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 Post subject: Hickok Model 1234B Cardmatic Tube Tester
PostPosted: May Sun 23, 2010 9:31 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 296
Location: Lethbridge, AB CA
Hi all:

My Hickok tester is calibrated and works 100% on dozens of tubes of different makes I have tested, but, --- the 12ax7a tubes test weird.

Here's my problem. In my Hickok tube tester I find that
most different makes of tubes, viz. JJ, Sylvania, GE, Chinese, etc. generally test low to weak, even in the red sometimes, however, if I take an RCA 12ax7a, it will top the scale. I also see in the AES Catalogue that it is the priciest. Is there actually a difference I'm not aware of? Musicians have phoned and asked me specifically for RCA 12ax7a's, as if no other make will do.

All the other tube makes the tubes test OK in my Jackson tester,
as does the RCA tube, but it also tests the highest here also..

Has anyone else experienced this problem with 12ax7a tubes in the Hickok testers and why would this be?

P.S. -- I'm talking about BRAND NEW tubes I'm testing.

Thank your for any info on this matter.

Puzzled. -- Ed.

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 Post subject:
PostPosted: May Mon 24, 2010 1:08 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 27070
Location: Pocasset, Cape Cod, MA
There's no guarantee that RCA actually made the tubes branded RCA, so I can't explain why they would test any differently. You might check your heater voltage at the socket.


Last edited by Alan Douglas on May Mon 24, 2010 1:14 am, edited 2 times in total.

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 Post subject:
PostPosted: May Mon 24, 2010 1:09 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 27070
Location: Pocasset, Cape Cod, MA
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 Post subject:
PostPosted: May Mon 24, 2010 2:32 am 
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Joined: Mar Mon 29, 2010 10:29 pm
Posts: 102
Location: CANADA
Are you referring to a single RCA...or do 3-4 RCA's all test high? I've had a single tube test off scale on my Jackson 648-1T...it could be a tube with gas?


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 Post subject:
PostPosted: May Mon 24, 2010 3:05 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 296
Location: Lethbridge, AB CA
WildBillHickok wrote:
Are you referring to a single RCA...or do 3-4 RCA's all test high? I've had a single tube test off scale on my Jackson 648-1T...it could be a tube with gas?

****************************************************
I only had one RCA tube unfortunately, but it doesn't test gassy on either tester. P.S. - My Jackson tester is the same model you have, WBH. It doesn't however, quite answer my question why the Hickok is so stingy, and the Jackson much more generous on all makes of 12ax7a's.

The 2 similar, but lower gain tubes, viz. 12at7a, 12au7a test just fine
in the Hickok. It's got me "stumped" -- because the tubes are all good.

I also have a STARK emission tester, but all tubes check OK on it, but it's just that, a cheap EMISSION Tester. -- Ed.

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 Post subject:
PostPosted: May Mon 24, 2010 8:09 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 106
Location: Monte Vista, CO. USA
I have a copy of a document that was published by Hickok dated April 18, 1972 that states the following:

Quote:

12AX7 MEASUREMENTS ON KS CARDMATIC TUBE TESTERS

The problems that have arisen are due to the fact that the manufacturers are no longer holding their tubes to published specs. In the published specs two sets of conditions are resultant transconductance values are listed:

1. 250V Eb -2V bias, 1600 umhos transconductance
2. 100V Eb -1V bias, 1250 umhos transconductance

For various reasons we have selected Condition #2 as a test condition to be used on the cardmatics. Now, it seems, most American manufacturers are only holding the transconductance at Condition #1; and as a matter of fact when measured under Condition #2 with lab standard equipment, tubes of recent manufacture (several different vendors) were found to have transconductance values of typically less than 50% of bogey. Since our cardmatic tube testers are set to reject tubes at 63% of bogey, these recent tubes will read "reject" on the cardmatic testers. Discussions with several vendors and the EIA office in Washington have not resolved this difficulty.

Unquote.

Because of this, I have included this document with all the Computerized Cardmatics I have sold.

-Phil


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 Post subject:
PostPosted: May Mon 24, 2010 3:09 pm 
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Joined: Mar Mon 29, 2010 10:29 pm
Posts: 102
Location: CANADA
The reject point for the 12AX7 is 950 umhos on my Hickok RD 1575. This cannot be compared directly to the 1234B values, but it is very low. The 12AU7 value is 1560; the 12AT7 is 2600 and the 5751 is even lower at 900.


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 Post subject:
PostPosted: May Mon 24, 2010 5:40 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 296
Location: Lethbridge, AB CA
PhilF wrote:
I have a copy of a document that was published by Hickok dated April 18, 1972 that states the following:

Quote:

12AX7 MEASUREMENTS ON KS CARDMATIC TUBE TESTERS

The problems that have arisen are due to the fact that the manufacturers are no longer holding their tubes to published specs. In the published specs two sets of conditions are resultant transconductance values are listed:

1. 250V Eb -2V bias, 1600 umhos transconductance
2. 100V Eb -1V bias, 1250 umhos transconductance

For various reasons we have selected Condition #2 as a test condition to be used on the cardmatics. Now, it seems, most American manufacturers are only holding the transconductance at Condition #1; and as a matter of fact when measured under Condition #2 with lab standard equipment, tubes of recent manufacture (several different vendors) were found to have transconductance values of typically less than 50% of bogey. Since our cardmatic tube testers are set to reject tubes at 63% of bogey, these recent tubes will read "reject" on the cardmatic testers. Discussions with several vendors and the EIA office in Washington have not resolved this difficulty.

Unquote.

Because of this, I have included this document with all the Computerized Cardmatics I have sold. -Phil

*************************************************
Hi Phil & WBH: -- Well now, isn't that interesting. I never knew any of this and am glad you have shed some light on this mystery. Thank you both for explaining the problem and now I can quit worrying about the test results. -- Again, I'm most grateful to you all for your help. --- Ed.

_________________
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