One shorted tube in a PP pair testing Question

[Platefire]

In one of my 6L6 PP amps I had a tube short out and stared blowing fuses. I put a new set of JJ 6L6GC's in and that fixed it, problem solved.


So my question is, how do I determine which tube was the bad one and which one is still good short of sticking each one in the socket and firing it up to see which one blows a fuse? I know you can use your multi-meter to check continuity between the two heater pins. I checked to see if there was continuity between the grids, plate and cathode and there wasn't. I don't have a tube tester any more, so is there a simple way to test them? Platefire 

[sluckey]

Fuses are cheap and disposable. 

[mresistor]

Try putting the amp on a LBL (current limiter) before you test the tubes to find the shorted one.   Might save the fuse ..

[Platefire]

Well the LBL did cross my mind. Seems like in blowing a fuse would put your power supply in a bind for a second or two. I don't know if it would be enough to do any damage?

The reason I'm asking is tubes are getting so expensive here lately I'm starting to look at tubes I've sidelined because of questions like this, and trying to figure out how to sort them out---good or bad

[PRR]

> tubes are getting so expensive here lately

Mostly cheaper  (on the hamburger index) than any time in your life.

Recently much cheaper than transformers, which is the next thing you will be smoking.

[PRR]

Pound of ground beef, prices since 1985:
{reposting b/c BLS does not cache graphs}

[Platefire]

Well if I can convert how many Big Macs in Franks/in France it takes to buy a MM Power Transformer compared to in the USA in USD-----yelp I guess it would be cheaper topay $60 for a set on new JJ 6L6GC's. Last I heard the inflation is way worst in France and it is here--or something like that

[tubeswell]

I checked to see if there was continuity between the grids, plate and cathode and there wasn't.

Did you check between the heater and the cathode?


any charring on the socket?

[mresistor]

trying to figure out how to sort them out---good or bad

Well  Plate  the way I have been testing old USA made or other tubes is to use my Hickock 800 and check them for shorts and log the transconductance value; if the tube checks out on the Hickock you can pretty much figure it will be OK in the amp, however the Hickock doesn't test for noise or other troubles the tube might have in actual operation. But since the tubes I've saved have come out of working amps they are usually fine.  This has worked for me.  In matching a pair up I get two whose transconductance values are fairly close and have found that then the pair is also fairly close in the amplifier.  I have been able to help some guys out with low cost solutions using this method of picking from old quads/duets I have saved.

[Platefire]

tubeswell----There were no conductance between heater and cathode. So there was no conductance between any of the different pins of the tube save heater pins. Seems to me that would prove the tube is not shorted out-----but my knowledge is limited on these things


mresistor----I use to have two tube testers but sold both of them. The need for maintenance, calibration on them and the cost to ship them and get all that done, I decided to sell. I was just thinking there should be an easy way to check a tube with a MM for shorts that would blow a fuse immediately the power switch was flipped on. I figured behaving that way, there had to be an inner part of the tube came loose and made contact with another part. What other things inside a tube could happen that would blow a fuse immediately? Loss of vacuum? Just a disconnect, without making contact with anything?

[sluckey]

The tube does not have to have a dead "short" to blow a fuse. Maybe the tube was simply drawing too much current due to an internal failure. Maybe a grid wire was sagging too much when it got hot and touched something it should not have touched. Heck, maybe even both tubes have failed. Maybe the problem isn't even the tubes. Could have been an intermittent loss of bias voltage due to a bad socket connection on pin 5. Reseating the tube could likely cure this kind of problem.

Anyhow, I suggest you toss both old tubes and forget about it. Otherwise, adjust the bias pot for maximum negative voltage on pin 5 of both sockets. Now plug in both old tubes and turn the amp on. Watch for signs of red plating in one or both tubes. If the fuse blows, throw both tubes in the trash after breaking the pins off. If all is OK slowly adjust the bias pot toward your normal operating point while watching for red plating. Tinker around as long as you like. Then pull the old tubes, break the pins off and throw them away.   

[Platefire]

OK, that's good sluckey. Language I can understand. Thanks! but breaking of the pins! That means I can't go back and blow another fuse

[dude]

OK, that's good sluckey. Language I can understand. Thanks! but breaking of the pins! That means I can't go back and blow another fuse

Or the guy that trash picks can’t blow his amp up

[PRR]

convert how many Big Macs in Franks/in France it takes ...

The point of my accursed graph (see re-post) is that from 1985 to today, beef prices have gone up 4X. (I actually remember good ground beef at $1/pound.)

