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Thread: Deluxe Reverb Build Problem!

  1. #1
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    Deluxe Reverb Build Problem!

    Hey, friends. My name is Michael and I'm a guitar player from Toronto, Canada. I enjoy working on guitars and building amps. This is the second amp I've built. The first one was a modified 5E3 that sounded absolutely incredible! With that being said, on to the problem...

    This amp started out as a Fender Deluxe Reverb Reissue. I decided to gut it and rebuild it using a Mojotone Deluxe Reverb Parts Kit as I'm a fan of the simplicity and workability of hand wired amps. I finished the build and the amp sounds superb; arguably better than any Deluxe Reverb I've heard! However, there is a loud buzz I can't seem to eliminate!

    Things I've noticed:

    Pulling V4 stops the hum but I can still play the Normal channel.

    Grounding pin 7 on V4 stops the hum but I can still play the Normal channel.

    Grounding the right lug on the Intensity pot stops the hum but I can still play the normal channel. Is this strange?

    Tapping on almost every capacitor and wire associated with V4 can be heard loudly through the speaker. This is prominent on the wire from V4 pin 7 and where the red wire from the Reverb transformer meets the green wire from the filter cap on the board.

    Both Volume pots affect the buzz.

    The amp buzzes with everything on zero regardless of if a guitar is plugged in or not.

    Moving wires around doesn't change anything.

    I've checked all grounds and everything appears to be fine.






    Here is an audio clip of the noise. It is louder than it sounds.
    https://soundcloud.com/mike-mastandrea-1/amp

    There is also another problem. I have the following modification installed. It literally has NO affect on the amp. I even tried switching the orientation of the wires but to no avail.
    https://robrobinette.com/AB763_Modif...ative_Feedback

    I'm running out of ideas here, haha. Any and ALL help would be greatly appreciated! I'm not too familiar with technical terms so please be as descriptive as possible in your replies.

    Cheers!
    Last edited by Penguin; 10-16-2017 at 06:09 PM.
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  2. #2
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    Images arenít viewable. Photobucket is useless unless you upgrade.
    Try imgur etc instead.

    Does the reverb control affect the buzz?

    If the NFB mod switch doesnít do anything maybe the NFB isnít working, eg something isnít wired up right. Remove the mod and wire up the amp stock in the first instance.

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    Thanks for the heads up! I changed the picture host.

    The Reverb control affects the buzz but only very slightly. The Volume controls affect it way more than anything else. Grounding the points I mentioned kill it completely.

    I'll return to the NFB to stock and see what happens with that.
    Last edited by Penguin; 10-16-2017 at 06:23 PM.

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    Penguin,

    When you get this right you'll be in tone heaven. Well, the first thing I noticed is that you're not using shielded wires on the grids (pins 2 and 7) of the first two tubes which has become a pretty standard practice. I see a ground buss wire running in back of the pots. I myself haven't had good luck with this type of grounding scheme in a Fender amp but I know others have.

    But this may not be the source of your problem. As you've seemed to have localized the hum the in and around V4, I would re-check your wiring in that area very carefully, double check, then after that, triple check it. You could replace the V4 tube as a precaution. Measure the voltages on both plates and cathodes and make sure that they are the expected voltages for those points. The same is true with measuring the ohmage of these points to ground (including the grids) but that data isn't as readily available. If you've missed grounding something however, it'll show up then. You could temporarily un-wire the reverb circuit as to eliminate it as the source of problems and hum and once the hum is eliminated, re-wire the reverb circuit back to as it should be. I have on occasion used shielded wires from the reverb pot on the front panel to their various respective points on the circuitboard. Sometimes, this helped and other times it made no difference. I would also check in and around V2. Also, I see a 220K resistor on the inside back, going between jacks. Now, if that is a grid load resistor, I'd ground that to where the cathode parts from that same stage are grounded.

    The Hoffman site has a good drawing of a good grounding scheme for their builds. Also, the Glass Audio article, 'The Remaking of a Champ' has an excellent grounding discussion. I'd measure in ohms every ground point in the amp to the transformer bolt and make sure all grounds read the same with your ohmmeter. In fact, if it were me, I'd only ground to ONE transformer bolt, not several. That may or may not make a difference, although it is alot of work to re-do.

    This is most probably a wiring error/mistake but it could also be something inherently flawed with your ground scheme. At any rate, I'd add those shielded grid wires to V1 and V2 as a first step. When you solve your hum problem, please report back and tell us what it was and how you fixed it as it will help others who will come after you. It is not uncommon to have some problems with a new build, just stick with it and be methodical.

    If all fails, as you're in Toronto, there will be a very sharp tech there who loves a challenge. You'll have to do a little investigating to find him.

    Good luck,

    Bob M.
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    How are you getting NFB? I can’t see any NFB wire connected to the output jack.
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    Quote Originally Posted by xtian View Post
    How are you getting NFB? I can’t see any NFB wire connected to the output jack.
    You're right! I can't believe I missed that wire. Thanks, Xtian!
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    UPDATE!

