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Thread: Screaming Bright Switch Cap??? - 1974 Fender SF Twin Reverb Master Volume Push Pull Switch

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    Screaming Bright Switch Cap??? - 1974 Fender SF Twin Reverb Master Volume Push Pull Switch

    Hello all,

    continuing my restoration project, the next hurdle is to have a good overdriven sound.
    When I push the Vibrato Channel Volume Past 7-8 I start hearing some high frequency clipping instead of a warm overdriven sound.

    Trying to force this failure mode I found the following combination:
    - Bright SWITCH on
    - Channel VOL 5+ (left it at 10 for a most dramatic effect)
    - Treble at 10
    - Middle and Bass at minimum

    Moving the Reverb potentiometer I only get the "screaming sound" either with Reverb at min or MAX, no noise with values in between.

    See video for a better understanding (be careful with the volume, the screaming noise is not nice)



    I am suspecting the Bright SW 120 pF cap could have gone bad



    Do you agree it might be the 120 pF cap?
    Any ideas about why it only "screams" with the Reverb Pot at either end of the track?
    In any case, this cap should have no effect when the switch is OFF (and still the overdriven sound has clipping highs. Additionally the 250 uF TREBLE cap is new)

    Thank you!

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    Last edited by TelRay; 02-23-2019 at 03:28 AM.

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    Why do you suspect the bright cap? I would only think that if the issue didn’t manifest with the bright off; is that the case?
    My guess is that it’s due to a bad ecap for the preamp HT node, or a bad 0V return connection to the chassis.
    The V4 cathode bypass ecap may also be bad.
    These things create positive feedback loops that can cause free running oscillation, given suitable control settings.
    What effect does the pullboost have on the issue? How about setting the master vol very low?

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    Hey! thank you very much for your reply and advice!

    Quote Originally Posted by pdf64 View Post
    Why do you suspect the bright cap?
    Well... I've changed every other cap in the amp (those orange things you see in the video)
    The only caps I have not changed are the 120 uF caps on NORMAL and VIBRATO Ch BRIGHT SWs

    Quote Originally Posted by pdf64 View Post
    I would only think that if the issue didn’t manifest with the bright off; is that the case?
    Yes, in the particular case of this "loud scream" (what you hear on the video), the failure cannot be reproduced with BRIGHT SW OFF
    As I mentioned above, the original problem I am trying to solve is that, when playing my guitar at VIBRATO Ch volumes of 7+, there is some high frequency clipping even when the BRIGHT SWITCH OFF.
    I've found this way of "creating a problem" with all the HIGHs frequencies to the MAX (BRIGHT SW ON + TREBLE at 10) looking for reasons for that (there might be not related)

    Quote Originally Posted by pdf64 View Post
    My guess is that it’s due to a bad ecap for the preamp HT node
    I'm sorry but (due to a severe case of inexperience) I would need help here. Which one is the HT node?
    Schematic Fender 100 Watts RMS AMP w/ Reverb and Vibrato (the white schematic, not the blue one)
    Nevertheless, if it's a cap, it has been surely been replaced already

    Quote Originally Posted by pdf64 View Post
    bad 0V return connection to the chassis
    that's interesting and something I have definitely not explored. Would it be possible for you to highlight the 0V return in the schematic?
    I believe these might be the connections you are referring to:


    Quote Originally Posted by pdf64 View Post
    The V4 cathode bypass ecap may also be bad.
    If this is the one, it has been replaced along with the associated resistor


    Quote Originally Posted by pdf64 View Post
    What effect does the pullboost have on the issue?
    As I initially thought the distorted high frequency could be leaking from the pull boost feature I have completely removed it from the amp.
    (meaning I physically removed the 4 wires coming from the back of the push/pull potentiometer and from the circuit)

    Quote Originally Posted by pdf64 View Post
    How about setting the master vol very low?
    the video was made at very low MASTER VOLUME (a bit above 2)

    thx!!!

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    Last edited by TelRay; 02-24-2019 at 12:42 AM.

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    Hi there, with Channel Volume maxed, the bright switch should have no effect. If it does, check the wiring or the lead dress.

