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 Post subject: really, I mean REALLY newbie questions on tubes
PostPosted: Sep Thu 24, 2020 12:35 am 
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Joined: Sep Thu 10, 2020 1:54 pm
Posts: 56
Location: Kearneysville, WV
So I have a newly acquired Precision Instruments 612 tester arrive today. Like most people I was eager to give it a try.

I first opened it up to make sure the underside didn't look like it had been butchered but it looks nicely original...although the one cpaacitor which I thought should be a 0.1 mfd 600V capacitor is in fact a 0.1mfd 400v unit. I assume someone wrongly replaced the original with this one.

Anyway, I digress...my question relates to testing tubes.

I pulled a couple of tubes from radios and am struggling to find them on the roll around viewer which lists the various tubes.

For example:

35Z5
41 - two of these in my 41-280

Does the 612 only test certain tubes and the reason I don't see these listed is that they aren't applicable OR that they are known by some other number that is listed in the scroll paper in the view window?

Next, I have a 7B7 I wanted to test. I couldn't find it on the roll but did locate it in a supplemental tube data booklet I have.

It is listed as 1 7 11 1 with 2-3-4-6 under F and Fil Cont 8.

So, I have set the following configuration.

A set to 1
B set to 7
C set to 11

Lever 1 moved to Fil Ret - D

Levers 2, 3,4 and 6 moved to F - test and watch the neon light when moving each one, it flickers on/off for each one. For lever 8 it remains on, is this the 'filament cont 8' I referred to above? i.e. you should get a flick on then off for 2, 3, 4 and 6 but it should remain on for 8?

I hit the Read Meter button and the needle falls to the far left of the meter...like a zero reading.

Now, allowing 3-4 minutes for the laughter to subside, what am I doing wrong here or is the tube really THAT bad.

I hope I have at least managed to provide some entertainment for the evening.

Paul

An addendum...

I see 2, 3, 4, 6 under F-test and figure that moving ;ever


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 Post subject: Re: really, I mean REALLY newbie questions on tubes
PostPosted: Sep Thu 24, 2020 2:38 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 16732
Location: Albuquerque, NM 87123
I think you should get the correct manual for your tester; Glendale Manuals sells the right ones on eBay. They are about $11 and $15 with test data. I don't know of a free source.


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 Post subject: Re: really, I mean REALLY newbie questions on tubes
PostPosted: Sep Thu 24, 2020 2:47 am 
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Joined: Jul Mon 06, 2015 11:25 am
Posts: 295
See if anything here will help: http://oldradios.50webs.com/precision/


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 Post subject: Re: really, I mean REALLY newbie questions on tubes
PostPosted: Sep Thu 24, 2020 10:59 am 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 8249
Location: Sunbury, Ohio 43074
This should take you directly to the roll chart in PDF form: http://oldradios.50webs.com/precision/600/600_series.pdf

Both of your tubes listed in your post are there. I'm not sure what the date of this chart is, but it seems pretty complete from my quick read of it.

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https://www.bbtvtestequipment.com


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 Post subject: Re: really, I mean REALLY newbie questions on tubes
PostPosted: Sep Thu 24, 2020 1:23 pm 
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Joined: Sep Thu 10, 2020 1:54 pm
Posts: 56
Location: Kearneysville, WV
Many thanks for the link to the spreadsheet above. I think that even just 12 hours later I am learning a lot more about how this thing works. I found a couple of videos on YT which show tubes being tested and based upon what I see, I was indeed (surprisingly) testing the tubes correctly.

The 'missing tubes' from the list it seems were down to my looking for 41 to be listed with the other 4's whereas I now see why the list is ordered like it is. The spreadsheet makes it a lot more obvious.

I am still getting identical results for each of the 4-5 tubes I have so far tried to test. The needle falls quickly to the far left indicating a total failure. Now, it is possible that each of them is so badly degraded that they provide that reading but I am suspicious that it might be something else, either wrong in the way I am testing or wrong with the meter itself.

When I test my two 41s I do get a short light remain lit for 6 (Fil Cont. 6) with one of them but not the other. So, it seems that at a minimum I will need a new 41. I will purchase that and then do a full test to see if the new 41 too provides a movement to the far left with the meter needle. If so I will assume there is an issue with the instrument itself.


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 Post subject: Re: really, I mean REALLY newbie questions on tubes
PostPosted: Sep Thu 24, 2020 1:29 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 8249
Location: Sunbury, Ohio 43074
The meter pegging to the left is indicating something wrong with the tester, or something wrong with the test procedures. Nothing wrong with the tubes will do that, particularly since it's doing it with all of them.

As to WHAT might be wrong, that could be a long process to figure out, but it's generally oxidized switches on these type of things, followed by a close second of "someone fixing it incorrectly" in the past.

