Setup Tek 576 for Tube Curve Tracer?

[Robert M. Braught]

Hi Ya'l!

I wonder if anyone here has already jumped through the hoops to
configure the test fixture input connections, build a socket switcher,
filament + screen supply etc. for a Tektronix 576 for use as a tube
c-tracer? (I don't want to reinvent the wheel if I can avoid it,
needless to say I'd like to save time/frustration...)

Thanks go to Mr. Alan Douglas, whos' (sp?) book* I bought through AES
for tipping me that the 576 would be one to have, w/1500KV available
stock for PlateV. Got one yesterday recently retired in GWO. I'm
preparing to gut a guitar amp chassis for use as my tube test fixture,
both 9pin min and 8octal for common preamp/power tube testing/matching.
Maybe two chassis's, one for each purpose?

(*'Tube Testers and Classic Electronoc Test Gear', what a great
compendem! I didn't realize other folk could be a geeked as I am about
old test gear!)

If anyone has done this before, any thoughts/guidance things-to-avoid
will be greatly appreciated, I'm anticipating that stray capacitance,
shielding, wiring layout could be issues... ...and that I'll have to
'trick' the HV interlock...any reversable mods to a stock 576 that would
make it more suitable for vacuum tube use?

Thanks very much in advance,
-Robert
QTS
http://www.Braught.com

[Chuck Harris]

Hi Robert,

There is nothing to it! I did it with my 577/177 curve tracer just
to see if it would. I only tried a 12AU7. All I did was plug bananna
plug leads into the EBC sockets on the plugin, and supply 12.6V to the
tube, and off it went. Just pretend it is a mosfet... best to keep
the grid in the negative voltage ranges.

If you wanted to do a beam tube, or a pentode, you would have to hook
up a fixed screen supply.... but otherwise things would be the same.

If you are using a tube that really likes to oscillate, you will need
to put ferrite beads on the leads up at the tube.

The 577 is cheaper than the 576, goes up to a kilovolt, and 100W
from the plate (collector) supply.

-Chuck, WA3UQV

Robert M. Braught wrote:
> Hi Ya'l!
>
> I wonder if anyone here has already jumped through the hoops to
> configure the test fixture input connections, build a socket switcher,
> filament + screen supply etc. for a Tektronix 576 for use as a tube
> c-tracer? (I don't want to reinvent the wheel if I can avoid it,
> needless to say I'd like to save time/frustration...)
>
> Thanks go to Mr. Alan Douglas, whos' (sp?) book* I bought through AES
> for tipping me that the 576 would be one to have, w/1500KV available
> stock for PlateV. Got one yesterday recently retired in GWO. I'm
> preparing to gut a guitar amp chassis for use as my tube test fixture,
> both 9pin min and 8octal for common preamp/power tube testing/matching.
> Maybe two chassis's, one for each purpose?
>
> (*'Tube Testers and Classic Electronoc Test Gear', what a great
> compendem! I didn't realize other folk could be a geeked as I am about
> old test gear!)
>
> If anyone has done this before, any thoughts/guidance things-to-avoid
> will be greatly appreciated, I'm anticipating that stray capacitance,
> shielding, wiring layout could be issues... ...and that I'll have to
> 'trick' the HV interlock...any reversable mods to a stock 576 that would
> make it more suitable for vacuum tube use?
>
> Thanks very much in advance,
> -Robert
> QTS
> http://www.Braught.com
>

[Alan Douglas]

Hi,

>If anyone has done this before, any thoughts/guidance things-to-avoid
>will be greatly appreciated, I'm anticipating that stray capacitance,
>shielding, wiring layout could be issues... ...and that I'll have to
>'trick' the HV interlock...

Yours must have led a sheltered life: I've never seen a 576 with a
working interlock, or the plastic cover. Mine had a toothpick jammed
in the switch (which I left in place).

The only tricky part would be the switching for comparing two
tubes. In the 570, the tubes are in parallel all the time, and the
unwanted grid is biased at -300V through 10 megohms. The lever switch
has three positions: in the center or "off" position both grids are
biased off. Throwing the switch one way or the other, transfers the
grid to the 570 circuitry. I presume the switch is a shorting type,
to avoid floating the grid, even momentarily.

Cheers, Alan

[Robert M. Braught]

Chuck Harris wrote:
<snip>
> If you are using a tube that really likes to oscillate, you will need
> to put ferrite beads on the leads up at the tube.

Alan Douglas wrote:
<snip>
> The only tricky part would be the switching for comparing two
> tubes. In the 570, the tubes are in parallel all the time, and the
> unwanted grid is biased at -300V through 10 megohms. The lever switch
> has three positions: in the center or "off" position both grids are
> biased off. Throwing the switch one way or the other, transfers the
> grid to the 570 circuitry. I presume the switch is a shorting type,
> to avoid floating the grid, even momentarily.
>
> Cheers, Alan


Thanks very much, Chuck and Alan! Two gems I hadn't considered yet,
which makes me darned glad I asked...

-ferrite beads it is; I've fabricated socket extensions in the past, and
evidently immediately forgot the learning experience (w/oscillation.)

-and the switching tubes (switching grids, and plates too maybe?)
concern; I should have been pondering that. I expect 'slightly' time
delayed relay circuits (50~100ms 'overlap') should do it (?) as I want
to have four test socket positions to rapidly go back and forth from,
and doubt I could easily come up with the right make before break switch
(? but I haven't looked yet either.)

Thanks again!
-Robert