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Schiit Lyr Tube Rollers
Jul 23, 2018 at 1:07 AM Post #18,557 of 23,494
TK16 said:
Longer warm up 5 minutes, still takes way longer than 5-10 seconds per triode but is faster than before, lot of my tubes tested for GM seem weaker than their advertised specs. Don`t know what 1000 hours do to the GM readings vs new though.
Edit: seems the longer the tester is on the shorter the time for GM readings.
Click to expand...
Depends on the tube type and the tester they were measured on regarding the advertised reading. I found that the Hickok 539c and 752 were the same for 5670/6n3p etc, and also ECC88/6dj8, but differed for 6922/E88CC - The 752 readings were between 500 to 1000 umho lower on the 752. This could well be related to incorrect settings on the roll chart. There are a few errors on the charts found by various experts in the past.

On the 539c you set the bias to -3v for 6dj8, and only -2.6v for 6922. On the 752, you set the bias knob to 20 for 6dj8, and 21 for 6922 which is the other way around. I suspect this should be 19, not 21.

Someone on another forum had their 752 calibrated by the late Chris Headt (Hickok engineer). Here's the original post quote:

"RE: 12ax7: I own a 752. It was restored by Chris Haedt in December of 2004. One of his notes on the sheet he sent me was, this is an issue with 752 testers. He told me the bias should be set to 13 not 14 as stated in the tube data chart by Hickok. He also told me that 6550 tubes should have their bias set to 31 not 13 as stated in the tube data chart. I hope this helps with some of the questions."

I wouldn't be surprised if it was the same for 6922. If you set it to 19 for those, you get the same readings as the 539c, so then all 5670/6n3p, 6dj8/ECC88, and 6922/E88CC all match across both testers.

I also found that the other Hickoks such as the 600, 800, and 6000s give around the same readings within reason - there is more variance on them - here's an excerpt from a Hickok engineer:

"If you want greater accuracy get a tester that has fixed Gm ranges (switch selectable) like 3000, 6000, and 15000. Not units like the Hickok 600 series, 800 series, or 6000 series, which use a variable control to set the ranges. The accuracy and repeatability of the test results are not as good on these testers. These testers have an overall accuracy of +/- 15% This relates to a 30% variance range from high to low. So a tube which has a true Gm of say 6000 could read a low of 5100 Gm to a high 6900 Gm (range of 1800 Gm), and would be within the accuracy range of the testers calibration standards.

These testers are good for vintage radios/TV and service work. Situations which they were designed for like finding bad or weak tubes, but not for evaluating tubes for accuracy, or for purchasing expensive tubes or for selling tubes! If you need or want an accurate test result with repeatability these are not the models for you!"

As far as I can find, the 752 and 539c have a 5-10% accuracy, so that might explain the variance in results. Add the variance in how well calibrated a seller's tester is, as well as differences across other brands, and it should explain any differences you might find.
 
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Jul 23, 2018 at 4:43 AM Post #18,558 of 23,494
Think I am going to give bias @19 a whirl, thanks for that.
Was rather disappointed in the 6922`s I tested GM wise.
Hey AC on the roll chart do I choose ECC83 6.3v to test 6CC41? Got a pair being delivered today. Dont think I saw 12AX7 in the chart. Thanks.
 
Last edited:
Jul 23, 2018 at 7:21 PM Post #18,560 of 23,494
AuditoryCanvas said:
Depends on the tube type and the tester they were measured on regarding the advertised reading. I found that the Hickok 539c and 752 were the same for 5670/6n3p etc, and also ECC88/6dj8, but differed for 6922/E88CC - The 752 readings were between 500 to 1000 umho lower on the 752. This could well be related to incorrect settings on the roll chart. There are a few errors on the charts found by various experts in the past.

On the 539c you set the bias to -3v for 6dj8, and only -2.6v for 6922. On the 752, you set the bias knob to 20 for 6dj8, and 21 for 6922 which is the other way around. I suspect this should be 19, not 21.

Someone on another forum had their 752 calibrated by the late Chris Headt (Hickok engineer). Here's the original post quote:

"RE: 12ax7: I own a 752. It was restored by Chris Haedt in December of 2004. One of his notes on the sheet he sent me was, this is an issue with 752 testers. He told me the bias should be set to 13 not 14 as stated in the tube data chart by Hickok. He also told me that 6550 tubes should have their bias set to 31 not 13 as stated in the tube data chart. I hope this helps with some of the questions."

I wouldn't be surprised if it was the same for 6922. If you set it to 19 for those, you get the same readings as the 539c, so then all 5670/6n3p, 6dj8/ECC88, and 6922/E88CC all match across both testers.

I also found that the other Hickoks such as the 600, 800, and 6000s give around the same readings within reason - there is more variance on them - here's an excerpt from a Hickok engineer:

"If you want greater accuracy get a tester that has fixed Gm ranges (switch selectable) like 3000, 6000, and 15000. Not units like the Hickok 600 series, 800 series, or 6000 series, which use a variable control to set the ranges. The accuracy and repeatability of the test results are not as good on these testers. These testers have an overall accuracy of +/- 15% This relates to a 30% variance range from high to low. So a tube which has a true Gm of say 6000 could read a low of 5100 Gm to a high 6900 Gm (range of 1800 Gm), and would be within the accuracy range of the testers calibration standards.

These testers are good for vintage radios/TV and service work. Situations which they were designed for like finding bad or weak tubes, but not for evaluating tubes for accuracy, or for purchasing expensive tubes or for selling tubes! If you need or want an accurate test result with repeatability these are not the models for you!"

As far as I can find, the 752 and 539c have a 5-10% accuracy, so that might explain the variance in results. Add the variance in how well calibrated a seller's tester is, as well as differences across other brands, and it should explain any differences you might find.
Click to expand...

Great info. Thanks AC.
 
Jul 24, 2018 at 6:14 AM Post #18,562 of 23,494
billerb1 said:
First impression of AC's Tesla ECC88's...me likey. A lot. Ballsy. If these aren't even burned in at all yet, I'm scared.
Click to expand...
They all succumb in the end. Welcome to the dark side.
 
Jul 24, 2018 at 9:17 AM Post #18,563 of 23,494
Jul 25, 2018 at 2:40 AM Post #18,566 of 23,494
I have a pair of late 50s pair and mid 60s pair of Foton 6ns7 equivalents I received in a batch of other tubes yesterday if anyone is after any for cheap? Still have to test them, but give me a PM if you're interested.

I also have about 10 pairs of these too: 1960s Novosibirsk 6H8C (6SN7 equiv.) NOS m/pairs - $15.
 
Jul 25, 2018 at 5:39 PM Post #18,567 of 23,494
 
Last edited:
Jul 25, 2018 at 6:07 PM Post #18,568 of 23,494
 
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