|
Title: Why did they make resistors like this 60 years ago, and is there a replacement? Post by: KJ4OLL on August 03, 2016, 05:34:51 PM Hi,
Still working on calibrating/restoring a 1950's vintage tube tester. Using the "Daniel Schoo, V4.1" procedure for Hickok 539C. The "13 V.R. MILLIAMPERE METER TEST" result is that the meter reads a little high. The advice to correct it is "13.1 Adjustment - Check resistors R43 / 198 ohms and R44 / 2 ohms." These resistors (White ceramic tower in the photo) are in the schematic, but not in the parts list. Were these hand-wound during production, so as to custom set the required values per unit? Afraid to touch them. Is there any modern replacement? I don't understand why they did it that way. 73 Frank KJ4OLL Title: Re: Why did they make resistors like this 60 years ago, and is there a replacement? Post by: MikeKE0ZUinkcmo on August 04, 2016, 09:03:08 AM Quote These resistors (White ceramic tower in the photo) are in the schematic, but not in the parts list. Yes, You could get some resistance wire (maybe) and roll your own, but I suspect finding the wire would be the hard part.Were these hand-wound during production, so as to custom set the required values per unit? How far off is the meter, and did you verify the power off "zero" is correct before checking the meter full scale? Mike Title: Re: Why did they make resistors like this 60 years ago, and is there a replacement? Post by: WBear2GCR on August 05, 2016, 07:12:20 PM smaller, cheaper and probably easier to get custom values.
also, if these are tapped resistors, that would explain even more... you'd have to buy a ton of the same ones from a production resistor company. and, these may have been sourced from a custom resistor company anyhow... IF they are low, you can drop something in series, high, drop something in parallel! Title: Re: Why did they make resistors like this 60 years ago, and is there a replacement? Post by: w4bfs on August 05, 2016, 08:45:43 PM Hi, Still working on calibrating/restoring a 1950's vintage tube tester. Using the "Daniel Schoo, V4.1" procedure for Hickok 539C..... sorry ...I'm not familiar with his method .... the usual reason for high readings from Hickok testers is replacement of the 5Y3 rectifier with ss diodes .... this will throw them well out of calibration due to less voltage drop in the diodes .... its ok to replace the MV hv rectidooer with 2 diodes and 2 ten ohm resistors in a 4 pin plug... can't think of hardly any reason to have to replace those resistors unless the connections in them have corroded ...clean up and go Title: Re: Why did they make resistors like this 60 years ago, and is there a replacement? Post by: KJ4OLL on August 06, 2016, 06:35:19 AM Hi,
After performing more testing, I'm not so sure the old test equipment I am using to work on the old test equipment is not the problem! The HP 3478A I was using to measure voltage might be way off. It has not been calibrated in ???? years, and seem to recall changing the 3volt battery at some point, that can cause it to wipe the last call data. I have another HP multimeter I want to try, it was calibrated a couple years ago. Starting over on the testing........with what I hope is more accurate measuring tools...... Title: Re: Why did they make resistors like this 60 years ago, and is there a replacement? Post by: DMOD on August 06, 2016, 11:22:43 AM i agree with Beefus.
I have two Hickok tube testers, a 533A and an 800 and the rectifiers are usually problematic, especially the 83 rectifier which are getting much harder to find. Meter reading droop after warmup of the tube under test has been the major anomaly and is an indication the old 83 is on its way out. The circuit below has proven to cure the rectifier problems. Phil - AC0OB Title: Re: Why did they make resistors like this 60 years ago, and is there a replacement? Post by: KJ4OLL on August 06, 2016, 12:41:25 PM One of the reasons I am doing the calibration is because I put in new 83 and 5Y3GT tubes.
(Thanks to Jim @ vacuumtubesinc, a local tube shop) After doing more testing this morning with a calibrated HP 3478A, I conclude the bias meter is just a little off. So for the time being, I am just making up a chart: BIAS METER SOCKET VOLTS 1V .92 2V 1.75 3V 2.6 I would like to try solid state rectifiers, because it is easier on the transformer, as more current is available for testing vs being used to run the tubes. Thanks for the circuit schematic! Frank KJ4OLL Title: Re: Why did they make resistors like this 60 years ago, and is there a replacement? Post by: KB2WIG on August 06, 2016, 06:52:23 PM F, You might consider adding a separate 5v fil. transformer and take 25 watts off of the main transformer.... klc Title: Re: Why did they make resistors like this 60 years ago, and is there a replacement? Post by: DMOD on August 06, 2016, 08:39:17 PM According to this,
http://www.desmith.net/NMdS/Electronics/Hickok/Hickok%20539C%20Calibration%20V4.1.pdf the bias voltage adjustment is made by, Quote adjust the maximum bias voltage by loosening the screw on the sliding tap of R18 / 8.5K tapped power resistor and sliding it to the position which gives the correct reading... This adjustment may also affect the screen voltage that was tested in the previous step. The screen voltage should be retested if an adjustment is made. If the bias volts meter calibration is off check resistors R49 / 40K, R50 / 9.9K and R51 / 200 ohms. Phil - AC0OB Title: Re: Why did they make resistors like this 60 years ago, and is there a replacement? Post by: KJ4OLL on August 06, 2016, 09:49:24 PM Phil,
Yep, I set R18 to yield 40 volts at the socket, as the 4.1 version of the instruction states. Also tested R49, R50, R51 (out of the circuit), they are all OK. Thus the voltage deviation chart! I know there is a digital replacement meter available, but rather than put that much $$$ into this ancient 539B, I'll just live with the meter being off a little, as I now know exactly how much to compensate for when I set the bias. Frank Title: Re: Why did they make resistors like this 60 years ago, and is there a replacement? Post by: KD6VXI on August 07, 2016, 11:58:10 AM If you'd like to get technical, I have a meter program, by Jim Tonne that will allow you to make a new meter face. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
The freeware allows for one scale. The commercial version is SO much better. --Shane KD6VXI |