How can I tell if my tubes are ok?

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Cap217

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when I buy an amp I now assume I need new tubes. I have all the bias probes and can install a new matched set, bias, and install new preamp tubes. But how would I know if a set of el34 are bad? But more importantly preamp tubes?

Seems like a waste to just assume I need all new tubes. But if you don’t know what the amp sounds like with new tubes, then you can’t say it doesn’t have the punch or the drive it should. You don’t have anything to compare it to.

I’ve looked for testers with no luck.

And how do testers work? Do they give you a gain number for preamp tubes? Per side?
 
I guess without buying a very expensive tester you'll just have to plug n play, see for yourself how it sounds/responds. Usually if tubes are going you'll be able to tell fairly quickly...weird sounds and tone that just doesn't sound healthy. By checking each tubes' bias will also let you know. If 3/4 are within a normal range (30-40ma for instance) and the 4th is way off i.e. super low/super high you can pretty much tell the 4th is on it's way out, unless the tube is of a totally different brand to the others which suggests it's a replacement.
I have a super old small tube tester, probably used by TV repairmen and carried into the home. But it only tells if the tube is good, how strong and if there are shorts. It was 50 bucks. The super nice testers are north of 1K.
 
Whenever i get a new amp i always re-tube the power section so there are no surprises and i bias my own.
In my experience alot of sellers when selling an amp pull their good tubes for themselves and put in crappy ones to sell.
I don't but alot do.
Last few amps i sold were with $100's of bucks worth of NOS glass and i even threw in extra tubes but thats me.
I don't believe in screwing people.
 
Cap217 said:
Ok, what do I need to spend? $200, $500? I dont want to spend $1k.
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Prices on everything are crazy right now. Try looking on eBay for a Hickok 600a or 6000a that’s been recalibrated. It might take a bit to find a deal though
 
LP Freak said:
You’ll get nothing but unreliable junk for $50, just warning you
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Haha it's not junk; it is limited though in what it can tell you. Just the basics...is the tube good? Leaks/shorts? Emissions? That's about it. Basically I use it to make sure that any tube I buy (not much these days as I have a pretty good stash) is still in workable condition vs throwing a tube in that might be bad, and take out something after I install it.
But I bought this 5 years ago, before the jump in prices. It doesn't compare to the more expensive tube testers.
 
Samhain said:
Whenever i get a new amp i always re-tube the power section so there are no surprises and i bias my own.
In my experience alot of sellers when selling an amp pull their good tubes for themselves and put in crappy ones to sell.
I don't but alot do.
Last few amps i sold were with $100's of bucks worth of NOS glass and i even threw in extra tubes but thats me.
I don't believe in screwing people.
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This is my approach. It makes no sense to buy a tube tester, unless you're a tube hoarder/tube buyer/seller.

Seems to me, buying an amp and then a tube tester to see of said amp has good tubes is kinda dumb. I make the assumption a used amp needs retubed, and in most cases, I have a preference in tubes/brands anyway.

Having spare tubes will bring more peace of mind than a tube tester. If a tube tests bad, guess what? You have to buy tubes..
 
Racerxrated said:
Haha it's not junk; it is limited though in what it can tell you. Just the basics...is the tube good? Leaks/shorts? Emissions? That's about it. Basically I use it to make sure that any tube I buy (not much these days as I have a pretty good stash) is still in workable condition vs throwing a tube in that might be bad, and take out something after I install it.
But I bought this 5 years ago, before the jump in prices. It doesn't compare to the more expensive tube testers.
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I wasn’t particularly talking about yours it was only a general statement
 
napalmdeath said:
This is my approach. It makes no sense to buy a tube tester, unless you're a tube hoarder/tube buyer/seller.

Seems to me, buying an amp and then a tube tester to see of said amp has good tubes is kinda dumb. I make the assumption a used amp needs retubed, and in most cases, I have a preference in tubes/brands anyway.
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Ever buy tubes from a trusted retailer only to have one red plate on you? Willing to take that risk + the hassle of going after the retailer to replace your transformer? Not me. I've had 5 separate instances where tubes from The Tube Depot, Eurotubes, Dougs and a few more that I forget have each had a bad power tube that IMMEDIATELY red plated. Bad out of the box. That scenario can EASILY take out a transformer and ruin a nice valuable vintage amp. Each time the retailer immediately sent a replacement, no hassles BUT the damage could have been disastrous. Luckily I watched as they warmed up and started to red plate so I was able to turn the amp off fast.
Yes, when you buy NEW tubes they can be bad right outta the box. These simple testers help identify a bad tube BEFORE it damages your amp.
 
Racerxrated said:
This is basically what I have.....

https://www.ebay.com/itm/185136510953?hash=item2b1afef7e9:g:DYEAAOSw6V1hfYIZ
Works great for what I use it for...just to make sure the tube is still good. Mine is the same brand/size etc. It may be a little older than this version. Hasn't steered me wrong yet.
If I were someone into selling tubes I would buy something more elaborate. For my needs this works just fine.
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So if I got this, what would I know about the tube? Im clueless on this so fill me in.
 
I'd say get it home. Make sure you can see all the tubes when lit. Fire it up. Look at the tubes. Do they look normal? Play the amp and make a logical conclusion. If they don't look normal, power it off and have it inspected. I'm not an amp tech but what little I know tells me it would have to redplate for a bit (seconds on end) before any damage would occur to the amp. Of course part of that depends on the amp.

What amp are you considering?
From where?
Can you have seller play through the amp for you before they remove the tubes and carefully wrap for shipment.
 
311splawndude said:
I'd say get it home. Make sure you can see all the tubes when lit. Fire it up. Look at the tubes. Do they look normal? Play the amp and make a logical conclusion. If they don't look normal, power it off and have it inspected. I'm not an amp tech but what little I know tells me it would have to redplate for a bit (seconds on end) before any damage would occur to the amp. Of course part of that depends on the amp.

What amp are you considering?
From where?
Can you have seller play through the amp for you before they remove the tubes and carefully wrap for shipment.
Click to expand...

I’m not talking about failed tubes. I’m talking about tubes and their life left.
 
Cap217 said:
So if I got this, what would I know about the tube? Im clueless on this so fill me in.
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So, with this one it will at least tell you if it's good enough to put in your amp; or when you buy an amp you can see if they are testing good i.e. with emissions, leaks etc. It won't tell you how much life is left however. I don't know of a tester that does. For example I've had some vintage Sylvania 6L6 that test on the 'barely good' range i.e. just into the green section and they've lasted for years. But I've also identified tubes that have showed up in amps that are not testing into the green part of the graph that I pulled immediately before firing the amp up; not taking any chances. What you do with this tester is, first look up the tube type in the little booklet that's included and the book will tell you which socket to put your tube into for testing, also which settings to use for that tube type. Very important to get it right or you WILL fry your tube..trust me I've done it lol. Then, if everything looks good that tube should be good to go in your amps.
The more expensive versions can actually match tubes so that when you install they are all around the same range in ma. But these cheaper ones are good for testing for BAD tubes; not much else really. But it's saved me a few times with some tube purchases that I returned very fast.
 
You need a palm reader/crystal ball & someone who can predict the future to know how long a tube will last.
Sometimes 50+ years. Sometimes 2 days.
 
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