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Plate current question EL34

gadget73 said:
might be an interesting experiment to pop a voltmeter into pins 2 and 7 to see what the heater supply actually is
Click to expand...

Yes- and I would do it with one tube, and then with three tubes (measuring from the fourth socket). See how much it changes.

Regards,
Gordon.
 
You'll be looking for AC volts at ~6.3 vac measured with the probes in pins 2 and 8 of the octal socket. The multimeter is the tool of choice.

EDIT: Sorry, brain fog. It should be pin 2 and 7.
 
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right. I would assume AC volts anyway, not a lot of reason to have a DC heater supply. If it reads nothing though, try DC and see what you get.
 
I'm really sorry, my information was bad. DOH! Should be 2 and 7 like the smart folks said. I will correct that.
 
If it takes 6.8V to get the one weak tube to "perk up"- then it DEFINITELY has filament sensitivity, and the cathode is definitely worn out and on the way out. Especially given how much it drops in output, when all four tubes are in (where, if my calculations of the internal heater impedance being just over 0.16 ohms or so are correct- the heater drop will be about 0.6V which would make it wind up right at exactly 6.3V with all four tubes in)...

I bet that if you put it in a normal tube tester, and turn the heater voltage down to 5.0V- the emission of the tube will drop, to pretty close to zero...

Regards,
Gordon.
 
yeah, its definitely not starving them for heater supply but that bump in heater voltage to make it start cooking is a sign of a tired tube. Some of the older testers had a "life test" thing that had you knock down the heater supply by one setting, or sometimes there was a button or switch that did the same thing. If it dropped off significantly, it was a sign the tube was tired.
 
So i decided to return the tubes thanks for all the input i learned some stuff. now im wondering if i test tubes with the maxi matcher 2 should i do them solo or load all the sockets to get the most accurate reading?
 
Chrisxo55441 said:
So i decided to return the tubes thanks for all the input i learned some stuff. now im wondering if i test tubes with the maxi matcher 2 should i do them solo or load all the sockets to get the most accurate reading?
Click to expand...
In my experience there is no significant difference if a tube is measured alone or with 3 others. But i
always test brand new tubes.
 
peterh said:
In my experience there is no significant difference if a tube is measured alone or with 3 others. But i
always test brand new tubes.
Click to expand...

The plate current seems to drop the more tubes that are loaded on this tester. I guess what I was wondering is higher better than lower . Or doesn't matter for matching purposes
 
single tube appears to give you higher heater supply, so it will read stronger. Strong tubes won't have a significant change as heater voltage drops, but if you are measuring tubes at +5% nominal, what they will actually be operating under in the amp may be lower.

personal opinion, I'd do all 4 at one go so its measuring at closer to nominal heater supply. That should be closer to real operating conditions. Even if the amp runs them a bit higher than 6.3v, having a worst-case number is more useful than a best case number IMO.
 
unless its using regulated supplies, thats going to happen. Bump the heater voltage and you get more emission, especially on a slightly worn tube. I'm assuming B+ is regulated, but if its not a lack of load there will also affect things.

When all else fails RTFM. What does the manufacturer say to do? Fair bet they know their product better than random people on the internet. I've never owned one so I'm certainly one of those random people. One thing I can say with fair certainty is that unless you have repeatable test conditions, there isn't much chance you will have repeatable results.
 
6DZ7 said:
I think I'd send the tester back, too.
Click to expand...
A little late Ive had it a few years. It does a good job matching. I've taken direct readings from matched tubes that are installed in my 500C then checked them in the maxi matcher and the readings stay consistent but maybe off by 1 mA which is to be expected as the amp and tester plate voltage is different
 
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