Tubelab Simple SE Rectifier Problem?

[eddiemeddiem]

Well, I finally got my Simple SE all hooked up. In order to test it out, I hooked it up in triode mode without feedback. When I first tried to turn it on, I blew the diodes in the rectifier. After doing a little bit of research, I found an existing thread from about nine months ago. Here's a link - the section is on the second page, about halfway down:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=108504&perpage=25&highlight=&pagenumber=3

It turns out that when I orginally order all the parts for my amp, the supplier was out of the recommended DSEI12-12A diode, and I opted to go with one with similar specs, although 1000V instead of the recommended 1200V, obvoiusly not knowing about the above referencd problem. So, I just ordered a couple more diodes, this time the ones rated for 1200V and 17A.

In the meantime, anxious to hear my amp make some sound, I decided to switch over to the tube rectifier. So, I desoldered the diodes and jumpered (instead of a switch) the terminals for tube rectification. After rechecking all the connections, I switched it on. I heard a slight hum for a few seconds, then some crackle/pops sounding like they came from some where on the board, followed a blown 3A fuse (my last). Three of the tubes had little glowing orange spots, but one of the EL34 power tubes did not, and if I had to guess, this is where the crackling came from.

So, I'm wondering where I should proceed next for troubleshooting? To start with, it seemed to me that the vacuum tubes went into their respective sockets very easily (too easily), so I'm thinking that I'll use a small pick to tighten up the socket connectors, for fear that they might be loose.

I'll hit up the store tomorrow after work and get some more fuses...

Any and all (no matter how simple) suggestions are appreciated!!!

Thanks,
Eddie

 

[whitelabrat]

Photos?

Double and triple check your wiring. Sounds almost like a short. If you don't find anything odd there then check your soldering. I've done this by using a DMM and the "beep" function to determine continuity.

I don't see why a 1000V diode wouldn't work. I fried my FREDs and plan to replace them with a UF4007 rated for 1000V (mouser 625-UF4007-E3). Perhaps not as high performance, but it should do. I've just not had time to get it on the bench, though.

 

[w5jag]

So, I desoldered the diodes and jumpered (instead of a switch) the terminals for tube rectification. After rechecking all the connections, I switched it on. I heard a slight hum for a few seconds, then some crackle/pops sounding like they came from some where on the board, followed a blown 3A fuse (my last).

Check the polarity of your electrolytic caps following the rectifier. You may have one or both installed backwards.

Win W5JAG

 

[eddiemeddiem]

Well, after tightening up the tube sockets, it seems like I’ve fixed the problem in the one power tube, however I’ve found another. I power on the amplifier (without any volume), and let it sit for ~30 seconds or so, and then I see a blue arc/flash in the GZ34 rectifier tube, and the fuse blows. I checked the voltage out of the transformer that I’m using for the tube rectifier, and it’s reading a hair over 6V, instead of the 5V like the spec said when I ordered it. I checked this voltage with the transformer disconnected from the board at the leads, and then when connected to the board at the tube socket. Should the rectifier tube be able to handle the 6V instead of 5V?

While I was at it, I checked the high voltage taps out of the primary transformer, and it’s reading about 860V, instead of the 800V like it’s spec’ed out as. FYI, the line voltage at my house is 123V. I know my line voltage is high, I would think that the components/design should be able to handle this?

Anyways, I’m not convinced that these higher voltages are necessarily my problem. Hopefully tonight I’ll have some more time to check continuity and do some more trouble shooting.

I tried to attach a couple of pictures, but I'm having trouble with the file size. I'll find somewhere else to host them tonight.

Thanks!
Eddie

 

[whitelabrat]

The voltages from the transformer should be a bit high when unloaded. A load should cause the voltage to sag down to something more appropriate for the job.

Did you remove your dead diodes? I had to remove mine after they shorted to get the ball rolling.

