Hi,
got a fairly nice tester that had some previous work on it, and for a reason there is an alone loose wite going nowhere?
Of course it does have to be related to the Short selector, but where it should be connected?
From the facing plate this wire is on the 4th deck of the shorts selector.
It is white/black stripe.
From ohmeter measurement it connects on position 3-4-5 to the same 4th deck going to a red wire that is connected to R21 , a 47 ohms resistor on the screen selector.
A bit of search yes helping with the schematics, but still parts are unidentified inside the Hickok 750.
either this wire was cut? Or it is going to a nearby selector, switch ot post, it is actually about 6 inches long, so it cannot acroos the whole tester??
See the pictures...
Otherwise the 49 small bias fuse light bulb is burned. Trying to find some replacement.
I could do line test fine, so meter circuit id OK.
But cannot test a 6L6 for Gm or emission, no needle mouvement...
got a fairly nice tester that had some previous work on it, and for a reason there is an alone loose wite going nowhere?
Of course it does have to be related to the Short selector, but where it should be connected?
From the facing plate this wire is on the 4th deck of the shorts selector.
It is white/black stripe.
From ohmeter measurement it connects on position 3-4-5 to the same 4th deck going to a red wire that is connected to R21 , a 47 ohms resistor on the screen selector.
A bit of search yes helping with the schematics, but still parts are unidentified inside the Hickok 750.
either this wire was cut? Or it is going to a nearby selector, switch ot post, it is actually about 6 inches long, so it cannot acroos the whole tester??
See the pictures...
Otherwise the 49 small bias fuse light bulb is burned. Trying to find some replacement.
I could do line test fine, so meter circuit id OK.
But cannot test a 6L6 for Gm or emission, no needle mouvement...
Attachments
It seems there are various versions of the Hickok 750 so if its not showing on the schematic it might be a different version.
There are different schematics for each version.
This is 903W schematic ( there are others ).
What puzzles me is that if Hickock go to the trouble of coloring each wire differently then there must be a color code somewhere ------- probably residing in the hands of the Hickock local agent,s shop ?
Tube Tester Manuals – Vintage Tube Electronics
Scroll down for it.
On a USA "Hickock experts " website he does not recommend buying a 750 .
I post this not for your information --Stereohifi but for any DIY Audio poster,s information in case they think of buying one --other models of Hickock get a "good " write up .
He wont go into the reasons why .
There are different schematics for each version.
This is 903W schematic ( there are others ).
What puzzles me is that if Hickock go to the trouble of coloring each wire differently then there must be a color code somewhere ------- probably residing in the hands of the Hickock local agent,s shop ?
Tube Tester Manuals – Vintage Tube Electronics
Scroll down for it.
On a USA "Hickock experts " website he does not recommend buying a 750 .
I post this not for your information --Stereohifi but for any DIY Audio poster,s information in case they think of buying one --other models of Hickock get a "good " write up .
He wont go into the reasons why .
Last edited:
Hickok 750 with 903W schematics version.
Yes thanks, i've found this 903W version a couple of days ago, but could not work on my 750 since.
And for un-recomendation of the Hickok 750, it's the first time i saw this.
Maybe due to this uncanny schematics and color codes of wiring?
But it's not my first Hickok i work on.
I just want to compare information with a similar version from another 750 tester.
And i know there are some.
Jacmusic.com in Germany is one of them.
Otherwise P4 circuit is not showing emission or Gm on the meter when tube is inserted like a 6L6.
May be this issur have more importance then the loose wire on Short selector??
P7 line test works and test fine for the 93vac on primary of the PT of the 750.
Yes thanks, i've found this 903W version a couple of days ago, but could not work on my 750 since.
And for un-recomendation of the Hickok 750, it's the first time i saw this.
Maybe due to this uncanny schematics and color codes of wiring?
But it's not my first Hickok i work on.
I just want to compare information with a similar version from another 750 tester.
And i know there are some.
Jacmusic.com in Germany is one of them.
Otherwise P4 circuit is not showing emission or Gm on the meter when tube is inserted like a 6L6.
May be this issur have more importance then the loose wire on Short selector??
P7 line test works and test fine for the 93vac on primary of the PT of the 750.
