Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TubeJunkie on September 08, 2019, 02:39:41 pm
-
Hi All,
Need some :help: with a HRDx (2009) I purchased at a great price. The previous owner did some mods, and in his words "broke it good." The price was good enough that I felt it was worth bringing home to see if I could get it running. When turned on, the amp has very little volume, and that's only if the amp is turned all the way up, as well as the guitar. I opened up the amp and got the following readings:
Test
Point Measured Spec
==========================
1 0.2mV 4.0mV
2 156.1V 180mV
3 2.58V +1.93Vdc
4 -0.2mV 13.0mV
5 154.5V 354mV
6 2.46V +1.93Vdc
7 0.0mV 58mV
8 209.3V 1.49V
9 1.59V +1.93Vdc
10 0.0V 1.0V
11 210.6V 23.6V
12 1.56V +1.93Vdc
13 0.0V 1.45V
14 0.0V 78mV
15 3.4mV 78mV
16 0.0V 78mV
17 5.4mV 1.54V
18 0.0V 1.37V
19 17.4mV 1.32V
20 19.2mV 13.8V
21 0.0mV 12mV
22 -4.7V 1.22V
23 0.0V 920.mV
24 252.9V 11.5V
25 241.5V 11.5V
26 31.46V +42.8Vdc
27 410.9V 66.5V
28 412.4V 66.5V
29 0.0V 5.34V
30 76.4mV 60mV
31 1.32V +1.39V
32 0.55V +0.54V
33 16.12V +16.0V
34 -12.25V -12.5V
35 -0.56mV +0.52V
36 -15.7V -15.5V
37 408.9V 431V
38 406.8V 430V
39 367.8V 392V
40 313.3V 345V
41 ---- -106V
42 45.7V +48Vdc
43 -45.8V -48Vdc
44 ---- 39Vac
Here are some additional readings I took:
TP42 and TP43 are for one side of resistors R78 and R79 respectively, and the reading on the other side is:
R78 = +16.9V +16V (spec)
R78 = -16.9V -16V (spec)
Speaker1 = 405.1V 431V (spec)
Speaker2 = 403.8V 430V (spec)
R76 = -100.7V -53V (spec)
R97 = 37.8Vac 39Vac (spec)
Here's the readings from the Power Transformer:
______________
( Red
(
(
(
( 331.5Vac 330Vac (spec
(
(
(
(Red___________
______________
( Green
(
( 6.94Vac 7Vac (spec
(
(Green_________
______________
( Brown
(
(
( 40.3Vac 40Vac (spec
(
(
(Brown_________
Here's a link to the schematic:
https://el34world.com/charts/Schematics/files/Fender/Fender_hotrod_deluxe.pdf (https://el34world.com/charts/Schematics/files/Fender/Fender_hotrod_deluxe.pdf)
As you can see, many of the reading are way off, and all the B+ voltages are off by about 30Vdc.
(info continued on next post)
-
(part 2)
Here's a list of the mods the previous owner said he did:
• Replaced resistors: R78, R79 470Ω 5W Cement
• Replaced filter cap: C31 to 100uf 500V F&T
• Replaced filter cap: C33, C35, C36 to 22uf 500V F&T
• Replaced Master Volume pot: 250k Audio
• Replaced Reverb pot: Use old 100k Linear from Master Volume
• Replaced Plate Load Resistor: R57 to 82kΩ (1/2 watt Carbon Comp)
• Replaced Plate Load Resistors: R4, R11, R16, R22, R58 to 100kΩ (1/2 watt Carbon Comp)
• Replaced power tube screen resistors: R61, R62 1kΩ 5W 750V High-Temp
• Replaced Bass control resistor: R105 100kΩ (1/2 watt Carbon Comp)
• Replaced coupling caps: C2, C10 to .047uf Orange Drop
• Replaced coupling cap: C11 to 1000pf Silver Mica
• Fixed Mid pot: Jumper from Wiper Leg to Bass Leg (What would this look like?)
• Fixed reverb issues: Remove R103 & C52
• Replaced: R1, R2 to 68kΩ Carbon Comp
• Less Bass Gain: C1 47uf to 22uf 25V (electrolytic)
• Highs & Gain Boost: R9 220kΩ to 100kΩ (1/2 watt)
• Tone Slope Resistor: R12 130kΩ to 56kΩ (1/2watt)
• Harsh Drive & More Max Gain: C8 1uf to 22uf 100V (electrolytic)
• More Bass to Drive: C23 1.5nf to .01uf (Orange Drop)
• Treble Tone Cap: C7 500pf (Silver Mica)
• Bass Tone Cap: C5 .1uf to .047uf (Orange Drop)
• Mid Tone Cap: C6 .022 to .047uf (Orange Drop)
• Less Muddy Tone @Low Volume (Vol Pot): 220pF (Silver Mica) Middle Leg to Right Leg (From Wiper to Input?)
• Less Muddy Tone @Low Volume (Drv Pot): 360pF (Silver Mica) Middle Leg to Right Leg (From Wiper to Input?)
:w2: I appreciate any and all input that can help me resolve these issues. Thanks in Advance!!!
Sorry about the length, but wanted to include as much important info as I could.
-
I'm guessing you did not inject a test signal (4mV, 1KHz, Sine wave) into input jack J1? Until you do that, all of your "oval" test point readings are meaningless. You need a sig gen and a scope to make those readings. You also need to read all notes so you can set the knobs to the required setting to make those signal readings meaningful.
-
Gut it and do this...
https://ampgarage.com/forum/viewtopic.php?f=8&t=31844
At least, that's what I would do and I am actively looking for broken HRD's to do just that.
-
Problem fixed . . . :icon_biggrin: . . . found a couple bad components and a few bad solder joints. Everything's back together, voltages all look good, and I just made a $75 purchase worth about $450 . . . not bad for a few days work.