 

[Merlinb]

I see a blue arc/flash in the GZ34 rectifier tube, and the fuse blows. I checked the voltage out of the transformer that I’m using for the tube rectifier, and it’s reading a hair over 6V,

Unfortunately, most of the TubeLab power supplies are poorly designed, so I am not particularly surprised you're getting a problem.
Firstly, what value capacitor are you using for the reservoir? (C1 in the schematic). It should be no more than 60uF.
Second, are you saying that you're using a separate transformer to power the GZ34 heater? If it's an ordinary little 5V transformer then its insulation may be suffering by having the DC imposed on (which could lead to the arcing you see).
There is, of course, a small chance that the rectifier itself is bad.

 

[Tubelab_com]

Unfortunately, most of the TubeLab power supplies are poorly designed, so I am not particularly surprised you're getting a problem.

Merlinb

Please explain your comment. The power supply in the Simple SE is textbook stuff except for the solid state rectifier option which most builders don't use. What is poorly designed about a textbook FWCT rectifier (5AR4) followed by a CLC or CRC filter?The recommended value for C1 is 47uF which is acceptable for a 5AR4. The Simple SE power supply has been thoroughly tested and simulated in PSUD and LT spice. If it is properly built, it WILL work.

The entire Simple SE design is mostly (old) textbook stuff except for the CCS. There have been dozens of them built with very few problems (3). Except for a few zapped diodes which were caused by the standby switch in the transformer CT, there have been ZERO power supply issues. The standby switch is no longer recommended. There has been only one other instance of a Simple SE that did not work on power up that I am aware of which turned out to be a speaker connector that was shorted to ground.

eddiemeddiem

There should be no jumper in the SW1 connector for tube rectifier operation, although it won't matter if the diodes are removed.

What are you using for a main power transformer? You mention an 800 volt rating which is a bit high. You are measuring 860 volts which is too high. I am guessing that since you asked about a seperate 5 volt rectifier transformer that you are using an Antek 800 volt toroid.

I have connected a Simple SE up to an Antek 800 volt toroid to see what would happen. The B+ voltage was about 525 volts under load with a 120 volt line voltage. You will be getting 530 to 540 volts. This voltage is far too high for 500 volt rated capacitors, and all but the best output tubes. If this is the case be aware that the electrolytic capacitors are capable of violently exploding if operated above their rated voltage. I removed the capacitors from my board and used external motor run capacitors capable of 630 volt operation. Most EL34's can't handle this much voltage, so I used EH KT88's. In the end, I decided that the extra watt per channel wasn't worth the effort, so I put back the 750 VCT transformer and saved the big Antek for a big Push Pull amp.

In your case, one of the capacitors C1 or C2 may be breaking down causing an arc in the rectifier tube and a blown fuse. If the power supply capacitors are not the problem, one or more of the EL34's may be going into a runaway condition at this high of a voltage. Either way the easiest solution is to use a more conservative power transformer. It may be possible to use higher voltage rated electrolytics, but they are hard to find, or off board the capacitors, but then the tube issue will come up. If your EL34's will survive at 500+ volts the cathode bias resistor will need to be increased. Some experimentation will be needed to find the proper value.

 

[kenpeter]

Probably just hating over yer power supply with the PIC...

Bank switched memory and I/O? One working register?
Poorly filled with an inferior grade of magic blue smoke.

Shoulda gone AVR there.... Dude, I'm tellin ya! Or that
classic Ruskie MCU that executes PDP-11 instructions.
Yeah, that ones the ticket!

I'll only forgive if your next abuses some Nixies.

 

[eddiemeddiem]

Yes, I removed the dead diodes, then jumpered SW1. I did this assuming that I blew the diodes while it was "open" and running the SS rectifier. I guess I was wrong (not the first time).

The power transformer that I'm using is the big SE Edcors - XPWR110, rated at 400-0-400V and 200 mA. For the 5V heater, I'm running a Hammond 166MS, rated at 5V and 3A.

The C1 that I'm running is a 47uF 500V, while C2 is a 180uF 500V.

I just removed the jumper so that SW1 is "open" and daringly switched it on. The result was the same - it powered on for about 30 seconds, then there was a blue arc/flash in the GZ34, and blew the fuse. It didn't last long enough to try to measure B+. I've got Electro Harmonics EL34's right now, an since I'm still trying to get it to work, I'd rather not risk it... the tubes or my life.

