Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Johnnydoright on January 06, 2022, 05:08:03 pm
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Hi guys, since I am new, and finally figured out how to post to the forum, I will introduce myself, and kill 2 birds as they say. Johnnydoright here, ( though it doesn't ever seem to work out that way). I just joined you folks, and am impressed. I am retired, and decided as a hobby, I would try to build an amp kit. Put together a 5E3 clone, and was pretty stoked. Decided to try to do one cheap, and things went sideways. Long story short, horrible distortion, and low filiments voltage. My question is regarding power transformer grounding.
If my transformer to the lamp has a ground for the filiments (6.3 volt to the lamp), do I then not install the 2- 100 ohm resistors tied together and run to ground. I am working from nice layout for a 5E3 Tweed deluxe that I downloaded from the forum. The schematic I was supplied was poor in that I'd does not show the lamp, but it does show the center tap of the 6.3 volt leg as being grounded. As I say, I am quite new at building, and really need help. I joined this particular group because it seems to be a place for fellas like me that want to do this, but lack experience. Any help is appreciated, oh and as a side note, I think I might have toasted my Chinese supplied transformer. I don't mark it as a huge loss, and have got a replacement that I think will work.
Thanks for any help, and please excuse my stupidity😁
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Hello and welcome to the forum !
If you post the schematic you are following helps people to help you, or the link for it will also work.
About the filament wiring and artificial center tap, if the PT doesn't have a CT for the 6.3v, then use the 100ohms resistors, if the PT have the CT use that, although it is possible to not use the CT(tape it for insulation) and instead use the 100ohms resistors. Use one or another but not both.
Also check the links on the top of Tube Amp Building - Tweaks - Repairs (https://el34world.com/Forum/index.php?board=13.0) board, you will find lots of info there.
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Measure your filament voltage. Put one meter probe on pin 2 of a 6V6. Put the other probe on pin 7 of the same 6V6. What have you?
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Well, I found a layout with the 6.3 volt portion of the transformer grounded, and found I do not need the 2 100 ohm resistors tied together going to ground. The amp works better, but still sounds distorted in a poor way. I am going to try different tubes, and of course check back with you guys and hope someone with similar experience can give me some insighg. Thanks for listening to the new guy. Hope someone has had similar experience and is enjoying my ignorance. Keep smiling😃
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I am fairly new also but I have built a 5E3....it was/is a finicky amp by all reports....
The distortion you hear could possibly be normal..If you search you will find many
Threads all over the net with the same complaint. Speaker selection is important
And there are lots of mods to "tame" the 5E3....be careful you can take the 5E3 right
Out of the 5E3...
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Thanks so much for your kind helpful remarks. I will do more digging. The schematic I was following is an actual 5E3 take from "THE TUBE AMP BOOK II". I used the Layout for a 5E3 clone kit I got from STUMAC, as I built one from a kit I purchased on line from them. I made it as close as I could, but due to my lack of experience, and trying to build the cheapest copy of it I could, I made some major mistakes. First, I bought parts from outside the U.S., through a third party, resulting in a total fiasco when I had questions. Working from the provided schematic, I assembled the amp, painstakingly testing each resistor as I organized them for the build, and again as I installed them. As I assembled, I was both concerned, and elated. Concerned, because I realized the STUMAC amp I was copying was different than the original schematic.Resistor values were the same, but Capacitor values were clearly diferent. Looking cat the Stumac turret board, starting at the left, and working right, the first cap is 25mf, 50 volts, but I was provided a 25mf, 25 volt cap. This matches the original 5E3 diagram. The next cap in the STUMAC build is 22mf 500volts, I used a 16mf 450 volt here and in the next 2 cap positions, where there were 22mf 500volt in my first build. The next 2 caps were .1mf 600volt,small and yellow, but stumac has the same value , but they are"orange drop" caps, which I have come to may be better quality. Keep in mind, I understand the value of the components, but as for differences in quality, I have no clue. So, closely following the provided schematic, I continued. Once I got the turret board done, I continued and energy thing went ok, until I tried to solder up the power transformer. The diagram provided did not agree with the transformer provided. Uh oh...so I emailed them(through my 3rd party) and they responded the next day, indicating "do not see the wire. Only see the voltage blackcand brown is for 110V. black and blue is forc125V . Which one is good for you? Green yellow green is forc340-0-340V for 5Y3 pins 4 and 6. Yellow black yellow is for 6.3 volts pilot light and filiments. Don't forget to ground the black wire. Black-
White is 5y3 pin 2 and 8." So that was how I wired it up. And I did my usual voltage test, no tubes, then rectifier only, then rectifier and
preamp tubes, and the voltages weren't too far out, except my filiments voltage was way low ( any wonder as it had a 50 ohm resistor to ground + the middle tap was grounded.) A t any rate, I continued, installed the power tubes, and plugged in the speaker, and turned it. No smoke, amp hums, sounds ok, so I plug in my strat. TERRIBLE DISTORTION AT ALL VOLUMES... The long and short is a lesson learned. As I have worked on this project for some time now, I have learned a little bit. First, this is a very accurate reproduction of the original. It is possible that the sound I am experiencing is normal for this build, but not the sound I desire. I have since that time corresponded several times with these people, and been told they can not help me with the distortion issue. I installed another P/T. Also put a 12AY7 in v1, as that is correct for this build. The sound is bettter, but still too over the top for me. Plenty of volume, but no headroom. I have purchased the higher value orange drop caps , and am considering changing them to see what happens. After I replace d the Transformer, and v1 my voltages are almost the same as the other amp. Many thanks to you guys for having this forum. It is super neat to find other people that dig tube amps. And it is wonderful to have the fountain of information and knowledge provided. I will keep plugging along on this ampp, and with time, patience, a little help from my new friends and some luck, I will get there. I think I read something about higher value capacitors smoothing out the sound of an amp, and so far,to me at least, that might be the case. Keep building, oh and I hope what I lack in actual knowledge, is off set by the entertainment value of a guy who can't find a stick in the middle of a forest
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Does your amp have negative feedback loop ? Adding it may reduce the distortion and add headroom.
