Good discussion. Lots of folks very familiar with these machines. My original intent was not to make the 752 into a lab instrument, just to make it "par" after some repairs/rebuild. Thanks to all.
This unfortunately took a turn for the worse, as I discovered one transformer winding is open. Does anyone know where I can get a 752 transformer or one that is functionally equivalent?
This unfortunately took a turn for the worse, as I discovered one transformer winding is open. Does anyone know where I can get a 752 transformer or one that is functionally equivalent?
That sucks. Sorry to read this. I have a Hickok 580A that has an open screen supply winding. I've checked into replacements and there aren't any. I plan to use a small transformer like a Stancor P8181 (150V 25mA) half wave to serve as a stand-in. But it's become a back burner project since I have other testers. Hamond also makes a small 100-0-100 volt unit that might work. Mounting it is the biggest challenge, but it's doable.
I believe the main problem with finding a replacement transformer for the Hickok 752 and the military models is that they combine all the supplies into one transformer, which makes it almost impossible to get a new transformer wound (and the cost would be very high). Alltubetesters does have some replacements transformers that he has custom wound, he does indicate that he has replacements for the Hickok 539 tube tester and I believe also the 580/A (I discussed it with him several years ago). The 539 uses two transformers; the 580/A has a separate filament, screen and plate transformer. The latter two transformers are wound with different voltages with multiple voltage taps (they are not the same). I have both of these testers, but with a number of mods to improve their accuracy/reliability. You might email a couple of the people who repair these testers to see if they have any options. Best of luck.
I'm going to go out on a limb here and suggest a possible source for tube type equipment transformers. Deane Kidd, former Tektronics engineer of great note is apparently still kicking around as of Nov. 2011. He "HAD" a major stock of old tektronics parts and manuals. Don't know on what -if any- level he might still be active, but you might give him a shot at: Deane Kidd dektyr@teleport.com
I think it best not to list his phone and address here.
Anyway, it is just possible he has a stock of old tube type tek transformers. When I've dealt with him in the past on Tek parts he was more than reasonable about pricing.
Just a suggestion.
Doc
I think it best not to list his phone and address here.
Anyway, it is just possible he has a stock of old tube type tek transformers. When I've dealt with him in the past on Tek parts he was more than reasonable about pricing.
Just a suggestion.
Doc
Not so much of a limb, it seems, as someone already had a full page about Tek scope transformers up, linked back to here.
Tek power transformers
Now question remains as to if Deane Kidd has any around.
Doc
Tek power transformers
Now question remains as to if Deane Kidd has any around.
Doc
There is a possible last resort attempt at repairing the secondary 150v windings.
A retired tech gave me some advise for repairing open windings on field coil speakers. He said that he has used a high voltage transformer like the type used for the old neon lights. I have one that is 120v primary,12,000v secondary. With the coil disconnected and isolated, you can connect the 2 high voltage leads to the open coil and inergize if for about 3-5 seconds, then hit it again for about the same time. What this will sometimes do is weld the open wires back in place. I have actually used this method 2 times with success and, to my suprise, had the proper resistance back in the field coil.
The 2 field coils I applied this to were 8.2k and the speakers are still working fine after 2 years now.
The 150v windings would have fewer turns than what I used this method for, but with a variac you may be able to apply lower supply to lower the secondary voltages and acomplish the repair. If your transformer is going to be removed and trashed anyway, it may be worth a shot.
Anyone know what the actual resistance should be for the 150v winding?
A retired tech gave me some advise for repairing open windings on field coil speakers. He said that he has used a high voltage transformer like the type used for the old neon lights. I have one that is 120v primary,12,000v secondary. With the coil disconnected and isolated, you can connect the 2 high voltage leads to the open coil and inergize if for about 3-5 seconds, then hit it again for about the same time. What this will sometimes do is weld the open wires back in place. I have actually used this method 2 times with success and, to my suprise, had the proper resistance back in the field coil.
The 2 field coils I applied this to were 8.2k and the speakers are still working fine after 2 years now.
The 150v windings would have fewer turns than what I used this method for, but with a variac you may be able to apply lower supply to lower the secondary voltages and acomplish the repair. If your transformer is going to be removed and trashed anyway, it may be worth a shot.
Anyone know what the actual resistance should be for the 150v winding?
The bad winding is U-VV-V, specifically the VV-V section of it.
