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Rookie Build: Champ 5F1

Discussion in 'Shock Brother's DIY Amps' started by TeleSlug, Jul 15, 2020.

  1. screefer

    screefer Tele-Holic Silver Supporter

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    My two cents sez...
    run your K-bypass cap leads to the eyelets to gain separation from your 470 0hm resistor as that resistor gets hot. Make sure that resistor is not touching your board. I used a piece of popsicle stick as a temporary spacer while soldering. Flip the resistor around so you can 'read' it. Making your components readable helps down the road if changes are needed.

    Check out this site... https://robrobinette.com/How_Amps_Work.htm
    [​IMG]
     
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  2. King Fan

    King Fan Poster Extraordinaire

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    Yep, separating the bias cap from that big white resistor is important... and easy. As Screefer says, no need to wrap the lead, just angle it up / down to the shared eyelets. (You may need to wrap the shorter resistor leads on the V1 bypass cap, but even so, try for some separation.) Resistors make heat, caps don't like it.

    Screefer also makes a great point about reading labels. Caps and labeled components that you can turn label-up, do. Orange drops are harder, but the labels are less intuitive anyway.

    As for frayed cloth ends, fray doesn't hurt much, but you're right, it looks bad. Experiment to find your wire snips that cut it clean and which wire strippers do better on cloth. Good strippers may still leave a couple white threads that need trimming with fine scissors. Or slide the wire back inside the cloth and trim just the cloth with iris scissors or sewing scissors. On hidden wires and long runs where you won't see the bunching up, use the 'pushback' trick to avoid stripping. I've also taken to a dab of clear nail polish before stripping, wait 10 sec, blot off the shine.
     
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  3. tubegeek

    tubegeek Friend of Leo's

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    One item - the white ceramic item is a resistor, not a cap. It's a definite heat source and should be separated from the nearby cap as much as possible. It's big and made of ceramic to allow it to survive considerably more heat than the smaller resistors you see everywhere else. It's a little oversized for safety but it is that type for good reason.
     
  4. TeleSlug

    TeleSlug TDPRI Member Silver Supporter

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    Yes, I've been checking against Rob's site but missed the separation on the ceramic resistor and that it's not a cap (thanks @tubegeek). I redid that part so the cap and resistor are separated. I also rotated the resistor. Thanks @screefer for the tip on popsicle sticks as spacers.

    Yes, the frayed ends look bad. When I used to rock climb we always dressed the knots to make it easier to see if there was anything done improperly. I'll have at them with the nail scissors.

    Thanks so much. I'm going to hold off on soldering until tomorrow so I can recheck with fresh eyes . . . and go buy popsicles!
     
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  5. TeleSlug

    TeleSlug TDPRI Member Silver Supporter

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    Steady but slow progress here with being back to working 6 days a week. I've got the circuit board all soldered and ready, chassis assembled, and the initial wiring done for the transformers. I've run into an issue and a question.

    The issue is that I went ahead and soldered the speaker leads, hoping to install it in the cabinet and reclaim some space in my home office. Well, one of the mounting screws is just a little bit off and the speaker won't seat properly. I tried gently tapping the screw with a rubber mallet to get it to sit straight. No dice. Should I remove the baffle and try it from that angle?

    The question seems a little silly, but what do I do with the four extra wires coming out of the power transformer? In forum pics it looks like most folks just trim and wrap them in electrical tape. Is that the best way? Would a wire nut be a better choice?

    I'm done for this weekend and hope next Saturday to get closer to the finish line.
     
  6. King Fan

    King Fan Poster Extraordinaire

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    So your speaker has mounting bolts that go into holes (T-nuts etc.) in the baffle? Or do the speaker's mounting holes fit over upright studs fastened to the baffle? Especially with bolts, you're right to be careful; it's easy to get them cross threaded and if they seize up you can end up with the T-nut turning in the baffle and the bolt impossible to remove. (Don't ask....)

    Sometimes you can find an alignment where all 4 holes will thread -- it may help to thread the 'bad' one first and split the difference on the others. As you'll know, thread gently by hand and make sure it spins easily for a decent distance before applying tools.

