Tube test adaptor for Tektroinx 575 was: Re: [TekScopes] FS: miscellaneous Tektronix manuals

Brad Thompson

On 12/4/2018 4:52 PM, Dan Cordova via Groups.Io wrote:
Hi Brad,
Do you have or know anyone selling an adapter/fixture to match tubes on a Tektronix 575?
Or, do you know if there is a schematic I can buy?
Glydeck has a blog about this, but there is no schematic or info to contact him.
Hello, Dan and the group--

Thank you for your inquiry. Here's a column I wrote for Test & Measurement World
magazine (subsequently absorbed by EDN) which describes my version of
a tube-test adaptor for the Tek 575:

You can view a schematic and photos here...

I used an external tube socket, small PC board and some two-piece
surplus connectors to build an adaptor, which suffices for small tubes
that don't need plate voltages in excess of what the 575 can deliver.
Heater or filament and screen voltages get supplied by "wall warts" or
other power supplies

In the schematic, J1 and J2 form a "crossover network" to match a
particular tube's pinout. This approach requires wiring or rewiring
the J1-J2 adaptor to test each tube type and thus is best suited to
testing a batch of identically-pinned tubes at once.

Newcomers to tube technology may be surprised to learn that many tubes with different part numbers can share a common pinout. For example, JEDEC base code 8BD
defines an octal (8-pin) base which applies to the 6SN7-GT, the 6SL7-GT and their
heater-voltage cognates along with 25 or so other tube-part numbers. Providing 12 pins
accommodates "modern" Compactron tubes.

While I noted no spurious oscillations while testing a batch of 6SN7s, you
may need to slip ferrite beads onto plate and grid leads if needed for
parasitic-oscillation suppression.

One point: use care in selecting the grid/base voltage you apply to the
tube under test. If the tube manual states "maximum positive grid
voltage = 0 volts", believe it! Running the grid voltage positive causes
large amounts of grid current to flow can melt the grid.

Questions welcomed-- I don't have any spare adaptor boards left over
but would investigate making more if there's interest.


Brad aA1IP

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