David wrote:
On Dec 25, 10:04=A0am, (Scott Dorsey) wrote:
David wrote:

So here=3D92s my question: Building the pre-amp was a fun and useful
project, but is my scope=3D92s performance without the pre-amp typical?

No. =A0Something is wrong. =A0With the gain control set halfway, S9 signa=
ls
go way over the top of the CRT with my Collins R-390. =A0This is using
log scale, too.

If your problem is the same in both linear and log, that's one thing to
rule out.

The SB-610, which is crude oscilloscope, doesn't have a log scale.
Are you confusing it with the SB-620 pan adapter ("Scanalyzer") which
presents a frequency domain view of signals?

I was indeed.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article
,
David wrote:

I did just what you suggest--
I connected the 1pF cap to the top of the IF transformer's secondary
coil.

David-

Might the signal level be higher on the primary side, assuming the 1pf
capacitor can withstand the voltage?

Fred
K4DII

On Dec 26, 11:39*am, Fred McKenzie wrote:
In article
,

*David wrote:
I did just what you suggest--
I connected the 1pF cap to the top of the IF transformer's secondary
coil.

David-

Might the signal level be higher on the primary side, assuming the 1pf
capacitor can withstand the voltage?

Fred
K4DII

Fred,

That might very well be the case. I can go in with my o'scope and
see.

Thanks for the tip.

-Dave

Well, I fixed the problem.

My homemade coils/filters are OK. Using a signal generator, I applied
a 0.5 Vrms signal to the SB-610’s vertical amplifier input and got a
trace on the CRT that was about 1 inch high (thick), which meets the
specifications at 3.395 Mhz.

The problem was the 1 pf capacitor I used to couple the plate circuit
of the SB-301’s second IF amplifier to the SB-610. I raised this cap
to 6 pf and now have plenty of signal for the SB-610.

Thanks for all the advice. It saved time.

-Dave Drumheller, K3WQ

On Dec 25 2009, 8:26*am, Jeffrey D Angus
wrote:
David wrote:
So here’s my question: Building the pre-amp was a fun and useful
project, but is my scope’s performance without the pre-amp typical?

I have one of those...And yeah, sounds like your gain is down a
bit from normal.

Jeff

Yes, I think this is the problem.

I put my oscilloscope on an isolation transformer and placed its probe
across the tank circuit (filter) at the output of the vertical
amplifier that drives the SB-601's cathode ray tube. With the SB-301
receiver tuned to it's internal 100kHz crystal oscillator, I measured
an 80 Volt peak-to-peak swing for a 1/2-inch thick trace, indicating
that the deflection constant for the CRT is about half of what it's
supposed to be. I suppose I could re-engineer the SB-610 to account
for the weak CRT, but it isn't worth it.

-Dave Drumheller, K3WQ