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Thread: Blackstar ht40 No Sound

  1. #71
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    On some of the Blackstar amps the HT fuse is in a link cable that can appear to be coming directly off the PT. Looking at picture of this amp there's a HT fuseholder on the back panel. Without me reading the entire thread again - is the HT fuse on the good? Did you look where the wires from the fuseholder run from/to, and Is the fuse seated correctly and making contact? A schematic is one thing, but you have to take it as a rough guide and make a diagnosis based on what's in front of you. The simplest and most likely scenario as previously outlined is the tube broke, the amp was powered up and the HT fuse blew. A PT failure is way down on my list of failures, especially if the HT and other secondaries are fused.

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  2. #72
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    Iím glad nosaj made me double check because thereís a third red wire from sp2 to sp14 & I mistakenly measured for the OL reading....when I detangled the three red wires and measured the two from the PT I got 52 ohms! Iím running to the store for the F4 fuse & will report back.

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    Lifetime Member Enzo's Avatar
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    Praised the lord...


    I think I see my confusion. TO ME, the terms "SP1 and SP2" refer specifically to the POSTS on the circuit board. I THINK Perk uses "SP1, SP2" to refer to the wires themselves. SO in my mind I cannot remove SP1 and SP2 from the board, but I CAN remove the wires from SP1 and SP2. Now that we read the actual wires, we get a very good looking 52 ohms.

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  4. #74
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    Ok, so I put in a new slow blow F2 fuse & she powered right up. This just goes to show to check the fundamentals like we did when we were kids. The first thing I would have checked was the fuses but these days itís easier to scour the Internet for a schematic & a new transformer. I was able to bias at TP 10 for 50mV but not sure how to use the ďbalanceĒ pot to adjust yet. I canít thank you guys enough for your patience & doggedness. I love this hobby!

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  5. #75
    Supporting Member Jazz P Bass's Avatar
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    Attached is the bias and balance procedure: Blackstar Bias Procedure.pdf

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    Bent Member Chuck H's Avatar
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    Kudos to those who called out the in circuit fuses. And kudos to Perkinsman's attentive cooperation.

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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

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  7. #77
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    Thanks Jazz, Iíve seen that bias procedure but this HT40 is measured at TP10, not across d36. It actually has ď50mVĒ silkscreened at TP10.

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  8. #78
    Supporting Member Jazz P Bass's Avatar
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    Truthfully, I posted the procedure more for the balance adjust.

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by Jazz P Bass View Post
    Truthfully, I posted the procedure more for the balance adjust.
    It was in post 12.

    nosaj

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    Lifetime Member Enzo's Avatar
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    Perk, PLEASE look at your schematic. TP10 IS across D36.

    TP10 is at the cathode of the power tubes, and from there to ground are a 1 ohm resistor R217, and the parallel D36. The two descriptions refer to the same thing.

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    I'm glad this was resolved, but sweet Jesus this was a fricking long way to get to a bad fuse. I mean really?

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    It's weird, because it WAS working fine.....

  12. #82
    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by Randall View Post
    I'm glad this was resolved, but sweet Jesus this was a fricking long way to get to a bad fuse. I mean really?
    Patience grasshopper patience is all we've got in I've had plenty of moments as . Sometimes because learning can be scary when you're unsure of yourself.
    Nosaj

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    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

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    Lifetime Member Enzo's Avatar
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    SOmetimes it is hard to get them to take a step back and see what they are looking at, rather than focussing on each part.

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    Well I did say in post #6 to check if he had the correct voltages on the output tubes......

    I would still check the PI MOSFETS as well, though. I've not had one of these amps that didn't leak and need fixing. caught early enough it can save the amp.

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    I just installed the new fuse holder (pia!, since the board needs to be pulled). I'm not familiar enough with this amp to know whether the master needs to be turned up in order to increase the clean volume or is the clean independent. Before i put this back into the cab, id like to check voltages, since the volume seems low. Does anyone have the expected voltages for this amp, they're not on the schematic. Plates on v1 pins 1/6 preamp tubes approx 140vdc & v2 1/6 200vdc.

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  16. #86
    Lifetime Member Enzo's Avatar
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    We usually do not see high voltages on drawings. They vary a LOT. If we had a 480v B+, for every volt the mains changes, your B+ changes 4v. So if your mains goes from 119v to 125v, a 6v change, your B+ will rise 24v.

    The thing is, these are just guitar amps, nothing precision. It would be a total coincidence if a drawing said 438v B+ and yours was exactly that. What to worry about is whether the power supply voltage is even present or not. My amp will work fine with B+ or 480, 500, 520v. It won't work with zero volts there. And if your 500v supply reads more like 250v, then a problem exists. B+ half what you expect? First place to look is for a filter cap not working, so you have TONs of ripple.

    When I look at preamp tubes, I check the plate voltages. Hell I usually just go down the row and check them all, takes a few seconds. I expect to see three things. If I find the full B+ voltage there, then I know the tube is not conducting (or it is a cathode follower stage.). If I find 100-200v, then it seems the tube is working. If I see zero volts on a plate, then there is either no B+ of the plate resistor is open. Or a connection to it is open.

    Next I check all the cathodes. Pins 3 and 8 on a 12AX7. If I see zero volts, the tube is not conducting. I expect a volt or two usually. SOmetimes several volts. Exception is cathode followers or split load stages. Higher voltages there. WHy does a tube not conduct? Most often because the heater is not working. Almost never the tube's fault.

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  17. #87
    Supporting Member Jazz P Bass's Avatar
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    The Master Volume is just that.
    "15. Master Volume
    This controls the overall volume of your amplifier. Turning it clockwise increases the
    volume."
    It is a 'post preamp' control.
    https://blackstaramps.com/pdf/handbo...0-handbook.pdf

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  18. #88
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    Quote Originally Posted by Jazz P Bass View Post
    The Master Volume is just that.
    "15. Master Volume
    This controls the overall volume of your amplifier. Turning it clockwise increases the
    volume."
    It is a 'post preamp' control.
    https://blackstaramps.com/pdf/handbo...0-handbook.pdf
    Not sure what post preamp means......just trying to find out whether this amp should get rocking loud when turning just the Volume up or does it require the Master to be turned up before getting significantly loud.

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  19. #89
    Don't forget the joker g1's Avatar
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    What post preamp means is everything goes through it. So yes, you have to turn it up even for the clean preamp channel.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Perkinsman View Post
    Not sure what post preamp means......just trying to find out whether this amp should get rocking loud when turning just the Volume up or does it require the Master to be turned up before getting significantly loud.
    This seems to be a conundrum for a lot of players.

    The preamp has only so much headroom. The more you turn it up, the less it has. So if you wish to take advantage of headroom you must have the highest volume allowance already available when turning up the preamp volume. That means you must have the master volume at maximum setting for the loudest clean preamp signal.

    The preamp volume GOES THROUGH the master volume to get to the amplifiers output circuit. So if the master volume is low then the it limits the preamp volume. Or headroom. Not exactly the same thing but sort of for this purpose.

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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

  21. #91
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    Thanks guys, good to know. I was afraid that the amp still wasn't right. All my amps are just one volume control Fenders...so would it be accurate to
    say that the preamp tube volumes are controlled by the Volume control & the power tubes by the Master control in this amp.

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  22. #92
    Supporting Member Jazz P Bass's Avatar
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    "so would it be accurate to say that the preamp tube volumes are controlled by the Volume control & the power tubes by the Master control in this amp/"

    Yes. That is correct.
    In a very simplified manner.

    For the nuts & bolts of it look at the schematic.

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