Would this be a usefull method of matching tubes?

[Corben]

Ive got a hickok 605a tube tester and ive calibrated myself pretty well. It was a fairly in depth calibration procedure with 20 steps or so. It was pretty close to begin with actually. Now i know all the arguments as why this tube tester isnt as accurate as others do to the fact that it uses the bias pot instead of a fixed setting and how pots curves fluctuate so badly. But wouldnt that only mean that comparing the results of my tube tester to another tube tester would begin to show differences in the results. But if i was just comparing my testers results from one 6ca7 to another 6ca7 it really shouldnt matter.

Also iv been reading up on how tubes are matched and i was wondering would it be usefull to use a current metter and measure the current plate draw as im testing the tubes and match to those results instead of the hickoks meters results. I was thinking of setting up a little area with a couple dmms set to current with a socket tester in between the tube and the tester's socket to the more commen plate pin outs.

Ive heard attempting to match tubes to anything closer then 5 percent is useless due to tollorances of other components and fluctuations in voltage and ageing. And ive heard from a few sources that 20-25 percent can be sufficent matching. Now of course id like to get as close as possible with the gear i allready have and i know that the tubes wont be run at as high a voltage as they see in amps but i firgure this could be usefull for matching power tubes still and prob better at finding a preamp tube with very close dual triodes for inverters and things.

Also does any one know the testing procedure for 6550s and kt88s for the 605a tester?

[fyl]

Also does any one know the testing procedure for 6550s and kt88s for the 605a tester?

Check the KT88 entry:

http://www.saegerradio.com/downloads...%20Testers.pdf

[Corben]

big thanks for that! also i just figured i could just connect the dmm direct to the cathode switch i suppose. make things easier

[stokes]

Instead of messing with your tube tester,it would be easier to just get a bias-rite or such and measure the current in an amp.You will get much more reliable results at the higher voltage in an actual amp as opposed to the 150 or so volts of your tube tester.But it could be done with the tester,I have a Triplett 3444 that has a built in current meter that I use for just that purpose,my tester does use higher,250v's, on the plates tho.When you put the tubes in an amp with the higher volts,your mismatch will differ.Generally the target tolerance for tube matching in guitar amps is about 5ma's not 5%,but whatever sounds good without causing an unacceptable amount of hum is okay,I wouldnt avoid using a mismatch of 7-10ma's unless I noticed a lot of hum.The 5% target would be a bit tighter,but,in a PP output,tubes with a slight mismatch often have a sweeter tone than a perfect match,not to say that an exact match would sound bad,but if you were to adhere to the 5% target you may pass up a match that may actually sound a bit bettter.Sorry for the long winded response,but the short answer is,yes,you could use your tester as you describe.

[Corben]

Yeah im wondering how inaccurate it is when trying to match at such low plate voltage. But yeah testing in the amp is def the best way its just i have lots of tubes of difrent types i been wanting to match and dont have a piece of gear that uses each kind. I was actuelly thinking of modding my tester even more to show things like, heater current draw, maybe meters that shows what the ac volts and currents are and a few other things ive seen on some nicer tube testers.
I love the tripplet 3444 ive wanted one for a very long time that or possibly one of those very rare avos.

[stokes]

If you dont mind modding the tester,then it will work,as long as you are aware that when the tubes are used with higher voltages,the mismatch may be more than at the lower voltage.You can get tube socket adapters that have contact points for each pin,makes it a bit easier to measure voltages at the plate,grid etc. than to wire meters into the unit.But of course,it would make for an interesting "project" to do it as you describe.The 3444 is a nice tester,but as with any tester,the results must always be taken with a grain of salt.The only true or accurate test is in the actual circuit and with your own ears.The AVO's look really nice,but I doubt any tester is worth what these things are going for these days.TranscendentSound.com has an interesting looking kit available for about $700.