Tubelab - If you're relatively confident that I was aggressive and ordered too big of a power supply transformer, it's not a problem at all. It makes complete sense that that the tubes/capacitors can't handle the voltages. I'll probably go ahead and order a smaller transformer - me trying to learn this hobby isn't worth risking anyone's safety.

Here's two pictures that I promised earlier(I uninsulated the alligator clips for the photo):
http://i223.photobucket.com/albums/dd305/eddiemeddiem/Withouttubes.jpg
http://i223.photobucket.com/albums/dd305/eddiemeddiem/Withtubes.jpg


Thanks again,
Eddie

PS - I probably should get my circuts text book out from college and reteach my self how to calculate all the volts/amps at the different points.

 

[w5jag]

or off board the capacitors, but then the tube issue will come up. If your EL34's will survive at 500+ volts the cathode bias resistor will need to be increased. Some experimentation will be needed to find the proper value.

To the best of my recollection, when I was diddling with my Simple SE in the mid 500's, I started with 1.3K cathode resistors.

Wired as triodes, GE 6550A, GE 6L6GC, the Chinese coke bottle 6L6GC, and the New Sensor Tung Sol 6L6GC/STR all seemed fine at these voltages.

The cathode voltages went into the mid 50's - a bit past the 50 volt rating of the spec'ed bypass caps, but this never caused any problems.

The B+ would go up close to 700 volts before the tubes drawing power would drag it back down . I series connected capacitors to boost the voltage rating.

An Ei 6CA7 arced so hard at these voltages, that it took out the power xfmr, and ended all the fun , although I have since run them in the low to mid 400's without problems.

Win W5JAG

 

[chrish]

I am running a hammond 370-0-375 volt transformer, and the voltages are on the high side.

I was one of the first to have a problem with the power supply/standby switch. It blew my diodes a few times. After this I got arcing on my JJ GZ34 leading to fuse blowing (similar to your symptoms). I think I read somewhere that if you get arcing in the rectifier tube, there may be minute carbon tracks across the mica that sets up future pathways for arcing. My JJ GZ34 failed very soon after this all happened. I have since removed the SS diodes and removed the standby switch. Have tried half a dozen different tube rectifiers since with ZERO problems. I now have an ancient Australian made Mullard 5A (?)4 that I found at a movie prop department (along with a bunch of other old tubes) and it is ticking along sweetly!

Replace that GZ34 if it is arcing. Perhaps try something like a 5U4G, it will drop a few of those unwanted volts.

Cheers,

Chris

 

[Merlinb]

Merlinb

Please explain your comment. The power supply in the Simple SE is textbook stuff except for the solid state rectifier option which most builders don't use.

They are texbook on a simple level only.
The valve rectifier has no series limiting resistane, which, although they will work for a while, ultimately leads to their demise. Any old textbook will explain this, and demand their use.
The positioning of the standby switch, leading to nice big flyback spikes (which has been a reported problem, which the designer interestingly blames on the transformer!), and which also do not actually isolate the amp from the PSU. These are such simple errors that they betray a lack of design thoughfulness, which could be so easily avoided.

 

[Tweeker]

Some transformers will have much more flyback than others, it is a largely function of leakage inductance. A toroid should have much less than an EI. No comment on the circuit in question.

 

[korneluk]

...Or that classic Ruskie MCU that executes PDP-11 instructions...
I'll only forgive if your next abuses some Nixies.

kenpeter,

Just a quick comment since you do not accept forum email. Which Russian MCU are you referring to? Please check out this link and email me offline.

http://www.cpushack.net/soviet-cpus.html#2

TIA,

-- josé k.

 

[Tubelab_com]

The valve rectifier has no series limiting resistane, which, although they will work for a while, ultimately leads to their demise. Any old textbook will explain this, and demand their use.

