Restoring a 1974 Deluxe Reverb - Seeking Advice
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Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
Ok, I have another question... and I realize it may come off as rather stupid.
Exactly how clean is this amp supposed to be? I can't even seem to get it to break up even slightly unless I use humbuckers and hit full chords while the volume is at about 8.5.
The standard tricks only very subtley change that... Pulled V1. Swapped V2 for another 12ax7. Switched off NFB. Pulled off the grounded RCA jack for the Tremolo (that allows it to stay on without a pedal).
I'm pretty sure I could get a little breakup with single-coils around 5 on the volume before I started "fixing" the voltages.
It's not like this thing is quiet either. It's definitely in the "hurting the ears" volume range while it's still spanky clean... and I'm not a wuss. I like my loud music and loud guitar.
Is this normal for a silverface Deluxe? Where do most people expect a stock deluxe reverb to start breaking up on the dial? Am I just not used to Fenders? Is this why some people just have always-on boosters or compressors.... or should I be digging back into this thing and checking all my voltages?
I never did swap out all the little white cathode bypass caps because I heard that they usually hold up.
Exactly how clean is this amp supposed to be? I can't even seem to get it to break up even slightly unless I use humbuckers and hit full chords while the volume is at about 8.5.
The standard tricks only very subtley change that... Pulled V1. Swapped V2 for another 12ax7. Switched off NFB. Pulled off the grounded RCA jack for the Tremolo (that allows it to stay on without a pedal).
I'm pretty sure I could get a little breakup with single-coils around 5 on the volume before I started "fixing" the voltages.
It's not like this thing is quiet either. It's definitely in the "hurting the ears" volume range while it's still spanky clean... and I'm not a wuss. I like my loud music and loud guitar.
Is this normal for a silverface Deluxe? Where do most people expect a stock deluxe reverb to start breaking up on the dial? Am I just not used to Fenders? Is this why some people just have always-on boosters or compressors.... or should I be digging back into this thing and checking all my voltages?
I never did swap out all the little white cathode bypass caps because I heard that they usually hold up.
Last edited by bcmatt on Sun Mar 10, 2024 6:04 pm, edited 1 time in total.
- martin manning
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Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
I think you should be getting more distortion than you describe when it's turned up. Maybe a good idea to verify the preamp tube operating points. Perhaps you have some resistors that have drifted. What about the cathode bypass caps? have you replaced those?
Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
Sorry, I was distracted when I was writing my last post. I meant to say that I hadn't replaced the little white cathode bypass caps. I had bought replacements, but had heard they seldom drift so hadn't yet replaced them.martin manning wrote: ↑Sun Mar 10, 2024 4:15 pm I think you should be getting more distortion than you describe when it's turned up. Maybe a good idea to verify the preamp tube operating points. Perhaps you have some resistors that have drifted. What about the cathode bypass caps? have you replaced those?
Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
Hello —
Depending on guitar pickups somewhere round 4 to 5 is that obvious edge threshold. This was consistent within one notch across half dozen examples I had here at one time. Martin, as expected, has the guidance for you. Check preamp plate voltages too, if you haven’t already.
..
Depending on guitar pickups somewhere round 4 to 5 is that obvious edge threshold. This was consistent within one notch across half dozen examples I had here at one time. Martin, as expected, has the guidance for you. Check preamp plate voltages too, if you haven’t already.
..
Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
OK, I took some current voltages before changing out the old Mallory Cathode Bypass caps.
I guess I'll change the old Mallories out and check again.
Would it more likely be plate resisters drifting causing these high voltages?
The preamp plate voltages are all quite high. V1 and V2 are all between 80-120V over what the schematic says they should be while my power tubes are slightly lower than the schematic.I guess I'll change the old Mallories out and check again.
Would it more likely be plate resisters drifting causing these high voltages?
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- martin manning
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Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
B and C voltages are not too far out but D is way high. Is the 10k dropping resistor from C to D really 10k?
Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
Yup! I just had to double-check, to make sure:martin manning wrote: ↑Mon Mar 11, 2024 10:06 pm B and C voltages are not too far out but D is way high. Is the 10k dropping resistor from C to D really 10k?
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Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
Do you think I should try swapping it for something like a 27K resistor before replacing the cathode bypass caps?
- martin manning
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Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
You could give that a try. Hard to believe that those early stages can be that much higher than the schematic when the PI is only 15-20V high, and the power stage plates are only a few volts high. It's as if there is some leakage somewhere. Just for grins, pull the 10k and see if there is any voltage on the D node.
PS Measure the voltage across the 10k and see how much current is flowing through it.
PS Measure the voltage across the 10k and see how much current is flowing through it.
Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
I'll check the current in a moment when I re-attach it.martin manning wrote: ↑Mon Mar 11, 2024 10:55 pm You could give that a try. Hard to believe that those early stages can be that much higher than the schematic when the PI is only 15-20V high, and the power stage plates are only a few volts high. It's as if there is some leakage somewhere. Just for grins, pull the 10k and see if there is any voltage on the D node.
PS Measure the voltage across the 10k and see how much current is flowing through it.
With it pulled I get -0.85V on the D node when there is a bout +405V at the C node.
Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
It's about 5.1mA across the 10k Resistormartin manning wrote: ↑Mon Mar 11, 2024 10:55 pm You could give that a try. Hard to believe that those early stages can be that much higher than the schematic when the PI is only 15-20V high, and the power stage plates are only a few volts high. It's as if there is some leakage somewhere. Just for grins, pull the 10k and see if there is any voltage on the D node.
PS Measure the voltage across the 10k and see how much current is flowing through it.
- martin manning
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Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
That sounds reasonable, but how the input stages can be 100 volts high is a mystery. I guess I’d go ahead and replace the cathode bypass caps, and check the cathode resistor values while the cathode caps are out.
Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
What’s the story between B & C? Seems the elevated potential begins there ..
Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
So I finished the cathode bypass caps swap. I managed to check a few of the cathode resistors and they all seem to be quite reasonably within spec.
I checked voltages again and they are all about the same... Most have climbed about 4-10 volts because my wall voltage is up a few volts to about 125VAC since I took the earlier voltages when the wall was about 122.5VAC.
So obviously the sound is as spanky clean as before.
Any other thoughts?
Interestingly, I do think that I remember the amp would break up closer to 4-5 on the volume knob back before I began "fixing" my high B+ voltage. (I only had it like that for less than a week before I was trying to bring voltages down).
So, if I try increasing that 10K dropping resistor, a 3 Watt resistor should be fine, right? Because I do have a 3W 27K that I'm thinking I will try.
I'm guessing that would also end up pushing up the voltages before it at C and B? So I'd probably end up trying to increase the 2.2K resister in the process of balancing things...
Am I approaching this the right way?
I checked voltages again and they are all about the same... Most have climbed about 4-10 volts because my wall voltage is up a few volts to about 125VAC since I took the earlier voltages when the wall was about 122.5VAC.
So obviously the sound is as spanky clean as before.
Any other thoughts?
Interestingly, I do think that I remember the amp would break up closer to 4-5 on the volume knob back before I began "fixing" my high B+ voltage. (I only had it like that for less than a week before I was trying to bring voltages down).
So, if I try increasing that 10K dropping resistor, a 3 Watt resistor should be fine, right? Because I do have a 3W 27K that I'm thinking I will try.
I'm guessing that would also end up pushing up the voltages before it at C and B? So I'd probably end up trying to increase the 2.2K resister in the process of balancing things...
Am I approaching this the right way?
Re: Restoring a 1974 Deluxe Reverb - Seeking Advice
Just to clarify the present situation, the amp is now stock aside from 2 thermistors on the wall side of the PT, and 2 68 ohm resistors on the Rectifier Tube socket on the PT (AC) side.