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Thread: Blues Deluxe Reissue-No Sound

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    Blues Deluxe Reissue-No Sound

    Hi guys, the amp powers up, all the tubes test Good, the tubes light & I resoldered the tube pins. I plugged into the FX return and still very low sound. Does this mean that the problem is in the preamp?

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    Quote Originally Posted by Perkinsman View Post
    Hi guys, the amp powers up, all the tubes test Good, the tubes light & I resoldered the tube pins. I plugged into the FX return and still very low sound. Does this mean that the problem is in the preamp?
    If you plugged into the FX return that bypasses everything before it, which includes the preamp. So the problem points to the power amp side of the amp. To make sure the preamp is working plug into the main input and connect the FX Send to another amp. That will test the preamp to hear if it is putting out a strong signal.

    Edit: Please post the schematic you are using to diagnose this amp too.

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    If you plug a guitar into the FX return, the volume will be low, but should be clear. You can also plug a line-level signal (like a CD player or smart phone) into the FX return, and you should be able to get a nice loud (still clean) volume out of the power section.

    Also, try jumpering the FX OUT to FX IN jacks with a 1/4" patch cable. This will eliminate any malfunction of the FX switching jack's performance from the equation.

    After these tests, if sound still fails to get from the preamp to the power amp, I would suspect a failed preamp tube, and work from there.

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    Quote Originally Posted by xtian View Post
    If you plug a guitar into the FX return, the volume will be low, but should be clear. You can also plug a line-level signal (like a CD player or smart phone) into the FX return, and you should be able to get a nice loud (still clean) volume out of the power section.

    Also, try jumpering the FX OUT to FX IN jacks with a 1/4" patch cable. This will eliminate any malfunction of the FX switching jack's performance from the equation.

    After these tests, if sound still fails to get from the preamp to the power amp, I would suspect a failed preamp tube, and work from there.
    I re-read the title of the thread "No Sound". So yes Xtian is probably right that it is an high impedance audio source plugged into FX return, so yes try line level signal. Patch cable will rule out bad switching jacks.

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    Is the speaker jack connected where it should be?

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    I did check to make sure the speaker was in the correct jack. I ran the above tests & still no sound. The preamp tubes are new & tested “Good”, the 6L6’s are not new but tested strong. I do have a question regarding:
    “Also, try jumpering the FX OUT to FX IN jacks with a 1/4" patch cable. This will eliminate any malfunction of the FX switching jack's performance from the equation.”.
    Does this mean jump fx send to fx return on the same amp? Or do I also plug the guitar into the input as well?

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    Yes, jump fx send to return and plug the guitar into the input jack as you normally would. This takes the switching jack out of the equation.

    If that doesn't work, I'd also check plate voltages on preamp tubes. I've seen open preamp plate resistors often enough on these amps. Or, just do a quick resistance check of each plate resistor.

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    Yeah, well, you know, thats just, like, your opinion, man.

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    Lifetime Member Enzo's Avatar
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    In my experience, my guitar plugged into the FX return makes a nice strong signal. Maybe not full power, but certainly not hard to hear. A CD player works fine too, that was my standard bench signal.

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    Quote Originally Posted by The Dude View Post
    Yes, jump fx send to return and plug the guitar into the input jack as you normally would. This takes the switching jack out of the equation.

    Still no sound.

    If that doesn't work, I'd also check plate voltages on preamp tubes. I've seen open preamp plate resistors often enough on these amps. Or, just do a quick resistance check of each plate resistor.
    All Preamp plate voltages (except V2b) are running approx 240 vdc. All 5 plate resistors were good, not sure which resistor is on the plate of V2b. I can't find a schematic that shows expected voltages but these seem reasonable.

    I tested the speaker with a 9v. It clicks but I don't see it moving back & forth. Should it?

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    Yes, the speaker cone should move out if battery + is to speaker + (generally). You may have a shifted speaker gap- magnet/pole piece problem. I'd try the amp with a known good speaker. If you push lightly on the speaker cone, it should move in and out. If not and it's frozen, it's done.

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    I tried another speaker & still no sound, this one is fine. What kind of voltages should I expect from the preamp tube plates? Im getting around 240vdc but V2b shows zero. 420vdc on the power tube plates. Bias at 59mv.

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    Quote Originally Posted by Perkinsman View Post
    I tried another speaker & still no sound, this one is fine. What kind of voltages should I expect from the preamp tube plates? I’m getting around 240vdc but V2b shows zero. 420vdc on the power tube plates. Bias at 59mv.
    V2b is not used and is grounded out according to schematic. https://www.thetubestore.com/lib/the...atic-Rev-A.pdf
    240V sounds right for the plate voltage on the preamp tubes to me. You have 345V node voltage at "x" and if a triode draws 1mA with 100k plate resistors is should drop 100V from the node.
    Do you get any sort of pop at the speakers if you probe V3 with the power tubes in? Specifically pins 1,2,6,7.

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    Yes, I get a pop on each of those on V3.

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    I do have VERY low volume from channels 1& 2.

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    I just used my signal generator hooked up to a 1/4 jack to inject a signal at the input (channel 1) & got a strong, clear, loud signal...but when I plug the guitar in, very low volume.