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    Quote Originally Posted by strato56 View Post
    Hi there, with Channel Volume maxed, the bright switch should have no effect. If it does, check the wiring or the lead dress.
    good catch man! i was about to post this photo when i read your post

    solder has gone bad here


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    so... the solder was (partially) bad, the other lead of the cap was soldered to the other lug of the BRIGHT SWITCH and, having a solder iron in my hand, I decided to change the capacitor for a new one.

    what has not changed?
    the "screaming sound" is still there with all other pots at minimum, TREBLE and CH VOL at MAX and BRIGHT SW ON

    what has changed?
    now the noise is still present regardless of the REVERB potentiometer position
    the only pot that seems to have an effect (make the noise disappear) seems to be the MIDDLE pot.


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    Bent Member Chuck H's Avatar
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    I suspect something is wired incorrectly and/or there is a missing circuit ground. These things can cause a positive feedback loop. I suspect this because in the first video the reverb mitigated the problem at all settings but min and max. Yet the screech was reverberated indicating that it is manifesting before the reverb circuit. I know the reverb knob no longer affects the problem in the same way, but this is still a clue. The mid control includes the ground for the tone stack. There may also be wiring errors there for the control to affect the problem as it does.

    Can you provide clear photos of the wiring?

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    thx Chuck, you are right. In both videos the noise is reverberated 👍
    yes! i was just checking the wiring and I read your reply.
    you are right, the MID provides the ground, in this case shared with the VOL pot
    I have taken a photo but for the sake of clarity I added a drawing of what I see
    NOTE: when moving the pots the wire connecting the MID control to the VOL one and then to ground came loose 🤓 (could be an indication of failure)




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    Quote Originally Posted by TelRay View Post
    Well... I've changed every other cap in the amp (those orange things you see in the video)
    The only caps I have not changed are the 120 uF caps on NORMAL and VIBRATO Ch BRIGHT SWs
    ...I'm sorry but (due to a severe case of inexperience) I would need help here. Which one is the HT node?
    Just to be sure, have you replaced all the large filter caps in the 'doghouse' on the other side of the chassis?

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    Quote Originally Posted by g1 View Post
    Just to be sure, have you replaced all the large filter caps in the 'doghouse' on the other side of the chassis?
    yessir, the first thing I’ve done when I got the amp (a few months ago).

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    It may be that 22k grid stoppers on V3 solves the oscillation and nasty distortion issues.

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    Bent Member Chuck H's Avatar
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    I dunno.?. It's a pretty profound howling screech to think that a single grid stopper might solve it.?. Nothing to lose I suppose. I still think there's a wiring hitch or a bad ground. Maybe we could get a history of the problem. Did the amp always do this? If no, when did it start? etc. What have you done to this amp and what problems did it have?

    The picture I was hoping for would be of the full amp open chassis.

    Also, is this the model that sends a parallel signal from the reverb input direct to the summing triode in "boost" mode? That circuit has a hefty .01u cap in series with a 13k resistor to ground when the switch is engaged. It seems stability problems were recognized early on this one. Is the boost switch pulled when the problem is happening?

    EDIT: Never mind on whether the boost is engaged. I just caught the info in post #3. There may still be something to report on this. Still... A further history of what's been done to this amp and when the problem started may help.

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    Last edited by Chuck H; 02-24-2019 at 01:43 AM.
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    Hi guys and thank you again for your input so far.

    Regarding the AMP HISTORY:

    Bought it a few months ago for a fair price knowing I would need to invest time and money into it.

    It had that "broken-fried- high frequency distortion" when pushed beyond half way the channel volume.

    I observed the amp had only a couple of components replaced (one of the doghouse big electrolytic capacitor and a couple of resistors).The rest of the components were clearly 45 years old (Mallory paper caps, carbon resistors, etc).

    So step by step I started changing the old components by newer ones (with tighter tolerances, etc). There was no concrete change that improved the sound or corrected the previous stated problem, but it started to sound better and tighter (in another post I describe adding the Rob Robinette mod to add a BIAS Voltage regulation by keeping the BALANCE: "Biasing a 1974 Fender SF Twin Reverb Master Volume Push Pull Switch - Reading 13 mA").

    I have also added the .022 uF cap tremolo tick fix.

    What I have done is to bring the amp back to the Schematic provided earlier (there was a reverb resistor changed to 220K instead of 470 K, the resitor on the rectifier was 470 Ohm instead of 1 KOhm, etc, etc).

