New member here.
Just finished a new 5F1 amp ($300USD in parts) and I'm not really impressed with results regarding hum. The sound of my guitar thru the amp was very good for a day or so and now a crackle from the speaker when playing guitar at 1/2 to full volume. I expected lower noise from this amp (little or no hum) . Of course, when you hear the guitar playing thu the amp it cancels out the hum, but not the new crackle, gets worse with volume level. Is it normal for the amp to have a certain amount hum like this ? I know the crackle sound is not normal.
I've read thru a lot of 5F1 posts here and tried to apply different
solutions to lower the hum level with no real amazing results. I'm not new to building electronics gear, but this is my first tube amp build. I do understand good grounding techniques, but this build is particularly challenging.
This 5F1 looked to be an easy build, maybe not.
The amp has a incremental hum as the volume increases. not sure if this is normal
with a 5F1 champ. Tried two filament arrangements below. I have not tried the 100 ohm resistor
trick with a sudo center tap since I do not know how it is implemented - need a schematic to
understand it.
1. filament wires one grounded with HT center tap to chassis next to the PT transformer and the other soldered to pin 7 6v6 and 4-5 12ax7. Pin 1-2 6v6 and pin 9 12ax7 grounded to chassis nearest the tube socket. Pilot light receives one ground and one hot filament wire from PT transformer.
2. 2 Filaments wires (floating) directly to Pilot then to 6v6 (pins 7, 1-2) then to pin 9 and 4-5 of 12ax7. Wired away from other signal wires and tightly twisted to meet each tube socket.
If I compare the two, the floating filament arrangement has a hum and a buz.
the non-floating arrangement found on original Fender layout has a hum but
no buz. The hum increases as the volume knob is turned up. The floating arrangement has proven to be the worst with noise. moving the floating twisted wires around makes no difference in buz or hum.
a new problem occured when I turn the amp volume up and play a open bass
string (6) on a normal guitar, not bass guitar, the speaker has a horrible crackle in it. I connected another new speaker to the amp and it crackles as well. It's not a bad speaker, must be in the amp. Speaker polarity connection observed (+/-). The Speaker is a Jensen P8R alnico. The crackle was not evident the first day playing thru the amp , but its there now. Not sure why or how. What would cause this ? double checked all the components in the amp. is speaker coil fried ?
When I initially completed the amp I had a squeel which was solved by correcting the wire arrangement on the OT transformer. Just switched the secondary connections and fixed it. At this time there was no crackle sound coming from the amp. Actually sounded good except for presence of the hum which is still present.
Here are particulars and voltages associated with this 5F1 build.
Metal chassis nickel plated , cut outs, transformer orientation and component arragement very similar to
original Fender layout and metal box design.
New Sensor PT NSC125P1B
Primary - Black , Black
Secondary - red, red-yel/CT, Red 650V/CT @70ma
grn, grn 6.3v @2a
yel, yel 5v @2a
Hammond 125C OT - has selectable primary and secondary impedances.
primary blue, red/ct, brwn ( red wire center tap not used ) 6400 ohm primary impedance selected.
secondary (4, 6 tap) 4 ohm secondary selected
Jensen Alnico P8R , 4 ohm
Measured Voltages
Line voltage 122 vac ( a bit high )
40ma bias set on 6v6 using 1 ohm resistor in line before 450 ohm 5W and 200 ohm 2W adjustable pot. Allows
bias adjustment on 6v6 tube from 35ma to 45ma.
Heater Voltage set to 6.04 VAC ( 1 ohm 2W resistor in line with one filament wire ) resistor used to bring voltage down from 6.9 vac , due to elevated line voltage
6V6- voltages
pin 3, 402vdc
pin 4, 363vdc
pin 8, 20.62vdc
12ax7- voltages
pin 1, 216vdc
pin 6, 211vdc
pin 3, 1.45vdc
pin 8, 1.27vdc
5y3 - voltages
pin 4-6, 351vac on each leg ( approx 700 vac, should be 650 vac) a bit high , may need a dropping resistor here.
pin 2-8, 5.3vac
pin 8 to first filter cap 16uf/475 cap is 409 vdc
Links to chassis layout images
http://img.photobucket.com/albums/v6...wall/5F1_2.jpg
http://img.photobucket.com/albums/v6...wall/5F1_3.jpg
http://img.photobucket.com/albums/v6...wall/5F1_4.jpg
http://img.photobucket.com/albums/v6...wall/5F1_5.jpg
All tubes tested with Hickok 600A tester prior to initial power up.
tube sets include one NOS set , and one new Sovtek set. no differences
heard between the two with hum levels. Using ceramic tube sockets on chassis.
All components tested with cap checkers and all resistors check for resistance
before and after completion of the build. All components chosen within 5% tolerance of original.
resistors are carbon composition. bias resistors are wire wound.
components connected and soldered using x2 terminal blocks rather than turret board. Ground bus wire connecting all components exactly in original fender layout and grounded to chassis. chassis is being used
as star grounding point. All grounding points are .1 ohm and less to each other.
15uf/50V cap across the 1.5K 1/2W resistor connected to 12ax7 pin 3.
1.5 vdc measured across the resistor.
seperate clarostat sealed volume pot and on/off switch. pot grounded to
input jacks. jacks grouned to chassis.
Shielded wire to volume pot center tap from 12ax7 pin 7 , shield connected to input jack ground. input jack grounded to chassis.
measured all electrolytic caps for shorts to ground , no issues.
Why does my speaker crackle and can I reduce hum noise level ?
any help from veteran amp builders would be great.