The rectifier surge current is limited by the internal DC resistance of the power transformer and the size of the input capacitor. My usual recommendation is to use a Hammond 274BX or an Allied 6K7VG which are electrically identical. PSUD II and LT spice both concur that the surge current is within spec under these conditions. Yes, most old textbooks explain this, and I did thoroughly explore the possibilities during the design and testing of this amp. I can not possibly design for and test every possible power transformer combination during the design phase. A series resistance could be warranted if a transformer with a low DCR is used.

eddiemeddiem is experiencing an arc in the rectifier tube at about 30 seconds. It is possible that this is due to the initial surge current, but my experience has shown that a rectifier tube that is experiencing an overload due to low DCR and a large input cap will arc at about 10 seconds. Yes, I have intentionally put a 150 uF cap in the C1 position to see what happens, and the tube does indeed spark out. I still believe that the problem is being caused by too high of a B+. Unfortunately this is a dangerous situation that is hard to trouble shoot remotely since even with a big resistor added in series with the rectifier the risk of a capacitor explosion is very real!

The positioning of the standby switch, leading to nice big flyback spikes (which has been a reported problem, which the designer interestingly blames on the transformer!), and which also do not actually isolate the amp from the PSU. These are such simple errors that they betray a lack of design thoughfulness, which could be so easily avoided.

The designer is NOT blaming the inductive spike on the transformer, only explaining that every transformer IS different. I am an Electronics Engineer with 35 years of design experience at a major electronics company, and I figured out what happens when you put a coil of wire across a battery and then disconnect it at a very young age.

I admit that the standby switch was added to the design late at the request of one of the early testers. I am no longer recommending its use and that is stated boldly on several of my web pages. It will be removed from the web site with the next revision.

The design of the Simple SE power supply is sound when used under the recommended operating conditions. The Simple SE amplifier is intended for first time builders. It must remain simple for that reason. I could add a resistor in series with the CT of the power transformer for the few transformers that may require it, but then there would be the need for an explanation, and a chart to determine its value. This would require some knowledge of the particular transformer. I will add this to the manual after I cover the updates requested by the current builders. Many of the complaints that I get concern the charts that are in the manual currently. The builders state that they are just too hard to understand, "we just want to know what transformers to use without trying to understand how it works."

The assembly manual is considered by many to be the best available. It is the reason that many users decide to build a Simple SE. One person working part time can not possibly write a Heathkit style manual, but I am trying. A revision is in the works to add what most users are asking for, a new parts list with better detail in the areas of transformer selection for the 3 common recommended configurations. I have started a new web page that lists tubes and transformers for 3 popular combinations (750 VCT Hammond or Allied, KT88 - EL34 - 6L6GC, 5K ohm OPT), (650 VCT, KT88 - EL34 - 6L6GC, 3.6 K ohm OPT) and (550 VCT 6V6 5 or 6K OPT), with part numbers. I have also done the same for the TubelabSE, but I have not had the time to make them web site ready.

The cathode voltages went into the mid 50's - a bit past the 50 volt rating of the spec'ed bypass caps, but this never caused any problems.

The new parts list shows 63 volt caps for 2 reasons. My testing shows that the ESR of the Panasonic 63 volt caps is lower than the Panasonic 50 volt caps. There are a few fringe users out there (you and me) that will try to find the limits of these things. 63 volt caps buys a bit more margin especially under the temperature extremes that may be encountered in a tube amp. I have a KT 88 amp using the recommended Allied transformer. The B+ is 430 to 440 volts (depending on bias current and line voltage) with the tube rectifier and up to 460 volts on SS. I have operated the EH KT88's as high as 100 Ma and I have seen the cathode voltage approach 50 volts.

Lets see here, I have a full time job that demands 50 hour work weeks, 2 relatives have passed away within the past year and 2 more are seriously ill (1 is terminal) all requiring a lot of travel time, the web site keeps going down, and some lawyer is demanding that I remove all references to the name SimpleSE from my web site or face legal action, and I am spending time defending my design instead of improving the manual. My wife has been telling me that I have spent 5 years on Tubelab. It used to be fun, but it is becoming a chore (I don't have time to play with tubes any more), and Tubelab has yet to make any money. She says I should give it up and move on to something else. Maybe she is right.

