Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tylerrussell on February 15, 2014, 04:49:06 pm
-
Newbie (very) I built a 5E3, following the triode layout. Used a light bulb limiter to power up. Had to touch up some soldering. Everything worked, with a bad hum/buzz. Then I noticed that the 2-100 ohm resistors were not installed from pilot light to ground. After those were installed, the hum/buzz decreased to a very acceptable level. Then I noticed that, as I was playing, that it didn't clean up well~and all this time it's plugged into the light-bulb limiter. Plugged it into the wall and it sounds like a 100 watt marshall on 10 with the guitar cable unplugged. Extremely loud hum. Did I damage anything/something playing this through the limiter for half an hour? If so, what would it be? If not I'm listening. Seriously, I am a newbie; and can be safe with regard to checking things~ but things have to be way dumbed down for me to follow. Thank you for any help you may provide. I'll be staring at her tomorrow in the hopes that something clicks in my head. (You don't know how thrilled I was when she fired up without incidence....and sounded a little crunchy.... but worked!
-
As a side note, it hums so loud that I haven't let it run like that. Afraid of some smoke getting out.
-
As a side note, it hums so loud that I haven't let it run like that. Afraid of some smoke getting out.
Does it hum loud with your instrument plugged in? Check your build against the schematic, to see if you have the inputs built like it's drawn. You should have four closed circuit inputs. And if wired correctly, your inputs are connected to signal ground. Confirm this before looking further.
Jack
-
Does it hum loud with your instrument plugged in? Check your build against the schematic, to see if you have the inputs built like it's drawn. You should have four closed circuit inputs. And if wired correctly, your inputs are connected to signal ground. Confirm this before looking further.
Yep, what Jack said, +1.
Brad :icon_biggrin:
-
... Did I damage anything/something playing this through the limiter for half an hour? If so, what would it be? ...
I can't think of anything you might have damaged by playing with the lamp limiter.
-
Thank you all for your input. The hum is there with or/and without the guitar plugged in. Gets louder as amp volume increases. It is gone with the amp volume on "0". Checked the input wiring yet again; it is wired like the Triode layout.
-
The ground wires from the volume pots (Y on the layout) are attached to a PT bolt; as are the other three "Y's"~the two Y's from the top of the board and the one Y from the speaker jack. Also, the two 100 ohm resistors from the pilot light are connected there. The AC line white wire is connected to a bolt on the PT on an opposite corner. Is this correct? The PT is a Hammond 290AX. The input jacks are not isolated from the chassis~and the chassis is a bit microphonic. There is only one speaker jack currently. Hammond 1750E 8 ohm OT. I've been over the solder joints, compared my amp to the layout and don't believe anything is amiss. Just a HUMMMMMMMMMMMM. Obviously something is a tad goofy here. Thank you all for your time and input.
-
Also, since the PT is different, it is wired: 2 Blacks/one to line white, one to fuse center.
2 Reds/to V5 5y3 pins 4 and 6
2 Yellow/to V5 5y3 pins 2 and 8
2 Greens/to pilot light
1 Red w yellow stripe to PT bolt along with Green from the line cord.
OT is as the layout pic, minus the yellow 4 ohm wire.
-
It would help greatly at this point if you would post clear close up pictures of the inside of the chassis and the outside (PT, OT, tube sockets layout) so the guys can see if it's your lead dress wiring.
Brad :icon_biggrin:
-
The hum is there with or/and without the guitar plugged in. Gets louder as amp volume increases. It is gone with the amp volume on "0".
The hum is gone when either volume is on zero? Or only when both are on zero? Or hums only when one volume is turned up?
-
Since it's my first effort :l2: is expected, although drilling the holes in the chassis HAD to be the most nerve-racking part. (So far....)
Also, the hum is gone only with both volumes on zero.
-
The AC line white wire is connected to a bolt on the PT on an opposite corner. Is this correct?
