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Thread: Ď93 Blues DeVille - low volume

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    Ď93 Blues DeVille - low volume

    Hello

    Iím looking at an old Blues DeVille that has low somewhat distorted volume.

    Iíve already tried replacing the old tubes one by one (no change) and have run a hot soldering iron over the solder joints for the power resistors R85 and R86. I know that these often melt the solder at their connections but that doesnít seem to be the case here. The plus and minus 16 measures good at these resistors.

    I also had to resolder the input jacks.

    Iíve been looking at and measuring the DC voltages on the circuit board with reference to the schematic.

    All look normal save for the positive lead ends of capacitors C42 (schem says it should be 364vdc but it reads 234) and C35 (schem says 413 and it measures 231).

    Anyone have a thought on this one?

    Additionally Iíd like to ask about a problem Iím having when trying to measure AC voltages on the board. When I try to measure the voltages they immediately go down, especially the millivolt measurements. Iím using a Fluke DMM meter, actually two different ones, and both exhibit the same problems. What am I doing wrong or missing?

    Thanks in advance - schematic listed below

    earache

    https://www.thetubestore.com/lib/the...-Schematic.pdf

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    Check the plate voltages on the PI tube. One of the resistors for the PI plates may have opened.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by earache View Post
    All look normal save for the positive lead ends of capacitors C42 (schem says it should be 364vdc but it reads 234) and C35 (schem says 413 and it measures 231)
    Those capacitors are second in a totem pole arrangement and do not have any voltages indicated on the schematic. The TOP capacitors + lead in those totem arrangements should measure to the voltages indicated. As far as I can tell your voltages at the indicated capacitors is as it should be. I think we need to look for your problem elsewhere.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    Lifetime Member Enzo's Avatar
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    I automatically resolder the power tube socket pins on those. And I agree to check pins 1 and 6 on the phase inverter for missing B+.

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    The totem pole caps Chuck mentions have the voltage shared between the two caps and the resistors across them are there to make sure they get equal share. So for the two caps together the total end-to-end voltage for each respective pair should read what it says on the schematic but the voltage across each cap will read half of that. I always check the voltages at mid point as well as end to end as I've had amps where a resistor has failed and resulted in one cap getting most of the voltage.

    PI load resistors are a common failure, as are screen resistors if the amp has previously had a tube failure. Make sure both tubes are conducting - the symptoms are the same for either fault.

    Unrelated to the problem - If it has the original grey Illinois caps check for signs of leakage and inspect the solder joints. I don't see these amps very often where these caps are good.

    Your DMM probably has a resistance of 10M Ohms on the volts ranges. This is what the meter loads the circuit with between the probes. If you take a measurement across a high impedance circuit this resistance may be significant. Not in tube amps usually, except under unusual fault conditions (apart from the PI under signal conditions, which can get loaded down) but say in a condenser mic across a 5G or 10G Ohm load resistor. Now that meter resistance is like a near-short.

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    Quote Originally Posted by Mick Bailey View Post
    across a 5G or 10G Ohm load resistor. Now that meter resistance is like a near-short.
    Gig-ohms huh, new one on me. I'm still caught out occasionally with milli-farads, I can get away with it, but it's not a good look for a high end cap dealer to not be able to keep their ufd and mfd straight. https://solen.ca/product-category/ca...facturer=solen

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    Lifetime Member Enzo's Avatar
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    10 gig ohms? Isn't that just... the air?

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    Quote Originally Posted by Enzo View Post
    10 gig ohms? Isn't that just... the air?
    That's what I thought too, but: https://www.mouser.com/Passive-Compo...5g9n?P=1z0vknw

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    Mick Bailey - So to measure the AC voltages on the schematic, Iím better off using an oscilloscope? Or maybe a different kind of meter?

    Chuck H - the voltages I measured and found lacking at C42 and C35 were in reference to the expected voltages that are shown in the layout drawing 047005

    Enzo - I measured 262 VDC at pins 1 and 6 of the phase inverter

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by earache View Post
    the voltages I measured and found lacking at C42 and C35 were in reference to the expected voltages that are shown in the layout drawing 047005
    Image? Link?

    I'll wager that if the layout numbers are consistent with the schematic and it actually shows those voltages for those locations that the layout is just wrong (it happens). According to the schematic your voltage measurements are just as they should be.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    I only use a DMM for measuring amp voltages - AC or DC. Also, whenever you get unexpected or strange readings (such as a measured voltage dropping) the first thing to check is you DMM battery.

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    Chuck H

    I really appreciate your input, thanks! Not to belabor the point, but the schematic was linked in my opening post.

    https://www.thetubestore.com/lib/the...-Schematic.pdf

    The voltages I mentioned are on the layout drawing on the second page.

    Mick B - I will put some new batteries in both DMMs and see if that improves my readings.

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    Quote Originally Posted by Enzo View Post
    10 gig ohms? Isn't that just... the air?
    10G and 100G resistors were common where I worked. They were used as the feedback resistor of a mass spectrometer electrometer amplifier. They had to be mounted on ptfe standoffs and you couldn't touch them with your fingers because the surface contamination would make the amplifier noisy.

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    Bent Member Chuck H's Avatar
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    Ah! Ok. Thank you. I did not "scroll" so I was only seeing the schematic. I'll stand by what I said though. The voltages should be equally divided across the caps in the totem pole arrangements. So I don't know how the voltages indicated on the layout were derived but the voltages you report seem correct to me.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    Quote Originally Posted by earache View Post
    The voltages I mentioned are on the layout drawing on the second page.
    That's an error. The voltages on the layout drawing shown for C35 & C42 should be shown at C45 & C46.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by g1 View Post
    The voltages on the layout drawing shown for C35 & C42 should be shown at C45 & C46.
    Ah, You're right. That must be where it went funny. I couldn't figure out how they got those voltages.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    Hey all

    Well it seems this issue is resolved...by just plugging the speaker into the correct output and not the extension speaker jack!

    The back panel of these amps doesn’t list which is which, and this is the way it came in. The amp is from a high school music club and so who knows what kind of monkeying was done with it.

    It was from reading other posts about the Blues Deville and Deluxe on this forum that I found a post by Enzo that suggested that perhaps that person’s amp had the speaker in the wrong jack.

    A lot of necessary maintenance got taken care of on this Amp so it wasn’t a total waste of time.

    Thanks everybody for their kind and helpful attention!

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    I think there may be a sticker inside the cab that shows which jack is which, but like you say, they are not labelled on the back panel.

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    Lifetime Member Enzo's Avatar
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    Once you have been in a few Fender amps you recognize the main speaker jack is the one with the shorting contact, the extension jack lacks it. Been a long time ago now, but we had a run of HR DeVilles through that had bad main speaker jacks. They are the right type, but the contact blade was slightly out of shape, and so the speaker plug did not reliably open the shunt contact. It is just on the edge of touching, so now and then... A tiny tweak with my duckbills and all good.

    I am glad you sorted it out.

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    Last edited by Enzo; Yesterday at 03:05 AM.
    Education is what you're left with after you have forgotten what you have learned.

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    Enzo - thanks and much respect to you for all the help and knowledge you've sent my way over the years. You Rock!

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    Bent Member Chuck H's Avatar
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    Hey! At the very least this thread detected a gross error in this models layout diagram. And that could help someone in the future

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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