Tubelab - If you're relatively confident that I was aggressive and ordered too big of a power supply transformer, it's not a problem at all. It makes complete sense that that the tubes/capacitors can't handle the voltages. I'll probably go ahead and order a smaller transformer - me trying to learn this hobby isn't worth risking anyone's safety.

I am not familiar with the Edcor power transformers. I simply do not have the funds to try out every possible power transformer out there. If this is your first amplifier build I would recommend building it the same way most users have. This is a known combination that works well. Use a power transformer that puts out a maximum of 750 VCT. Most users in the US use a Hammond 274BX or an Allied 6K7VG. These are the same transformer, the Allied is made by Hammond but is cheaper (www.alliedelec.com). Users in 230 volt countries are using the Hammond 374BX. If you were measuring 860 volts on your Edcor power transformer you were probably getting a B+ voltage of well over 600 volts before the output tubes warmed up. This may have damaged the 500 volt capacitors. I would replace them.

Bank switched memory and I/O? One working register?
Poorly filled with an inferior grade of magic blue smoke.
Shoulda gone AVR there.... Dude, I'm tellin ya!

Microchip has upgraded the quality of magic smoke that they put into their current chips. I can tell you from experience that it is no longer blue, it is now kind of grey. The smoke hides the 16 bit X 16 working register array. Besides I hide behind the C compiler so I don't have to deal with it (code wimp, I know). The whole thing was done for a Microchip sponsored design contest so I kind of think that the AVR wouldn't have done as well.

I'll only forgive if your next abuses some Nixies.

Been there, tried that. Nixies are no fun. No matter how much you try you can't make them glow. They will arc if severely abused, and the envelope darkens so that you can't read the numbers. Don't even think of popping one into the microwave oven.

 

[dubdub]

Im not an tube expert by any means but I think the design behind SimpleSE board is really good, there are very few tube kits/pcbs or for the beginner that can either be built to a minimal spec on a small budget or a high end version with loads of options and flexibility (mode switch, ss rectifier, feedback switch all changeable through switches). I think this allows someone like me to experiment with my diy project very easily, I know good design philosophy when I see it.

In selecting the parts for the pcb Im also learning allot about tubes/valves and getting to join up great communities to get advice/feedback read what others are saying etc. This is obviously my opinion, but I think to say that the designer is thoughtless is unfair, it is a good sign that the designer should wish to amend building instructions and continue to provide feedback to builders when there may be a unique problem.

Although we should admit no design is above criticism, I think your comments are too negative.

 

[kevinkr]

Hi George,
I'm saddened to hear about what's going on in your life currently, my wife and I have had a somewhat similar experience over the last six months.

Don't give up on your business unless your heart is no longer truly in it. I never made any money either, gave it my best shot, hung on to the bitter end (last $100 in my pocket) and finally got out just before it consumed me. I was very bitter over the business failure for a long time.. (Dreams die hard) The upside is with the business basically gone I can get back to what got me started, a love of music well produced, and endless opportunity to tinker..

I doubt Merlinb has ever had first had experience of one of your amplifiers. I have and thought it an excellent introduction to SE amplification for anyone just learning the ropes. I thought it was nothing more than a gratuitous attack (sour grapes?) and perhaps indicative of his lack of experience in trying to design and sell a product that people can actually build. His comments would have to apply to just about every guitar amplifier ever built, and most classic tube amplifiers as well.

I think the respect with which most people regard you speaks for itself, as does the contribution (of freely shared knowledge) you make here.

Edit:

Deleted my last comment as being redundant, but I will say there is a naysayer in every crowd. And I would not let it bother you too much, chalk it up to the fact that you are at least noticed.

My best regards..

 

[kevinkr]

They are texbook on a simple level only.
The valve rectifier has no series limiting resistane, which, although they will work for a while, ultimately leads to their demise. Any old textbook will explain this, and demand their use.
The positioning of the standby switch, leading to nice big flyback spikes (which has been a reported problem, which the designer interestingly blames on the transformer!), and which also do not actually isolate the amp from the PSU. These are such simple errors that they betray a lack of design thoughfulness, which could be so easily avoided.

