Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: aleos on November 05, 2020, 11:45:03 am
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1st post.
Hey everyone, thanks for taking the time to look at this.
Some great minds here, super lucky for me to be able to ask some questions.
I built my first 5E3, from mojotone. It worked immediately after finishing, and sounds like the heavens.
I have two small issues, one is common, and the other, well, I’m just new and don’t get it.
First is 60 cycle hum. Volume knob doesnt change the level of hum. It’s not a deal breaker, but it reminds me that i messed up somewhere every time I go to practice in the morning. Frustrating.
2nd problem is the more frustrating. The speaker jack/wire/solder joints will short out. Sometimes from the vibrations of me playing, sometimes just randomly. If i wiggle/rotate the plug in the jack, I can sometimes reconnect. And then it will work again for hours, or maybe a minute. I’ve changed the wire, desoldered and resoldered, changed the plug, and the problem still persists. Is there some basic fundamentals I’m missing? I read a lot, and have found nowhere in beginner literature that mention how finicky a speaker connection can be.
Is it possible it is the jack?
I realise this is far beneath the average level of electronics here, so instead of askign questions every time, I’m also wondering about good clear resources to reference when I want to learn the theory. What did you guys use?
Cheers from Montreal.
Hope everyone is good.
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Use a Switchcraft 12A jack if not already doing so. Make good solder connections. Should not be any problems. Show us a hi-rez closeup pic of your speaker jack. Maybe we can spot an issue.
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Sorry, meant to include in original post. Was having some troubles uploading photos.
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On your hum issue your heater wiring could be a little tidier. It needs to be twisted symetrically - I put one set of ends of a pair of wires in a vice, the other ends in the chuck of a hand drill and slowly wind till it's nice and tight and even.
Looks to me like the cathode bypass cap on V2A is in backwards, should be the same orientation as the V1 cathode cap - crimped end is positive and should face the valve socket. Quite low voltage across it which is why it hasn't gone bang yet but it won't be helping anything!
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Looks to me like the cathode bypass cap on V2A is in backwards, should be the same orientation as the V1 cathode cap - crimped end is positive and should face the valve socket. Quite low voltage across it which is why it hasn't gone bang yet but it won't be helping anything!
Holy crap, youre right. After talking to myself saying “the one thing you wont do is put a cap on backwards....”.
Man, that’s embarrassing. It’s amazing how your eyes stop seeing things. Like ears after a 10 hour recording session. Thanks so much for pointing it out.
I’ll tighten the heater wire too. I found it difficult to judge the lengths when I was twisting and cutting.
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You definitely need to redo the speaker jack wiring. Both of them. Strip the wires, tin them, poke through the lug holes, and finally crimp them to the lugs ***BEFORE*** soldering them. Do this and you will have a very reliable speaker jack connection.
If your speaker plug soldering job looks like the jack wiring, then redo that too.
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I think It's very likely that the connection problem is the jack itself. Maybe the wire is broken at the soldering. So you don't see that immediately. Btw, that type of jack is very easy to ruin while soldering. I don't use those anymore. Only neutrik for me..
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Thanks for everyone’s input and patience on these beginner inquiries.
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Hi Aleos,
Just adding my 1 cents worth with a picture (worth a thousand words :laugh:), and a little late as I'm in Aussie.
I'm attaching a photo of the output sockets in a factory Fender Deluxe Rev Reissue to highlight sluckey's last comment.
There is a nice flow (wetting) around the wires to socket terminals.
The only changes I would make is to remove the excess flux from the joints, as flux does have corrosive properties and it takes away from the nice shiny solder surface.
Kind Regards
Mirek
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I’ve jumped back in, tidied up my soldering, reversed the cap, twisted the heater wire as much as I could, think I’m heading to bed.
Appreciate the advice. Will report in the morning when I’m fresh and plug it in.
Hopefully it’ll be a nice practice session tomorrow with clean amp.
Cheers
A
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Why the use of a death cap ?
There is no wires to the switch
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Looks to me like the cathode bypass cap on V2A is in backwards, should be the same orientation as the V1 cathode cap -
I agree
Original Mojo kit :
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On your hum issue your heater wiring could be a little tidier. It needs to be twisted symetrically
I agree. Heater wire look to be a issue
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Looks to me like the cathode bypass cap on V2A is in backwards, should be the same orientation as the V1 cathode cap -
I agree
Original Mojo kit :
that layout is a lousy reference - all of the 1/4" jacks are depicted incorrectly, and that could be confusing to a novice builder.
