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UK

Ulf Kylenfall

Mon, Sep 11, 2017 9:56 AM

Continuing my efforts to fix the 5065A...

There was something wrong in the A7 (AC Amplifier assembly).

DC balance of the input stage was completely off-scale
and one of the 1854-0023 transistors had an open junction.Luckily I had a small supply of them but I also discovered that
the OP-Amps were old "seven of nines" (709).

There are several different manuals floating around on the internet,
and the hard copy that I have shows two different versions
of A7. One with 709 and one using 741 that is also different
in terms of circuit design and layout.

I am considering redesigning A7 using modern CAD and also
purchasing boards from a professional vendor, but first I would like
to know if anyone has tried both versions and if there are any
improvements. The modern 741-version uses DIP-socketed
OP-Amps so that version could be tried with even better
types.
BR
Ulf Kylenfall SM6GXV

Continuing my efforts to fix the 5065A... There was something wrong in the A7 (AC Amplifier assembly). DC balance of the input stage was completely off-scale and one of the 1854-0023 transistors had an open junction.Luckily I had a small supply of them but I also discovered that the OP-Amps were old "seven of nines" (709). There are several different manuals floating around on the internet, and the hard copy that I have shows two different versions of A7. One with 709 and one using 741 that is also different in terms of circuit design and layout. I am considering redesigning A7 using modern CAD and also purchasing boards from a professional vendor, but first I would like to know if anyone has tried both versions and if there are any improvements. The modern 741-version uses DIP-socketed OP-Amps so that version could be tried with even better types. BR Ulf Kylenfall SM6GXV

PS

paul swed

Mon, Sep 11, 2017 1:36 PM

I would simply slap a 741 into position to see how it behaves.
Also check those zeners for +/- 14.7V. They go bad.
Regards
Paul
WB8TSL

On Mon, Sep 11, 2017 at 5:56 AM, Ulf Kylenfall via time-nuts <
time-nuts@febo.com> wrote:

Continuing my efforts to fix the 5065A...

There was something wrong in the A7 (AC Amplifier assembly).

DC balance of the input stage was completely off-scale
and one of the 1854-0023 transistors had an open junction.Luckily I had a
small supply of them but I also discovered that
the OP-Amps were old "seven of nines" (709).

There are several different manuals floating around on the internet,
and the hard copy that I have shows two different versions
of A7. One with 709 and one using 741 that is also different
in terms of circuit design and layout.

I am considering redesigning A7 using modern CAD and also
purchasing boards from a professional vendor, but first I would like
to know if anyone has tried both versions and if there are any
improvements. The modern 741-version uses DIP-socketed
OP-Amps so that version could be tried with even better
types.
BR
Ulf Kylenfall SM6GXV

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/
mailman/listinfo/time-nuts
and follow the instructions there.

I would simply slap a 741 into position to see how it behaves. Also check those zeners for +/- 14.7V. They go bad. Regards Paul WB8TSL On Mon, Sep 11, 2017 at 5:56 AM, Ulf Kylenfall via time-nuts < time-nuts@febo.com> wrote: > > Continuing my efforts to fix the 5065A... > > There was something wrong in the A7 (AC Amplifier assembly). > > DC balance of the input stage was completely off-scale > and one of the 1854-0023 transistors had an open junction.Luckily I had a > small supply of them but I also discovered that > the OP-Amps were old "seven of nines" (709). > > There are several different manuals floating around on the internet, > and the hard copy that I have shows two different versions > of A7. One with 709 and one using 741 that is also different > in terms of circuit design and layout. > > I am considering redesigning A7 using modern CAD and also > purchasing boards from a professional vendor, but first I would like > to know if anyone has tried both versions and if there are any > improvements. The modern 741-version uses DIP-socketed > OP-Amps so that version could be tried with even better > types. > BR > Ulf Kylenfall SM6GXV > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. >

JH

Jim Harman

Mon, Sep 11, 2017 3:55 PM

On Mon, Sep 11, 2017 at 9:36 AM, paul swed paulswedb@gmail.com wrote:

I would simply slap a 741 into position to see how it behaves.
Also check those zeners for +/- 14.7V. They go bad.
Regards
Paul
WB8TSL

... but leave the pins that the 709 uses for external frequency

compensation (1, 5, and 8 on the can or mini-DIP) unconnected. The 741 has
internal frequency comp and uses pins 1 and 5 for an optional offset null
instead.

