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"5F1 Follies" or "For Posterity Sake. Because I'm a Posterior."

Discussion in 'Shock Brother's DIY Amps' started by bigguy12321, Apr 6, 2019.

  1. bigguy12321

    bigguy12321 Tele-Meister

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    Ok. Nothing special here but I wanted to share some troubleshooting that I had to do because I wasn't careful enough upon first wiring.

    Just finished this 5F1 style amp and I had some trouble getting it going. I powered it up incrementally several times while building because it really makes sense to do this. Checking for proper voltages and for short to grounds along the way.

    First collected all components (that I knew I had to have... There is always something I forget) and laid them out on a legal pad. I copied the board layout from one found on eBay and I thought I would try it out because I had some radial capacitors.

    Wired the board, piece by piece, making sure to check all values before soldering them in. After that I made sure there wasn't a short to ground anywhere on the board.

    IMG_20190307_130724111.jpg

    IMG_20190307_131100322.jpg


    I also tried bee hive grommets. They work fine but only hold 3 conductors comfortably. I was able to change some components and they held up really well. (more on that later)

    Next installed sockets, lamp, cord, pot, input and output jacks and transformers . Wired heaters and checked for continuity there to make sure there wasn't a short to ground in the heaters.

    IMG_20190307_131225941.jpg

    Quick pic of soldering station used for this amp. Really. I sometimes like the immediacy of the gun and wasn't expecting to finish wiring all in one shot. I did also use a small pencil for the 12ax7 pins.

    IMG_20190307_163014407.jpg
    IMG_20190307_163028468.jpg

    Since I was using a board for this amp I was being extra careful with labeling. (I thought) I usually build point to point so I made sure to leave leads long enough and well labeled.

    IMG_20190401_132106_01.jpg

    IMG_20190406_142929774.jpg

    I have a VERY difficult time remembering to take pics during wire-up. I get in a zone and forget to stop and snap pics along the way. Those of you who do this have my utmost respect. Once I started peeling off labels and cutting leads to length and soldering, I didn't take any more until it was complete.

    Now for first power-up.

    My final sanity check is looking for short to ground from first B+ to chassis.

    Good there.

    Plugged in with just 6X5 rectifier and turned on. Voltages as expected all around.

    Good there.

    Put in 6V6 and 12ax7.

    This is going to be a VERY quiet amp... In fact, no sound at all. No hum, no buzz, no scratching on plates either preamp tube or power tube.

    Check voltages. 2 volts on 6V6 cathode, 287 volts pin 1- 12ax7 178 volts pin 5- 12ax7.

    Ok, I start all my new amps with old used tubes. Probably have some bads.

    New tubes Pin 8 6V6 18 volts. Cool.

    Pin 1 12ax7 290 volts. Not so good. I used a couple of used resistors here so I may have a bad one. Resistance shows good but I've got more so I'll swap it.

    Wait, I should still be getting a scratching sound when probing pin 5 6V6... Nothing... Nothing there or from pin 1 or 6 12ax7. Something fishy. Stop for the day and think and search TDPRI posts for clues. Found the usual input and output jack problems. Checked those and they seemed correct. Rechecked all wiring.

    Whoops. I mixed up pins 1 and 3 when wiring 12ax7. I was sending plate voltage to the cathode and grounding the plate. Sweet!!! swap those, turn on,

    Nothing! Same as before. Put in another 12ax7 in case it was bad. No change.

    I'm using used transformers that I know worked because I've had them in some other experiments. But now signs lead to output transformer being bad.

    Measure transformer resistance. 270 ohms one side .8 ohms the other.

    BACKWARDS!!!

    Some idiot mis-labeled primary and secondary on the frame of the transformer.

    (ahem... it was me. I am the idiot. My wife was correct... this time)

    Swapped around the leads and Viola!!! Sound. But not very loud. Quick check of voltages and sure enough, plate voltages are still screwy at the 12ax7.

    Verify resistance of plate resistors and one is 97k and one is 1.5k. Well there you go. Change out that bad resistor and restart and...

    Wait for it...

    VERY quiet again. Voltage is now at 287 at both plates! grr... Shut it down and search TDPRI again for no voltage drop after plate resistor.

    Found it!!

    And here is where the posterior part comes in.

    The quote from an old post was "verify correct value of plate resistor." When I first replaced that original plate resistor I thought might be bad, I went from memory and inserted 1.5k ohm resistors instead of 100k. And I did it twice. When I found there was a problem with plate voltage after startup I swapped in the wrong value right away then went on to compound the problem by changing the other one to the wrong value.

    It feels good to get it working after all that and I learned some more about how signal travels through the tube. Win win.

    Total time of troubleshooting was about three days. Checking, testing, reading and thinking. Always having a speaker hooked up, a guitar plugged in and one hand in a pocket. If I got frustrated, I walked away. I have multi-compounded issues before because of working too long on a problem.

    I guess this post was only for me to show how downward spirals can and do happen and when they do, don't panic and use this websites search function or just google your symptom with the addition of TDPRI (like "plate voltage not dropping tdpri")

    There are many people here to help and they have been helping for a long while. The most important thing is safety and the next is fun. Have lot's of both!!!

    Sorry for the long winded post but I felt that the sequence of mistakes were important.

    a
     
  2. tikitorch

    tikitorch TDPRI Member

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    What are bee hive grommets? Also, what did you mean when you said you used a small pencil on the 12ax7 pins?
     
    Last edited: Apr 8, 2019
  3. tikitorch

    tikitorch TDPRI Member

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    Oops double post
     
  4. gigante

    gigante Tele-Meister

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    He's talking about the style of soldering iron, I believe. I think he used the gun for most of it, but the pencil style for the 9-pin
     
  5. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    Hey OP. Cool project.

    Your AC incoming wiring, fuse, switch, ground - your pics aren't final. Can you post clear pics of that section in final form? Or have somebody qualified look it over? That stuff, you don't want to get wrong.
     
  6. bigguy12321

    bigguy12321 Tele-Meister

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    No, good catch! I didn't have the fuse in there yet. Poor practice I know so I tried not to draw attention to it. Amp is up and running and already killed one old tube!!! I use old tired tubes for first start up and this amp is biased at 12.1 watts and very loud.

    Also 6X5 rectifier and two separate filament winding on this P.T.

    I am trying to decide how to go on speaker selection. Right now I have 2-8" speakers that are former stereo speakers and it sounds pretty good. Cheap speakers in a Champ is a thing you know. I built an "almost Deluxe sized box" 14X19. There is more base projected than I expected. I'll post pics soon.

    Thanks for watching out for me!

    a
     
  7. bigguy12321

    bigguy12321 Tele-Meister

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    What gigante said about the pencil style iron.

    @tikitorch Bee hive eyelets are used when building bee hives as wire guides.

    Wiring-Frame-2-1102x350.jpg

    they are brass and smaller than amp eyelets but will hold 3 conductors pretty easily. I've used them for a couple Champ builds but will probably stick to using them for bias boards and the such. I ran across them on eBay while searching for alternate eyelets for amp builds.

    a
     
    tikitorch likes this.
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