    Schematic Fender 100 Watts RMS AMP w/ Reverb and Vibrato (the white schematic, not the blue one)

    To conclude this section, as stated before, I have removed completely the PULL wires to make sure this "feature" was not leaking any distortion into the clean sound (no real difference or improvement after this last step)

    In general I would say that the original problem has shown an improvement of 75% and I am able to use the amp with a fairly clean sound at Channel Volumes below 5.


    I hope the description of my history with this amp is what you were looking for.

    Here is a view of the WHOLE CIRCUIT BOARD (it's quite a big Pano)



    I appreciate the suggestion of adding a screen resistor, however I have avoided all temptations of implementing any of the multiple mods available (blackfacing, removing the NFB, etc) as my primary intention is first to bring the amp to its former glory before deciding to modify anything at all.

    UPDATE on the SCREECH SOUND: I have removed the V1 tube some days ago (to see if I could achieve a bit of overdrive at a lower channel volume without the "nasty effect").
    A few hours ago I was tryting to see if I could reproduce the "SCREECH" also in the NORMAL CHANNEL, I couldn't. And, moreover, I couldn't make the VIBRATO CHANNEL "SCREECH" again with the V1 tube engaged.
    Removing the V1 tube brought the SCREECH to the VIBRATO CHANNEL again.

    (as a reminder, I found out about this "SCREECH" sound just a few days ago looking for problems associated with extreme TREBLE settings as my problem was always the distortion on this frequency range)

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    Bent Member Chuck H's Avatar
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    Ok!!! You may have microphonic preamp tubes and/or dirty/oxidized connections in the pin sockets. You should clean, deox, pot cleaner everything and try putting known good tubes in the V1 and V2 positions. That would be my next move fo shizzle.

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    Hi!
    I did DEOXIT all sockets (including the power tubes) and moved tubes around a couple of days ago.
    Yesterday, after finding out that the "SCREECH" cannot be reproduced with the V1 in the circuit, I found that if I move (rocking back and forth) the V1 tube there is a "pop" (like disconnecting and connecting something).
    I've tried different tubes in the V1 position and some do this "pop" and some don't, I am guessing it is because of slight differences in the pins geometry (some more open, some closer). Nevertheless, I might replace that socket today.

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    Bent Member Chuck H's Avatar
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    Well there's a good possibility that the socket is worn, what with the "tube rolling" mentality***. But it may not be. Can you please report on whether all tubes tried cause the screech. I'm thinking it could be oxide on the tube pins themselves since some of the tubes you've tried pop and others do not. It doesn't come up often, but I've seen it. I had a small bucket full of 12au7 tubes pulled from a Conn organ that sat out in the rain. I had to use one of those brass wire toothbrushes from the hardware store to clean off the pins on most of them to get good contact in any socket. Also, what is the nature of the other tubes you are trying in those sockets? Are they new? NOS? Used but test good? Unknown? Also, it may even be V4 that's microphonic. Granted you are only detecting this issue on the trem channel right now, but I wouldn't rule out the possibility. The screech is very much like some of the worst microphonioc tubes I've heard. You really do need to plug in some known good preamp tubes.

    ***Tube rolling is an internet term used to describe the practice of trying multiple tubes in any given circuit position to find the best sounding combination and/or order for the tubes available. Many sockets take an unnecessary beating with this practice because time and frustration can lead to aggressive pulling and plugging. This is especially bad for amps that have PCB mounted sockets because it increases the risk of failed pads and traces.

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    Supporting Member Jazz P Bass's Avatar
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    I would try 'retensioning' the socket tabs of V1.

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    Hey guys, thank you!

    I have replaced the V1 socket by a new one. SCREECH is still there when I pull the V1 tube out.

    Regarding the question about the TUBES.I have about 12x 12AX7s in various stages of wear. Some NOS Sylvania and Tungsol (that I am just trying now), TAD used moderately, JJs (1 year old but not much use), etc.

    I have tested all of them (both triodes) in a Tube tester I bought some months ago. All of them shown different "health" status between 75-100%. Filament continuity was also tested.



    As far as if any tube is microphonic, I am using probability (tube rolling) to tell me if that could be the case. I took the V1 (NORMAL CHANNEL) and V5 (TREMOLO) tubes out and I am rolling every other tube. As I do not have more than 2 12AT7s when I finished with the 12AX7s I used them also in V3 (REVERB) and V6 (PHASE INVERTER).

