[Peter Wieck]

Just for giggles, I tested the tubes on this beast, something I usually
do not do unless I have other reasons to do so.

Well....

Just goes to show you how much resilience these things have. Of the 14
tubes, only the rectifier and the 6C4 tested at-or-above minimums (per
my Hickok 539B). Several of the dual-section tubes had one-or-the-other
sections barely lifting the pin. The rest of them were no better than
40% of minimum.

All measurements verified against NOS tubes in-hand which _DID_ test
correctly.

And it "worked".

Now, of course, it works much better, the stereo separation is much
sharper, the muting action much crisper, and the AFC actually appears
to do something.

So, recapping got my MPX back. New tubes and it is, for lack of a
better word, a Neat little tuner. I also have to admit that this is the
very first time I have come across such worn tubes in any tuner of the
many that have passed through my hands. This thing must have been run
hard and put away wet for years before I tripped over it.

Peter Wieck
Wyncote, PA

[Patrick Turner]

Peter Wieck wrote:

Just for giggles, I tested the tubes on this beast, something I usually
do not do unless I have other reasons to do so.

Well....

Just goes to show you how much resilience these things have. Of the 14
tubes, only the rectifier and the 6C4 tested at-or-above minimums (per
my Hickok 539B). Several of the dual-section tubes had one-or-the-other
sections barely lifting the pin. The rest of them were no better than
40% of minimum.

All measurements verified against NOS tubes in-hand which _DID_ test
correctly.

And it "worked".

Now, of course, it works much better, the stereo separation is much
sharper, the muting action much crisper, and the AFC actually appears
to do something.

So, recapping got my MPX back. New tubes and it is, for lack of a
better word, a Neat little tuner. I also have to admit that this is the
very first time I have come across such worn tubes in any tuner of the
many that have passed through my hands. This thing must have been run
hard and put away wet for years before I tripped over it.

Peter Wieck
Wyncote, PA

Remarkably, tube circuts will work if gm is only a small fraction
of the gm mentioned in the tube data.
Except they don't work quite as well as they should......

Tubed tuners can offer superlative performance....

Patrick Turner.