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Thread: New Tube Amp, Volume Cut Out...

  1. #1
    Senior Member guildman63's Avatar
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    New Tube Amp, Volume Cut Out...

    To all the tube geeks out here, perhaps you can enlighten me.

    I just got a new 25 watt tube amp yesterday. I plugged it in and it sounded great. I played through it for a few hours, then put it down for a short time. When I picked it up again the power was still on, yet there was no volume. The amp was very hot, so I turned it off and went to bed. This morning all was fine. I will test it again tonight, but does that make any sense? I know nothing about electronics and therefore have no clue. I want to make sure all is fine to decide whether to keep it or return it.

    Thanks!
    David

  2. #2
    Senior Member adorshki's Avatar
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    Got a suspicion your amp has some kind of overheating protection, probably more to prevent fires than anything else, but it may also be a self-protection circuit that kicks in above certain temps.
    Pretty cheap and simple to build in a circuit that'll sense temp and kick in a relay at a critical temp to cut off power to the transformer(s).
    Power light lets you know it's still getting current even though the transformer(s) are cut out since they and the tubes generate the most heat. And tubes do degrade over time from heat.
    Everything does actually, just that solid-state stuff ("Transistors") can generally handle higher temps for longer periods.
    If all was fine this morning you're probably ok but you might want to check your owner's manual to verify that's what's going on, it should make a note that it has "thermal overload" protection, somewhere.
    Al
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    All bought new!

  3. #3
    What amp is it? It may be a design flaw.
    Chris
    ---
    '56 A-50, '57 CE-100, '60 X-150, '61 M-20, '62 F-20, '64 S-50 Jetstar, '64 Mark II, '65 SFIV, '71 S-90, '75 F-112, '75 Mark IVp, '81 M-80,
    '82 S-275, '86 T-250, '88 Detonator, '90 Pilot SB602, '93 X-500, '97 Bluesbird, '99 F-30, '16 NS S-200 Thunderbird
    '54 Masteramp, '60 99j, '66 Thunderbass, '69 Thunderstar, '92 G-500
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  4. #4
    Senior Member guildman63's Avatar
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    Well, I think it may have been operator error. I plugged it in again last night, and after about three hours it cut out again. I emailed the dealer for a return label and was ready to send it back. As I went to turn off the amp I jiggled the cable and the volume returned. I then replaced the cable with a new one and had no problems. It appears that the cable was overheating, not the amp. Is that even possible? I had no problems at all for 2.5 - 3 hours, then it acted up. I have gotten rid of the old cable and expect to have no problems with the new cable.

  5. #5
    I've never heard of a cable overheating, but maybe as the amp gets hot, the cord's jack plug gets hot and a loose solder connection starts acting up.

    I too, would like to know what the amp is. What are the power tubes? 6V6? EL-84? 6L6? I assume 'cable' is the guitar cord?

    My guess is that when the amp gets hot enough, interior components like the Printed Circuit board expand and the cord's jack plug end is incrementally moved away from the female cord receptacle contact points.

    I just went over this scenario with a friend who builds Marshall and Fender type amps for fun (30, so far). A buddy asked him to fix a Crate 'Vintage 30' (?) amp for the third time. Without opening the amp, my friend/amp guru described the same symptoms you have with your amp, then told me the fix would involve moving enough parts around to insure a steady contact. With reference to the Crate amp, he said it's not the design, it's the materials....

    What kind of amp? :)
    Last edited by gilded; 10-28-2016 at 03:04 PM.
    Quote Originally Posted by fronobulax View Post

    And I like Harry's approach.
    '66 Starfire I SB bass, '75 Mark 4 P, '00 Black Bird,
    '66 Thunderbird amp, '68 Thunder 1 RVT amp

  6. #6
    Quote Originally Posted by gilded View Post
    The cable is not overheating. I too, would like to know what the amp is. I assume 'cable' is the guitar cord?

    If it is, then my guess is that when the amp gets hot enough, interior components expand and the cord's jack plug end is incrementally moved away from the female cord receptacle contact points.

    I just went over this scenario with a friend who builds Marshall and Fender type amps for fun (30, so far). A buddy asked him to fix a Crate 'Vintage 30' (?) amp for the third time and without opening the amp, he described the same symptoms you have an told me what the fix would be. He said it's not the design it's the materials....

    What kind of amp? :)
    I have heard overheating issues with Crate as well; and the new Fender Bassbreakers seem to have issues.

    Dont assume it's you, or the cable. If the amp was very hot, as you said, I don't think that could be the fault of the cable.
    Last edited by AcornHouse; 10-28-2016 at 03:04 PM.
    Chris
    ---
    '56 A-50, '57 CE-100, '60 X-150, '61 M-20, '62 F-20, '64 S-50 Jetstar, '64 Mark II, '65 SFIV, '71 S-90, '75 F-112, '75 Mark IVp, '81 M-80,
    '82 S-275, '86 T-250, '88 Detonator, '90 Pilot SB602, '93 X-500, '97 Bluesbird, '99 F-30, '16 NS S-200 Thunderbird
    '54 Masteramp, '60 99j, '66 Thunderbass, '69 Thunderstar, '92 G-500
    Acorn House
    '08 Parlor, '10 Butternut Deuce, '13 Rounder, '14 Kulakeiki

    '94 G&L Legacy
    '03 Elder Lute
    ---
    http://acornhouseworkshop.com/

  7. #7
    Hey Chris, I changed my wording a bit and your Quote from my post is the 'original' wording, not the 'new improved' wording. It ain't much different, I just thought I was being too sure of myself with a blanket statement like, 'the cable is not overheating.'
    Quote Originally Posted by fronobulax View Post

    And I like Harry's approach.
    '66 Starfire I SB bass, '75 Mark 4 P, '00 Black Bird,
    '66 Thunderbird amp, '68 Thunder 1 RVT amp

  8. #8
    Super Moderator Default's Avatar
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    Tube amps don't do that if everything is in proper shape. It may be a known issue with the amp, but we can't read your mind.
    "Steve, you are a man of many goats."~ capnjuan
    "8 of 18", "19 of 22", "25 of 25" (and a couple of amps)

    "Alternatively, you could just go the ultra-relic route with it. Basically go for a look that says the amp was on fire and they put it out using belt sanders. "

  9. #9
    Senior Member guildman63's Avatar
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    It's a brand new Supro Tremo-verb, and it uses 6973 power tubes. Yes, the amp was hot after being on for three hours, but all I know is that there was no volume with the first cable, and then after I switched cables it worked perfectly. The amp had not cooled down at all, so at this point I can only assume that the cable is wearing down. I will be playing it a lot this weekend with the new cable, and if I have no issues the problem will be solved.

  10. #10
    Super Moderator Default's Avatar
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    Call Supro.
    "Steve, you are a man of many goats."~ capnjuan
    "8 of 18", "19 of 22", "25 of 25" (and a couple of amps)

    "Alternatively, you could just go the ultra-relic route with it. Basically go for a look that says the amp was on fire and they put it out using belt sanders. "

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