    I call this common condition Vintage Amp Hypertension.

    Un-regulated Tube Amp Power Supplies, with primaries wound to an older standard of 115V or 117V, are prime candidates for some TLC and Norvasc 5mg.

    Hammond makes a series of new Power Transformers that offers dual primaries 117/125 VAC.

    This I have found to work very well, especially in Cathode Bias designs where the Tube Current Draw permanently aggravated by boosted Secondary Voltages, not to mention the AC filaments that I have measured at 7 to 7.3 VAC on my old Stromberg AR-411 Amps.

    Using a Variac is a temporary solution as there is really nothing better than a Power Transformer that is wound to work well with the AC line voltages we have today, I would call these "The Millennial Series".

    All of the Amps that I build, are designed to account for this difference. And when my friends ask me to work on their older Vintage Amps, I always offer to replace the Power Transformer to optimize the Amp to be plug-n-play in any modern AC Mains. Its always better to operate an amp at or slightly under the steady state voltages that the factory publishes. You would be surprised by the Voltage and Current measurements otherwise.

    But the best solution is to replace these older Power Transformers with modern units that are wound with sensible primaries or have dual primaries.

    I have experimented with the Dynaco Reissue Plate and Filament Transformers, with some success.

    My Dynaco MK3 Clones work fine, and these are Fixed Bias so I can turn the Tube Current down to compensate, although this also tends to boost the DC voltages as the load on the Power Supply decreases.

    My ST-35 is one amp that I needs replacement of the Dynaclone Power Transformer,

    Even using the ST-35 Bias Boardm, the amp operates mostly out of range, and it loves to gobble EL-84's for Breakfast, Lunch and Dinner.

    The only tubes that stand up to this abuse are the Russian variants that operate up to 450V on the plates.

    But to my ears, they lose the EL84 sweet magic, we all love, they have a colder, dryer presentation, some may even prefer it as accurate.

    When I operate my ST-35 with a Variac, I can see the whole amp relax, and the filaments operate as intended, not as surrogate night-lights in the dark

    Good luk!!!
    danmartinic
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    Post by danmartinic on Wed Apr 29, 2020 8:47 am

    Thank you for the input!

    I have ordered 600v axial caps 1 x 30uf and 3 x 20uf.  My plan is to place these on a terminal strip under the chassis and keep the can for aesthetics.  I am assuming this is a simple modification: the caps are small and I will simply solder the connections as they were on the can, tying the negatives together and soldering to the ground located next to the can.

    When the caps arrive and I perform the above, I will take measurements and report the values--first with the GZ37.  If anything looks suspicious, I will look into sourcing a GZ34 and possibly a new power transformer.

    Stay tuned!
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    Post by shermanaudio on Wed Apr 29, 2020 10:06 am

    Nice, that is perfect, as 600V Electrolytic Caps will stand up to the most demanding DC voltages, even with the tubes removed, something that can be a disaster when using 500-525V Caps when troubleshooting.

    Note that the GZ37 may not be the best GZ34/5AR5 substitute, the filament on a GZ34/5AR5 will draw 2 amps RMS AC at 5 VAC. The GZ37 draws 2.8 amps RMS AC at 5 VAC, and that may make your stock ST-70 Power Transformer break a sweat. But an advantage of the GZ37 over the GZ34/5AR4 is that you will get a higher voltage drop across the rectifier, so it will also lower the DC rectified voltage some, not a bad thing at all.

    So I searched for the secondary winding specifications of a stock ST70 Power Transformer, and could not find published data or an an exact value for the 5V Secondary RMS AC RMS current delivery capability.

    My suggestion is to start out with a 5AR4 first, then measure the AC voltage across the Filaments and jot that down. Then plug in a GZ37 and measure again and note this value down.

    If the value does not drop by more than 10%, I would say that the 5V Filament Winding is OK.