Like Brad stated, pictures of what you are describing will go a long way. By your layout, it appears that a terminal strip is attached to the PT bolt, which should be above (not connected to) chassis ground. The white should be attached to this terminal strip, if I'm seeing the drawing correctly. If yours is indeed connected directly to the PT bolt, lift it and tie it directly to the PT wire. Insulate it and give it a try.
I can't say that this is the hum fix, but just trying to fit your description with the drawing.
Jack
-
Pic
-
Pic
-
Jack~that ground on the PT, on my amp, is connected to the bolt where it enters through the chassis; then a washer and nut applied. So those wires touch both the chassis and the OT bolt. As a matter of face, the PT housing touches the chassis where it drops through the chassis.
-
Oh, the PT and OT in the layout pic are not the one's I used. On mine, the white 120 line is connected to the black line on the PT~lifted from the chassis.
-
Also, the hum is gone only with both volumes on zero.
The the source of the hum has to be before the volume controls, but not exclusive to only one channel.
Try unsoldering the wires that go to pins 2 & 7 of the input (V1) tube.
Probably unrelated: what is that tube you're using for V1?
-
That tube is a 12BH7A. I read it could be subbed for a 12AY7A. I also tried 12AX7A's in V1. What might unsoldering 2 and 7 tell me? (us).
Try unsoldering the wires that go to pins 2 & 7 of the input (V1) tube.
Probably unrelated: what is that tube you're using for V1?
[/quote]
-
Unsoldered 2 and 7 on V1. Hum is a lot louder now when turning the amp volume up; but there is no hum with the volume(s) set at "0".
-
That tube is a 12BH7A. I read it could be subbed for a 12AY7A. I also tried 12AX7A's in V1.
A 12BH7A has the same pinout as a 12AY7 but it has an Amplification Factor of 16.5 versus the 12AY7's factor of 44.
While it will function, you will have a lot less overall gain than a 12AY7 (or a 12AX7). This can be dealt with later, after you sort out the noise issue, but long term,I don't think you want a 12BH7A in V1.
-
I only have that and some 12AX7's and a 12AY7. I've tried them all to the same end.
-
Unsoldered 2 and 7 on V1. Hum is a lot louder now when turning the amp volume up; but there is no hum with the volume(s) set at "0".
HBP might have a different "next step",
But while the soldering iron is hot, get a length of wire. attach one side to ground, and one side to pin 2. do the same with another wire for pin 7.
turn volumes up and see what happens.
-
Unsoldered 2 and 7 on V1. Hum is a lot louder now when turning the amp volume up; but there is no hum with the volume(s) set at "0".
HBP might have a different "next step",
Is this with the original wires off of pins 2 and 7?
But while the soldering iron is hot, get a length of wire. attach one side to ground, and one side to pin 2. do the same with another wire for pin 7.
turn volumes up and see what happens.
-
Tyler, you might have had a edit problem on your last post.
Did you trying grounding pins 2 and 7 ?
-
No, I have not tried grounding pins 2 and 7. Do that with the original pin wires on or off?
-
No, I have not tried grounding pins 2 and 7. Do that with the original pin wires on or off?
try it with the original wiring off, just two ground wires running from pin 2 and 7 to ground (somewhere).
turn volume up, see if its better, same, worse...
-
OK. Soldered wires to pins 2 and 7. Grounded to chassis. She's really buzzing and humming and sounds like she's gonna' blow up. I hit the power off real fast!
-
So with grids (pins 2 and 7) grounded, it is actually louder -noise wise- than before, with original wiring attached.
if there was a wiring problem with the input jacks, it should be quiet. Are you sure you have a good ground connection at the chassis? maybe alligator clip the wires to the circuit ground? ( "Y" in the diagram, the negative (-) side of one of the 16uf caps?
maybe time to post DC voltages for pins 1,2,3 and 6,7,8 on V1.. plus the DC voltages across each of the three 16uf capacitors. do this with the amp on. you can reconnect the original wiring, and perform the readings.
also, (with amp turned off, unplugged) ohm readings with a DMM from the negative (-) side of the 16uf filter caps to all the "Y" points on your pots, the input jacks, as well as the "Y" point on the cathode resistor and by-pass cap (820ohm and 225uf at far end of board)
-
Since it's my first effort :l2: is expected, although drilling the holes in the chassis HAD to be the most nerve-racking part. (So far....)
