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 Post subject: 5, 6 to 7, 9 or Octal pin vacuum tube substitutes
PostPosted: Dec Mon 25, 2017 4:18 am 
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I've seen a 3AU6 used to replace a 57 with the use of an adapter in a Hammond Model A pre-amplifier. I know that the specs are slightly different for the two VTs, filament voltage, and other specs.

Also for instance a 5Z3 is the same as a 5U4 with the exception of the pin configuration.

Without completely scouring many tube manuals is there a pin out substitute for the 56, 57 or 2A3?

I was looking to possibly create an adapter(s) in order that I might check the emission of a 56. 57 or 2A3 on my Seco 107B which has no 4, 5 or 6 pin sockets.

My idea was that I might be able to test a 56, 57 or 2A3 to see if it has good emission or if it is time that it need to be replaced.

The other alternative is to save my pennies and have the meter movement repaired/replaced and the "zap hazard" leaky filament/B+ transformers of my Hickock 539B either rewound or replaced.

I do not see very many 56, 57 and 2A3s in an old tone cabinets however it would be nice to know something about their condition (emission/gassy-ness) "other than testing the filament with a multimeter prior to applying power.

Thanks

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Donald R. Resor
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 Post subject: Re: 5, 6 to 7, 9 or Octal pin vacuum tube substitutes
PostPosted: Dec Mon 25, 2017 5:43 am 
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You could do it. A 2A3 is same as 6B4G (octal) but with a 2.5 volt filament. Could use 6J5 (octal)settings for 56 used with adapter and 2.5 volt filament. Most older tubes have later ones with similar characteristics.

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 Post subject: Re: 5, 6 to 7, 9 or Octal pin vacuum tube substitutes
PostPosted: Dec Mon 25, 2017 9:17 am 
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Mr. Leal,

Thank you so much for pointing me in the right direction.

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Donald R. Resor
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 Post subject: Re: 5, 6 to 7, 9 or Octal pin vacuum tube substitutes
PostPosted: Dec Mon 25, 2017 3:46 pm 
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A great many tube tubes are simply re-based or re-packaged versions of older tubes. For example, the 5Y3 is an octal based 80, a 6F6 is an octal based 42, etc. There are many good references (Radiomuseum.org) being one that will tell you the types similar to and equivalent to a tube in question. Another good resource to have is the last editions of the RCA Tube Manual such as RC-30. These are thicker than the older editions and contain much more data useful for cross-referencing tube types.

As for making adapters to test older tubes on testers not originally equipped for them, you have to be careful. Many of the older 1.5 and 2.5 volt tubes drew very high filament and heater current. Just because a newer tube tester has a two-volt filament setting does not mean it can deliver the necessary current for older tubes. For example, the designers of the Seco 107 (a late 1950s tube tester aimed at the TV repair shop trade) might have figured on 600 mA as the maximum current a two-volt TV tube would draw. Try powering a 57 tube with a 2.5-volt, 1-amp filament and you may exceed the current limit of that section of the power transformer winding. It probably wouldn't light the tube fully, and going a step up would be too much voltage, so either way the test results would be wrong--aside from the risk of smoking the power transformer.

There are many older model tube testers, including Hickoks, which do not sell for very much money because they only test tubes made prior to the advent of TV in the early 1950s--which also leaves out most audio tubes of interest. Picking up an older tube tester that was designed for those earlier tube types is often a better answer than trying to force a newer tube tester to test tubes it may not be capable of handling.

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 Post subject: Re: 5, 6 to 7, 9 or Octal pin vacuum tube substitutes
PostPosted: Dec Mon 25, 2017 7:17 pm 
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Location: Rochester NY USA
Jim Cross has a table on his web (vacuumtubesinc.com) that shows the equivalents with different bases. I expanded it further - http://www.audiophool.com/Equiv_similar.htm


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 Post subject: Re: 5, 6 to 7, 9 or Octal pin vacuum tube substitutes
PostPosted: Dec Tue 26, 2017 9:39 pm 
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Location: Orlando, FL, USA
Test the 56 as a 6P5 with the filament reduced to 2.5V

Test the 57 as a 6J7 with the filament reduced to 2.5V

Test the 2A3 as a 6B4G with the filament reduced to 2.5V

Of course, adapters to an octal socket would be necessary for all.

