Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ES125guy on November 10, 2022, 09:11:41 am
-
Hey everyone,
Long-time lurker, first time poster. Spent the past few months plugging away at building Sluckey's AC15. Pics for attention:
(https://i.imgur.com/dvGArtr.jpg) (https://i.imgur.com/NalobuO.jpg)
I've got sound/guitar output coming from both the normal and vibrato channels (woohoo!), but no vibrato. Swapped out the LED for a 1.5k resistor. Followed other threads switchcraft 12a jack for footswitch, and connecting the ground and shunt, with the ground wire from the board going to the tip lug. Still no vibrato. Tried a couple different 12ax7 tubes for V6 and still getting low cathode voltage on pin 8 (4v).
Also noticed some questionable voltages on V1 pin 8, and V5 pin 6 (phase inverter). Here are my voltages for the entire amp. Curious if anyone has any ideas?
V1 - 12AX7
1-145v
2-
3- 1.2v
4- 5.9v ac across heater
5- 5.9v ac across heater
6- 240v
7-
8- 3v (should be 17v)
9- 5.9v ac across heater
V2 - EF86
1- 83v
2-
3- 3v
4- 5.9v ac across heater
5- 5.9v ac across heater
6- 81v
7-
8- 3v
9-
V3 - EZ81 (rectifier)
1- 281v ac (with tube installed)
2-
3- 342v
4- 5.9v ac across heater
5- 5.9v ac across heater
6-
7- 281v ac (with tube installed)
8-
9-
V4 - 12AU7
1- 87v
2-
3- 4v
4- 5.9v ac across heater
5- 5.9v ac across heater
6- 87v
7-
8- 4v
9- 5.9v ac across heater
V5 - 12AX7 (phase inverter)
1- 234v (Should be 245v)
2- 35v
3- 76v
4- 5.9v ac across heater
5- 5.9v ac across heater
6- 328v (Way too high? Should be 243v)
7- 19v
8- 76v
9- 5.9v ac across heater
V6 - 12AX7
1- 130v
2-
3- 2v
4- 5.9v ac across heater
5- 5.9v ac across heater
6- 242v
7-
8- 4v (vibrato to resistor or led) should be 23v
9- 5.9v ac across heater
V7 - EL84
1-
2-
3- 11v
4- 5.9v ac across heater
5- 5.9v ac across heater
6-
7- 324v
8-
9- 328v
V8 - EL84
1-
2-
3- 11v
4- 5.9v ac across heater
5- 5.9v ac across heater
6-
7- 324v
8-
9- 328v
Letters below correspond to Sluckey's voltage testing points on http://sluckeyamps.com/VAC15/Vox_AC15.pdf:
A - 333v
B - 279v
C - 303v
D- 253v
Please excuse some of the questionable lead dress... Planning to tidy up more once I get things sorted out:
(https://i.imgur.com/Kb6x1at.jpg)
Appreciate any thoughts anyone might have on what to check next re: no vibrato and voltage on V1 and V5 PI.
Thanks!
Chris
-
Tell you what those cabinets are artwork. Face plate too. Good luck, I'm sure you'll have it all sorted.
-
Tell you what those cabinets are artwork. Face plate too. Good luck, I'm sure you'll have it all sorted.
Thank you! I certainly hope so!
I spent a good bit of time on the aesthetics of the project. Concept is a 60's Brazilian knock off of a Vox. Turned the Vox crown logo into a humming bird feeder and changed the branding to Voz (voice in Portuguese). Copied Sluckey's faceplate and made some tweaks. Had it produced by Front Panel Express. I designed the badge from scratch and had a friend 3D print it. Cabinets are African Mahogany made by a raw cab seller on eBay out of Fresno, CA. I finished the cabs with sanding and Odie's oil and butter/wax.
-
Discovered a bad connection on a jumper under the board near the PI. I fixed that and now V5 PI voltages are happy. Still no vibrato, however.
Updated voltage readings:
V1 - 12AX7
1-148v
2-
3- 2v
4- 5.9v ac across heater
5- 5.9v ac across heater
6- 246v
7-
8- 3v (should be 17v)
9- 5.9v ac across heater
V2 - EF86
1- 83v
2-
3- 3v
4- 5.9v ac across heater
5- 5.9v ac across heater
6- 81v
7-
8- 3v
9-
V3 - EZ81 (rectifier)
1- 281v ac (with tube installed)
2-
3- 342v
4- 5.9v ac across heater
5- 5.9v ac across heater
6-
7- 281v ac (with tube installed)
8-
9-
V4 - 12AU7
1- 87v
2-
3- 4v
4- 5.9v ac across heater
5- 5.9v ac across heater
6- 87v
7-
8- 4v
9- 5.9v ac across heater
V5 - 12AX7 (phase inverter)
1- 218v
2- 22v
3- 62v
4- 5.9v ac across heater
5- 5.9v ac across heater
6- 229v
7- 24v
8- 62v
9- 5.9v ac across heater
V6 - 12AX7
1- 199v
2-
3- 2v
4- 5.9v ac across heater
5- 5.9v ac across heater
6- 248v
7-
8- 5v (vibrato to resistor or led) should be 23v
9- 5.9v ac across heater
V7 - EL84
1-
2-
3- 11v
4- 5.9v ac across heater
5- 5.9v ac across heater
6-
7- 324v
8-
9- 328v
V8 - EL84
1-
2-
3- 11v
4- 5.9v ac across heater
5- 5.9v ac across heater
6-
7- 324v
8-
9- 328v
Letters below correspond to Sluckey's voltage testing points on http://sluckeyamps.com/VAC15/Vox_AC15.pdf:
A - 332v
B - 298v
C - 301v
D- 253v
-
Measure resistance between V6 pin 7 and ground. What have you?
Measure resistance between V6 pin 8 and ground. What have you?
-
Measure resistance between V6 pin 7 and ground. What have you?
Measure resistance between V6 pin 8 and ground. What have you?
Pin 8 - maxed out 1. at 2M ohm setting not able to get a value
Pin 7 - fluctuates up and down between 450k to 730k ohm
-
Pin 8 - maxed out 1. at 2M ohm setting not able to get a value
That's a big clue. Reading should be 23.5K.
Check R55 and R52. Also be sure of the ground connection to R52.
-
Pin 8 - maxed out 1. at 2M ohm setting not able to get a value
That's a big clue. Reading should be 23.5K.
Check R55 and R52. Also be sure of the ground connection to R52.
It just took some prompting from you. All fixed!!! Reflowed the top side jumpers in two parts of the vibrato circuit and now she sings! Thanks!!!
-
There should be a jumper between the two circled turrets. I don't see one.
-
There should be a jumper between the two circled turrets. I don't see one.
Indeed! That was part of it.