New Tube Amp, Volume Cut Out...

guildman63

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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
 

adorshki

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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.
 

guildman63

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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.
 

gilded

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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? :)
 
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AcornHouse

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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.
 
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gilded

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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.'
 

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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.
 

guildman63

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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.
 

guildman63

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Already did. Again, after replacing the cable everything worked fine. I suspect the problem was an old cable that was on its last legs.
 

adorshki

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Already did. Again, after replacing the cable everything worked fine. I suspect the problem was an old cable that was on its last legs.
I'm laughing because, "Yeah that's one of the oldest problems in the book".
It being a new amp, can understand the natural inclination to think it's the amp.
Have to go along with the advice to check with Supro on the temp issue though.
Default's got a lot more experience than I do and it sounds like it shouldn't be getting that "hot", but that's a relative term in itself.
 
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guildman63

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Interestingly, once I turned the amp off after 3+ hours of use it was pretty cool within a few minutes. I'm not sure how to quantify how hot it was when on, so in all likelihood it was pretty normal. I've been using SS amps for a while, and I'm getting older, so my memory is probably the issue. :stupid:
 

AcornHouse

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Interestingly, once I turned the amp off after 3+ hours of use it was pretty cool within a few minutes. I'm not sure how to quantify how hot it was when on, so in all likelihood it was pretty normal. I've been using SS amps for a while, and I'm getting older, so my memory is probably the issue. :stupid:
Some amps are notorious for getting hot: Voxs, Hiwatts, etc... (Daltrey has told of drying mics out between sets by placing them on the overheated Hiwatts.) Best to call Supro just to check; it can't hurt.
 

Quantum Strummer

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Some tube amps do run hotter than others. I have an old National Val-Verb (Valco design & manufacture, they also made the original Supros, uses 6973 power tubes) that gets pretty warm, though not what I'd call "hot." It's been like that for as long as I've owned it…about 20 years. Your Supro likely uses a similar circuit, and if so warm may be part of the deal. I'd keep a close eye on it, though.

I've certainly had cables go wonky often enough that you'd think I'd remember all the previous times each time it happens again. Nope. ;)

BTW, here's a pic of the Val-Verb. According to a recent Vintage Guitar article it was likely the very first combo amp with reverb on the market.

18D383A6-81BC-4C7A-9992-B9FFE82796C4_zpsrhuy5fjv.jpg


-Dave-
 
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guildman63

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I haven't had any problems since switching to a new cable. The amp sounds great, and yes, it is designed based on the 1964 Tremo-Verb with the same 6973 power tubes. The main difference is that in 1964 it was a 5 watt amp. Now, it is 25 watts similar to the Dual-Tone model.
 

gilded

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You know, I don't want to beat a dead horse, but everybody assumes that cable jack plug ends are exactly the same dimensions.

Truth is, they're not. I have a friend who had an old Parker Fly that came from an era where they had problems with the female jack plug receptacle on the guitar (pre 2002, look it up under 'parker fly jack problems, or check out this service bulletin): http://www.parkerguitars.com/support/manuals/ParkerElectronicsTechnicalBulletin.pdf

The bottom line is, the old Parker receptacles break and the tech charges are several hundred dollars to fix. Really. OR, you just get a Monster cable and the jack receptacle will work. Why? Monster Jack Plugs dimensions are slightly larger and will usually work with the old Parkers. The down side is that once you go the Monster way, you can't use 'normal' cables anymore, at least on the Parkers.

So, your amp's heat could have opened up a cold solder joint on the cable, or the vibration from the amp could have done the same, or your new replacement cable jack plug could be larger and still have better contact with the amp after it heats up and things expand.

And that is the last thing I'm writing about this subject.
 
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