    If it's worse than that, remind us, who made your cab? (Not necessarily the name, but was it a vendor or yourself or a friend or a passing hobo?)
     
  7. tubegeek

    tubegeek Friend of Leo's

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    Not in my opinion. Here's what I usually do.

    - cut the end, not short, just so that no wire appears beyond the insulation (in case you re-purpose the transformer someday)

    - fold over about 1 cm of the wire on itself

    - trap it like that in a short piece of heat shrink tubing

    - add a second layer of HS tubing that completely covers the inner one and extends beyond the fold a little bit

    - then if you like, bundle all the now-insulated extras and secure the bundle with a cable tie.

    This seems to me to be the safest way to keep the extra wire but render it neat and tidy.
     
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  8. TeleSlug

    TeleSlug TDPRI Member Silver Supporter

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    It's the studs version. And I posted before my wife looked at it. She asked, "You're ready for this to be installed?" I said yes. She fiddled with it for two minutes and handed it back so I could put on the keps nuts. All good now.

    The vendor is a guy on Reverb. Other than that and some sloppy application of the shielding tape I'm happy with the cabinet.

    Thank you @tubegeek for the explanation on the extra wires. That seems easy enough!
     
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  9. TeleSlug

    TeleSlug TDPRI Member Silver Supporter

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    Okay, still making progress but slowly (this having to work thing is a real drag!).

    Today I began Rob's amp startup procedure by plugging into my light bulb limiter. No light. No smoke. So far so good. Then I checked voltage on pins 4, 5, and 7 of the preamp and pins 2 and 7 of the power tube. They all read at 3.5V, which is lower than both Rob's listed values and what Mojotone states (7.5V).

    The pilot did not initially light up, but when I tipped the chassis back (yes, with one hand in my pocket) it did come on. I once again used a wooden chopstick to check all my connections and they all seem solid, but obviously something isn't right.

    I've put away the project until next Saturday when I can take a look with fresh eyes. I'm thinking my connection between the white power cord wire and the white power transformer wire is a probable issue.

    Any suggestions on other likely culprits?
     
  10. tubegeek

    tubegeek Friend of Leo's

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    If this connection is not secure, literally nothing would be getting power.

    Filament voltage measurement can be a little confusing because there are a couple ways to measure. But first, some info.

    In guitar amps, filaments are lit with AC power. This is a continuous cycle and we compare two points in the circuit with each other in order to evaluate it. The AC voltage setting on the meter is appropriate, not DC.

    Many kit instructions measure EVERYTHING compared to the chassis, a/k/a ground, a/k/a 0 volts.

    On the small tubes, one measurement point is the common connection of pins 4&5. The other is pin 9. ***not pin 7***. These two points should see a difference of 6.3 V AC between them.

    Pin 2 & 7 on the 6V6 should also measure 6.3 VAC between them, and 3.65 VAC each to ground.

    Each one individually, should register 3.65 V AC compared with ground.

    All of these voltages - all voltages in the amp - will measure too high if there are no tubes plugged in, drawing power. This is normal.

    Now, the pilot light. There are two kinds. One (a vintage type) is made with a connection built-in to the chassis ground. It's designed to get only one other wire, 6.3V AC compared to ground. If this type is used with the modern scheme of balanced AC, 3.65 - 0 - 3.65, it will short-circuit one of those 3.65 V connections to ground. No good. The other 3.65 V will be feeding a 6.3V light bulb and failing to light it up.

    I bring this up because it's not clear what's wrong with your pilot light.

    Make sure neither the inner connection nor the outer connection of the socket measures 0V compared to the chassis. The pilot should measure like the filaments: 3.65 V each to ground, 6.3V compared to each other.

    **Most likely, though** is a bad connection at the pilot socket, including perhaps a poorly seated bulb.
     
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  11. andrewRneumann

    andrewRneumann Tele-Holic

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    *cough*new math*ahem*:p:p:p
     
  12. TeleSlug

    TeleSlug TDPRI Member Silver Supporter

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    Okay, back at it today. I reseated the pilot bulb and that seems to have been the problem. Easy-peasy.

