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  #1  
Old 02-14-2017, 04:55 PM
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Kawooa Kawooa is offline
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B&K CRT 400 reads lower then 465

I have a CRT 400 which I replaced all bad resistors in and the selinum recitifer. A new silicon diode is in series with a 5w 200ohm resistor for roughly the same voltage drop as orginal. My 465 is also partly restored up. There are a couple resistors I need to check but everything else seems fine. I replaced the capacitors in both.

When I test a 17BP4? on the 400 it glows the two half of the neon lamps for no shorts dimly. On emission it will only read 150-200 at best. I even tried two other 6X4 tubes in it to no avail. My 465 reads no shorts as well but on emission it reads 450-500ua. I did hit the tube with the rejuv. low using the 400 as the emission was quite low. Before the rejuv. The 465 would read about 200-300ua. I left the tube on the 465 for an hour and the reading increased slightly.

I want to know why my 400 reads so much lower then the 465. I did calibrate the heater voltage on the 465 meter to exactly dead on when using 117vac as per the manual. I will check the 400's heater voltage at some point but since it's a set voltage for then grids I haven't been comfortable enough to handle the connector.

This all started when I decided to test a 5DEP31 tube from a busted heathkit oscilloscope. The tube shows no emission at all! I tried repairing open elements but nothing worked. I think it's a different pin out even though it uses the same connector. So I tried both testers and same result. So I tried them on my 17BP4 to be sure it was the tube and not my testers. The 465 was set to read the heater voltage a little low so 6.3v on the meter was really 6.5v. So before I rejuv the reading was about 200-300ua. After rejuv it reliably shows 460ish ua.

And on the 465 cutoff is fantastic at just over 25v G1. The setup chart states 22-77v G1. So right now I'm more inclined to believe the 465 is accurate or at least close. But somethings off with the 400 as it reads much to low for me to pass. If it was within 50 I'd be fine.i want to solve this before I try to sell as I don't need it. Pm me if you want it. Otherwise eBay it goes.

Thanks for the help
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Old 02-15-2017, 05:50 PM
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Kawooa Kawooa is offline
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I just found out an awesome mod for the 465. My meter on heater voltage was reading way high on the 11-13v range and low on the 0-3v range. I had it set exactly at 6v. I was experimenting with capacitors in parallel with the meter. I went from 1nf all the way to 470uf. The capacitors solved a jittery needle but didn't solve the inaccurate readings. So I took a 1n4001 diode to test in place of the orginal meter diode for the heater voltage. But I didn't feel like heating the iron up again.

I took the diode in parallel with the meter. The anode is to meter positive and cathode to meter negative. My meter was accurate now! But when I did a emission test on my 17BP4 tube it was now 180ua. Not the 460ua before. My diode screwed with my reading! So I took the diodes anode off the meter and attached some wire to the diode. The cathode remained on the meter. I ran the wire from the diode over the the wiper of the calibration pot(schematic shows 20kohm). This way the diode is in parallel with the meter when in the heater voltage setting but not in emission and other ranges. I'm bridging the mode switch as per the schematic but everything works fine.

I'll get some pictures tomorrow. I put the tester up and don't feel like pulling it back out. Try this mod if your meter is off. It sure bugged me. But now it's fixed.
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Old 02-16-2017, 11:02 AM
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DavGoodlin DavGoodlin is offline
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I have a B&K 445, first one with the color gun selector switch. It seems to read accurately. The filament voltage selector is all it has, so I should probably be checking those voltages.
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