    The NFB switch is now working. On the setting with no NFB, the buzz is still prominent. On the setting with the stock 820 ohm resistor, the buzz is slightly reduced.

    I decided to take some preamp voltage readings.

    V1
    Pin 1: 172
    Pin 6: 179

    V2
    Pin 1: 177
    Pin 6: 181

    V3
    Pin 1: 405
    Pin 6: 405

    V4
    Pin 1: 177
    Pin 6: 181

    V5
    Pin 1: 401
    Pin 6: 354

    V6
    Pin 1: 192
    Pin 6: 188

    Is it me or are some of those too high?

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    Regarding the voltages, what is the HT voltage and power tube plate or cathode current at idle?
    And the mains and heater V ac?

    Regarding the buzz, that symptom is often related to the heater circuit. What is the resistance between any point on the heater circuit and any circuit 0v point, eg chassis?

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    Are both hum balance resistors making good connection to ground? they appear to be going into a crimp eyelet.
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    Quote Originally Posted by pdf64 View Post
    Regarding the voltages, what is the HT voltage and power tube plate or cathode current at idle?
    And the mains and heater V ac?

    Regarding the buzz, that symptom is often related to the heater circuit. What is the resistance between any point on the heater circuit and any circuit 0v point, eg chassis?
    I hope I calculated this correctly, haha. Please bear with me as I am still fairly new to this.

    Wall Mains: 122 VAC

    OT Voltage: 414V

    Both Power Tube Plates: 405V

    Heater Voltage: 6.3V

    Voltage Drop: 9V

    OT Resistance to Plates: 21 ohms

    9V/21 ohms = 42.8mA

    Only one heater reads "0" in relation to ground. Is this normal?

    Keep in mind that grounding V4 Pin 4 as well as the right terminal on the Intensity pot kills the buzz.

    Both hum balance resistors are securely grounded.

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    Have you got one side of your heaters grounded?

    Edit - check at the panel light to make sure you don't have a short.
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    Quote Originally Posted by Mick Bailey View Post
    Have you got one side of your heaters grounded?

    Edit - check at the panel light to make sure you don't have a short.
    I certainly hope I don't have one of the heaters grounded, haha. When I touched one heater it read "0" to ground. When I touched the other the reading stayed at "1."

    By "panel light" do you mean the bulb assembly? I have the green wires from the OT and heater wires connected to it. I also have the hum balance resistors connected from the bulb assembly to ground.

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    Hoping isn't the same as checking. Did you check that there isn't a connection to ground at the back of the bulb assembly that would short out one of your hum balance resistors? Your heater chain should 'float' with either side of the heater winding connected via each 100 Ohm resistor to ground. Because the heater winding is low resistance, then you should read both 100 ohm resistors in parallel (50 Ohms) when measuring resistance from either side of the heater chain. Your readings suggest to me you have a short and it could be one of your resistors is touching the grounded mounting bracket on the bulb holder or you have a solder bridge.

    To put it another way, your heaters should each read 3.15v AC from either side to ground with the amp powered.
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    Assuming that the measurements are correct, the 6V6 (?) are idling crazy hot, >17W.
    Half that current is appropriate.
    1 ohm cathode resistors are helpful in making accurate power tube current measurements.

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    That OT resistance of 21 Ohms is way off what I'd expect.
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    Well spotted, expect maybe x10 that value!

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    Quote Originally Posted by Mick Bailey View Post
    Hoping isn't the same as checking. Did you check that there isn't a connection to ground at the back of the bulb assembly that would short out one of your hum balance resistors?
    BINGO! There was a tiny amount of solder that was connecting one of the bulb wings to ground! Excluding the hiss from the carbon composition resistors, sheís quieter than I am when trying to sneak a piece of cheesecake at 3AM!

    Iíd like to SINCERELY thank everyone who contributed their time and knowledge. It means a lot, friends.
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    Nice work Mick
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    Cheesecake? I'll be right over.....
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    Quote Originally Posted by 1ampman View Post
    Cheesecake? I'll be right over.....
    I'll bring the strawberries!!
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    Quote Originally Posted by 1ampman View Post
    Cheesecake? I'll be right over.....
    Youíll have to make it by Moose first...


    Now that Iíve had a chance to really play it, Iíve noticed a few things. First, the amp doesnít make a sound until ď3Ē on the volume knobs! Itís literally silent up until that point. Second, it doesnít overdrive. It basically sounds like a Twin, haha. Someone mentioned that my bias appears to be too hot but it seems too cold to my ears. Thoughts?

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    The volume control thing seems fairly normal, bear in mind that it starts at 1.
    The correct BF Fender taper for volume controls is ~35% audio; regular 10 or 15% audio taper pots may seem to come up too slowly.

    Your plate current measurement of 42.8mA seemed wonky; 1 ohm resistors in the power tube cathode returns may be beneficial to making a good reading.
    Last edited by pdf64; 10-18-2017 at 09:13 PM.

