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Old 20th September 2012, 08:27 PM   #11
skidave is offline skidave  United States
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Thanks Tom!
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Old 20th September 2012, 09:14 PM   #12
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That's 8903... and I found it online...

anyone happen to know what the -15v TO-3 can regulator that sits on the back panel is? I can't seem to find where they hid it in the parts list in the service manual... I am assuming it is a standard regulator.

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Old 21st September 2012, 02:58 PM   #13
macboy is offline macboy  Canada
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Quote:
Originally Posted by bear View Post
That's 8903... and I found it online...

anyone happen to know what the -15v TO-3 can regulator that sits on the back panel is? I can't seem to find where they hid it in the parts list in the service manual... I am assuming it is a standard regulator.
Tricky to find, as they are not listed for sheet A13. Page 6-104 (page 97 in volume 1). They are TO-3 LM340-15 and LM320-15 which are equivalent to 7815 or 7915, but are rated at 1.5 A.
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Old 24th September 2012, 01:03 AM   #14
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Well, it seems the -15v reg TO-3 is ok... there is/was a strange mechanical intermittent somewhere near the three electrolytic caps and the plug-in vreg board. As near as I can tell, something caused the crowbar to actuate, frying the -15v fuse! It would do this with a nice little tap on the board or the electrolytics... As of now, I seem to have eliminated the failure. If it happens again, I'll go back in and have at it again. I was suspicious of the connection to the cap opening up and causing an over voltage... or maybe a ground reference lifting, same effect.... dunno. Seems stable now after some poking about and touching up solder... Tnx for the input/info!

The loop through as of today was about 0.0029 iirc... seems like it was higher today than the first time I turned it on...

I am unsure of the effects of changing modes and levels upon the amplitude level. But I am mostly just pushing buttons to see how things work.

There may or may not still be some flaws in the operation. I'll have to run through the operation manual and see, then maybe the calibration proceedure...

I am wondering if the noise floor can be dropped by some better regulation and if the distortion measurement limit might be improved by putting in some new ultra low distortion opamps...

_-_-bear
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Old 24th September 2012, 01:35 AM   #15
klewis is offline klewis  United States
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Quote:
Originally Posted by bear View Post
Well, it seems the -15v reg TO-3 is ok... there is/was a strange mechanical intermittent somewhere near the three electrolytic caps and the plug-in vreg board. As near as I can tell, something caused the crowbar to actuate, frying the -15v fuse! It would do this with a nice little tap on the board or the electrolytics... As of now, I seem to have eliminated the failure. If it happens again, I'll go back in and have at it again. I was suspicious of the connection to the cap opening up and causing an over voltage... or maybe a ground reference lifting, same effect.... dunno. Seems stable now after some poking about and touching up solder... Tnx for the input/info!

The loop through as of today was about 0.0029 iirc... seems like it was higher today than the first time I turned it on...

I am unsure of the effects of changing modes and levels upon the amplitude level. But I am mostly just pushing buttons to see how things work.

There may or may not still be some flaws in the operation. I'll have to run through the operation manual and see, then maybe the calibration proceedure...

I am wondering if the noise floor can be dropped by some better regulation and if the distortion measurement limit might be improved by putting in some new ultra low distortion opamps...

_-_-bear
Bear,
Mine runs right at .0029, .003 as well. I would be quite interested to hear if you can improve things by rolling opamps. Please keep us posted.

Ken
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Old 24th September 2012, 01:49 AM   #16
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Ken,

Did you run through the alignment proceedure??

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Old 24th September 2012, 04:52 AM   #17
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The other thing is that the Cordell "Distortion Magnifier" will improve the performance by 20dB or more... but it won't permit automatic measurements.

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Old 24th September 2012, 05:11 AM   #18
klewis is offline klewis  United States
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Ken,

Did you run through the alignment proceedure??

_-_-bear
I don't think that I did, but it's been a while since I messed with it. I purchased some extender boards but haven't used them yet. I got a used hp3562a spectrum analyzer and use it to look at the specific harmonics. So the 8903 has been relagated to more of a support role.
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Old 24th September 2012, 05:27 AM   #19
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What's the dynamic range on the 3562?
Is it good enough, or do you use the 8903 and then look at the residue?

You know about Pete Millet's software? (I have yet to try it)
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Old 24th September 2012, 03:37 PM   #20
klewis is offline klewis  United States
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Quote:
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What's the dynamic range on the 3562?
Is it good enough, or do you use the 8903 and then look at the residue?

You know about Pete Millet's software? (I have yet to try it)
Bear,

The dynamic range is 0 to 100 kHz. I use Richiem Twin-T notch filter to null the fundamental about 50 db or so. Build -- Active Twin-T notch filter for distortion analysis

The 3562 has a 85 db bandwidth so, if the fundamental is nulled to -50 then I can get down to -130 db resolution of harmonics. The practical limit is more like -125db. I haven't tried using the null of the 8903 for these measurements, but, now that you mention it, I will give it a try.

Initially I had difficulty using Pete's software, ended up buying a student version of VEE and Pete was kind enough to give me the un-compiled programs he created. Since then, I haven't had any issues and have written VEE scripts to run the 3562 in all sorts of neat ways. The only limitation of the student edition is that I can't compile the scripts.
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