Merren Audio
CA
United States
ph: (310) 426-8726
sales
HICKOK 870
Here is the Hickok Model 870 Transistor Tester. Dated from 1961.
The use of two NiCad battery packs provide clean Base and Collector currents.
The 870 measures the AC or DC BETA at your choice of operating conditions. This is an important parameter since BETA is dependent on Collector current. For AC BETA, the Base is driven with 5uA pk-pk 1kHz signal and is user adjusted to this operating point when the meter is sitting on CALIBRATION point, which is 20% of full meter deflection. Durring testing the AC current is amplified by the Transistor Under Test with a (100//50) 33.33 Ohm resistor in the collector.. This is then applied to a 2-stage tube amplifier with a fixed GAIN due to negative feedback internal adjust resistor R21. The amplified signal is rectified via a balanced crystal diode bridge. This drives the meter to show BETA. The meter will have full deflection of BETA= 300 when a 50mV pk-pk signal is applied to the input of the 2-stage amplifier.
Good for checking the Icbo leakage current, especially for old Germanium transistors. Most of the classic germanium transistors NKT275, OC81D, AC128, OC44...ect..were originaly spec'ed for 10uA or less leakage current.
I was not entirely pleased with the BETA accuracy of the stock circuit, since there is some room for error. I spent some time re-designing and modifying the circuit to improve the accuracy to better than 1% for BETA.
The only cosmetic mod I made is the installation of an IEC plug in place of the grommet and cord. Hopefully this should not upset any Hickok collectors.
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TRIPLETT 3444
My Work-horse Triplett 3444
The Triplett 3444 is a fairly descent tube tester..The cool thing about this tester is that it uses filtered DC voltage for the Plate, Screen and Grid Bias. I would not go as far as calling this a "Laboratory Grade Analyzer" until some significant mods are done. Many of the 3444 testers I work on have about 225V to 235V instead of 250VDC on the plates and screens, mostly due to the selenium rectifier bridge needing repalcement. Once replaced you will typically see 263V DC on the plate terminals "UNLOADED" and roughly 250VDC under "LOAD" durring testing. One major issue is that the DC voltages are not regulated, the Screen voltage being the most critical for gm testing. I modifed the 3444 to have regulated Plate and Screen voltages by using a voltage doubler circuit prior to using a descrete linear regulator circuit. the selector is now wired to change the reference voltage for the regulator. Another weak spot is the transformer. The excitation current (core loss) and temperature rise is a bit excessive for it's size due to the low grade core material and the 3x3 stacking of the EI laminations. The second mod involved removing the transformer, removing the core material and re-stacking 1x1 with M6 grain oriented steel and the final step is a deep vacuum varnishing of the transformer for dead quiet operation. After performing these mods, the 3444 is now a more reliable and accurate tester. The 3444A version utilizes solid state oscillator and has a larger DC current range on meter. Besides the solid-state circuit, these are simple mods to re-scale the meter for higher current reading. Calibrating these units is very straight forward, replacing a few resistors with trim-pots will make the calibration go by like a breeze..
I may offer a 3444 calibration manual of my own which will include mods to increase precision along with color photos and descriptions...
For those with a sharp eye...Not all 3444 units are the same........Compare the lower photo to the photo above...
Hi Quality Roll Charts are available for the 3444 ... enquire..
CG Adapter...Tube Socket Extension Box for 3444...NOS condition.
33 tap Power Transformer overhaul
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TRIPLETT 3444-A
The Triplett 3444-A is similair to the 3444 model ..Major difference is the solid state oscillator circuit and the ability to measure DC current as high as 150mA.
Some of the slider toggles have been replaced by push-button switches..
Also more tube sockets....no need for the CG ADAPTER as used on the 3444.
I still prefer the large BIAS dial on the 3444 model for better precision..
This is my mint NOS conditional unit I brought back in my time machine, even the roll chart hasn't faded...
Hi Quality Roll Charts are available for the 3444-A....enquire..
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HICKOK TV-2A/U
The TV-2A/U tube tester has the advantage of monitoring and controling the voltages for Plate, Screen, Grid and Heater... This way you are not in the dark when it comes to what the applied voltages are... This tester is simple for calibration since you only need to verify the AC signal for gm testing.. The Quality % meter is the only nuisance for this tester... This is a meter that goes up to 150% at full scale... If you know the applied AC signal voltage at the grid, the meter sensitivity as indicated in the manual and the SHUNT resistance , then the effecive transconductance can be figured based on multiplying the % by a constant. The TV-2B has a few small changes to where two wires are re-located on the transformer changes..THE TV-2C has the addition of small ferrite beads added to each wire lead at the tube sockets for RF supression.