I have never seen a commercially produced amplifier whether of British, German or American origin that actually used external resistors in series with the 5AR4 plate leads, this is because the power transformer can usually be designed to have enough combined primary and high voltage secondary DCR to take care of the resistance requirement. The Mullard book I have suggests the addition of external resistors only in the event that the winding resistance is insufficient to meet the design criteria.

How much actual design experience do you have? Anyone who had done any serious design would have figured this out. You should be very careful about the allegations you make, and think about the potential consequences of your comments. It doesn't present you as anyone having anything more than an axe to grind, and your comments betray a simplistic interpretation of book learning and not much else.

 

[Tubelab_com]

I have never seen a commercially produced amplifier whether of British, German or American origin that actually used external resistors in series with the 5AR4 plate leads,

I have never seen a product with the resistors either and I have been dissecting tube gear since the mid 1960's. The addition of extra resistance will add to the ESR of the power supply if it is not really needed. Most commercially produced consumer grade tube gear has the power transformer size dictated by product cost. This usually insures enough DCR. A problem could arise if an oversized power transformer is used.

A better solution from a "design thoughtfullness" standpoint is to include a NTC device (also known as an inrush current limiter) either is series with the line (mains) voltage or in series with the center tap of the HV winding. I routinely add these devices to most of my amplifiers. I put them in series with the fuse holder on the primary side of the power transformer. This also eases the initial surge current seen at turn on when all of the tubes are cold. I have mentioned the use of these devices on the forums, and in my web site, but it is not explicitly spelled out in the assembly manuals. It will be added. The size needs to be determined experimentally to allow the voltage to come up slowly for each amplifier design. I use a CL-80 in the Simple SE the 300B version of the Tubelab SE and a CL-90 in the 45 version of the Tubelab SE. See the data sheet:

http://www.alliedelec.com/Images/Pr...ture-Sensing_Actives-and-Passives_8370011.pdf

Please excuse my cranky demeanor in the last few days. On top of all of the other "stuff" that has come down lately, the company that I work for has fallen on tough times and laid off over half of its work force in the past few years. Last month they whacked 355 engineers in the facility where I work, including most of my friends (and a couple of forum members). Most have already left, but today was the last day for the remaining few. Everyone who is still there can read the writing on the wall. Like I said, more changes are coming.

kevinkr, thanks for the encouraging words. I recieve a lot of email that is very positive and similar to yours generally thanking me for being a source of free knowledge that can not be found elsewhere. There have been the few naysayers which are mostly critical of my use of "sand" in tube amps. I can't even print some of the flak that I got for the Minitron (DSP controlled vacuum tube amp), but I expected it. I didn't understand the reason for this posting, and I still don't. Every engineering effort is always a compromise. Products that are to be assembled by users of varying skill levels are an especially challenging compromise, as is the manual. I have been doing DIY products since the mid 1970's (SS-50 bus computer boards), and the Simple SE has seen the best "plug it in and it works" rate yet. I know of two out of about 100 (this being the second) with issues. The other was a shorted speaker connector.

Sherri and I still need to talk and crunch some numbers to decide whether Tubelab will continue as is, be scaled back, or be expanded. I have previously been financially succesful with embedded controllers. I have been brushing up on my uP skills since my 35 year carrier at one company may not have much life left in it. The worst part is the uncertainty. I don't know if I will be employed for 5 minutes, or 5 years.

 

[Boris_The_Blade]

I have never seen a commercially produced amplifier whether of British, German or American origin that actually used external resistors in series with the 5AR4 plate leads, this is because the power transformer can usually be designed to have enough combined primary and high voltage secondary DCR to take care of the resistance requirement. The Mullard book I have suggests the addition of external resistors only in the event that the winding resistance is insufficient to meet the design criteria.

The GE MS4000 does indeed have external plate resistors. I was surprised to see them as well. Other similar GE models don't have them though. I'm curious why they did it for this model - probably an engineer's decision for longevity, but removed later by the sales team.

http://gregory.webng.com/G7700/GE_MS-4000_schem.gif