No laughing, looks real good. Some of the wiring might need to be shortened a little and moved around a little but it's not bad at all.
Yeah, drilling out a chassis can be nerve wracking.
Brad :icon_biggrin:
-
Tyler,
another thing I noticed is that the diagram has lime green wire connecting input jack grounds to the "Y" ground, which it looks like you recreated. It also looks like you are using switchcraft jacks. Were there small phelonic and fiberboard spacers included with the jacks? so the sleeve portion of the jack is isolated from the chassis?
-
Ok. Thank you all for bearing through this :help:
Voltages on V1: pin 1=109
2=0
3=1.78
6=101
7=0
8=1.78
Voltages across 16uf's starting closest to PT:
336
296
212
Ohms readings from 16uf's neg side to "Y" points and to the 820 resistor/25uf cap junction all start at 3 or 4 and immediately drop to .3 or .2 on the lowest scale on my meter, which is 200.
Hope that's everything.
-
Tyler,
another thing I noticed is that the diagram has lime green wire connecting input jack grounds to the "Y" ground, which it looks like you recreated. It also looks like you are using switchcraft jacks. Were there small phelonic and fiberboard spacers included with the jacks? so the sleeve portion of the jack is isolated from the chassis?
There were are no type of washers/spacers on the input jacks
-
Since it's my first effort :l2: is expected, although drilling the holes in the chassis HAD to be the most nerve-racking part. (So far....)
No laughing, looks real good. Some of the wiring might need to be shortened a little and moved around a little but it's not bad at all.
Yeah, drilling out a chassis can be nerve wracking.
Brad :icon_biggrin:
I figure I could tidy things up if it actually worked! It does, and I'm relatively thrilled with this first effort. Once things are ironed out I'll clean it up. Got the chassis for $10. All bent up~~~but with no holes at all. Jeeesh.
-
Tyler,
another thing I noticed is that the diagram has lime green wire connecting input jack grounds to the "Y" ground, which it looks like you recreated. It also looks like you are using switchcraft jacks. Were there small phelonic and fiberboard spacers included with the jacks? so the sleeve portion of the jack is isolated from the chassis?
There were are no type of washers/spacers on the input jacks
I think the only way to isolate the sleeve portion of the jack from the chassis is with a bushing, no?
-
That tube is a 12BH7A. I read it could be subbed for a 12AY7A.
The 12BH7 is a high-dissipation 12AU7. Some people (like me) have old audio gear that needs that specific tube. I'd recommend sticking with the 12AY7 or a 12AX7/12AU7. The 12BH7 is too-nice & too-expensive IMO for the 5E3 input.
What might unsoldering 2 and 7 tell me?
You need to have an organized, divide & conquer approach to sorting out this hum.
Right now, you say if you have both volumes on 0 you get no hum, but turning either volume above zero gives hum. That means the hum is common to both channels and is before the volume pots.
It's perhaps not obvious from the layout, but the schematic (http://www.el34world.com/charts/Schematics/files/fender/Fender_DELUXE_5E3.pdf) shows that ahead of the volume controls are each side of V1 and the input jacks. I wanted to eliminate input jack wiring error as a possible fault, so I told you to unsolder the wires from the input jacks to V1.
Unsoldered 2 and 7 on V1. Hum is a lot louder now when turning the amp volume up; but there is no hum with the volume(s) set at "0".
Pull V1 from its socket, and try adjusting the volumes. The hum should be gone. Is it?
If the hum is gone with V1 pulled from the socket, move to the 0.1uF caps which connect to V1 pins 1 & 6. One at a time, unsolder the leg of the 0.1uF caps that is not connected to the 100kΩ resistor). In other words, the end connecting to the volume pot and not V1.
Does unsoldering one of those stop the hum? Does it require unsoldering both to stop the hum?