    But if you measure a significant RMS AC voltage drop using a GZ37 vs. GZ34/5AR4, it may be wise to substitute the Power Transformer for a modern replacement that I can see from searching the WWW do offer the extra 5V filament Current Handling Headroom, plus these Modern Substitutes do offer as well a Primary ready to deal with 123VAC from our friendly Power Company and secondaries with extra umpfff.

    Our friendly Electric Utilities know well the consequences of the I-squared * R losses across their Grid, hence by boosting their sending end Voltages Vs, they achieve less P = I^2 * R losses over the Transmission Lines, and that saves them money lost to the resistive parts of the Transmission lines.

    Enjoy the Music, let us know how your ST-70 sings the Blues.
    danmartinic
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    Post by danmartinic on Wed Apr 29, 2020 10:43 am

    Thanks for the info!  I will follow up when the caps arrive.

    The ST70--playing vinyl through an all-tube custom preamp--has been playing the blues, jazz, and European folk music for twenty years wonderfully Smile
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    Post by PeterCapo on Wed Apr 29, 2020 10:52 am

    With 117VAC mains, the spec for the first section of the quad cap right after the rectifier tube is 435VDC, which is well clear of its 525 Working-VDC rating.  Remember that electrolytics also carry a surge rating, beyond the working voltage rating.

    Even with the AC mains up around 123VAC, the quad cap should last a long time.  Again, Dynaco warrantied the Stereo 70 with 117VAC power transformer up to 125VAC mains.  There are a lot of original Stereo 70s that ran their original quad capacitors for a very long time without them blowing up.  I've measured the voltage on that first quad cap section with the AC mains up to 125VAC via my variac, and it still cleared the 525 WVDC rating by a good margin.  Nevertheless, as I previously mentioned, a CL80 thermistor costs something like $3 and will reduce the level of AC mains that the power transformer primary sees.  You could even use two CL80s in series for a bigger voltage drop, if you like.

    The reference values in the manual's voltage chart are referenced to 117 VAC across the power transformer primary and with a 5AR4/GZ34 tube in use.  If the GZ37 is used for testing, and/or if the AC mains isn't 117 VAC at the power transformer primary winding, then there's no basis for comparing readings to the reference values in the manual's voltage chart.
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    Post by avi.inc on Wed Apr 29, 2020 11:16 am

    Can you use the can from a ST-120 I've had this one for ten years no prob. It came with the kit from Bob.


    https://www.dropbox.com/s/4zojxd5ynqa3od2/20200429_080513.jpg?dl=0]AuthentiCap

    80 MFD 550 V 600V
    40 MFD 550 V 600V
    30 MFD 525 V 575 V
    20 MFD 550 V 600V
    -10 / +20 %


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    danmartinic
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    Post by danmartinic on Wed Apr 29, 2020 11:17 am

    I understand that the manual numbers will not provide a basis when using a GZ37.  However, I'm betting that GZ37-based measurements will at least shed some light on what the operating conditions are and be sufficient to reveal a major issue or lack thereof.  Will be fun to see!

    I read up on what a thermistor is and I'm a little confused: it's a temperature-dependant resistor than can be used a current limiter?  Are there any disadvantages in using it as a mains voltage-dropping device?


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    Post by danmartinic on Wed Apr 29, 2020 11:20 am

    [quote="avi.inc"]Can you use the can from a ST-120 I've had this one for ten years no prob. It came with the kit from Bob.


    I understand that can is a good sub but it's $60USD which translates to over eighty bucks for this Canadian.. plus shipping add another twenty CDN for me.  I got the four 600v small caps for less than half (45CDN) shipping included
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    Post by avi.inc on Wed Apr 29, 2020 11:30 am

    danmartinic wrote:
    avi.inc wrote:Can you use the can from a ST-120 I've had this one for ten years no prob. It came with the kit from Bob.


