[Heathkit] Tube chart compatibility

Thu Jul 25 14:15:43 EDT 2013

But it's also a fun process to figure out what Heathkit was thinking and
doing as they progressed from model to model.

Gary H. Harmon, Jr. - K5JWK
6003 Archwood
San Antonio, TX 78239-1504
210.657.1549h / 210.884.6926c/t

"Retirement means every day is a Saturday except Sunday"
http://www.grissomroadcoc.org

-----Original Message-----
From: heathkit-bounces at mailman.qth.net
[mailto:heathkit-bounces at mailman.qth.net] On Behalf Of manualman at juno.com
Sent: Thursday, July 25, 2013 1:07 PM
To: Heathkit at mailman.qth.net
Subject: Re: [Heathkit] Tube chart compatibility

Obviously, it's just plain simpler to get the correct chart for your tube
tester and forgo the head scratching and thought process.

Pete, wa2cwa
http://www.manualman.com

On Thu, 25 Jul 2013 06:51:34 -0700 Chuck Penson <wa7zze at gmail.com>
writes:
> If this is old news, I apologize in advance.
> 
> There has been some discussion recently about the compatibility of 
> tube chart data between and amongst the TC-1, TC-2 and TC-3, and the
> IT-21 ,
> IT-17, and IT-3117. As there was some difference of opinion, and since 
> I need to nail this down for my book, I thought I would dig into it a 
> little deeper.
> 
> Setting aside the TT-1(A), Heath's tube checkers fall into two groups. 
> The older group includes the TC-1, TC-2 and TC-3. The newer group 
> includes the IT-21, IT-17 and IT-3117.  Within each group the models 
> are essentially identical and chart data from one model will work on 
> the other models within the group. The primary difference between the 
> two groups is that the newer group (starting with the IT-21) has three 
> additional selector levers.
> The older group has 10 selectors (A-K, minus I) and the newer group 
> has 13 (A-N, minus I). Heath added these three new selectors to 
> accommodate a new crop of tubes that had been introduced since the 
> TC-1 was released in 1949.
> Obviously then, there will be tubes listed on the IT-21 et al that are 
> not testable on the TC-1 et al. So backward compatibility will be 
> limited.
> 
> What about forward compatibility? Will the settings on the TC-1, 2 and 
> 3 work on the IT-21 and newer models? To answer this question I 
> compared chart data for the two groups. Only two charts were required. 
> For the older group I used a chart dated 1-1-65 and labeled 
> specifically for use with the
> TC-1 and 2 (but which also applies to the TC-3) and for the newer 
> group a chart dated 1979 and specifically labeled for use with the 
> IT-21, 17 and
> 3117 (Both charts are available online as PDFs).
> 
> As I compared the charts I began to notice that the only differences 
> appeared to be related to the use of the "K" and "N" selector levers.
> In
> every case tubes on the older chart that required use of the "K" 
> lever were
> listed on the newer chart as using the "N" lever. A short list of such 
> tubes includes (but is not limited to) 12A7, 12B6, 12B8, 12C8, 12F5, 
> 12J7, 12K7, 12Q8 and  their counterparts using other filament 
> voltages.
> 
> A little research revealed that what all these tubes have in common is 
> a cap. A large random sample of other tubes not requiring the "K"
> lever found
> no capped tubes.  It is important to note that in all cases the other 
> settings (type, filament voltage, plate setting, up and down levers) 
> were identical between the older and newer charts.
> 
> This suggests that settings from charts in the older group will work 
> on testers in the newer group, and that tubes listed on charts in the 
> newer group that don't require the use of the L, M or N selector 
> levers should be fine when used on older testers.  It also suggests 
> that if the tube you are trying to check has a cap and you have an 
> older chart but a newer tester, all you need to do is use the "N" 
> selector where the "K" selector is specified.
> 
> One more thought: Forward chart compatibility makes perfect sense from  
> an economic perspective. Figuring out all the settings for all the 
> tubes must have required a huge investment of time and effort. And as 
> Einstein observed, TIME + EFFORT = MONEY. Once Heath had spent the 
> money to accumulate all the data for their first tube tester it would 
> not have made economic sense to change everything and then have to 
> figure it out all over again for some newer model. At Heath, money 
> ruled.
> 
> I only have an IT-21 so I am unable to do the tests required to prove 
> some of the compatibility questions, but the experiments would be easy 
> enough given the right sample of tubes. That said, my level of 
> confidence is high.
> 
> Hope this sheds some clarity on the subject.
> 
> Chuck Penson / WA7ZZE
> ______________________________________________________________
> Heathkit mailing list
> Home: http://mailman.qth.net/mailman/listinfo/heathkit
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Heathkit at mailman.qth.net
> 
> List Administrator: Duane Fischer, W8DBF
> ** For Assistance: dfischer at usol.com **
> 
> 
> This list hosted by: http://www.qsl.net Please help support this email 
> list: http://www.qsl.net/donate.html
> 

______________________________________________________________
Heathkit mailing list
Home: http://mailman.qth.net/mailman/listinfo/heathkit
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Heathkit at mailman.qth.net

List Administrator: Duane Fischer, W8DBF
** For Assistance: dfischer at usol.com **

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html