-
I think the only way to isolate the sleeve portion of the jack from the chassis is with a bushing, no?
yep.
http://www.hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Screws (http://www.hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Screws)
You need to drill your chassis holes slightly larger.
Without them, and with that lime-green indicated ground wire, what you have is potential ground loop that travels from the jack to your intended ground lug at the transformer, in two directions (hence the loop). you can remove that wire, or get isolation washers. The later is probably most desirable (but even the former is preferred to a potential loop).
regarding the ohm readings, when you start it starts at 3 or 4 ohm and drops to 0 ohms, do you mean all tested points are 0ohms? you just get a reading of 3 ohms at first contact? Or are some connections consistently 3 or 4 ohms (that's not good, should be 0ohm).
with pin 2 and 7 on V1 grounded, your amp should be quiet.
-
Without them, and with that lime-green indicated ground wire, what you have is potential ground loop that travels from the jack to your intended ground lug at the transformer, in two directions (hence the loop). you can remove that wire, or get isolation washers. The later is probably most desirable (but even the former is preferred to a potential loop).
Respectfully, I think this is a side-show. Fender didn't have isolated jacks, and the tweed amps were as quiet as tubes & CC resistors will allow.
And since he proved the input jacks aren't the source of the hum (by disconnecting the from V1), it might be better to attack what's left.
Oh yeah, if I didn't say it before, leave the wires to V1 pins 2 & 7 unsoldered. Let's eliminate the jacks as the culprit while we keep attacking whatever is causing the hum @ V1 to the volume controls.
-
Respectfully, I think this is a side-show. Fender didn't have isolated jacks, and the tweed amps were as quiet as tubes & CC resistors will allow.
I agree. save that for later. If grids aren't connected to the jacks, they are irrelevant to the noise issue.
-
Right now, you say if you have both volumes on 0 you get no hum, but turning either volume above zero gives hum. That means the hum is common to both channels and is before the volume pots.
It's perhaps not obvious from the layout, but the schematic (http://www.el34world.com/charts/Schematics/files/fender/Fender_DELUXE_5E3.pdf) shows that ahead of the volume controls are each side of V1 and the input jacks. I wanted to eliminate input jack wiring error as a possible fault, so I told you to unsolder the wires from the input jacks to V1.
Unsoldered 2 and 7 on V1. Hum is a lot louder now when turning the amp volume up; but there is no hum with the volume(s) set at "0".
Pull V1 from its socket, and try adjusting the volumes. The hum should be gone. Is it?
If the hum is gone with V1 pulled from the socket, move to the 0.1uF caps which connect to V1 pins 1 & 6. One at a time, unsolder the leg of the 0.1uF caps that is not connected to the 100kΩ resistor). In other words, the end connecting to the volume pot and not V1.
Does unsoldering one of those stop the hum? Does it require unsoldering both to stop the hum?
Sorry for the delay...things got hectic over here. I can't (once again) thank you guys enough.
12AX7 now available for V1.
Pulled V1 No Hum
Un-soldered 0.1 No hum with 1st volume pot up. Hum with second volume pot up. 12AX7 in V1.
Un-soldered next 0.1. No hum with both volumes turned up. 12AX7 in V1.
This is with the wires back on pins 2 and 7 of V1. Was unclear if they should have been left off or not.
0.1 caps atill disconnected at one end.
edit by sluckey... fixed quote
-
Are you saying you lifted the end of 1, 0.1 cap and then lifted the end of the 2nd 0.1 cap so then both caps were disconnected at the same time?
If so now try it with the 1st cap reconnected and leave the 2nd cap disconnected.
Brad :icon_biggrin:
-
I dis-connected the caps one at a time. First cap leg disconnected: it's channel had no hum when raising the volume. The second channel did have hum when raising the volume. Second cap leg disconnected, first cap reconnected: Respective volume pot produced no hum. The channel that was reconnected did produce hum. Hope I explained OK.
-
I also tried removing the wire from the inputs to the first volume pot with 0.1 caps connected. No difference. Hum was still there. Also, the hum appears to have the pitch of Bb, if that indicates anything. I did clean all the tube sockets and tube pins.
