Got a box of 20 or so russian el84's - Can I match these?

[yalesmith]

Got a box of 20 or so Russian el84's - Can I match these? and how do i do it?

Thanks,

David

[Phil_S]

Two or three choices I know of:
1) Send them to the guy with the Amplitrex. Maybe he will PM you. It's a private matter that I can't get directly involved with, but he's a good guy. You'll pay by the tube plus shipping, but I think it's still a good value. It is the simplest and probably best quality route.

2) Build yourself a fixed bias amp and use that as your tester. It is not perfect but still OK. I'd say, build a SE fixed bias amp, like a fixed bias Champ or similar. Put in a bias pot. This lets you get several readings across a variety of grid voltages and you can calc transconductance and get a pretty clear idea of how the tube tests. The problem here is that as you vary grid voltage, plate voltage will also vary, making the evaluation a bit more subjective. It is preferable to hold plate voltage constant and at something that approximates real operating conditions -- in this case something between about 250v and 300v.

3) Build your own test rig. This is better than #2, but probably no better than #1 and it will cost you a bundle of money. You can probably do it cheaper than purchasing an Amplitrex. You can find plans on the internet. I suggest this is the worst of the 3 choices unless you are going to get into the tube selling business.

4) You can buy a "drug store" tube tester on eBait and pretend the readings actually mean something

Just use them and don't bother with matching?

[xtian]

My second favorite deep-religion argument, after the one about standby switches, is the one about matched power tubes. One camp wants matched, another camp says mismatched tubes create moar awesomz even-order harmonics.

Who do you trust? (Besides your own ears.) Good reading on the net?

[diagrammatiks]

you can actually get a rough reading with a cathode biased amp.

make sure each tube has its own bias resistor and make sure the bias resistors are matched.

then just read off the cathode voltages.

[rock_mumbles]

I've measured the cathode voltage on SE amps or with just one tube installed at a time in a pp amp. The advantage of doing this is the tubes are operating at 'real voltages' where most tube testers run the tubes at low voltages.

While I agree that the balanced tube thing is a marketing ploy I do think it's a good idea to use tubes that are at least close to each other.

Another thing you can do is measure the plate current using the shunt method ... I had 5 or 6 6P14P-EV tubes one was significantly different than the others ... I selected a pair that were close and sounded good ...

[diagrammatiks]

My second favorite deep-religion argument, after the one about standby switches, is the one about matched power tubes. One camp wants matched, another camp says mismatched tubes create moar awesomz even-order harmonics.

Who do you trust? (Besides your own ears.) Good reading on the net?

if your tubes are mismatched too much they will hum.

if you don't mind the hum and want all the exciting things that a pair of unmatched tubes might or might not give you then go for it.

[yalesmith]

i will try cathode measurement idea for now. I also had issues with red plating..... then i put another mixture of tubes and they work fine.... I like the idea of making my own rig....anyone have any suggestions? or plans?

Thanks

[tubeswell]

Systematically plug consecutive pairs into a PP tube amp, and the pairs that hum the least are matched the most.

[Phil_S]

i will try cathode measurement idea for now. I also had issues with red plating..... then i put another mixture of tubes and they work fine.... I like the idea of making my own rig....anyone have any suggestions? or plans?

Thanks

A quick search for "vacuum tube matching rig" turned up this:
http://home.comcast.net/~priceamp/
IMO, you should be able to build this on the cheap. See if you can buy the transformers on eBay. That's where your cost is.

Edit: Thinking about this...I'd rather build an amp than a tester. Your amp is a tester, just limited to a particular type of tube. Money doesn't grow on trees. Use it where you'll get the best bang for the buck.

[cbass]

So ou don't have a fixed bias amp to match them in?

You can use this method to measure the current of each tube in a cathode or fixed bias amp.

I copied this from Aiken's website.Its how I bias my amps.Its easier for me cause I can first calculate the voltage drop i need and turn the bias pot(or replace bisa resistor) till i get there.