Could be component failure as well, but it doesn't sound like it. Do you have experience in fixing electronic equipment from the stone age ? Just asking so we can give advice accordingly.

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https://www.bbtvtestequipment.com


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 Post subject: Re: really, I mean REALLY newbie questions on tubes
PostPosted: Sep Thu 24, 2020 1:49 pm 
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Joined: Sep Thu 10, 2020 1:54 pm
Posts: 56
Location: Kearneysville, WV
Barry H Bennett wrote:
The meter pegging to the left is indicating something wrong with the tester, or something wrong with the test procedures. Nothing wrong with the tubes will do that, particularly since it's doing it with all of them.

As to WHAT might be wrong, that could be a long process to figure out, but it's generally oxidized switches on these type of things, followed by a close second of "someone fixing it incorrectly" in the past.

Could be component failure as well, but it doesn't sound like it. Do you have experience in fixing electronic equipment from the stone age ? Just asking so we can give advice accordingly.


Barry

I used to work as a technician in BT (British Telecom) in the UK for 20 years back in the 80s and 90s. I worked on the old Strowger telephone exchanges playing with old relays and jointing larger (15,000 wire) cables etc. So to answer your question...I don't have direct experience in playing with this stuff but I am 'fairly' able and willing to dive into a circuit diagram and refresh LONG dormant knowledge. I assume a decent soldering iron, meter and a diagram will be the bare necessities?

I do agree that it is unlikely that 4-5 tubes would give an identical pegged to the left reading and figured it was likely an issue with the instrument itself. But, where to start...?

Paul


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 Post subject: Re: really, I mean REALLY newbie questions on tubes
PostPosted: Sep Thu 24, 2020 4:24 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 2563
Location: Dallas, TX
If you follow the link that Hondo posted there is a page about 612 calibration. It begins with some suggestions about replacing parts (like the capacitor) and cleaning switches, etc.
By the time you would get through calibration the tester should be for the most part working. You might still have problems with individual sockets.

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Tim
It's not the Destination, It's the Journey.


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 Post subject: Re: really, I mean REALLY newbie questions on tubes
PostPosted: Sep Thu 24, 2020 6:00 pm 
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Joined: Sep Thu 10, 2020 1:54 pm
Posts: 56
Location: Kearneysville, WV
Notimetolooz wrote:
If you follow the link that Hondo posted there is a page about 612 calibration. It begins with some suggestions about replacing parts (like the capacitor) and cleaning switches, etc.
By the time you would get through calibration the tester should be for the most part working. You might still have problems with individual sockets.


Thanks Tim, I will check back into that link now. I did see a reference to automatically replacing the capacitor which I will do. I will also try to check the various resistors and clean the switches.


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 Post subject: Re: really, I mean REALLY newbie questions on tubes
PostPosted: Sep Thu 24, 2020 10:52 pm 
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Joined: Dec Tue 23, 2014 6:51 pm
Posts: 1908
Location: N. Palm Bch, Fl.
I got my 612 a couple of years ago which was in fair shape and didn't work. The documentation they gave you along with the supplemental chart is all you need. It took me a few days to go over everything, but it pays off. The 7 and 9 pin tube sockets are my biggest problem. I got spray gun cleaning brushes from HF and the small one with contact cleaner helps. I have found when the meter swings left, it's bad tube contact, operator error, or just a dead tube.
It's basically a simple box and a damb good tube tester for what I need.

Freeman


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 Post subject: Re: really, I mean REALLY newbie questions on tubes
PostPosted: Sep Fri 25, 2020 1:08 pm 
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Joined: Sep Thu 10, 2020 1:54 pm
Posts: 56
Location: Kearneysville, WV
Freeman wrote:
I got my 612 a couple of years ago which was in fair shape and didn't work. The documentation they gave you along with the supplemental chart is all you need. It took me a few days to go over everything, but it pays off. The 7 and 9 pin tube sockets are my biggest problem. I got spray gun cleaning brushes from HF and the small one with contact cleaner helps. I have found when the meter swings left, it's bad tube contact, operator error, or just a dead tube.
It's basically a simple box and a damb good tube tester for what I need.

Freeman


I have ordered replacement capacitor and resistors and will work my way through the beast on Monday/Tuesday when they arrive. I am already seeing resistor values that seem a little 'off' although I assume they used something that was within tolerance as opposed to a precise value. For example, the R6 which is indicated on the schematic as 20K is a 22K (10% tol). With this meaning the resistor could be 22K +-10% this means we could be seeing 24.2K on a specc'd 20K so I figure these circuits are fairly robust in not needing precise values.

It seems from the comments above that replacing old components and cleaning switches is the initial way to go so that is where I will start.

Paul


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