Iron Tester

[CJ]

it is a hassle to un-rack a mic pre in order to test input and output transformers as well as plate inductors,

so we kludged up a fixture which will allow us to check all of the above,

this is for tube related iron, based on a V72, used the same layout but expanded it a bit to make wiring easy,

still have to get some alligator clips to insert into the banana plugs for easy hookup,

has an XLR cable for a microphone and a 1/4 inch jack for output into a mixer for listening tests,

phantom would be nice, maybe we will add that down the road a piece,

EF804s for input and EF86 for output since we want to go cheap and not waste the whole tube caddy on this thing,

plate inductors are best tested in the circuit in which they are used in order to get accurate results for inductance measurements,

going to power it with an external supply

we also have wound a Peerless K-241-D input on a 625 EI core of super Q that performs as well as the original but has more headroom and bass, the stock Peerless is rated at 8 dbv input if i remember correctly, the 625 EI version will take about twice that level,

here is how it came out, input on the left, choke on the top, output on the right,>

 

[pacemaker]

wouah ,
that mic pre look amazing !
So DIY , CJ you rules ;-)
Francois

 

[joaquins]

Nice idea and usefull!

JS

 

[CJ]

thanks!

just a 3 day project with scrap parts,

note that the ef86 is exactly like the ef804s only different,

the base has a different pinout, 

just a few wires, no biggy,

 

[Moby]

it is a hassle to un-rack a mic pre in order to test input and output transformers as well as plate inductors,

so we kludged up a fixture which will allow us to check all of the above,


plate inductors are best tested in the circuit in which they are used in order to get accurate results for inductance measurements,

Good one. I figured out too that measuring inductance of core based coils doesn't do the job, specially because of frequency dependance. Only way to test it, is the real circuit
Btw, why do you speak in plural????

 

[CJ]

when you say "I" all the time it can sound egotistical, so we try not to do that, 
no, i do not have a lab partner doing bench work for me,

yes you want a modulated DC signal to test inductance so that the AC current is the same as it would be in the circuit,

if you simulate a DC bias by using a battery or power supply, the AC current from the signal generator will have a path through the blocking cap and then it will be across the DC source, so if the DC source has a lower Z than the original circuit, your AC current readings will be off, a battery has a low internal resistance so if you try and use a cap and battery to simulate DC, then the signal goes right thru the cap in gets shorted out by the battery, same thing with a DC power supply, there are filter caps across the output, so some of your AC signal will short out through the filter caps, so you need a series resistor that matches up with the plate resistance of the tube which is used in the actual circuit, this could mean a value of 100 K or more, so if you need 5 ma through a 100 K resistor, then your DC supply has to be 0.005 x 100,000 -= 500 volts to force that much current through the resistor, this can be a dangerous hassle as not too many people have a supply of this nature,

 

[Moby]

when you say "I" all the time it can sound egotistical, so we try not to do that, 
no, i do not have a lab partner doing bench work for me,

Like we are the heroes

 

[mjrippe]

Or as the Rastas say "I and I"  8)

 

[CJ]

what about the Opium Eaters?

http://www.youtube.com/watch?v=nII7PGvZm04

nicknamed the xfmr jig Iron Man,

Sabbath's new album is doing very well, and i hope Tony beats the dreaded C.

 

[shabtek]

Nobody wants to hear me speak about shabtek in 3rd person omniscient.

CJ knows Shabtek is very excited and pleased by the developments presented in this thread.

 

[tubegeek]

I just assumed it was The Royal We on account of because CJ is the King Of Coils!

 

[mitsos]

we also have wound a Peerless K-241-D input on a 625 EI core of super Q that performs as well as the original but has more headroom and bass, the stock Peerless is rated at 8 dbv input if i remember correctly, the 625 EI version will take about twice that level,

Hi CJ,
nice iron tester!  Question about the K241 remake... IIRC from your old posts, the old ones used a much smaller EE lam. Did you use the same type of winding method.. bifi primaries with side by side secondaries?  When you go to a much bigger core, do you recalculate the wire gauge to fill the bobbin so you end up with the same turns? 
thanks!

 

[CJ]

we just  wound another version of the K-241-D, the last one had a rise at about 10 k and reached resonance too quickly, so we just a did a rev wind sec for 1 pie and did the pri bi fi stuff as two pies side by side, so just like a dual chamber bobbin, split the pri and sec winds, we will see how this one works,

#42 wire this time, last time was a pain to use #39  for the sec,
and the closer you are to the center leg, the less leakage,

 

[mitsos]

OK, thanks for the update.  So you skipped the primary bifi winding completely and wound it as if it we two bobbins... half pri and half sec on one side, the other half pri and half sec on the other side? I think I've got some 49% 625, you think it might work OK?