"The plate current can also be measured by first measuring the resistance across each side of the output transformer primary (it will usually be different on each side) with the power off. Make a note of the resistance on each side, and then, with the amplifier on, measure the DC voltage drop across each side of the output transformer. Divide this number by the previously measured resistance, and you end up with the plate current for the tubes on that side. Again, if there is more than one tube on each side, you must divide the total current by the number of tubes. This method is extremely accurate, and much safer than the shunt current measurement method, because a slip of the probe won't short anything out due to the high resistance of the voltage measurement setting on the meter compared to the very low resistance of the current measurement setting. You can also make a safer measurement by clipping the negative side of the voltmeter on ground, and measuring the center-tap voltage of the output transformer and the voltage at the plate of each output tube. Subtract the plate voltage from the center-tap voltage and you have the voltage drop across each side, and can then use this to calculate the current in each tube, again dividing by the number of tubes on each side."

[renshen1957]

My second favorite deep-religion argument, after the one about standby switches, is the one about matched power tubes. One camp wants matched, another camp says mismatched tubes create moar awesomz even-order harmonics.

Who do you trust? (Besides your own ears.) Good reading on the net?

Hi,

Argument against matched tubes, "Fender, Marshall, Vox, etc., did not install matched tubes into their amps back in the day."

Tubes were of higher quality (few failures as tube manufacturers made tubes for the military or for their own electronic products sold under their brand name, i.e., Radios and Televisions)

Back in the 1960's, High End Hi Fi manufacturers of PP stereos sold matched power tubes sets under their labels (The Fisher, Bogen, Harmon Kardon, etc). The tube were tested and sourced from Telefunkin, Mullard, etc.

However we don't live back in the Golder Age Of Vacuum Tubes (Valves)

Argument for matched tubes.

Matched sets are tested and screened tubes as current tube manufacturers products aren't up to snuff as to quality or reliability, plus the tubes have greater variance then during the golden age tubes. The "bad" tubes are elminated.

Back to the real world

Argument against matched tubes, Groove Tubes' (deserved) reputation (pre Fender buy out and post Fender Buy out).

My opinion, when Pittman could still source NOS (US made tubes, especially), no problem, but as these evaporated and Groove Tube had to resort to New Production from the China, Eastern Europe, and "Sovtek" Russian tubes the complaints began to climb in the forums.

Opinions vary (choose your internet forum) as to Ruby, Mesa Boogie, or TAD.

The STR tubes (and the later generation Chinese 12AX7) do receive some good reviews.

Third Option,

On fixed Bias amps, provide a bias pot for each tube, problem solved.

I went for the later option.

Cathode Bias Amps, mix and match, trust your ears.

I do own a Hickok tube tester which measures Gm, the former owners were an aviation company. Even re-tested, pre-tested matched tubes can and will fail in a circuit, it is the nature of the beast with tubes.

If you are going to purchase matched sets, a seller of NOS tubes is a good place to start.

Best Regards,

Steve

[Prairie Dawg]

i will try cathode measurement idea for now. I also had issues with red plating..... then i put another mixture of tubes and they work fine.... I like the idea of making my own rig....anyone have any suggestions? or plans?

Thanks

A quick search for "vacuum tube matching rig" turned up this:
http://home.comcast.net/~priceamp/
IMO, you should be able to build this on the cheap. See if you can buy the transformers on eBay. That's where your cost is.

I built one loosely based on the Jack Price tube matcher with a couple of differences. My power transformer didn't have a bias tap so I took it off one side of the HV winding. I also had to make a few changes to the circuit to make it more stable. It's not set up for EL84s or 7591s but I can do a lot of stuff with it, including getting plate voltage up to about 650v which is what you want for testing KT88s and slightly less for EL34s. The only really new thing on it is the small parts and the tube sockets. The power transformer came out of a bunch of stuff I got at an auction and the filament transformer came from an old organ. The chassis is a recycled Bogen PA amp chassis.

Full story here.

http://judyboxamp.blogspot.com/2011/05/ ... lding.html

[jjman]

I use a PP amp that has 2 separate bias-sensing resistors. Leave one side's tube in and only change the other side. Take a reading on the side that is being changed out and record that as each tubes "rating." The range I've seen on 6v6 tubes is wide.