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Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Super Bassman troubleshooting help

Discussion in 'Glowing Bottle Tube Amp Forum' started by PMELIUS, Aug 7, 2017.

  1. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    Definitely at a point where I want to start playing around with this sort of thing. Just a couple more stability things I'm concerned with first...

    I wish I had a signal generator capable of this! Is there anything else I can do to measure this?
     

  2. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    Everything sounded pretty good after playing through it yesterday! Still a couple things going on with the power section that I don't like.

    V7 (the socket I had previously replaced) was putting on a new light show. This is with controls pretty maxed out (except bass - see next symptom)

    Best seen on the last note - just striking open really hard because I'm holding a camera.



    I have an issue with the way this power section is laid out because the B+ is networked through the rest of the power section via this socket. Just bothers me, I'm not actually sure if it causes this tube to draw more current or anything? Can I just send fork the B+ off of a terminal to each half of the power section instead? Idk if this contributes to this issue, but this socket it really crammed full of leads because everything is networked off of it.

    The other issue is still this weird oscillating that happens if the bass is above 4 and the volume is particularly high (the way I like it). If I strike a note, this will just keep going until I turn either pot done or flip the standby. Drives me nuts. Could this be an electrolytic not carrying it's weight?



    I have some 3w 470 for the plate resistors in the power section as well as some better quality grid stoppers in the mail (I just have something in temporary now for the grid stoppers which I'm not happy with as a permanent solution.)

    If you're interested, here's how the amp sounds. Made a quick clip for my buddy (the actual owner of the amp).
    First part is guitar straight in, second part is clean boost, third part is a fuzz pedal I built.

     

  3. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia

  4. Commodore 64

    Commodore 64 Friend of Leo's Ad Free Member

    Age:
    42
    Mar 1, 2010
    Kent, OH
    The amp sounds the same to me, regardless of the pedals you put in front. Some of that is the clipping of your phone camera. But some of it is just because there's so much clipping in the circuit. When you crank the volume, even just a little bit, you are sending square waves throughout the whole amp. I really hate that circuit, especially the plush one with all the cathode resistors at 1.5k and fully bypassed.

    I think there's a lot of power supply sag going on. And maybe some oscillation (too much gain and no order to the lead dress), too.

    If that were my amp, and this is what I did to the Bassman 10, I would gut it completely and reuse the iron. Start over and make a logical eyelet or turret layout. I'd be happy to give you my DIYLC files for my Bassman 10 (to get you started).

    Seems like it's the holy grail, people carrying on about P2P these days. But I think it's an untraceable mess (not just your amp, but all P2P).

    Also, in my rebuild, I'd lose 2 of the power tubes. End this question of power supply sag right there and lose 2 of the power tubes. There's no need for 4 big bottles in a tube guitar amp. My ears are destroyed from local bands bringing full stacks and 100W heads to a bar that holds maybe 100 people. Ridiculous. :p

    Ask me, and I WILL peel the paint off your walls with my UL JCM800 (that was once a UL Bassman 10), and it only has 2 6L6GC. And it's running through a quad of inefficent Carvin PS10 (96.7 db), at that.
     
    Last edited: Sep 11, 2017
    fidopunk likes this.

  5. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    Definitely more noticeable differences in person. I'm going to play around with it some more before I resort to something like gutting it. I just hate to do that to something like this for some reason. If it were an old PA system or something else generally un-useable I would do that in a heart beat (I have a few things in line after this which will be more along these lines).

    Personally I really like PTP so far. It's the only style I've really worked on as far as amps go and I'm really worried about messing up traces on PCBs in amps more than I am the pedals and other random junk I've played with. Still dialing in the perfect temp for my iron and every time I get a PCB in my hands I feel like I'm just cooking it. My soldering station only has a 1-5 dial and not a temp gauge.

    I'm personally a fan of obnoxiously loud amps...so you won't see me ditching power tubes any time soon hahaha. I love 100w amps, but I don't play out much.

    Here's a video of the current limiter I built reacting to the oscillation that occurs with bass above 3-4 and volume particularly high. This is driving me crazy...just can't have it!

    In this video, the oscillation is induced by the pop from the "deep" switch.

     

  6. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    Thanks again for all of the help so far Commodore and robrob especially. I really have come a long way with this amp and learned a lot along the way.

    Edit: I just realized we probably could have gotten some more input had I posted this in Amp Tech :confused:
     

  7. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    I was pretty busy since my test run last week - built the bulb current limiter, went back and fixed a lot of little things with the amp I had done to temporarily test things. Upgraded the screen grid resistors to 3w, upgraded the grid resistors to higher quality ones as well as all of the cathode bias resistors in the preamp because the ones I had in were all random and different power ratings. Made that upper half plate load resistor on the PI an actual 86k instead of two random resistors I found tied in series. I also put the cathode bypass caps back in so I can hear what those sound like with the whole circuit now being more stable. Another sound test will come this week.

    Any advice on this weird oscillation is greatly appreciated!

    I'm wondering if my filtering is insufficient - under-designed from the start. Since all of my voltages are high compared to the schematic, I'm wondering if I should change the diodes in the rectification circuit to knock some off or perhaps convert it to be fully bridge rectified. Seems like this symptom I have could potentially be some ripple getting through to the power section when everything is being pushed?

    Just some of my thoughts based on the knowledge I have hahaha.
     

  8. Commodore 64

    Commodore 64 Friend of Leo's Ad Free Member

    Age:
    42
    Mar 1, 2010
    Kent, OH
    You are drawing too much current somewhere. In pulses.

    Changing your diodes/rectifier is not what you need to be chasing. You have a center-tapped PT. A diode bridge would require you to lift the center tap, and will result in less current capacity and higher voltage.

    You are already pushing the current capacity of that PT right now, IMHO, given the massive amounts of sag that appears to be going on. At this point some possibilities that I would be chasing:

    1. Your bias voltage isn't stable due to the extreme sag of the power supply. This is causing some crazy tube pulsing.
    2. You've got oscillation or some other type of interaction going on due to so much gain and crazy lead dress.
    3. Your 1-ohm cathode resistors may be intermittent causing bias fluctuation. I'd tack on new 1-ohm resistors to be sure, if I had 'em handy.
    4. I don't think it's a filtering issue, when I've had those, there's an unmistakable 120hz hum component.
    5. Some other component somewhere is shorted, leading to excessive current draw.

    How hot is that PT getting under load? Like warm to the touch? Or like hot enough to stimulate the drawback reflex? Or somewhere in between?
     

  9. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    As far as the PT temp goes, I would say somewhere in between. It definitely gets very warm, but not so hot that you can't touch it. I'll try throwing some new 1ohms in there. My bias circuit all looks pretty good. It's almost entirely new components from whoever had this amp before me, but that doesn't mean something hasn't happened to them since.

    Part of me is considering putting this aside until I can get an entry level oscilloscope and signal generator and try to trace the source of my problem. However, that could be a while...and be a while until I really learn how to use them properly. This amp is getting almost to a point where I've rebuilt it from the ground up because I've shotgunned so many components in and out haha
     

  10. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    I'll add to my last post that I have taken measurements in the bias circuit and no components seem to be falling short of their duty
     

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