This is one of the 2 matched plate voltage windings (labeled 170V on diagram). Each has a middle tap (roughly 47%) for "low plate" and the good winding also has a 20V tap for the diode test circuit. I can keep that 20V winding.
Any off the shelf xfmr that looks like that? Thanks.
This is one of the 2 matched plate voltage windings (labeled 170V on diagram). Each has a middle tap (roughly 47%) for "low plate" and the good winding also has a 20V tap for the diode test circuit. I can keep that 20V winding.
Any off the shelf xfmr that looks like that? Thanks.
I am not sure I follow completely, these are two different windings. If the whole u-vv-v winding is shot that is one thing, if both have a problem that is another. Hammond may have something, email them if it is the u-vv-v winding. If just the u-vv-v winding is gone, having two trannies each with the right voltage and in series can cure the problem. If so, you may need to reverse the line in if the phase is out with respect to the original tranny.
I can look and see how many Hickoks used this tranny, it should be most. On occasion I see Hickok parts on eBay including trannies. You might also email Alan Douglas and see if he has any, I think he got many parts when Chris H. passed a few years ago. You might also email Kara Chaffee at Home Page she is a wizzard, I just love her, and one of the oldest in the business ( and won't screw you like some others who 'repair' testers) and could have spare transformers.
I can look and see how many Hickoks used this tranny, it should be most. On occasion I see Hickok parts on eBay including trannies. You might also email Alan Douglas and see if he has any, I think he got many parts when Chris H. passed a few years ago. You might also email Kara Chaffee at Home Page she is a wizzard, I just love her, and one of the oldest in the business ( and won't screw you like some others who 'repair' testers) and could have spare transformers.
Sorry for not being clear.
There are 2 identical HV windings supplying the 2 halves of the 83 rectifier. These windings need to be identical and isolated, as the operating principle depends on it.
These 2 separate windings are U-VV-V (i.e. U-V with a tap at VV) and T-S-R (i.e. T-R with tap at S). The middle taps are for reduced voltage in the "low plate" test mode.
The first winding is faulty, with an open between VV and V.
Essentially what would be needed for a "partial replacement" transformer is something with 2 separate 170V secondaries, each secondary with a 47% voltage tap.
To complicate matters, the secondaries are labeled 170V each (on the schematic). Presumably measured with a 1000 ohm/V meter, but the good one measures 212V with a high impedance meter. I'll have to check if the 170V on the schematic is correct when measured with a 170k load. I bet it's not.
So bottom line, it's not exactly clear what the secondary voltage should be for a potential replacement. All we really know is that they want 150VDC at the plate (68V for the "low plate" position) and that is rectified AC, unfiltered and measured with a DC meter. Might take a bit of experimenting.
There are 2 identical HV windings supplying the 2 halves of the 83 rectifier. These windings need to be identical and isolated, as the operating principle depends on it.
These 2 separate windings are U-VV-V (i.e. U-V with a tap at VV) and T-S-R (i.e. T-R with tap at S). The middle taps are for reduced voltage in the "low plate" test mode.
The first winding is faulty, with an open between VV and V.
Essentially what would be needed for a "partial replacement" transformer is something with 2 separate 170V secondaries, each secondary with a 47% voltage tap.
To complicate matters, the secondaries are labeled 170V each (on the schematic). Presumably measured with a 1000 ohm/V meter, but the good one measures 212V with a high impedance meter. I'll have to check if the 170V on the schematic is correct when measured with a 170k load. I bet it's not.
So bottom line, it's not exactly clear what the secondary voltage should be for a potential replacement. All we really know is that they want 150VDC at the plate (68V for the "low plate" position) and that is rectified AC, unfiltered and measured with a DC meter. Might take a bit of experimenting.
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I thought that was what you meant, wanted to be sure.
I have a 752 here. Let me know if you want me to take the readings. Loading of the meter depends on the scale. I have Fluke 87 III everything is in 4's, so on the 400 volt I need to load it with 400K to read 150 right. On the Sencore scope it reads right. I looked at several schematics and the trannies for any that do not use two, are more or less the same. But boy trading one out, what a nightmare.