    I understand that can is a good sub but it's $60USD which translates to over eighty bucks for this Canadian.. plus shipping add another twenty CDN for me.  I got the four 600v small caps for less than half (45CDN) shipping included

    WOW That's just nuts, I try to get there every year for the Three Flags Classic (3FC) and the cost is a eye opener.
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    Post by shermanaudio on Wed Apr 29, 2020 12:13 pm

    PeterCapo wrote:With 117VAC mains, the spec for the first section of the quad cap right after the rectifier tube is 435VDC, which is well clear of its 525 Working-VDC rating.  Remember that electrolytics also carry a surge rating, beyond the working voltage rating.

    Even with the AC mains up around 123VAC, the quad cap should last a long time.  Again, Dynaco warrantied the Stereo 70 with 117VAC power transformer up to 125VAC mains.  There are a lot of original Stereo 70s that ran their original quad capacitors for a very long time without them blowing up.  I've measured the voltage on that first quad cap section with the AC mains up to 125VAC via my variac, and it still cleared the 525 WVDC rating by a good margin.  Nevertheless, as I previously mentioned, a CL80 thermistor costs something like $3 and will reduce the level of AC mains that the power transformer primary sees.  You could even use two CL80s in series for a bigger voltage drop, if you like.

    The reference values in the manual's voltage chart are referenced to 117 VAC across the power transformer primary and with a 5AR4/GZ34 tube in use.  If the GZ37 is used for testing, and/or if the AC mains isn't 117 VAC at the power transformer primary winding, then there's no basis for comparing readings to the reference values in the manual's voltage chart.

    Fully agree.. yet those 525V CE caps seem to fail often as I read on the various forums. And even at the voltages we would expect them not to. So, I switched to JJ Multi Section Caps about 12 years ago and no fails yet. The few CE Caps I have used in Leslie and Hammond Organs, so far, no fails reported to date. So some QC issues are suspected. How many, I have no stats, only personal experience on at least 3 of these CE's in MK3, ST-70 and also ST35, they leach the chemical after a few months.
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    Post by PeterCapo on Wed Apr 29, 2020 12:24 pm

    Well, I can't deny the possibility of manufacturing defects. But, I think it would be appropriate to at least rule out the amplifier as a source of the problem.
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    Post by PeterCapo on Wed Apr 29, 2020 12:36 pm

    danmartinic wrote: ... I read up on what a thermistor is and I'm a little confused: it's a temperature-dependant resistor than can be used a current limiter?  Are there any disadvantages in using it as a mains voltage-dropping device?

    There are at least a couple of different types of thermistors.  The kind often-enough discussed for tube amps are the NTC, or negative temperature coefficient, thermistors.  What this means is that when the thermistor is cold, it has a higher resistance.  When the amplifier is turned on, the thermistor warms up and its resistance drops quite a bit.  In the case of the CL80, it is rated for 3A steady state current, and its cold resistance is 47 ohms.  When the amplifier is turned on, it soft-starts the amplifier as it warms up and its resistance drops.

    Looking at the datasheet for the CL80, you can see that when the current reaches 50% of its maximum rating of 3 amps, the CL80’s resistance is 1.2-ohms.  The original Stereo 70 circuit draws around 1.5 amps (at idle, anyway).  So, you get approximately a 2 VAC drop in your AC mains at the power transformer primary, because the thermistor is installed in series with the power transformer primary circuit.  So, if the AC mains from your wall is 123 VAC, then your power transformer will see approximately 121 VAC, and this is well within tolerance for the original Stereo 70.  This is, again, assuming that the Stereo 70 is in the original configuration and in proper operating condition.

    The current limiting part I would think refers to its hot resistance, which is low.  There may be some kind of small loading effect on the transformer, but it nevertheless works well.  Some even use NTC thermistors in series with the B+.  In fact, some great amplifiers have used them.  I have a vintage McIntosh MC30 that used one, and I strongly suspect that other amplifiers used them, as well, from the factory.


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