Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: timmyjoe on January 15, 2022, 09:43:14 pm
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Pulled off a new genius move :BangHead:
Working on a new 5E3 build. Powered on today but has horrible noise to it.
The 5Y3 wasn't coming on when I powered up for a voltage check. Figured out I had it installed one pin off. Had to rotate it counterclockwise to get it right. (By the way the labels on the JJ 6v6 line up with the key. This 5Y3 does not. Is it common for labels to not line up with the key?)
I've been going over the grounds, but this has got me thinking that maybe the problem is the filter caps. It's hard to hear the guitar over the noise. Could putting in the 5Y3 wrong have gotten them?
Other thoughts on possible noise:
*Wire rating? I used some solid 18 awg wire on the pre-amp tubes. The stranded wire on those small things scared me in terms of keeping things from arcing. But the insulation on the 18 awg was pretty thin. I added heat shrink to them. Maybe they still don't cut it for the voltage?
*I twisted some of the preamp tube leads that go to the board together. This was to clean up the space. When chop sticking around I found they really interact with each other, but don't seem to be making the big awful hum. Should I avoid twisting any of these lines coming off the pre-amp? Also thought about making some shielded cables for these spots.
*Any recommendations on wire? Not liking cloth for connecting to the tubes. But seems really hard to find colored wire rated to 600v and at 20 or 18awg.
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Again, I am new to this also but you need to look at how fender wired the original and copy that as close as you can.....
I know it gets messy looking but noise free is more important than looks when it comes to wiring to me...
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" This 5Y3 does not. Is it common for labels to not line up with the key? "
Never trust labels
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Can you please post some pictures of your build chassis interior?
Have you tried other tubes? Perhaps you have a bad tube (especially since the 5Y3 mistake)?
Have you checked the voltages to see if they are reasonably within specs?
Have you safely chopsticked your solder joints and wiring to see if that changes anything? Sometimes a bad solder joint (particularly on the B+ rail) can cause hum.
IF you have changed anything at all from an original 5E3 schematic, can you post the schematic that you are using?
With respect, Tubenit
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Other thoughts on possible noise:
*Wire rating? I used some solid 18 awg wire on the pre-amp tubes. The stranded wire on those small things scared me in terms of keeping things from arcing. But the insulation on the 18 awg was pretty thin. I added heat shrink to them. Maybe they still don't cut it for the voltage?
This won't make one bit of difference regarding noise.
... seems really hard to find colored wire rated to 600v and at 20 or 18awg.
Counterintuitive, but you do not need 600v wire. 300v wire is plenty, even when you have 400+ volts present inside. 600v insulation is just absurdly thick, which you will figure out if you get inside a lot of commercially-manufactured amps.
... Not liking cloth for connecting to the tubes. But seems really hard to find colored wire rated to 600v and at 20 or 18awg.
The cloth wire Hoffman carries is exactly like the wire in vintage Fender amps. Anyone else's cloth wire is crap IMO. I could go into why, but if you bought it from someone other than Hoffman you already know why it's crap & unwieldy to use.
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Someone is going to go crazy seeing all the talk about wire. :icon_biggrin:
It would be very rare to require 18AWG wire inside a guitar amp. There is simply not enough current to warrant that.
It is true that long speaker cable runs might need that (or more) ampacity, but that would be external to the amp.
22AWG carries 7 amps w/o difficulty . . . Some of the premier builders on this forum use 24AWG bus wire.
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The schematic is normal 5E3 with common additions. No real change to basic design. All things from Robrobinette.
*negative feedback switch with cap bypass
*foot switch for negative feedback
*dummy loads to protect amp if speaker comes unplugged (guess this is a change other don't do often).
*Preamp master volume using the train wreck design (I disconnected just to see if this was problem)
I'll do a full schematic and wiring diagram if people think this project will work in long run.
Thank you all for the details on wire selection. Helps me figure out what can be done rather than just doing what other do with amps. How do you deal with the wires going to the pre-amp? The connections look so close I'm scared one of the pins is going to knock into another one. I shrink wrapped my connections at those location to make sure that can't happen. Good or bad idea? I'll get some of Hoffman wire.
Notice on this design picture that the volume and tone controls are far from the board. Not ideal, but the only way to make things fit in space I have.
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More comments on drawing. Computer is dying and I don't have power cord. So fast posting.
*green thing is the space for the board
*gold things is space used by jacks.
*output transformer is by the volume controls.
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Far out man! :huh:
That's the most unusual 5E3 I've ever seen. You really must know your stuff to be successful with that oddball layout.
Actual hi-rez photographs of your project (inside and outside) would be much more valuable to us to help analyze your issues. I don't even know what to say at this point. :dontknow:
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... the pre-amp? The connections look so close I'm scared one of the pins is going to knock into another one. ...
The tube socket pins are not able to move enough to allow one pin to contact its neighbor.
You would be wise to have a tube in the socket when you attach the wiring & socket the tube socket pins. That will cause the pins to move where they need to be to allow a tube to be inserted.
You can always bend the pins somewhat if they need to be repositioned before soldering.
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Some 300V wire, UL AWM Style 1007 as an example, has a 600V peak rating for electronics.
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Checked the following:
*5Y3 tube changed
*Filter caps changed
*Moved ground from outlet away from common from power transformer.