Honestly, I think you should consider selling it as parts. With the 83 pull down from the heater, using a separate tranny the main tranny is not going to feel that heater pull down. All these voltages float with eachother as any one feels a change. That pull down was part of Hickok's gm number results. Even going to a SS 150 volt plate may or may not give the right readings on any given tube. I have a very good 83 SS design using zeners that will work for Hickok and accounts for that filament pull down and supplies 150 spot on, but will it work for you...I don't know in this application. The zeners allow for ' a range of supply voltages' but won't regulate them, just cap them at 150 PtoP. Going back to eariler posts, it is uneven peaks that alter the gm not the source of the peaks themselves ( SS diodes can have 0.5 volt difference in the same batch when you take a reading and that maters to a Hickok).
Try those source leads I sent. If you give up, I might be interested in some parts...I say might be, not that I need them.
I have a 752 here. Let me know if you want me to take the readings. Loading of the meter depends on the scale. I have Fluke 87 III everything is in 4's, so on the 400 volt I need to load it with 400K to read 150 right. On the Sencore scope it reads right. I looked at several schematics and the trannies for any that do not use two, are more or less the same. But boy trading one out, what a nightmare.
Honestly, I think you should consider selling it as parts. With the 83 pull down from the heater, using a separate tranny the main tranny is not going to feel that heater pull down. All these voltages float with eachother as any one feels a change. That pull down was part of Hickok's gm number results. Even going to a SS 150 volt plate may or may not give the right readings on any given tube. I have a very good 83 SS design using zeners that will work for Hickok and accounts for that filament pull down and supplies 150 spot on, but will it work for you...I don't know in this application. The zeners allow for ' a range of supply voltages' but won't regulate them, just cap them at 150 PtoP. Going back to eariler posts, it is uneven peaks that alter the gm not the source of the peaks themselves ( SS diodes can have 0.5 volt difference in the same batch when you take a reading and that maters to a Hickok).
Try those source leads I sent. If you give up, I might be interested in some parts...I say might be, not that I need them.
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Thanks. If you don't mind, I would like you to verify that the voltage at U-V and T-R is somewhere around 200-210VAC with both rectifier tubes in place, drawing heater current. And the voltage at U-VV and T-S somewhere around 95VAC.
After some thought I think it may be possible to do a "partial" replacement transformer. I might be able to use one with voltage a bit on the high side and use a "line adjust" pot in the primary just like Hickok does, and adjust for 150V at the plate of the DUT.
You bring up an interesting point about meter impedance. You need to match THEIR meter, not yours. So if they measured 170VAC with a 1,000 ohm/V meter on the 250V scale, they had 250k loading the circuit. If they used a meter that only had a 300V or 500V scale, then they loaded the circuit with 300k or 500k. We'll never know, hopefully the difference between 0.7mA and 0.3mA doesn't change the voltage much, but we don't know.
After some thought I think it may be possible to do a "partial" replacement transformer. I might be able to use one with voltage a bit on the high side and use a "line adjust" pot in the primary just like Hickok does, and adjust for 150V at the plate of the DUT.
You bring up an interesting point about meter impedance. You need to match THEIR meter, not yours. So if they measured 170VAC with a 1,000 ohm/V meter on the 250V scale, they had 250k loading the circuit. If they used a meter that only had a 300V or 500V scale, then they loaded the circuit with 300k or 500k. We'll never know, hopefully the difference between 0.7mA and 0.3mA doesn't change the voltage much, but we don't know.
I'll get the numbers later today and send them, can't this morning.
A digital meter is a high impeadance type, you must load acording to the scale on your meter's end range setting. If i use 150k and I am on my 400 volt range, the reading is wrong...to high. This is a important point that Daniel Shoo brought up back in 2007 when he made the first 539b/c and 600series calibration manual. So to read 150 I need 400k loading to match my meters range setting. Below 60 or so volts it does not seem to matter if the loading is there or not.
If you can find two trannies and put them in series, you will have the center tap. The line voltage trimmer you mention may not work as you think. The line trimmer is, in effect, an extention of the transformer winding, adding or subtracting windings to get the correct AC line voltage. Some models have that trimmer used as in-line, some as a shunt across the last few windings. Try an off the shelf transformer hooked up to your 752 line trimmer and see if you can reduce the added tranny voltage before you drop $20 or $30 on a reostat.
A digital meter is a high impeadance type, you must load acording to the scale on your meter's end range setting. If i use 150k and I am on my 400 volt range, the reading is wrong...to high. This is a important point that Daniel Shoo brought up back in 2007 when he made the first 539b/c and 600series calibration manual. So to read 150 I need 400k loading to match my meters range setting. Below 60 or so volts it does not seem to matter if the loading is there or not.