    I plugged the amp into the light bulb limiter and checked the AC voltages. The values are all what @tubegeek posted last week. So far so good.

    I unplugged the amp, installed the tubes, and turned it back on. The tubes lit up and all looked good.

    I set my multimeter to DC voltage and attached the ground lead to the chassis with an alligator clip. I started checking from right to left as shown in the photo below. All the connections with green circles tested at zero or .05V. When I got to the connections circled in red, I got a little spark from the multimeter lead at the connections for the two 8uF caps. At the far left connection, there was a spark and the light bulb flashed on.

    I unplugged everything and rechecked the solder joints with a wooden chopstick. Everything seems solid. No wiggling.

    Any thoughts on what to check for or where to start with troubleshooting this? Thanks!

    [​IMG]
     
  13. tubegeek

    tubegeek Friend of Leo's

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    What's the max rating of your meter? Some meters may not be rated for a high voltage DC supply.
     
  14. TeleSlug

    TeleSlug TDPRI Member Silver Supporter

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    The max on the meter (Klein MM400) is 600 volts. I used the >400mA setting and made sure I was testing DC using the 10A function.

    Would a problem with the meter cause the bulb in my limiter to flash?

    I also feel like the preamp tube was not lighting up as much as the rectifier and power tubes, but that could just be my eyes playing tricks on me.
     
  15. andrewRneumann

    andrewRneumann Tele-Holic

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    I really does sound like you shorted your amp out with the meter. Thankfully you had the bulb limiter! Are you sure you were in the volts mode and not in current mode or resistance mode?
     
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  16. TeleSlug

    TeleSlug TDPRI Member Silver Supporter

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    Yes, I am so grateful everyone recommended building the limiter first.

    For this meter (link to pic) to measure voltage >400mA you put the red lead in the 10A at the bottom left, ground lead at the bottom center. I set the dial to 10A (to left of the off position) and used the SEL button to set it to measure DC.

    So, does this mean I potentially shorted out my amp? Or did the limiter do its job?

    I did turn on the amp again a bit ago and the tubes still lit up, so at least that's good news?
     
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  17. andrewRneumann

    andrewRneumann Tele-Holic

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    Most likely everything is fine because you had the bulb limiter. Black wire in COM, red wire in the right socket labelled V. Selector set on V to measure volts. You had it set to measure current instead of volts.
     
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  18. awasson

    awasson Poster Extraordinaire Gold Supporter

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    for measuring voltage, you keep the red probe in the right socket, black in the common.

    EDIT: @andrewRneumann beat me to it. You are lucky that you’ve got the light bulb limiter. That’s such a great advertisement for such a device. Carry On. I think you’re almost there.
     
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  19. TeleSlug

    TeleSlug TDPRI Member Silver Supporter

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    Thank you @andrewRneumann and @awasson for very politely pointing out my bonehead error.

    When using the meter correctly, I found some hot spots. Going left the right across the bottom:

    B+1 = 336.4

    B+2 = 313.6

    B+3 = 290.7

    Power Tube Cathode/Cathode Bypass = 233.6 (supposed to be 19)

    Between the 22K and 1.5K resistor = 216.4 (supposed to be 1.65)

    100K/Coupling cap/preamp pin 6 connection = 287 (supposed to be 165)

    100K/Coupling cap/preamp pin 1 connection = 195.3 (supposed to be 165)

    Cathode/preamp pin 3 = 1.44

    rectifier tube pin 8 = 2.9

    power tube pin 5 = 0 but then seemed to measure at 191 after a moment.​

    So, closer but not quite there, yet.
     
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  20. andrewRneumann

    andrewRneumann Tele-Holic

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    Bummer! I don’t know why for sure, but I have a sense that something’s not grounded properly. With AMP OFF and CAPS DRAINED, can you measure resistance (Greek letter omega on your multimeter) from these points to the chassis? They should all be very close to 0.

    276CD59F-DB92-4C8D-8570-EE7B2962F902.jpeg

    A full set of interior photos clearly showing all connections plus a table with all tube socket voltages will help the group diagnose very quickly. Hope this helps. Good luck!
     
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