--pete
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These kit are for beginner IMO. A pros don't need that.
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Good morning friends, thanks again for all the many tips yesterday.
So I began to check things out this morning. Turned amp on, and while I may have reduced ed the hum a little bit with the heater wire twisting, the speaker jack is still acting like a jerk. I am not sure why it is doing this, as I resoldered everything, verified that it looked good, turned amp on, and the jack is behaving in the exact same way. I even rewired the plug, then tried changing the plug, i used new wire for the speaker cable.
The connection is behaving the same as before. If I swivel the plug when it is inserted, it will make/break connection.
Is there a way to determine if it is a faulty plug, i doubt it, but it’s sure nice to cross-off possible culprits when troubleshooting.
I took a short video of the behaviour, not sure if video is allowed here.
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Are you plugged into the correct jack?
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I took a short video of the behaviour, not sure if video is allowed here.
post your video on youtube, then copy paste the link here
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Are you plugged into the correct jack?
Hehe, yup.
:laugh:
I’m not that terrible. CLose, but not quite. It’s not that there isn’t sound, I just practiced for an hour, and the amp sounds, arguably, like some of the most beautiful tones I’ve heard in 30 years of serious guitar playing. It’s marvellous. But as I practiced, every 10-15 minutes the jack would disconnect (I’m assuming from vibrations) and I’d have to swivel it to get it to reconnect. Now, in my mind, it would seem a bad solder joint or something owing to the amateur nature of my skills. But it’s strange that the whole amp, and all the other solder joints are working fine, except for this plug. Even after I redo all the wiring of the jack/plug/speaker with hyper attention payed to solving this problem, what are the chances I make the same mistake in exactly the same place again. So that the exact behaviour continues.
I green, so maybe this happens a lot. Just seems strange.
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Try this... Remove the OT leads from the speaker jacks and disconnect the speaker plug/wires from speaker. Now connect the speaker directly to the OT secondary leads. Any joy?
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All the experts are on top of things here and have you looking at the right potential sources. So, I am going to tell a story about a solid state Peavey bass amp that I bought new in 1980 and was behaving the same way. I took it back to the music store (owned by a neighbor) an this tech Brian spent an amount of time on it and could not get it to act up. He checked all the likely stuff and swapped the jack and speaker wiring and gave it back to me saying: I did not find an obvious problem but did x,y,z so let's see how it goes.
I still had the same problem, cut in and out for a minute or a day at a time.
So Brian grabs a bass of the rack and says show me. I played a good long while and it was perfect.
I took the amp back home and same problem. Puzzled i tried it with my 6 string and it worked! back to the bass no go.
Turns out the bass had a shitty jack that was the culprit.
Moral of the story: IMO change the jacks and check the connection at the speaker end, especially if you have slip on connectors there. Sluckey's last post is suggesting to bypass those as he wants you to test for the same source of trouble.
Cheers!
Jerry
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Thanks for the amazing tips fellas. I had to hit a recording session the last couple of days, and I brought the amp with me. Worked great, the hum seems to be gone! Can’t believe it was just some tighter wiring of the heaters. I’m learning. Recorded with it all yesterday and today and it sounds good and hasn’t cut out like it was. But i havent tried Sluckey’s suggestion because it’s rolling right now and I have a few more days recording to do and I’m scared I’ll mess it up.
But will get to it in a couple days.
Thank you for all jumping in and helping me.
I’d really love to educate myself more, if you know any good directions to help get my electronics theory better, I’d love suggestions. I know it’s just a matter of “just doing it”, but I’d love to expand my understanding in addition to practical.
Thx
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Welcome. You initial post I believe mentioned it seemed to be vibration related. This would have me looking at the speaker end of the connection and the male jack on the speaker wire that you say rotating tends to fix. Try a different cable just for grins and giggles and see what happens.
As for resources... this forum is the best resource I have found bar none. The quick and friendly responses are unparalleled.
Next to this, you may want to get some books for the theory. There was/is a little bit of a language barrier learning terminology which can be a little confusing to a newbie. Things like why a cathode is signified on many drawings with a K, what a cathode follower is. What an RC network is. (has nothing to do with Remote Control) Are best explained by a ton of reading mixed with study of schematics, drawings and making use of the search field here on the forum. Keep the faith and iron on.