[Corben]

Yeah ive got some of those things that look just like tube socket savers but they have little tabs for each pin to make it easy to measure everything. Mine arent adapters but i think you can open some of them up and change the wireing. I have a 12 pin 8 pin and 9 pin they are super usefull actually. It was one of the first things i bought when i starting messing with tube gear.
Ill check out that kit for sure.
I heard theres some maximatcher or something made specifically for matching tubes. Havent checked that out yet.

[Corben]

I ment to say i have the 605 not the 605a so a still havent found anything anywhere with the tube data for kt88/6550

[stokes]

I used to have something similar to the maxi-matcher that I built myself,all you need is a PT some sockets and a few caps,diodes and resistors,pretty simple actually.Just add some pinouts to connect your multi-meter.

[Corben]

Oh yeah that be great if you hand the plans. I need to go read up on the maximatcher im not familiar with its circuit. Also i was wondering is putting a 1 ohm resistor straight from the plate or from the cathode to gound the best way to measure current draw? could that hurt the tester?

[stokes]

I guess the 1ohm on the cathodes would be okay,I dont know how much,if any,it would throw off the normal test results of your tester.Tube Matcher this is a link to the plans for the tube matcher.The one I built wasnt exactly like this,I used a PT that had the heater winding so I didnt use a seperate heater tranny.The PT I used was some old tranny I had stripped from an old radio or something,it was a long time ago and I have since stripped it for parts.I didnt use the fuse on each socket either and I only used 2 octal sockets and they werent switchable,I had a test point for each socket at first.I did eventually connect a dc ma meter in series with the plate of each socket and that was switchable.I prefer to read the plate current rather than the cathode current via the 1 ohm,if the 1 ohm is off by just the slightest bit,your reading will be off.It is important to use 1% tolerance resistors there.These plans will give you a basic idea,you can of course improvise and make it simpler or more complex as you want.I think this would be better than messing with a tube tester.Your tester is quite old and adding things or modifying it could mess things up.

[Corben]

well id def make the cathode resistor selectable. wouldnt do both at the same time.

If i can find a good power transformer i might build me something like that. Course id need a decent variac coil, unless i could find a transformer with enough taps for several diffrent voltages. Actuelly i have an old laffeyette simple emissions tube tester. That would be great to use for parts so i could run and match all diffrent sizes and pin outs of tubes. Have a selectable bias.

But i do have 2 extra 605 testers with conditons unknown but i think one works but is uncalibrated so if something hurts my tester i could fix it i have all the parts. I need to see what my 605 runs the tubes at as far as plate voltages and bias.

[stokes]

Since your only concern is if the tubes are matched,you really dont need much adjustment except for the bias.Any PT that will give you at least 300 volts on your plates will do.

[legendre]

I see that this thread is a bit old, but I felt compelled to add something.

I owned a Hickok 6000A for MANY years, and having some knowledge of their internal workings, I'd be quite wary of testing 6550s on one of these units. This includes all testers in the 600/6000 series, despite the fact that they have KT88 settings on the roll charts.

When you plug a 6550 into one of these testers, you can immediately see the voltage sag.. and the glow from the fuse lamp. Then when it's time to actually hit the Gm test button, things get even tougher. Fialment, plate and bias voltages sag, and the unit is pretty much pushed to the edges (and beyond) of its design goals.

The basic accuracy of these testers is around +/- 15%, and when run to the extremes, I can see them falling out of spec. Perhaps I'm misguided, here, but it seems like an awful lot to ask from a small, lightweight tester (with a single, small transformer). TBH, I don't even like testing 6550s on my 539B..

[custom_amp_30]

Build a tube matcher: If you want the power level large enough to handle KT88, can't you use a Transformer that would support those requirements? Alter this schematic and improve it. Chances are your modifications would prove very useful to everybody here. I'm new, so don't shoot down this messenger, I'm just learning myself...LOL.

http://priceamp.home.comcast.net/~pr.../schematic.pdf