-
Don't disconnect the wires from pins 2 and 7 to check for hum because with the wires removed, the tube cannot bias properly.
Instead...
Connect pin 2 and pin 7 to chassis ground. It's OK to use gator clips. Does the hum go away?
-
You mean: leave the connections to pin 2 and 7 intact; then add two wire from 2 and 7 to chassis ground? Just want to make sure I understand.
-
You mean: leave the connections to pin 2 and 7 intact; then add two wire from 2 and 7 to chassis ground? Just want to make sure I understand.
Yes
-
Both 0.1 caps connected?
-
Tacked wires to pins 2 and 7. Grounded to chassis with alligator clips. Hum is the same; loud when volume is raised, no hum with volumes off. 0.1 caps were connected during this.
-
It's probably the tube then, unless you have a poor ground connection in the V1 circuit. Try a real 12AY7 or a 5751.
-
The AC line white wire is connected to a bolt on the PT on an opposite corner. Is this correct?
That's wrong. The AC line white wire connects to one of the transformer black wires as you said elsewhere, but it does not connect directly to a PT bolt. Probably not your hum issue but it needs to be corrected.
-
It's probably the tube then, unless you have a poor ground connection in the V1 circuit.
Tyler, you tried a 12BH7 and a 12AX7, do you have other tubes to try?
I suspect ground problem. especially since both triodes share the same cathode resistor and bypass cap...
find the ground turret for the 820ohm R and the 25uf cap. call it turret "A". disconnect the ground wire to "A"., take a jumper wire (hookup wire with two alligator clips if you have) connect to "A" and connect the other side to the (-) negative ground side of the 16uf filter caps. (you mentioned 3ohm to ground for some ground connections, it wasn't clear to me if that was 0ohm or 3ohm)...
If you can easily disconnect the ground wire to "A" (under the board?), its still can be a valid test to do the above jumper wire test from "A" the (-) turret of the filter caps.
this could be a cold solder joint somewhere. If not on the ground circuit, then on the B+ side, (grid is ruled out, what else is left? tube, ground, B+).
-
If you are using switchcraft jacks then you don't need to run a separate ground wire as their already grounded to the chassis by their sleeve. Adding a separate ground wire by definition is a ground loop. You should try disconnecting any separate/extra ground wires from the jacks.
Brad :icon_biggrin:
-
It's probably the tube then, unless you have a poor ground connection in the V1 circuit.
Tyler, you tried a 12BH7 and a 12AX7, do you have other tubes to try?
I suspect ground problem. especially since both triodes share the same cathode resistor and bypass cap...
find the ground turret for the 820ohm R and the 25uf cap. call it turret "A". disconnect the ground wire to "A"., take a jumper wire (hookup wire with two alligator clips if you have) connect to "A" and connect the other side to the (-) negative ground side of the 16uf filter caps. (you mentioned 3ohm to ground for some ground connections, it wasn't clear to me if that was 0ohm or 3ohm)...
I believe the board will have to be pulled. I checked with a beeper on the meter from chassis to the interconnected turrets on the neg side and do not have continuity at the 1.5k/25uf; but have continuity at the 16uf's, 820/25uf, and 220k's. I believe there should be continuity at the 1.5k/25uf. It'll be a while!
If you can easily disconnect the ground wire to "A" (under the board?), its still can be a valid test to do the above jumper wire test from "A" the (-) turret of the filter caps.
this could be a cold solder joint somewhere. If not on the ground circuit, then on the B+ side, (grid is ruled out, what else is left? tube, ground, B+).
-
If you are using switchcraft jacks then you don't need to run a separate ground wire as their already grounded to the chassis by their sleeve. Adding a separate ground wire by definition is a ground loop. You should try disconnecting any separate/extra ground wires from the jacks.
Brad :icon_biggrin:
This will be easier to try before removing the board.
-
Check your 100ohm Artificial CT resistors. They have given me much problems recently.
-
If you are using switchcraft jacks then you don't need to run a separate ground wire as their already grounded to the chassis by their sleeve. Adding a separate ground wire by definition is a ground loop. You should try disconnecting any separate/extra ground wires from the jacks.
