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 Post subject: Triplett 3444 calibration notes
PostPosted: Apr Fri 03, 2020 8:52 pm 

Joined: Nov Thu 22, 2007 11:31 pm
Posts: 919
Location: Johnston, Iowa
All, having lots of time on my hands I’m calibrating all my tube testers. I dove into my Triplett 3444 when I developed a problem testing rectifier tubes. After going through the tester and swapping out X2, X3 and X4, followed by a complete recalibration, my rectifier problem is now gone. I suspect that’s because of the switch exercising and cleaning that was done during the calibration. I did take some measurements on the selenium X2 bridge rectifier and the voltages were within the 3444 calibration specs published on BAMA. There is some question as to what the unloaded plate voltages should be. A post on this website showed a calibration datasheet suggesting that the unloaded max plate voltage should be 263V ( while all the Triplett documents say it should be 250V. This calibration sheet was dated 2012 so my guess is that it’s not an official Triplett document and perhaps one from Merren Audio (plate voltages from this datasheet are shown in last column of table). Merren Audio offers 3444 calibration and their webpage says they set the highest plate voltage to 263V unloaded . I managed to look over a tester rebuilt by Bud Allen at CG industries ( a prodigy of the late Chris Haedt Triplett expert) and his 3444 was set to a maximum plate voltage of 250V. Since my original X2 rectifier matched the published specs I choose a 220Ω dropping resistor (recommended by Chris Haedt ( ) with a silicon bridge to replace X2. Old and new plate voltages are shown below. I spent days tracing the wiring and noting the position of each resistor and following is my “photofact” that I put together from my notes. Interestingly, R34 is shown on the schematic but no value is listed on the parts list (anyone know the proper value?). R26 was almost impossible to find and on my machine, the C-Switch needs to be completely removed to find it. It was worth the effort since C26 was way out of tolerance. I made these photos for my own reference but thought it may help someone else in the future. I suspect there are some variations between machines but here’s what my machine looks like. The area around R3 had definitely been worked on before and the component locations may be altered. Let me know if you find any errors.

plate voltage table.jpg
plate voltage table.jpg [ 104.42 KiB | Viewed 191 times ]
resistor page 2.jpg
resistor page 2.jpg [ 307.91 KiB | Viewed 191 times ]
resistor page 1.jpg
resistor page 1.jpg [ 339.29 KiB | Viewed 191 times ]
3444 resistor page 3.jpg
3444 resistor page 3.jpg [ 303.73 KiB | Viewed 191 times ]
3444 resistor page 4.jpg
3444 resistor page 4.jpg [ 335.7 KiB | Viewed 191 times ]
3444 resistor page 5.jpg
3444 resistor page 5.jpg [ 343.36 KiB | Viewed 191 times ]
 Post subject: Re: Triplett 3444 calibration notes
PostPosted: Apr Sat 04, 2020 6:36 pm 
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Joined: May Wed 18, 2011 2:40 am
Posts: 4589
Location: Littleton, MA
Thanks for sharing your detailed notes. While I don't currently own a 3444, one never knows what might turn up at the next swap meet. The 3444 looks like a great tube tester.

Steve Byan

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