Re: Tube test adaptor for Tektroinx 575 was: Re: [TekScopes] FS: miscellaneous Tektronix manuals
Dan Cordova <danny_cordov@...>
Brad,toggle quoted messageShow quoted text
My main interest is audio tubes. I have >1000 different tubes, mostly audio output and small signal/preamp tubes. I also own a Hickok 580A tube tester and a Tektronix 575 Curve Tracer. Thus my interest in using a Tek 575 to match tubes for use in DIY preamps and amps I am planning to make.
I was a electronics tech in the military a long time ago, in the time when tubes were going away and being replaced with solid state, but before the internet and PCs. I don't write code, although I did take a course in Fortran back in the early 1980s.
This group has been a tremendous resource. I truly appreciate the responses that I have humbly received from you and others in the group. I say humbly received because I'm just a audio hobbyist and ME who is humbled because I realize that I know so little about audio electronics who is trying to learn.
For example, I didn't know until recently that tubes usually use AC voltage for the heater. I'm also learning the different terms, such as the anode is usually called the plate. It's humbling that this old technology was invented well before I was born and is still useful today.
Again, thanks to all who responded with the lessons and great information.
On Wednesday, December 5, 2018, 1:28:41 PM PST, Brad Thompson <firstname.lastname@example.org> wrote:
On 12/4/2018 4:52 PM, Dan Cordova via Groups.Io wrote:
Hi Brad,Hello, Dan and the group--
Thank you for your inquiry. Here's a column I wrote for Test &
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
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
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.