Just finished a new 5F1 amp ($300USD in parts) and I'm not really impressed with results regarding hum. The sound of my guitar thru the amp was very good for a day or so and now a crackle from the speaker when playing guitar at 1/2 to full volume. I expected lower noise from this amp (little or no hum) . Of course, when you hear the guitar playing thu the amp it cancels out the hum, but not the new crackle, gets worse with volume level. Is it normal for the amp to have a certain amount hum like this ? I know the crackle sound is not normal.
I've read thru a lot of 5F1 posts here and tried to apply different
solutions to lower the hum level with no real amazing results. I'm not new to building electronics gear, but this is my first tube amp build. I do understand good grounding techniques, but this build is particularly challenging.
This 5F1 looked to be an easy build, maybe not.
The amp has a incremental hum as the volume increases. not sure if this is normal
with a 5F1 champ. Tried two filament arrangements below. I have not tried the 100 ohm resistor
trick with a sudo center tap since I do not know how it is implemented - need a schematic to
understand it.
1. filament wires one grounded with HT center tap to chassis next to the PT transformer and the other soldered to pin 7 6v6 and 4-5 12ax7. Pin 1-2 6v6 and pin 9 12ax7 grounded to chassis nearest the tube socket. Pilot light receives one ground and one hot filament wire from PT transformer.
2. 2 Filaments wires (floating) directly to Pilot then to 6v6 (pins 7, 1-2) then to pin 9 and 4-5 of 12ax7. Wired away from other signal wires and tightly twisted to meet each tube socket.
If I compare the two, the floating filament arrangement has a hum and a buz.
the non-floating arrangement found on original Fender layout has a hum but
no buz. The hum increases as the volume knob is turned up. The floating arrangement has proven to be the worst with noise. moving the floating twisted wires around makes no difference in buz or hum.
a new problem occured when I turn the amp volume up and play a open bass
string (6) on a normal guitar, not bass guitar, the speaker has a horrible crackle in it. I connected another new speaker to the amp and it crackles as well. It's not a bad speaker, must be in the amp. Speaker polarity connection observed (+/-). The Speaker is a Jensen P8R alnico. The crackle was not evident the first day playing thru the amp , but its there now. Not sure why or how. What would cause this ? double checked all the components in the amp. is speaker coil fried ?
When I initially completed the amp I had a squeel which was solved by correcting the wire arrangement on the OT transformer. Just switched the secondary connections and fixed it. At this time there was no crackle sound coming from the amp. Actually sounded good except for presence of the hum which is still present.
Here are particulars and voltages associated with this 5F1 build.
Metal chassis nickel plated , cut outs, transformer orientation and component arragement very similar to
original Fender layout and metal box design.
New Sensor PT NSC125P1B
Primary - Black , Black
Secondary - red, red-yel/CT, Red 650V/CT @70ma
grn, grn 6.3v @2a
yel, yel 5v @2a
Hammond 125C OT - has selectable primary and secondary impedances.
primary blue, red/ct, brwn ( red wire center tap not used ) 6400 ohm primary impedance selected.
secondary (4, 6 tap) 4 ohm secondary selected
Jensen Alnico P8R , 4 ohm
Measured Voltages
Line voltage 122 vac ( a bit high )
40ma bias set on 6v6 using 1 ohm resistor in line before 450 ohm 5W and 200 ohm 2W adjustable pot. Allows
bias adjustment on 6v6 tube from 35ma to 45ma.
Heater Voltage set to 6.04 VAC ( 1 ohm 2W resistor in line with one filament wire ) resistor used to bring voltage down from 6.9 vac , due to elevated line voltage
6V6- voltages
pin 3, 402vdc
pin 4, 363vdc
pin 8, 20.62vdc
12ax7- voltages
pin 1, 216vdc
pin 6, 211vdc
pin 3, 1.45vdc
pin 8, 1.27vdc
5y3 - voltages
pin 4-6, 351vac on each leg ( approx 700 vac, should be 650 vac) a bit high , may need a dropping resistor here.
pin 2-8, 5.3vac
pin 8 to first filter cap 16uf/475 cap is 409 vdc
Links to chassis layout images
http://img.photobucket.com/albums/v6...wall/5F1_2.jpg
http://img.photobucket.com/albums/v6...wall/5F1_3.jpg
http://img.photobucket.com/albums/v6...wall/5F1_4.jpg
http://img.photobucket.com/albums/v6...wall/5F1_5.jpg
All tubes tested with Hickok 600A tester prior to initial power up.
tube sets include one NOS set , and one new Sovtek set. no differences
heard between the two with hum levels. Using ceramic tube sockets on chassis.
All components tested with cap checkers and all resistors check for resistance
before and after completion of the build. All components chosen within 5% tolerance of original.
resistors are carbon composition. bias resistors are wire wound.
components connected and soldered using x2 terminal blocks rather than turret board. Ground bus wire connecting all components exactly in original fender layout and grounded to chassis. chassis is being used
as star grounding point. All grounding points are .1 ohm and less to each other.
15uf/50V cap across the 1.5K 1/2W resistor connected to 12ax7 pin 3.
1.5 vdc measured across the resistor.
seperate clarostat sealed volume pot and on/off switch. pot grounded to
input jacks. jacks grouned to chassis.
Shielded wire to volume pot center tap from 12ax7 pin 7 , shield connected to input jack ground. input jack grounded to chassis.
measured all electrolytic caps for shorts to ground , no issues.
Why does my speaker crackle and can I reduce hum noise level ?
any help from veteran amp builders would be great.
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