    My conclusion is that the problem is not in the TUBES (see table below, every combination produced a SCREECH - edited from previous post, the AMPEREX also did, the settings were not right)

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Precision_Appar_10_12.jpg 
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    Last edited by TelRay; 02-24-2019 at 08:17 PM.

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    Bent Member Chuck H's Avatar
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    That's a hell of an effort. Thank you.

    I have to ask why you replaced the V1 socket when it's the V2 socket involved with the channel that is having a problem.?.

    And I have to ask... Are you certain that the problem does not manifest at all with the normal channel?

    Something to know is that the cathode is shared between V1b and V2b. When you unplug V1 you incidentally heat the bias and increase the gain of V2b. I'm not sure why you have V1 removed at this time.

    If you could, please, measure and post voltages on V2. You may have posted them in a previous thread, but new readings would be better.

    Also, you noted that the reverb no longer affects the screeching while now the mid pot does. But the test parameters in the videos are not equal. In the first video you left the volume at max and the reverb did stop the screech set between min and max. And you didn't turn the mid knob at all. In the second video you turned the volume down to just where it manifests the screech at around 3.5. So, if you put the volume at max does the reverb again stop the screech between min and max settings?

    Ok... Chasing parasitic oscillation now since I no longer believe it's tube microphonics. Though it still may be a dirty or bad socket. The voltage measurements may tell us something there.

    It's hard to tell looking into the spaghetti plate that is the silver face amps and the photo angle is such that some face deck wiring is obscured, but I would actually strip out any wiring associated with the boost switch. Having them bundled may have been keeping the amp stable when they were connected to the switch. Now, with leads hanging on one end there is a different relationship between those leads. They are carrying small signal information over a lot of real estate and could be causing instability. So I mean EVERY lead associated with the boost including those from the board or the reverb pan jacks.

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    Last edited by Chuck H; 02-24-2019 at 09:09 PM.
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    Quote Originally Posted by Chuck H View Post
    I have to ask why you replaced the V1 socket when it's the V2 socket involved with the channel that is having a problem.?
    Sure. If you remember, the SCREECH can only be generated with the V1 out of the circuit. Additionally, I found that if I move (rocking back and forth) the V1 tube (when in the circuit) there was a "pop" (like disconnecting and connecting something). That gave me the idea that the V1 socket was not good (no other tube made any noise when moving them) and thought that maybe when removing the V1 tube I could be generating a bridge between some of the V1 socket leads (that are more freely to move without being held by the tube).

    I believe that by removing the V1 tube, the additional gain on V2 makes the problem more evident (by creating the SCREECH, which - i believe - an extreme example of the high frequency distortion I hear when playing the guitar at higher VIBRATO CHANNEL volumes

    Quote Originally Posted by Chuck H View Post
    And I have to ask... Are you certain that the problem does not manifest at all with the normal channel?
    No. When playing the NORMAL CHANNEL the guitar does not even enter in overdrive at CH VOL = 10 (it's super clean all the way). So I am guessing that because of the lower gain on V1 I cannot reproduce the SCREECH.

    One might wonder what would happen if I increase the gain on V1 by pulling V2 out of the circuit... maybe I'll try

    Quote Originally Posted by Chuck H View Post
    Something to know is that the cathode is shared between V1b and V2b. When you unplug V1 you incidentally heat the bias and increase the gain of V2b. I'm not sure why you have V1 removed at this time.
    Yepp... that cable bridging pin 8 of V1 to the same pin on V2.
    Well, the idea of taking out V1 was one of the many attempts to do something that would reduce that high freq distortion. I wanted to try if putting more gain on the V2 tube and the guitar breaking up at a lower channel volume setting would make any difference. It didn't.
    Since it wasn't either better or worst I didn't put V1 back (hence saving some $$$)

    Quote Originally Posted by Chuck H View Post
    If you could, please, measure and post voltages on V2. You may have posted them in a previous thread, but new readings would be better.