If you can find two trannies and put them in series, you will have the center tap. The line voltage trimmer you mention may not work as you think. The line trimmer is, in effect, an extention of the transformer winding, adding or subtracting windings to get the correct AC line voltage. Some models have that trimmer used as in-line, some as a shunt across the last few windings. Try an off the shelf transformer hooked up to your 752 line trimmer and see if you can reduce the added tranny voltage before you drop $20 or $30 on a reostat.
here you go:
15 minutes warm up on constantvolt, meter line center, gm pushed & confirm 150.2 DC plate on Fluke 87 III loaded.
Transformer AC terminals reads (loading not necessary, will read the same):
u-v=159.3
t-r=157.9
t-tt=70.8
u-vv=70.7
t-s=18.22
As a last thought, if the tubes requiring 'low'plate' are not ones you need to test/use, conscientrate on the 160/170 volt goal and forget low plate. If you find a tranny that works, remember you still need to reference the voltage back to the cathode '0' .
15 minutes warm up on constantvolt, meter line center, gm pushed & confirm 150.2 DC plate on Fluke 87 III loaded.
Transformer AC terminals reads (loading not necessary, will read the same):
u-v=159.3
t-r=157.9
t-tt=70.8
u-vv=70.7
t-s=18.22
As a last thought, if the tubes requiring 'low'plate' are not ones you need to test/use, conscientrate on the 160/170 volt goal and forget low plate. If you find a tranny that works, remember you still need to reference the voltage back to the cathode '0' .
Hickok's are sensitive to transformer winding mismatch/rectifier tube mismatch which leads to errors in GM. It is unlikely that the 50ohm bridge balance pot would be able to adjust for the transformer differences if you do not have both halves of the HV secondary windings closely matched. So one alternative to consider is having a high voltage transformer wound with the appropriate taps for both secondary sides. I would still be concerned about the longevity of the stock transformer. The Hickok 580 is notorious for this problem between the different voltage tap windings which lead to significant errors in GM unless you rebalanced (0) the meter with different tubes and at the different voltages. I tried different configurations in the plate rectification/balance circuit, and the standard 50 ohm pot did not have enough range to compensate for variations in the different windings at higher voltages. The 580 has a separate plate back balance pot to compensate for this, which should be mounted on the tester's face. Antique Radio Forums • View topic - Hickok 580 Tube Testor
In the Hickok 539 series the maximum diode mismatch in forward voltage that I was able to compensate with the balance pot for was <0.4V in Vf of diodes. This was using matched high voltage (HV05-08 or 12) diodes to emulate the forward drop of the 83 tube. I also match the standard low voltage (1000V) solid state diodes/zeners for Vf under static and load conditions, so they can be matched to <20mv Vf at different operating points. The bridge balance pot is dead center when calibrated according to Daniel Shoo's document using an oscilloscope. Tubesound also has a nice little dissertation on calibration of the Hickok 6000 showing issues of mismatch. TubeSound Blog Archive Hickok 6000 calibration . As posted in the earlier link to ARF, I use two standard 3A 1000V diodes each back to back with 5W zeners (5.6V is what worked for me with 10 ohm 2W resistors) to give the desired voltage drop at 1000ohm/v followed in an X with two matched resisters. You can choose the resistors/wattage for the load you want to present to the filament winding. Using this SS configuration, there may be variations with some Hickok testers/tubes, but using a range of standard calibration tubes in the 539, the results have been much better then the innate accuracy (inaccuracy) of these tube testers. There are different variant SS substitutes out there, pick what works best for your situation if this is what you choose.
I might suggest seeing if you can have your transformer rewound. Gary Brown in Oronto Maine was previously mentioned as rewinding transformers for Hickock Tube testers as well as many other old Radio, and Amateur gear. He probably can give you guidance on what options might work best for your situation. Hollowstate might also look at seeing if the screen transformer can be rewound, as the 580 is a nice tube tester once you iron out some of it's fobbles. Hope you have a good desoldering iron.
Gary Brown's TRS web site info:
Transformer Rewinding Service
Contact information:
Contact Us
or
Phone: 1-207-942-5745
Between 4:00 PM and 7:00 PM, EST
(Email:xfrmrs@roadrunner.com)
Reviews of his work:
WZ1M - Transformer Rewinding Service Product Reviews
If the transformer can be rewound, or you can get a suitable HV transformer wound, it would keep the old girl running. The rewound transformer should last a lifetime.