As for hummmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm.......
One of my books Vaccuum Tube Amplifier Basics by EJ Jucrich, suggests a .47uF filament bypass cap right after the transformer to filter AC hum. I have not seen this used on many projects here or in very many schematics. Perhaps experts and hobbyists can comment on whether this would be appropriate here along with better lead dress. Tucking filament wiring in corners of the chassis can also help eliminate some noise according to theory. I have also read it is best practice to keep the polarity of heater wires the same among all tubes, particularly the output power tubes. This is difficult to determine visually when all wires are the same color, hence some builders use green and white for easy visual verification, or you can use a meter to check. How many amps follow this practice and how much difference it makes I have no clue. There is a fair amount of mysticism involved to which green horns like myself are particularly susceptible. Some of the gray beards here perhaps will straighten me out if this is one of those mythical beliefs or if it is grounded in truth. I have seen some vintage amps which sounded pretty good and were fairly quiet that had sloppy dress and observed none of the above advised best practices.
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Can’t believe it was just some tighter wiring of the heaters.
That's good, since it's more likely you moved them away from some wire, or touched up a solder joint?.
twists are good for esthetics, hum reduction not so much, "phasing" them don't make them quiet.
The key is know which wires are the sensitive snowflake type and keep the loud and obnoxious heater wires FAR away, AND perpendicular to the sensitive ones IF they must cross each others path. remember you are working in 3D space also, use it
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> Vaccuum Tube Amplifier Basics by EJ Jucrich
Vacuum Tube Amplifier Basics by EJ Jurich:
https://www.amazon.com/Vacuum-Tube-Amplifier-Basics-Jurich/dp/1500938866
https://www.abebooks.com/servlet/SearchResults?an=jurich&tn=vacuum%20tube%20amplifier%20basics
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Can’t believe it was just some tighter wiring of the heaters.
That's good, since it's more likely you moved them away from some wire, or touched up a solder joint?.
Good to know, thanks. Yes, I did unsolder them, removed them and wound them, and then put back, so i must have touched up the solder joints and placing.
Sorry I have been away for a few days, recording took some attention away. The amp worked fine while stable at the studio, and now I brought it home, and it’s wonky again. Most likely from the move.
I really must be missing some basic knolwedge about the speaker connection/wire/jack. I’ve got some basic pancake-style plugs, that seem like a short waiting ot happen, but really, is there something you experienced folks know that us beginner’s don’t? About simple speaker wiring? I find it strange that I built the whole amp, and arguably it worked right out of the gate, except the most simple part, the speaker, is eluding my troubleshooting. Even though I’ve replaced the plug, resoldered the jacks, the speaker connection. And the exact same behaviour continues. Weird.
Thanks everyone.
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Try this... Remove the OT leads from the speaker jacks and disconnect the speaker plug/wires from speaker. Now connect the speaker directly to the OT secondary leads. Any joy?
Going to try this evening. Thanks so much Sluckey.
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You are already on-track to try the direct, wire-to-wire connection recommended by Sluckey as a trouble-shooting step. I agree - it is a good way to determine whether the jacks or other removed elements are the cause.
Here are some additional ideas for your consideration.
You said "If I swivel the plug when it is inserted, it will make/break connection."
Here are three possibilities that occurred to me, following that statement.
First, how about the soldering and the connections inside the plug assembly? In the angled type of metal metal plug you are using, there is usually some kind of insulating disk or wafer, to keep the signal wire / signal terminal from grounding out on the metal housing. Is that wafer or other insulating material in-place, and doing its job? What about the bare portions of the two wires - are they sufficiently separated from one another inside that plug assembly, so that they can never contact, even when there is movement or vibration? What about the soldering job in there - is it up to snuff?
Second, take a peak at the connections on the speaker itself, per the speaker photo you provided. It looks to me like the black / negative connection might be poorly soldered?
Finally, you mentioned replacing the jacks once already, so this one doesn't seem likely - but maybe: did you over-tighten the nuts on the jacks? If you tighten too far on that kind of jack, the threaded tubing that makes the actual "tunnel", passing through and making connection with the ground-tab / ground connection of the parts of the jack inside the amp, can get pulled out / pulled loose from being well-connected to the rest of the jack. Over tightening can damage that mechanical connection, which might result in the behavior you have described.