--Jim Harman

On Mon, Sep 11, 2017 at 9:36 AM, paul swed <paulswedb@gmail.com> wrote: > I would simply slap a 741 into position to see how it behaves. > Also check those zeners for +/- 14.7V. They go bad. > Regards > Paul > WB8TSL > > ... but leave the pins that the 709 uses for external frequency compensation (1, 5, and 8 on the can or mini-DIP) unconnected. The 741 has internal frequency comp and uses pins 1 and 5 for an optional offset null instead. --Jim Harman

BK

Bob kb8tq

Mon, Sep 11, 2017 4:53 PM

Hi

It’s been a long time since the 709 or 741 were “best” in any regard. I would not go with
socketed parts. I’ve seen more problems from sockets than from the parts that go into them.
Semiconductor quality / reliability has come a long way since the 1960’s.

How to redesign the board mostly involves figuring out what it does and how things like offset
and drift impact the overall performance. The choice in general is between very low leakage
(= high impedance) parts with high(er) offsets or very low offset parts (= low impedance) with
high(er) bias currents. Yes, there are a bunch of other things, but that’s the first branch in the
path for DC control stuff. Noise is obviously an issue, but the 709 / 741 are pretty noisy by
today’s standards.

Bob

On Sep 11, 2017, at 5:56 AM, Ulf Kylenfall via time-nuts time-nuts@febo.com wrote:

Continuing my efforts to fix the 5065A...

There was something wrong in the A7 (AC Amplifier assembly).

DC balance of the input stage was completely off-scale
and one of the 1854-0023 transistors had an open junction.Luckily I had a small supply of them but I also discovered that
the OP-Amps were old "seven of nines" (709).

There are several different manuals floating around on the internet,
and the hard copy that I have shows two different versions
of A7. One with 709 and one using 741 that is also different
in terms of circuit design and layout.

I am considering redesigning A7 using modern CAD and also
purchasing boards from a professional vendor, but first I would like
to know if anyone has tried both versions and if there are any
improvements. The modern 741-version uses DIP-socketed
OP-Amps so that version could be tried with even better
types.
BR
Ulf Kylenfall SM6GXV

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Hi It’s been a *long* time since the 709 or 741 were “best” in any regard. I would not go with socketed parts. I’ve seen more problems from sockets than from the parts that go into them. Semiconductor quality / reliability has come a *long* way since the 1960’s. How to redesign the board mostly involves figuring out what it does and how things like offset and drift impact the overall performance. The choice in general is between very low leakage (= high impedance) parts with high(er) offsets or very low offset parts (= low impedance) with high(er) bias currents. Yes, there are a bunch of other things, but that’s the first branch in the path for DC control stuff. Noise is obviously an issue, but the 709 / 741 are pretty noisy by today’s standards. Bob > On Sep 11, 2017, at 5:56 AM, Ulf Kylenfall via time-nuts <time-nuts@febo.com> wrote: > > > Continuing my efforts to fix the 5065A... > > There was something wrong in the A7 (AC Amplifier assembly). > > DC balance of the input stage was completely off-scale > and one of the 1854-0023 transistors had an open junction.Luckily I had a small supply of them but I also discovered that > the OP-Amps were old "seven of nines" (709). > > There are several different manuals floating around on the internet, > and the hard copy that I have shows two different versions > of A7. One with 709 and one using 741 that is also different > in terms of circuit design and layout. > > I am considering redesigning A7 using modern CAD and also > purchasing boards from a professional vendor, but first I would like > to know if anyone has tried both versions and if there are any > improvements. The modern 741-version uses DIP-socketed > OP-Amps so that version could be tried with even better > types. > BR > Ulf Kylenfall SM6GXV > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

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Resoration of 5065A - continued...