In the Hickok 539 series the maximum diode mismatch in forward voltage that I was able to compensate with the balance pot for was <0.4V in Vf of diodes. This was using matched high voltage (HV05-08 or 12) diodes to emulate the forward drop of the 83 tube. I also match the standard low voltage (1000V) solid state diodes/zeners for Vf under static and load conditions, so they can be matched to <20mv Vf at different operating points. The bridge balance pot is dead center when calibrated according to Daniel Shoo's document using an oscilloscope. Tubesound also has a nice little dissertation on calibration of the Hickok 6000 showing issues of mismatch. TubeSound Blog Archive Hickok 6000 calibration . As posted in the earlier link to ARF, I use two standard 3A 1000V diodes each back to back with 5W zeners (5.6V is what worked for me with 10 ohm 2W resistors) to give the desired voltage drop at 1000ohm/v followed in an X with two matched resisters. You can choose the resistors/wattage for the load you want to present to the filament winding. Using this SS configuration, there may be variations with some Hickok testers/tubes, but using a range of standard calibration tubes in the 539, the results have been much better then the innate accuracy (inaccuracy) of these tube testers. There are different variant SS substitutes out there, pick what works best for your situation if this is what you choose.
I might suggest seeing if you can have your transformer rewound. Gary Brown in Oronto Maine was previously mentioned as rewinding transformers for Hickock Tube testers as well as many other old Radio, and Amateur gear. He probably can give you guidance on what options might work best for your situation. Hollowstate might also look at seeing if the screen transformer can be rewound, as the 580 is a nice tube tester once you iron out some of it's fobbles. Hope you have a good desoldering iron.
Gary Brown's TRS web site info:
Transformer Rewinding Service
Contact information:
Contact Us
or
Phone: 1-207-942-5745
Between 4:00 PM and 7:00 PM, EST
(Email:xfrmrs@roadrunner.com)
Reviews of his work:
WZ1M - Transformer Rewinding Service Product Reviews
If the transformer can be rewound, or you can get a suitable HV transformer wound, it would keep the old girl running. The rewound transformer should last a lifetime.
Thanks Glass. Apparently the voltages shown on the schematic are quite accurate.
MKSJ, thanks for the link. He does indeed list rewinding this transformer, $365. I think I'll pass. By the time I pay for shipping and the time it takes me to uninstall and reinstall it, I'm way over the value of a working 752.
MKSJ, thanks for the link. He does indeed list rewinding this transformer, $365. I think I'll pass. By the time I pay for shipping and the time it takes me to uninstall and reinstall it, I'm way over the value of a working 752.
You are correct, the loading of the meter Hickok used must be matched in your test setup. The TV7 manual specifies a TS-352/U multimeter. This meter has input jacks for 2.5, 10, 50, 250, 500, and 1000 volts. There are two columns of these jacks, one at 1000 Ohms/volt and the other at 20000 Ohms/volt.
I have a two page calibration procedure for the Hickok 533 tube tester. It specifies a multimeter with a 250 volt scale to measure the plate supply voltage. At 1000 Ohms/volt the reading should be 150 +/-2V and at 20000 Ohms/volt it is specified at 190V +/-2V. These settings match exactly the capability of the TS-352/U.
Based on this information, the tester plate supply has an open circuit voltage of 192.7 with a resistance of 71.1 Kohms. The table below shows the meter reading for several load resistance values, assuming an infinite input impedance meter.
250 Kohms 150.0 volts
400 Kohms 163.6 volts
5.0 Mohms 190.0 volts
10 Mohms 191.3 volts
ok my last idea.
Maybe a common 120 to 240 step up could work. I have seen them with 100 to 130 in and 200 to 240 out, cheap maybe 20 bucks. If a reostat could also be used, it just might supply the right voltage. You bad winding is the less critical one. If you can get to 5%, Hickok would be happy.
I was also thinking that a B&K 500 uses an 83 for the plates, but am not sure if it has two windings. You can find that one on eBay for $50.00.
Maybe a common 120 to 240 step up could work. I have seen them with 100 to 130 in and 200 to 240 out, cheap maybe 20 bucks. If a reostat could also be used, it just might supply the right voltage. You bad winding is the less critical one. If you can get to 5%, Hickok would be happy.
I was also thinking that a B&K 500 uses an 83 for the plates, but am not sure if it has two windings. You can find that one on eBay for $50.00.
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