Jim Cross


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 Post subject: Re: 5, 6 to 7, 9 or Octal pin vacuum tube substitutes
PostPosted: Dec Wed 27, 2017 5:52 am 
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The thought crossed my mind after it was mentioned about the filament consumption of the 56, 57 and 2A3 that an outboard 2.x volt transformer of ample current (around 3 amps) to power the filaments only might be a safe idea.

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Donald R. Resor
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 Post subject: Re: 5, 6 to 7, 9 or Octal pin vacuum tube substitutes
PostPosted: Jan Thu 18, 2018 5:26 am 
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This Seco 107B project I have been able to see through rather quickly after 3-4 days making the modifications and testing.

I added a 2.5v 3 amp Hammond Industries transformer to power the filaments of the 2A3, 56 and 57. The 57 being the one which consumes 3 amps for the filament.

There was room under the main vacuum testing chassis to mount the transformer. The 107C has it's auto transformer mounted in the same area which is in lieu of the line adjust rheostat.

I actually found a place to conveniently install a toggle switch change from 2.1v to 2.5v. Very little space under the chassis in this. Now there is even less.
p
The 2A3 adapter was straight forward. The 56 to 6J5 adapter was a bit trickier as I had to route pin 3 in between pin's 5 and 1, thus insulating it well to prevent an internal short.

Attachment:
File comment: 56 adapter routing
56to6J5adapter.jpg
56to6J5adapter.jpg [ 99.72 KiB | Viewed 780 times ]


Attachment:
File comment: Shown is the new filament switch with two of the adapters.
107bswitchandadapters-2.jpg
107bswitchandadapters-2.jpg [ 95.13 KiB | Viewed 780 times ]


Attachment:
File comment: Finally the testing of a VT 56 as a VT 6J5, success.
testing56-2.jpg
testing56-2.jpg [ 72.18 KiB | Viewed 780 times ]

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Donald R. Resor
N6KAW
www.hammondorganservice.com


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 Post subject: Re: 5, 6 to 7, 9 or Octal pin vacuum tube substitutes
PostPosted: Jan Thu 18, 2018 8:58 pm 
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That's really nice construction, much nicer than mine...

I generally use the extra wire clipped from fluorescent ballast that I've installed, rated 660v I figure it's good enuf... I mostly build to use tube as sub as I have Precision 912 & 920 that test big pin tubes... There is one for big pin 41, 42, 43 to octal 7S I'll use in the B&K 707...

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 Post subject: Re: 5, 6 to 7, 9 or Octal pin vacuum tube substitutes
PostPosted: Jan Fri 19, 2018 10:10 am 
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Location: los angeles, california, usa
I used tinned 18 AWG which I pulled from a spool of hook-up wire. The tube bases I ordered from VTI, and the Amphenol sockets I keep in stock as I commonly use them for the repairs I do.

The 2A3, 56 and 57 are the only vacuum tubes I run into which were manufactured before the Seco 107A, B, C were produced.

I now I can test the NOS vacuum tubes of these three types I purchase to be sure they are still up to par.

I know Alan has said the Seco wasn't anything like that of a Hickok 539B or 539C as it does not measure in MHOs, the vacuum tube amplifier does make the shorts test a bit more sensitive. The only drawback is I need a vacuum tube tester to test the 12AU7A in the Seco 107B.

My main concern is cathode shorts as those can damage a very expensive filament or output transformer.

Vacuum tubes that are completely flat are a secondary concern along with gassy tubes which can draw excessive current.

Once you learn the idiosyncrasies of your test equipment and try stay with in those boundaries all (for the most part) will be okay.

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Donald R. Resor
N6KAW
www.hammondorganservice.com


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 Post subject: Re: 5, 6 to 7, 9 or Octal pin vacuum tube substitutes
PostPosted: Feb Wed 07, 2018 1:43 pm 
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Location: los angeles, california, usa
When wiring the additional 3 amp filament transformer's primary I found that the main transformer of the Seco 107B has 3 taps on the primary along with the return. The three taps are wired through the "center tapped" line adjust rheostat.

Rather than trying to guess where I might connect the primary of the 2.5 volt 3 amp filament transformer, I decided to connect before the rheostat, which seems to be just fine.

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Donald R. Resor
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www.hammondorganservice.com


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