Here is one example in this post: https://el34world.com/Forum/index.php?topic=28370.msg312364#msg312364
Also if you can post what people ask they can help you trace down what need to be worked.
Measure your filament voltage. Put one meter probe on pin 2 of a 6V6. Put the other probe on pin 7 of the same 6V6. What have you?
that is AC voltage for the filaments, let us know what voltage you got there.
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Reading your reply #5 leads me to believe that you are chasing individual rabbits down individual holes. That is incredibly frustrating as you are finding out.
Also if you can post what people ask they can help you trace down what need to be worked.
that is so true. Sluckey and others here are expert and willing to help. They will often ask you to post pics and schematics and/or test voltages etc. If you head off and start changing other things, you will quickly get lost. I suggest a couple things. Your amp is not working right - get that taken care of first before you start changing caps and resistors trying to improve the sound.
And, you would benefit from taking a break from the soldering iron and do some more reading. For example, worrying that your 25uF bypass caps are 25V instead of 50V is a waste of time. That voltage is simply the rating for the cap. The voltage encountered at that cap is much lower than 25V. You may want to check out Rob Robinette's site for the pages; How Tube Amps Work and How the 5E3 works. And the pages that Doug Hoffman has put together on this site. Some background is really going to help you. And it'll help you stay safe too!
And you should decide on and stick to which schematic and layout to follow. Original Fender schematics and layouts are available here and many places. Tedweber.com (Weber speakers) site posts good schematics and layouts for their 5E3 kits.
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Hi again. After reading more posts on the site, I took another close look at the wiring. I determined the output transformer was wired incorrectly. I had the center tap to one of the 6V6's, instead of going back to the board. I corrected this, and the amp sounded fine, unpleasant distortion was gone. At this point, I did some more testing, and was bummed out to discover a howling in the Normal channel, when turned up with nothing plugged into it. Again, referring to posts on the forum, I read one regarding this concern and indicating it might be because the wires at the 6V6's from the output transformer could be switched. I swapped them , and the unusual howling was gone! The amp works great now. Thanks so much for all the help. I will add, not to make excuses, the wire colors in my supplied diagram for both transformers were not the same as the ones on the transformers themselves. Very confusing🤔. I have decided to upgrade these amps using the 5E3 layout on this site. It will give me an opportunity to redo them and really clean up everything. I used the parts list page in the store, and got a new turret board, caps resistors ect, and am looking forward to rebuilding them better. I can't thank you fellers enough for all your help. Oh, also, no feedback loop on either of these builds, but I might put one in next time. Thanks again.
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Good job! :icon_biggrin:
Searched the forum and fixed it yourself, nice!
You do know the volume controls on a 5E3 are interactive? Set the volume on the channel your plugged into at 12:00, now set the other channels volume full up. Adjust tone control to taste. Very clean with some chime and scooped mids, try it. :icon_biggrin:
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… I did some more testing, and was bummed out to discover a howling in the Normal channel, when turned up with nothing plugged into it. Again, referring to posts on the forum, I read one regarding this concern and indicating it might be because the wires at the 6V6's from the output transformer could be switched. I swapped them , and the unusual howling was gone! … no feedback loop …
The above seems weird. If there’s a feedback loop around it, swapping signal polarity in a balanced system will turn negative feedback positive, and visa versa. But in the absence of an intentional feedback loop, I can’t see why polarity inversion would stop howling?
Of course, due to parasitic effects, any real world amp is full of unintended feedback loops, but howling per se would be an unusual symptom of such in lowish gain designs.
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Nice going Johnny. Searching posts on the Forum is a great resource. The 5E3 is famous for good reason so I am glad you were able to find issues and correct them. I and others will be interested to hear how you make out with the upgrading of components.