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    I noticed a few years back that some pots - CTS especially - have a dead zone up to around 2 1/2. This appears to coincide with the beginning of rotation if a switch is fitted. So if you have a combined 'on' switch and volume the amp (or whatever) is just about at zero volume at the point where the switch operates. It's nothing more than a personal theory, but I think there's a production rationalization going on to make the same track fit switched or unswitched pots. For this reason I moved to the large Alpha pots and get a more even volume increase.

    Your original bias method is correct, but your readings are wrong - take another look at your OT primary resistance, the voltage drop, and recalculate. Rebiasing is perhaps unlikely to give you much drive improvement, especially if it is already optimally set. There are subtle gains to be had at high volume levels if you play around, but often at the expense of shortened tube life. You may need to tweak the preamp side to get earlier breakup.
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    Thank you for clarifying the pot issue. I just found it strange how the DRRIís volume started at ď1Ē and started to distort around ď6Ē or so. The rebuild is nothing like that.

    I imagine I should take all the readings again now that one of the heaters isnít grounded, haha.

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    I thought Ď1í was and is fullcounter clockwise, so the sound should be muted at that setting?
    ie have to turn it to about Ď2í before any sound gets through.

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    Rather than start a new thread, I'll ask this question here since it's related to the same amp.

    I'm currently in the process of modifying my Vibrato. I'm going to replace the 1M resistor under the optoisolator with a 220K resistor in order to deepen the Vibrato. Is this the correct mod?

    I plan on replacing both 0.01uF disc capacitors with 0.02uF capacitors in order to slow down the Vibrato. However, the Orange Drop capacitors I found are only rated for 200V. The stock ones are rated at 400V. The pin that connects to these capacitors only carries 177V. Can I get away with these?

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    Hi Penguin, welcome to the forum.

    really, it is best to start a new thread for your amp. it may be the same model, but is not the same amp. New threads don't cost anything. We prefer not to work on two identical amps in the same thread. gets confusing, especially for old people like me.

    I usually slow down my Fender trems as well, and doubling those caps is the way I go about it. But why cram huge orange drops in there? That oscillator circuit is not in the signal path, so plain old disc ceramics work just fine. They fit well, and easily found in high voltages.

    When the trem is off, do your voltages rise?
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    Quote Originally Posted by Enzo View Post
    Hi Penguin, welcome to the forum.

    really, it is best to start a new thread for your amp. it may be the same model, but is not the same amp. New threads don't cost anything. We prefer not to work on two identical amps in the same thread. gets confusing, especially for old people like me.

    I usually slow down my Fender trems as well, and doubling those caps is the way I go about it. But why cram huge orange drops in there? That oscillator circuit is not in the signal path, so plain old disc ceramics work just fine. They fit well, and easily found in high voltages.

    When the trem is off, do your voltages rise?
    Hey, Enzo. Thanks for the reply. I apologize for the confusion but this is related to the same exact amp that I started the thread about, haha.

    I haven't seen the voltages rise when the vibrato is off. However, I'll double check before I install them. I picked these capacitors up because the store I was at didn't have the discs. I may go for a drive and see if I can find some.
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  29. #29
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    Quote Originally Posted by Penguin View Post
    I'm going to replace the 1M resistor under the optoisolator with a 220K resistor in order to deepen the Vibrato. Is this the correct mod?
    What 1M ? I don't think a schematic has been posted yet, so can you post the correct one?
    Any references for this 'deepen' mod?
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    Quote Originally Posted by g1 View Post
    What 1M ? I don't think a schematic has been posted yet, so can you post the correct one?
    Any references for this 'deepen' mod?
    I apologize for the lack of information on my end, haha.

    The 1M resistor connects to one leg of the optoisolator.

    Schematic:
    http://www.mojotone.com/BF-Deluxe-Reverb-WD.gif

    I found that "deepen" mod on a thread about Princetons. I know they use a bias vibrato but apparently, it works with the Deluxe Reverb style vibrato as well. Unfortunately, I can't find the thread!
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    Hey Michael, if you ever get a chance to post a like to a few audio clips that would be awesome. Love to hear how these builds sound!!!

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    The speed mod will work for deluxe or princeton.
    There is no 1M connected to the opto, and as far as I know, no simple intensity mod such as the one for the bias vary trem.
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    Quote Originally Posted by g1 View Post
    The speed mod will work for deluxe or princeton.
    There is no 1M connected to the opto, and as far as I know, no simple intensity mod such as the one for the bias vary trem.
    Sorry, itís a 10M resistor! I should really go back to my LASIK surgeon, haha.

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    Penguin, my sincere apology, somehow I got he impression your post was new and not a continuation of your own thread. Sometimes I get off track. g1 was nice enough to tell me of my error.
    Education is what you're left with after you have forgotten what you have learned.

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    The 10 meg resistor is there for only one thing, it prevents the neon bulb circuit from "ticking". Noise from the bulb flash can leak into the audio without it.
    Education is what you're left with after you have forgotten what you have learned.

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