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    How large was the test signal you injected? Guitars do not usually put out a couple volts, while a generator can.

    Plug the output of a CD player or a tape deck into the amp input, how's that sound?

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    Good point but what would putting a CD player into the amp show us? Is it a bit higher voltage than a guitar input but less than the signal I injected?

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    Did not state what input voltage you used on signal generator. Sure CD player might be similar or stronger than guitar. I would inject signal 1k 100-200mv into the input then I would output the send FX to another amp to see if the signal was strong up to that point.

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    Lifetime Member Enzo's Avatar
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    Yes. The CD player is a known signal, and not too far off from normal input. You didn't answer what level your generator was set at, but I was concerned you had to turn it up way high to get an output from the amp. That could be all we need to explain why the generator is loud and the guitar is not.

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    Modern Fender schematics are usually marked up with test point voltages and I find these useful for troubleshooting. Ovals are AC, boxes are DC. Check all the DC voltages first, then inject a test signal as per the schematic and check them through with your DMM.

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    Quote Originally Posted by Enzo View Post
    Yes. The CD player is a known signal, and not too far off from normal input. You didn't answer what level your generator was set at, but I was concerned you had to turn it up way high to get an output from the amp. That could be all we need to explain why the generator is loud and the guitar is not.
    Not sure what the exact level was on my older HP 204b. Amplitude knob says 10mw max & I was probably about half way so Id take a wild guess approx 5mw. Also, how do I connect the rca Jax from the CD player to a 1/4 jack?

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    Quote Originally Posted by Perkinsman View Post
    Not sure what the exact level was on my older HP 204b. Amplitude knob says 10mw max & I was probably about half way so I’d take a wild guess approx 5mw. Also, how do I connect the rca Jax from the CD player to a 1/4” jack?
    Possibly 5mw is around 500mv RMS? Probably a good strong signal to pump through the amp, but I guess peak value alone might be why it got loud. Inject a known signal read the voltage points with a meter and trace it out as Mick suggested. Here is the schematic and all the test point have been labeled as Mick had pointed out.

    Reference to convert mw into related rms mv for test signal. << this is in reference to RF tables but I think it still applies to audio voltages.
    https://www.electronics-notes.com/ar...hart-table.php
    Attached Files Attached Files

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    There is no way to convert output power to output voltage without considering the load impedance.
    Accoding to the HP 204B manual its max output is 2.5VRMS into 600 Ohm and 5VRMS open circuit (no load).

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    Quote Originally Posted by Helmholtz View Post
    There is no way to convert output power to output voltage without considering the load impedance.
    Accoding to the HP 204B manual its max output is 2.5VRMS into 600 Ohm and 5VRMS open circuit (no load).
    Yes I see now and had just stumbled onto this as well. Can we measure AC mv value using a DMM at the input of the amp to have a reading of the input value?

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    Can we measure AC mv value using a DMM at the input of the amp to have a reading of the input value?
    Sure.
    If the level control is linear, the output voltage at 50% setting should be close to 2.5Vrms as the amp's input impedance is large compared to 600 Ohm (being the source impedance of the generator).

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    Quote Originally Posted by Helmholtz View Post
    Sure.
    If the level control is linear, the output voltage at 50% setting should be close to 2.5Vrms as the amp's input impedance is large compared to 600 Ohm (being the source impedance of the generator).
    Well that explains why the amp got so loud then hmmm....

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    Lifetime Member Enzo's Avatar
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    Exactly my point.

    And sure, just measure the voltage with a meter. Any good meter will be close enough.

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    Had to step away from the amp for a couple days but I'll be back at it this week. I love this hobby.

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    Quote Originally Posted by Perkinsman View Post
    Had to step away from the amp for a couple days but I'll be back at it this week. I love this hobby.
    Ok. Back at it today, Id like to input a signal from my HP 204b oscillator. A couple questions first. My leads from the HP have alligator clips. Can I simply attach them to a 1/4 jack for an input? If so, can I measure the ac signal voltage directly with my dmm leads?

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    Yes and yes. With the clips to 1/4" jack you lose some shielding you would have with a real cable, but this is just for testing, not usage.

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    With the clips to 1/4" jack you lose some shielding you would have with a real cable, but this is just for testing, not usage.
    ...and a low impedance source like a signal generator doesn't need much shielding.

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    But really, you have the HP unit, why not take a moment and complete the instrument? Make up a cord with 1/4" male on one end and a connector to match the HP on the other. In your case a dual banana plug. You know you are going to need it again and again. I always had a couple such cables on my bench rack.

    Got a guitar cord with a bad end? Clip that end off and wire a banana plug there. Two minute job.

    I had a few more that were the same but with zip cord for use as speaker cables. Good for connecting amps and cabs to my speaker/load patch panel on my bench.

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    What ac voltage should I input to the amp?

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    Last edited by Perkinsman; 01-17-2020 at 12:41 AM.

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    So what vac do I want to inject to the amp, the schematic only makes reference to 1k kHz

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    Looking back thru the thread 150-200mv was suggested so I’m going to use 150mv which I’m able to measure directly on the jack input. I ran a line from fx send to another amp input and unfortunately got nothing but hum. I guess I’ll start measuring ac voltages at the TP points & report back.

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