67 Super Reverb ugly distortion

[vintagekiki]

VK - the Fender schematic you posted is much more recent, do those voltage settings still apply?

Have time for schemarics, voltages, scope pictures ...
First needs to be started Vibrato ch step by step.

[vintagekiki]

So it looks like I might have a set back here.

I set up the latest test as Vintagekiki described, by putting in V2 and V4 tubes, and playing thru the "Vibrato" channel with controls at 5, reverb and vibrato off.
The test lead is still connected from point "X" to the .001 capacitor.

The setback, is that I'm now getting some of that distortion upon heavy attack of notes.

Perhaps it's because no one is home right now and I'm hitting the notes harder...

I switched back to just having V1 in place and connecting the test lead from P6 V1 to the .001 cap and still the distortion is there upon heavy attack, playing thru "Normal" channel.

i checked the speakers for voice coil rub but it didn't seem like there was any.

I am out of time for today, but the first thing I will do tomorrow is check the output jack and make sure that the ground connection to the chassis is good.

https://music-electronics-forum.com/attachment.php?attachmentid=55537&d=1570868287

If you followed the story neatly you would notice that (red point X) referred to Normal ch.

We will repeat the test procedure for Vibrato ch.
Temporarily connect test wire from .001uF with anode V2 (pin 1)
Turn on the guitar in vibrato ch and try the sound.
If the sound is a loud temporarily connect test wire to the anode V2 (pin 6) and try with a guitar.
If the sound is loud and clear and the volume and volume controls works, temporarily connect test wire to the anode V4 (pin 6) and try with a guitar.
If the sound is loud and clear and tone and volume controls work, check .1uF (pin 6 V4), network resistor 220k (blue point Y)

If the sound is still ugly:
- check the anode and cathode voltages on tube V2 and V4
- cleans from oxide ground connection input jacks on vibrato ch to the chassis
- check tube sockets V2 and V4 for cold solder joints

[earache]

“We will repeat the test procedure for Vibrato ch.
Temporarily connect test wire from .001uF with anode V2 (pin 1)
Turn on the guitar in vibrato ch and try the sound.”

The sound was loud, and not controllable with vibrato channel volume.

“If the sound is a loud temporarily connect test wire to the anode V2 (pin 6) and try with a guitar.”

The sound was NOT as loud and the volume and tone controls did not work.

“If the sound is loud and clear and the volume and volume controls works, temporarily connect test wire to the anode V4 (pin 6) and try with a guitar.”

I tried this test and the volume control and tone controls work. After a couple of minutes of chugging a low “E” chord, the bad distortion happens again upon the attack of the note.

“If the sound is loud and clear and tone and volume controls work, check .1uF (pin 6 V4), network resistor 220k (blue point Y)”

I will follow up with this last test in a little while

[vintagekiki]

Temporarily connect test wire from .001uF with anode V2 (pin 1)
Turn on the guitar in vibrato ch and try the sound.”

The sound was loud, and not controllable with vibrato channel volume.
OK

“If the sound is a loud temporarily connect test wire to the anode V2 (pin 6) and try with a guitar.”

The sound was NOT as loud and the volume and tone controls did not work.

If volume and tone controls not work at anode V2 (pin 6) check capacitor connection .1uF; .022 uF and 250 pF with tone control pots.
Check the anode and cathode voltages on tube socket V2.

[earache]

“...check .1uF (pin 6 V4), network resistor 220k (blue point Y)”

I lifted one end of the .1 uf cap and the 220K resistor





If the sound is still ugly:
- check the anode and cathode voltages on tube V2 and V4”

V2 P1 anode. 279
V2 P6 anode. 282
V2 P3 cathode. 2.3
V2 P8 cathode. 2.5

V4 P1 anode. 283
V4 P6 anode. 276
V4 P3 cathode. 2.6
V4 P8 cathode. 2.6. (soldered to P3)

I saw your last post and will continue to follow the directions and post results.

Sometimes I find that posting a picture of the test results is preferable as you can see exactly what the results were and the method of test (if it’s wrong you could comment)

[vintagekiki]

The voltages on V2 and V4 are fine.

[earache]

“If volume and tone controls not work at anode V2 (pin 6).....
check capacitor connection .1uF;


Looks ok

.......022 uF


Looks ok

....and 250 pF with tone control pots”


Value out of spec?

I continued on down the line and found what looks like a few bad caps







I unsoldered one leg of each component during test

[vintagekiki]

[ATTACH=CONFIG]55578[/ATTACH]

[ATTACH=CONFIG]55579[/ATTACH]
Or don't have good contact with elco, or cathode resistor is defective.