Keep in touch Stereohifi as to how you are progressing old tube testers interest me although I have to admit all the ones I have repaired/renovated are British models but I do know about the Hickok range .
It took several months work to get my AVO VCM MK4 up to scratch , repairing tube testers isn't a "5 minute job ".
It took several months work to get my AVO VCM MK4 up to scratch , repairing tube testers isn't a "5 minute job ".
Hi
Antique Radios - The Collector's Resource -forum is very useful for troubleshooting Hickok Tube testers. please post your problem and see the response. Also you can get the Hickok calibration document ( google it). Once you are able to calibrate your tester , it will work. I have done such work on more than a Dozen Hickok testers and most probably some safety resistors need to be replaced if they have burnt out - most likely in your tester. you can also verify how much your tester is following the schematics ( Hickok changed few things and not much in these testers!) They are all almost same - 750 version is one of the latest Hickok but not coveted as much as their 539 series
i have taken six months plus to troubleshoot and then calibrate a single tube tester - worth the trouble as you can sell them for decent change if you do
kannan
Antique Radios - The Collector's Resource -forum is very useful for troubleshooting Hickok Tube testers. please post your problem and see the response. Also you can get the Hickok calibration document ( google it). Once you are able to calibrate your tester , it will work. I have done such work on more than a Dozen Hickok testers and most probably some safety resistors need to be replaced if they have burnt out - most likely in your tester. you can also verify how much your tester is following the schematics ( Hickok changed few things and not much in these testers!) They are all almost same - 750 version is one of the latest Hickok but not coveted as much as their 539 series
i have taken six months plus to troubleshoot and then calibrate a single tube tester - worth the trouble as you can sell them for decent change if you do
kannan
Also check the Voltages from two rectifier Tubes ( Schematics is Typical Hickok ) and possibly one of these may not be working. 5YGT3 and 83 Tubes are available and do not use Solid state Rectifiers as they tend to make calibration difficult. 83 tube is a mercury rectifier and handle it carefully. Your Tester looks very clean and i do not suspect any wire cut or going to wrong socket- nobody touches these anyway. good luck trouble shooting this tester
Hickok 750 tubes rectifiers mismatched!! Now OK!!Working 750.
Thanks for the answers, with now a real more up to date schematics version 903W I could work and follow wiring and trying to make sense of what's in there.
The seller told me he was not a tech, and all of a sudden tester stopped working!??
Yeah, i think he must have worked with the wrong schematics, and did really cannibalised the tester to say the least...
It did have solidstate rectifier unsteab of the 83 tube, that's ok but i did removed that in first place.
BUT wiring of the 5Y3 rectifier was wrong, and wiring for the 83 tube R26 , balance pot for the rectifier was wrong too.
So i never suspected this,
I was looking at every other components, but readings were not making sence at ALL.
So i did reverse engineering to find correct pinout that goes to each rectifiers and of course use now an 83 tube.
Now i can test Gm on Em, it might need some fine touch to have close to my Hickok 15750-L1 that i rely on, ,plus a calibration metal RCA 6L6 tube from Brent Jesse Recording & Supply .
So again thanks for the moral support and i just need to find a number 49 lamp here,bias fuse, that doesn't seem to be sold in Canada anymore??
Thanks for the answers, with now a real more up to date schematics version 903W I could work and follow wiring and trying to make sense of what's in there.
The seller told me he was not a tech, and all of a sudden tester stopped working!??
Yeah, i think he must have worked with the wrong schematics, and did really cannibalised the tester to say the least...
It did have solidstate rectifier unsteab of the 83 tube, that's ok but i did removed that in first place.
BUT wiring of the 5Y3 rectifier was wrong, and wiring for the 83 tube R26 , balance pot for the rectifier was wrong too.
So i never suspected this,
I was looking at every other components, but readings were not making sence at ALL.
So i did reverse engineering to find correct pinout that goes to each rectifiers and of course use now an 83 tube.
Now i can test Gm on Em, it might need some fine touch to have close to my Hickok 15750-L1 that i rely on, ,plus a calibration metal RCA 6L6 tube from Brent Jesse Recording & Supply .
So again thanks for the moral support and i just need to find a number 49 lamp here,bias fuse, that doesn't seem to be sold in Canada anymore??
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