Chopsticking the wires above the board changes the hum. But the underlying big hum is the same. Guessing I need to try separating wires above the board? Also could take out the negative feedback and dummy safety loads to eliminate them as problems.
Why are the 6.3v, 5v, and 50v wires twisted together? What does this do electrically? Was thinking that twisting some of the similar items like volume controls would do something similar.
With the aim being to make a pancaked 5E3, would shielding some of the cables be a way to make it possible?
Finally, with the board layout that I have, I realized that ideally I would have installed it upside down to have cables shorter and not crossing the board. Not sure I can pull that off, but maybe. My other thought is to mirror the boards diagram and remake it so I can keep lines short and solder with it in this position.
Will post pictures, but I'm getting the size warning error. So got to resize.....
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Pictures of the mess
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Looks like you have HV DC wires too close to the audio signal path, wires, components, jacks.
Gonna need shielded cable from input jacks, maybe from pots, ground one side of the cables only.
I been through it with unusual layout as well, better to follow proven layouts.
Might need to rearrange the wiring.
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timmyjoe
Thanks for the good quality photos.
I have a number of concerns with soldering. See attached photo. I'm concerned with the "wrap' and excess solder BUT poor wetting of joint "PS B2+ ?".
Where I have noted "GRND" I'm not sure enough solder was used to give a well formed joint. I am also concerned about the "excess" wire used and joined/terminated randomly with heatshrink.
As others have already said, really best to use a proven layout and adapt it to your preferred/available chassis. (I have built Fender preamps into 1 Rack Unit chassis very successfully, but was very stringent re Earthing and power Supply wiring)
I am not aware of your soldering skills but I saw a range of joints going from poorly wetted to solder splatter (excess heat?).
Having said this, you are in the right place to get encouragement and develop your skills. :icon_biggrin: There is a mountain of experience amongst our friends.
Kind regards
Mirek
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Man, that insulation is just to big. And is that heat shrink everywhere?
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Looks like you have HV DC wires too close to the audio signal path, wires, components, jacks.
Gonna need shielded cable from input jacks, maybe from pots, ground one side of the cables only.
I been through it with unusual layout as well, better to follow proven layouts.
Might need to rearrange the wiring.
Thanks Uki! I can work with getting the signal path and DC away from each other. How far apart is safe?
Looking at wires it seems like there are more signal paths than DC. Would it work to shield the DC instead of the signal paths?
Will look at how flipping the board could improve things if I decide to tackle a gut and redo.
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I've done maybe 2 dozen plus different build designs. "Several" of them were problematic and in the end, after unsuccessful troubleshooting, I removed the board and much of the wiring and started over. You may want to consider that in this case and try a more conventional known to be successful approach for your layout?
On an outside chance that this could be an issue ...............
*negative feedback switch with cap bypass
Have you tried disconnecting the negative feedback? Typically there will be a squeal with NFB if the OT wires need reversing, but I'm wondering if your hum could be connected to this somehow. It would be an easy effort to disconnect the NFB and simply ground that connection instead to rule that out as the problem.
With respect, Tubenit
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I can work with getting the signal path and DC away from each other. How far apart is safe?
Avoid having signal and DC wires crossing each other or in parallel, if there is no other way, shield the signal wires.
Would it work to shield the DC instead of the signal paths?
I'm not the most knowledge to answer that but I have the feeling that isn't the best. The signal wires will still exposed to magnetic fields.
Shield the wires from input jacks and pots if they are crossing DC wires.
Look the black cables in the picture.
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... underlying big hum ...
Did you "extend" the leads of your filter caps with stranded wire, heat shrink that joint, then use the stranded portion to make the connection to the turrets?
If yes, then there's a very good chance of a poor solder joint at one or more of those "extensions." And the photos look like that stranded wire was somewhat poorly wrapped/soldered around the turrets. This could be part of the hum problem (the mirrored board layout, necessitating wire to run further is another part).
Your controls are also way over next to the power section of the chassis. Those long wire runs do you no favors, and might be picking up hum from the PT.
FWIW, I'm not trying to beat you up. I too got over-ambitious with adding all kinds of changes to the usual methods when I built my first couple amps, and learned the hard way to stay closer to proven layouts & build techniques.
... you do not need 600v wire. 300v wire is plenty, even when you have 400+ volts present inside. 600v insulation is just absurdly thick ...
Man, that insulation is just to big. ...
I feel like I heard this somewhere before... :icon_biggrin:
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Nah, not the joints on the filters Blue Plate. The big buzz was there before I changed those out to what is in the picture.
I think you guys are underestimating the buzz/hum. It eats up half the volume.
Could it be the orientation of the transformers or the placement of them next to each other? I can fix the crossing of the DC lines with the signal path. But can't fix the placement of the transformers. That would end the idea of a pancake 5E3.
Anyway, I'm interested in understanding the why Leo did things the way it is instead of just building a clone. The explanations of wire magnet fields is very cool and appreciated. Reading up on transformer interaction now.
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I don't think anyone here is underestimating the degree of hum.
Your amp has a major problem. There is a chance that your layout is the problem, but it is also just as likely that there are other errors here as well.
It may be time to take stock, salvage your iron, and start again.