Brad :icon_biggrin:
This will be easier to try before removing the board.
You don't need to do this. You've already eliminated the jacks and tube grids as the source of hum when you grounded pins 2 and 7.
I believe the board will have to be pulled. I checked with a beeper on the meter from chassis to the interconnected turrets on the neg side and do not have continuity at the 1.5k/25uf; but have continuity at the 16uf's, 820/25uf, and 220k's. I believe there should be continuity at the 1.5k/25uf. It'll be a while!
You may be missing the underboard jumper. You don't need to pull the board to check this. Just put a gator clip jumper between chassis and the negative side of the 1.5k/25µF. If this cures the hum you can put a jumper on top of the board. See pic...
-
I lifted the board and re-soldered the bottom of the turret that connected the negative side of the 1.5k/25uf. Have that ground connection now. Also pulled the red/yellow PT wire off the bolt and soldered it to the chassis. Unfortunately..............Hummmm. I know I'm a true newbie, and I cannot thank you guys enough for all the thought, expertise, and input. Something is misconstruyoulated (new word) somewhere.... surely related to my ineptitude. Looked for loose wire hairs, cleaned tube pins, sockets, tried several 12AX7's from another working amp, cables; even tried a 12AT7....no difference. I'll keep looking.... have all avenues that were suggested been satisfied? Jeeeezus......at 62 years old-----this is very trying!
-
Check the 100ohm artificial center tap resistors. It is easy to do and I have had noise issues from them quite a few times. Psyco mentioned it to me once while I was chasing noise on a Princeton Reverb and I doubted it, but that was the problem. The very next week I had another Princeton with the same problem.
I do not know how it happens, but I think it could happen if you touch your probe to the plate of the power tubes and archs to the heater wire. Not sure about this so someone correct me if I am wrong.
Either way, checking them is easier than making a peanut butter sandwich.
-
Check the 100ohm artificial center tap resistors. It is easy to do and I have had noise issues from them quite a few times. Psyco mentioned it to me once while I was chasing noise on a Princeton Reverb and I doubted it, but that was the problem. The very next week I had another Princeton with the same problem.
I do not know how it happens, but I think it could happen if you touch your probe to the plate of the power tubes and archs to the heater wire. Not sure about this so someone correct me if I am wrong.
Either way, checking them is easier than making a peanut butter sandwich.
If we are speaking of the two 100 ohm resistors from the pilot light terminals to ground, they check out OK.
-
Let me ask this... Can you even get a guitar signal thru the amp or is the hum so overpowering that it makes it impossible to play guitar thru the amp?
-
I'm getting all kinds of signal through this thing. It's much louder than expected. Sounds very good. Tone control has a lot of range. Going through a8 ohm 60 watt 12". Something a little less efficient might be nicer, though. If I didn't know, I'd say if was 30 watts. But it's apparently not. Couldn't mic this amp due to the hum, though.
-
at 62 years old-----this is very trying!
Hang in there Tyler, you will figure it out!
Brad :icon_biggrin:
-
Ya' know I think it would be easier to build another one and get lucky than it is trying to figure this out! I'll keep reading and searching.
-
Ya' know I think it would be easier to build another one and get lucky than it is trying to figure this out! I'll keep reading and searching.
:laugh: Yeah it might feel like that now but you'll find it.
Sometimes it's best to step away from it for a little while, clear your head and go back in.
Brad :icon_biggrin:
-
Please accept a big "Thank you". You all got thing going. I found a second Triode layout that had a different grounding scheme. Followed that and the Huuuummmm id GONE. I'll attach the two different layouts. There's a slight buzz when it's dimed~a non issue. Thank you all again!
-
Great!
Do you understand the difference between the 2 grounding schemes?
(Our host Doug basically does the same thing.)
Brad :icon_biggrin:
-
Great!
Do you understand the difference between the 2 grounding schemes?
(Our host Doug basically does the same thing.)
Brad :icon_biggrin:
No, I don't. But I will work on it!