    (have not found any difference by measuring V2 with V5 in the circuit and no V1)

    My conclusion:
    isn't it strange that pulling V1 out the voltage on V2-8 drops from 1.9 to 1.4V? (I am almost sure it should go up... that additional gain on V2 statement)
    Also V2-6 drops from 231 to 193V

    Quote Originally Posted by Chuck H View Post
    Also, you noted that the reverb no longer affects the screeching while now the mid pot does. But the test parameters in the videos are not equal. In the first video you left the volume at max and the reverb did stop the screech set between min and max. And you didn't turn the mid knob at all. In the second video you turned the volume down to just where it manifests the screech at around 3.5. So, if you put the volume at max does the reverb again stop the screech between min and max settings?
    You are right, given the right knob position combinations I've found that the SCREECH can be eliminated by moving the MIDDLE, REVERB and TREMOLO INTENSITY KNOB out of the MIN position (this last one even when V5 is not in the circuit!)

    Quote Originally Posted by Chuck H View Post
    It's hard to tell looking into the spaghetti plate that is the silver face amps and the photo angle is such that some face deck wiring is obscured, but I would actually strip out any wiring associated with the boost switch. Having them bundled may have been keeping the amp stable when they were connected to the switch. Now, with leads hanging on one end there is a different relationship between those leads. They are carrying small signal information over a lot of real estate and could be causing instability. So I mean EVERY lead associated with the boost including those from the board or the reverb pan jacks.
    Yes, I had the same feeling and stripped down every wire that had to do with the PULL BOOST (meaning I did not just tape them and left them hanging around, they are totally out). Additionally have also changed the MASTER VOLUME potentiomenter.

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    Last edited by TelRay; 02-25-2019 at 12:14 AM.

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    Lifetime Member Enzo's Avatar
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    And has anyone thought to check for conductive eyelet board?

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    Quote Originally Posted by Enzo View Post
    And has anyone thought to check for conductive eyelet board?
    thx Enzo!

    i lifted the upper board board to check if there were any leads in between the the two a few days ago. I could only separate them by 1/4 inch but haven't seen anything strange.
    do you mean the the actual material could be conductive?

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    Bent Member Chuck H's Avatar
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    It's normal for the current through V2b to increase when v1 is pulled. The voltages drop because there's more current through the tube.

    You omitted grid pin measurements. They're probably zero (or whatever your meter reads at null). If there's any significant voltage there it could be a problem. Looking at your cathode and plate voltages I don't suspect that though.

    As to conductive circuit borard... OHHhhhh YEs!.!.! That's a real thing. Those old, black paper fiber boards can become conductive in a couple of ways. One is that they're made of paper fiber and have been known absorb moisture in humid environments. In these cases it's often possible to use a hair drier to bring things back to normal. It doesn't take much voltage to throw off things like preamp tube bias. An extra .2 or .3 volts on a grid or cathode is enough to make a big difference. Another way they become conductive is time and pressure under high voltage conditions. Why do you suppose those boards are black? Because they're pigmented with carbon. repeated soldering or long exposure to HV (which is common in these amps) can start to form conductive pathways in the carbon pigment. In this case the board needs to be replaced or the affected eyelet points must be floated off the board. I, personally, have had a disproportionate number of the black fiber boards I've experience demonstrate some degree of conductivity.

    Set your meter for low voltage and put the black probe on the chassis. Now stab the board in random places with the red probe. Especially near HV eyelets. You'll almost surely see SOMETHING. I always do. But don't worry about it unless it's more than a few mV.

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

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    Quote Originally Posted by Chuck H View Post
    You omitted grid pin measurements. They're probably zero (or whatever your meter reads at null). If there's any significant voltage there it could be a problem. Looking at your cathode and plate voltages I don't suspect that though.
    Yessir, those are 0V

    Quote Originally Posted by Chuck H View Post
    As to conductive circuit borard... OHHhhhh YEs!.!.!
    Oh no... sounds like a real pain in the a**. And surely will need to de-solder some wires, that board was not moving much more than 1/4 in when I inspected if there was something below.
    Sounds like another weekend of fun

    BY THE WAY:
    I have removed the BRIGHT SWITCH off the circuit (I thought maybe it was connected to ground somehow or leaking in between leads, etc).
    After it was out I've tried to reproduce the SCREECH with 3 different 120 pF capacitors (the original one and 2 new ones) by connecting them directly to the potentiometer leads, in all cases I got that ugly noise back.
    So, it's not the capacitor (by now I should have changed the name of the post ) and it's not the switch

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    Bent Member Chuck H's Avatar
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    Ok... So the middle knob, the reverb knob and the trem intensity knob can all stop the screech. The reverb knob only stops the screech when the volume is maxed. It's not microphonic tubes. If this were just a little less weird I'd think you were F'ing with us, but there's no way you can make this up

    I'm back to thinking there's a bad ground somewhere. Test grounds from the board eyelets that are supposed to lead to ground to the chassis. Not to the actual ground point.