If you find your 6L6 receipts from 1985... heck, there's old catalogs on-line.
https://worldradiohistory.com/Archive-Catalogs/Radio-Shack/Radio-Shack-1984-367.pdf
In 1984, Radio Shack would sell a good but own-brand 6L6GC for $11.29. Quadruple that, would be $45 today. Tube Depot sells 6L6GC today for $35, $45(as pair), or $60 (and up and up and up...).

My daddy bought a fine 1966 sedan for $3,100. I just got a slightly better 2023 one for $41,000.

I remember when a nickle bag cost $5 and was very near a quarter ounce.

[sluckey]

OK, that's good sluckey. Language I can understand. Thanks! but breaking of the pins! That means I can't go back and blow another fuse

That's true, but you were scared to try it, so nothing lost. It's still a good way to let this thread die and just drift away. 

You got better things to do. Now go play this song 10 times...

[Platefire]

My main source of tubes from late 60's through the early 80's was the Wag-a-Bag Convenience store. They had a tube tester and seemed to always have the tubes I needed in stock. As far as brand and cost, I just don't remember.


They also had a meat market in that little store and we got some of finest cut Rib-eye stakes there, of course cooked a home. Pretty cool to get your tubes and stakes at the same store. BTW I drove by there the other day and that Wag-a-bag is still got the same name and is still in business. Tube tester and tubes are long gone


OK it can all Drift Away now, back to the present;>}

 

[AlNewman]

Don't toss em.  You can sell em in 20 years as NOS....for 100 big macs.

Why is it the biggest beef producers spend the most on crappy McDonald's hamburgers? 

[mresistor]

In the future  will you really want a Big Mac?   

[bmccowan]

Well maybe a NOS Big Mac.

[PRR]

...BTW I drove by there the other day and that Wag-a-bag is still got the same name and is still in business. Tube tester and tubes are long gone

https://communityimpact.com/austin/round-rock/business/2021/05/05/round-rock-based-wag-a-bag-to-be-acquired-name-to-eventually-be-changed/

"Wag-A-Bag locations will keep the name for a period of time but will eventually be renamed Refuel. The Rabb family wanted to keep the Wag-A-Bag name in the family,"

[Platefire]

Thanks PRR, I never knew that Wag-A-Bag was a chain store. I have never seen one anywhere
else so I thought is was just local to Mansfield La, where I lived at that time.

[HotBluePlates]

> tubes are getting so expensive here lately

Mostly cheaper  (on the hamburger index) than any time in your life.

A Tung Sol 6L6GC would cost you $4.45 each in 1965.  A matched pair of 5881s were $11.

An inflation calculator says 6L6GC is equivalent to about $43, while the 5881 pair is equivalent to $105.

Note that tube supply disruptions from the closure of a major Chinese factory a few years ago along with disruption of Russian tubes pushed prices up faster than overall inflation.  Even though some of those pressures have eased, tube prices have been a bit like gas that "goes up like a rocket, comes down like a feather."


(Open in a new tab to zoom)

[Platefire]

Yelp, in 1965 could of had a set of big old fat TUNG-SOL 6L6GC's for the cost of Big Mac, fries and coke now. Makes you mouth water don't it? 

[PRR]

....fries and coke now. ...

I remember when GINOs hamburgers were 15 cents. film. I even know who Gino was.

[HotBluePlates]

> tubes are getting so expensive here lately

Mostly cheaper  (on the hamburger index) than any time in your life.

A Tung Sol 6L6GC would cost you $4.45 each in 1965.  A matched pair of 5881s were $11.

The plain McDonald's hamburger was $0.15 in 1965.  Today it costs $2.49, which is 16.6 times more.

The 1965 Tung Sol 6L6GC was $4.45.  The same 16.6 times more makes that $73.87.  And that pair of 5881s would be $182.60.

Even the supply-pressured Russian 6L6GCs are cheaper than cheap hamburgers.

[AlNewman]

Too bad we can't eat tubes.

[sluckey]

My first Krystal burger cost a dime. Last one I had cost 5 for $5 on special sale.

[Platefire]

I just wonder if those 15 cent burgers were fully loaded or just meat and bread? I remember getting fully loaded burgers for 25 cents in the small cafes in the town I was raised in. The wife and I have an ongoing quest to find the best home style made hamburgers. They are kind of like hunting for old vintage tube amps these days, Hard to find!!

[PRR]

Dash fried onion, tiny pickle slice, ketchup, mustard.