EMC testing of customer transformer
300 MHz Tektronix 3032B Oscilloscope
120 MHz Arbitrary Function Generator / Counter
BK 4087
Fluke meters and Hakko soldering station
600 Watt LOAD BOX
Network Analyzer HP 3577A
Excellent for measuring loop response for SMPS
Also used for measuring capacitor impedance
HP 3562A Dynamic Signal Analyzer
Excellent for measuring audio equipment
When I get time...need to put the X button back in front panel..
The HP 7470A Graphics Plotter.
This is still the work-horse printer in many defense contractor labs as well as the 6 pen carousel version HP 7475A.
This 7470A uses HP-IB interface (option 002).... aka IEEE standard GPIB
This was the 1980's heyday of the HP Rancho Bernardo Design Center.
Only maintainance required: Fresh pens, new pinch rollers and make sure belt tensioner and belt are good...
I keep two spare HP CRTs on hand for maintainance.
These go into HP 1345A Displays and are of P31 type.
Used in both the 3577A and 3562A Analyzers.
CRT part# HP 5083-6451
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TEKTRONIX CURVE TRACERS
Tektronix Type 576 Transistor Curve Tracer
This model can be easily adapted for use with small signal vacuum tubes and with a bit more effort larger power tubes can be tested.
Tektronix Type 577 Transistor Curve Tracer
Just like the 576, this can be easily adapted for use with small signal vacuum tubes and with a bit more effort larger power tubes with modification of the 177 plug-in.
Tektronix Type 575 Transistor Curve Tracer
A lot of similarities to it's older brother type 570, this can be modified for use with small signal vacuum tubes as well as larger power tubes.
The first upgrade is to convert it to MOD 122C this extends the peak sweep voltage to 400V. Basically MOD 122C configures the secondary winding of T702 in Full Wave Bridge configuration to make the 400V. With additional mods this can be made to sweep higher. ..Heater voltage and screen voltage selectors can be added since heater voltage is easily available from the internal heater supply, screen supply is also available from internal supply with use of voltage doubler circuit..
Tektronix Type 570 Vacuum Tube Curve Tracer
The "classic" vacuum tube curve tracer of the 1950's and 1960's...Used on numerous data sheets. Very cool looking machine. Looks right at home sitting next to McIntosh tube amps. No storage option, so a camera is mounted to the CRT for photos.. I am young enough to have used the Polariod attachments while working at Hughes Missile Systems.
While very impressive looking, the 570 is not all that it is cracked up to be...As soon as the novelty wears off of owning one, next comes the reality of precision and what the heck to do with all these curves since this is all subjective based on your eye and the graph and the alignment. Ideally you would like to have polynomials for these curves or atleast to put them to paper to plot load lines.. Even at it's best calibrated performance you have 3% here + 3% there + another 3% there...by the time you accumulate all the initial tolerances it becomes aparent that it's just a tool for relative comparison amongst similair tubes types. It is still usefull for checking the basic characteristics such as mu, gm, plate resistance, comparing and matching halves of small signal tubes..ect...
Type 570 relys on peak AC voltage for sweep...this is fine if you have really clean sine wave voltage in your mains...A power conditioner really helps here, if not then you get a dwell instead of a peak durring sweep... Heater supply is one weak spot. These can be modified to have much higher precision as well as higher voltage sweeps. I also prefer to modify the screen to go up to 500V. It is possible to install a GPIB BUS or use a robust CAN BUS with an ISO-1050 for interfacing data aquisition. I must admit they are a lot of fun to work on. My suggestion is to save your money and build your own. There are many larger NOS CRT's out there for cheap that were not used on popular equipement. Use these and just design your high voltage circuit as well as Horizontal and Vertical circuits to accomodate the CRT at hand. The step generator is fairly simple and is the heart of the circuit. A curve tracer can be built using tubes, solid-state or a hybrid of both. My preference is to use a micro-controller for the step generator with a digital display. This will save about 40 lbs of weight !!!
See Demonstration of TEKTRONIX 575 with MULLARD ECC83
This section is intended to display some of the test equipment calibrated and used at Merren Audio.
Each week I will try to add more photos and descriptions.
Test Equipment is all about scheduled maintainance and calibration. This is critical if you expect accuracy.
Copyright 2011 Merren Audio. All rights reserved.
Merren Audio
CA
United States
ph: (310) 426-8726
sales