    Are all knobs doing what they're supposed to? The "Middle" affects midrange, etc.?.

    This is a long shot, but... Try lifting one end of the 820R feedback resistor and see if that doesn't change anything.

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    Quote Originally Posted by Chuck H View Post
    ...If this were just a little less weird I'd think you were F'ing with us, but there's no way you can make this up
    hahahahaha... I kid you not!
    this is the original problem I am trying to solve
    the whole story about the SCREECH noise is just a way to reproduce this failure mode to the max




    Quote Originally Posted by Chuck H View Post
    Are all knobs doing what they're supposed to? The "Middle" affects midrange, etc.?.
    Yepp... the all work as expected, maybe the MID is more MID-LOW, but yes.

    Quote Originally Posted by Chuck H View Post
    This is a long shot, but... Try lifting one end of the 820R feedback resistor and see if that doesn't change anything.
    I was wanting to do that with the NFB resistor for a while but did not want to messs up with the amp until I got ot sounding good.
    I think it will provide more MIDs and probably provide with more overdrive.
    Will try thay probably on Tuesday and let you know

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    Last edited by TelRay; 02-25-2019 at 04:38 PM.

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    Lifetime Member Enzo's Avatar
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    You don't have to move the board to test for conductive surface. Just ground your meter to the chassis, then put your red meter probe right on the black material NEAR an eyelet and see if any DC voltage is measured. SImple as that.

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    Quote Originally Posted by Enzo View Post
    You don't have to move the board to test for conductive surface. Just ground your meter to the chassis, then put your red meter probe right on the black material NEAR an eyelet and see if any DC voltage is measured. SImple as that.
    that's great news, I thought that the board below could also be contributing (i think it is the same material) and that the two needed to be separated.

    will do it within the next couple of days and let you guys know

    thx!!!

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    Quote Originally Posted by TelRay View Post
    ...when moving the pots the wire connecting the MID control to the VOL one and then to ground came loose �� (could be an indication of failure)



    As I recall, Fenders are usually wired with the 0V circuit common connection to the mid control terminal as a short length of wire braid to the control panel brass plate; the wire in yours to the vol control's 0V terminal seems unusual. Is that definitely connected to the chassis / 0V circuit common?

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    Quote Originally Posted by pdf64 View Post
    ...the wire in yours to the vol control's 0V terminal seems unusual. Is that definitely connected to the chassis / 0V circuit common?
    Yes, you are right. It is actually the VIBRATO CHANNEL VOLUME potentiometer that is grounded to the chassis and the MID control "shares" that connection by means of the short white wire you see in the photo.
    I think this is OK according to the schematics (additionally, the same wiring is present on the NORMAL Ch tone stack):



    That shared connection seems original, as it looks like every other wire around the tone controls and I see no evidence of a previous wire running from the MID pot directly to the chassis.
    I've checked there is continuity between the VOL lug and the chassis and also the MID lug to the chassis. They were OK

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    Last edited by TelRay; 02-25-2019 at 10:27 PM.

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    Quote Originally Posted by Chuck H View Post
    ...stab the board in random places with the red probe. Especially near HV eyelets.
    Hey, I am guessing that the “doghouse” eyelets should be a target for this check as well, right?


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    Bent Member Chuck H's Avatar
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    I've never seen a board conduct enough voltage for it to cause more than a little hum or buzz from leakage on the doghouse board. More of an issue on the signal board. Stabbing near plate resistor junctions and then near grid and cathode associated eyelets. Not that the grids and cathodes are high voltage, but this is where leaky voltage can cause the biggest problems, so we check.

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    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

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    well, I found a couple of hours to do some measurements.

    Initially I wanted to gather reference values as I have no idea what voltage range was acceptable so I kind of probed the whole board. I've found values ranging from 10 to 160 mV DC. Which I am guessing that since I've measured my guitar output at 150 mV it might not be a good thing. The problem is that these higher values are more or less all over the place. Here's a mapping:


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    Last edited by TelRay; 02-26-2019 at 06:35 AM.

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    AC or DC?

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    all voltages DC

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