5F1 no sound

Discussion in 'Amp Tech Center' started by scottc311, Sep 30, 2019.

  1. peteb

    peteb Friend of Leo's

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    Heaters, 2,7 are good, the plate and screen are good, 3, 4.


    Are you sure the 20 VDC is on pin 5 and not pin 8?


    The cathode needs 20 VDC to show it is drawing current properly.



    Measure resistance from the cathode, pin 8, to ground. Does it measure 470 ohms like it should?



    You can calculate current draw from the cathode voltage using ohms law, V = IR or I = V/R



    If you really have a 236 voltsge drip accross a 470 ohm resistor then the current draw thru the 6v6 would be:


    I = v / r = 236 / 470 = 500 mA, about 10-12 times too high. Surely the tube would be red plating.



    Something is off with your measurements, I believe.
     
  2. Wally

    Wally Telefied Ad Free Member

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    P4&5 are in the heater filament circuit and should be tied together. If one measures from that 4/5 to ground, that voltage should be in the 3.15vac range..give or take..and match the voltage measured from pin9 to ground.if on measures from pin 9 to that pin4/5 junction, that voltage should be in the 6.3vac range...double the measurement from either of those points at pin 9 or pins 4/5.
     
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  3. Ten Over

    Ten Over Tele-Meister

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    You need to learn how to use your meter. Some of those readings are certifiably wrong.

    You didn't follow the layout correctly, either.
     
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  4. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    I'm really concerned about the "borrowed multimeter" and Wally's safety notes.

    How are you discharging the filter caps and checking them to ensure the amp is safe to work on? Do you understand some amps can kill you even when not plugged in from stored electricity in the caps? You could be working in a live amp and not know it. And did you have any idea as to the quality of the borrowed meter?

    This is the type of thing that scares me about much of the "kit assembly" I encounter. They are just "glued" with solder like a plastic model kit - but plastic models don't kill you. So I seriously am concerned for the builders. I've been doing this long enough tht I am aware of a few deaths and several ER trips - not necessarily kit bulders, but folks jumping into projects without proper knowledge.

    I believe the errors in wiring are directly related to inexperience - that's not an insult, just is what it is.

    But your wiring "lead dress" (the pattern of the wire length, how they are routed and cross, how certain ones are twisted etc) isn't even close to the rather nice, neat layout provided by Mojo (actually one of the best I've ever seen.). I'm trying to wrap my head around the wiring and am stumped -

    - a very specific example - the filaments are shown tightly twisted, but you ran one wire above the sockets and the other loosely over them. Twisted filaments are mentioned in every piece of basic "amplifier101" electronics documentation have ever seen. Did you do any reading or study before assembling the thing? Did you think what was shown in the layout was simply artistic but didn't matter?

    I know folks want to get these projects done, and I want to ENCOURAGE more to learn electronics, understand how to do these things, complete successful projects etc - the more the merrier.

    But - and again, I'm not trying to be insulting - the biggest problem I see in beginning kit building is impatience. Wanting to get it done so badly that "target fixation" overcomes common sense. Critical procedures, methods and testing are lost in lieu of a singular focus - "hoking things together".

    because of the number of wiring errors exposed by the voltage tests and the rather random lead dress, I honestly suggest removing/unsoldering EVERY wire; leaving the parts on the circuit board and the "hardware"in place, then:

    Review Rob Robinette's entire web section on the operation of the 5F1. Make sure you understand basic amp operation, signal flow and the purposes of each part before continuing.

    As you review Rob's material, check placement of every component on your circuit board.

    Rewire the entire amp, following the kit layout as exactly as possible.

    Check continuity of connections as you go - between tube socket pins and the *opposite* side of where each connecting wire, cap or resistor is attached.

    If you do this slowly, patiently and following directions you will likely end up with a working amp.

    I hope that helps.
     
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  5. Ten Over

    Ten Over Tele-Meister

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    Between Silverface's scolding and my scolding, I don't think scottc311 is coming back. I must learn to be more tactful.
     
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  6. Wally

    Wally Telefied Ad Free Member

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    Maybe he drained the caps and is busy going back through the circuit t find the error/s??
     
  7. scottc311

    scottc311 TDPRI Member

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    I took it to a shop and they said two caps weren’t grounded, thanks for your help everyone, minus silverface and tenover
     
  8. Wally

    Wally Telefied Ad Free Member

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    https://schematicheaven.net/fenderamps/champ_5f1_schem.pdf

    I don’t know how the schematic of your build compares to the 5F1, but I think it would be fairly close. If so, the possibilities of a couple of caps not being grounded are limited to two coupling caps, each of which goes to ground through a resistor. your voltages from the power supply we’re good, so we know that all of the electrolytics were good to ground.
    Learning opportunities arise each day. With the best of intentions, I would suggest that you look at the schematic and start...if you haven’t already become literate in the basic reading of a schematic...how to read that circuit. Use the circuit you have built to compare to the layout in the Fender papers and link that schematic to what you see in the layouts. The first coupling cap sits between the input preamp stage and the driver control grid. It goes to ground through a resistor. The second coupling cap is between the driver and the control grid of the power tube and also goes to ground through a resistor. When you see those coupling caps, you might call that tech, tell them that you have been trying to learn more about what you put together, and nicely ask if those two coupling caps are where the link to ground was missing. I would suggest being on some sort of informed basis before talking to them. You might be surprised how much insight that tech might give to a paying customer who is trying to learn.
     
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