[ATTACH=CONFIG]55580[/ATTACH]

I unsoldered one leg of each component during test
Correctly

Before testing, soldering elco contacts or clean from the oxide.
When testing cathode elco unsolder cathode resistor from elco

[earache]

Vintagekiki

Just as you had thought, the parts that tested bad in the last post tested ok after cleaning the corrosion off of the leads.

I have resoldered them all back in place.

Since my last post I have done the following:

Took off the output jacks, cleaned the chassis at that spot and then reattached the output jacks

Did the same for both input jacks at the normal and vibrato channels

Reversed the mod that put reverb and vibrato on both channels

Touched up the solder on all preamp tube sockets

I also disconnected one speaker at a time and played thru the amp to see if just one speaker was causing the distortion.
That didn’t prove anything as the ugly distortion is still there.

==============================

The distortion doesn’t show up right away when you turn on the Amp.

It happens especially when chugging on low notes, and above “5” on the volume

[The Dude]

......The distortion doesn’t show up right away when you turn on the Amp.

It happens especially when chugging on low notes, and above “5” on the volume

That is symptomatic of a failing filter cap much of the time. If you have a scope, look for ripple on supply lines. If not, measure AC with your DVM. You could also tack a known good cap with proper voltage rating across each filter and see if the problem goes away.

[earache]

Dude

I have a scope I’m just learning to use, can you elaborate on how to look for ripple on the supply?

Is some AC ripple acceptable? If so, how much?

I replaced all the filter caps back in 2011. Might it be a bad solder joint there? I used Sprague Blue Atoms back then... but I suppose anything can fail...I’ll check the solder tomorrow and look for your direction on the scope usage...thanks!

[The Dude]

First, make sure your scope is rated above B+ DCV. Use a X10 probe. There will be some ripple, but it will be a very small percentage in relation to the DCV. It could be a flaky joint or a bad cap...... or neither- I'm not guaranteeing that's your problem, that's why we test. Even new caps do sometimes go bad, especially if the vendor has had them sitting on a shelf for a while.

[earache]

Dude

Noob questions:

Would I just clip the scope leads over each individual filter cap to test?

Would I need to input a signal?

The scope would need to be rated better than the capacitor's rating I imagine, like 500V or better, correct?

Couldn't I just use my meter to measure for AC across the capacitor?

[vintagekiki]

Same story turns around over 100 posts, and we still don't know what Fender signal test voltages are.

https://music-electronics-forum.com/showthread.php?t=49793&page=3&p=541209&viewfull=1#post54 1209
Question
Set volume and all tone controls on 5, Reverb 0, Bright sw OFF
How many mV test signal 1 kHz on normal and on vibrato channel jacks gives a clear signal on dummy load of 2 Ohm and how many is this voltage value.

If distortion occurs after some time (when the tubes are warmed up) indicates GZ34 and 6L6. Check it.
Question
Are these tubes currently in the FSR new or "as new" ?

Distortion at low tones and at higher power usually occurs when poor DC voltage filtration or insufficient PT.
When distortion occurs
- measure (+465 VDC) the DC voltage on the first elco, does voltage drops with increasing power.
If the + DC voltage on the first elco drops with increasing power, check the GZ34 and the first elco.
- measure (360 VAC) the AC voltage at the anode GZ34, does voltage drops with increasing power.
If the AC voltage at the anode GZ34 drops with increasing power, check the PT.

Question
- Does distortion occur at low tones and at higher power only occurs on FSR 4x10 cab or on other guitar cab.
- Whether distortion occurs at low tones and at higher power occurs on both channels or on one channel.

Since you have working on FSR modes, check that one of the mode elements has not changed its value.

[The Dude]

Dude

Noob questions:

Would I just clip the scope leads over each individual filter cap to test?

Would I need to input a signal?

The scope would need to be rated better than the capacitor's rating I imagine, like 500V or better, correct?

Couldn't I just use my meter to measure for AC across the capacitor?

1) Would I just clip the scope leads over each individual filter cap to test? Yes, that will work.
2) Would I need to input a signal? Nope.
3) The scope would need to be rated better than the capacitor's rating I imagine, like 500V or better, correct? Basically, yes. Technically, you're only concerned about the actual voltage that is there, but usually caps are rated accordingly.
4) Couldn't I just use my meter to measure for AC across the capacitor? Yes, that's another way to do it. IMO, it's easier to see it on a scope.