Date   
Re: A6302 current probe excessive offset

Albert Otten
 

On Wed, Sep 18, 2019 at 10:18 PM, cmjones01 wrote:


I played with reducing the value of the resistor which feeds the offset
correction in to one pin of the amplifier, but even that wasn't enough. I
have now added a 3k3 resistor from the offset adjust pot's wiper to one end
of the hall sensor's output, and that allows me to bring the offset down
but at the expense of a very fussy offset adjustment and slight reduction
in gain. I could probably correct the latter by increasing the hall current
a bit, or devoting one AM503 to it with increased gain.
Some thoughts without studying the schematics too long.
I choose a similar remedy for a P6302. Soldered R18 to "A" and decreased the value. Wired side "E" of the Hall sensor to "K" (gnd) via 18k. Both action pulled the + of the opamp more negative.
A slight reduction in gain is only possible (I think) when there is not enough amplification by the DC amplifier (the feedback to zero out the DC flux component is not satisfying). Maybe your action put a heavier load on the Hall output. In my opinion the effect would be that the low frequency gain is now slightly smaller than the high frequency gain. AM503 Gain adjust R344 is common to both, so can't help. I'm not sure whether I ever carefully checked the frequency response of the P6302.
With that probe the scope trace is also very "jumpy". The probe is nearly useless in the most sensitive settings of the AM503. From all old messages at the time (especially by Steve Ditter) I concluded that the Hall sensor was desintegrating.

Albert

Re: A6302 current probe excessive offset

Ed
 

I believe that the offset resistor in these probes could be attached to either a + or - terminal on the board in the probe. Based on the number of probes I have taken apart, it looks like the resistor used was a select on test part as they all seem to be different values. This was likely to compensate for differences in the hall sensor. If you need a resistor as small as 3.3K though, the hall device may be NG.

ed

Re: Morning fun - working scope with no tubes?

Glenn Little
 

When these fanatics pay $2500.00 for a 1.5 meter power cord, where is the limit for tubes.

See:?? https://www.essentialsound.com/essence-power-cord.htm

Glenn

On 9/19/2019 4:28 PM, Roy Thistle wrote:
On Wed, Sep 18, 2019 at 07:13 PM, Jamie Ostrowski wrote:

I wish there was a way to find a way to keep the classic scopes out of the
hands of the tube harvesters.
Hi All:
The only way I found to do it was to offer more ( some times way more ) than what the tube hounds were willing to pay. Some people here are suggesting that solution.
In my experience, these tube harvesting guys are hard-bitten. And as far as I can reason, irrationally motivated by flummery they believe, or foist on their buyers.
Throwing money at the problem, will only be cause for asking for more money to be thrown.
I surmise, that the copious number of individuals willing to claim or believe, that brand X 12AX7 et. al. gives "a warm sweet chocolatey sound, with a hint of nutmeg" won't be deterred by the rational economic principle of diminishing returns. Quite the opposite: they will be thinking they are paying for a premium quality of sound that no one else has. The emperor is always willing to pay more for new clothes.
The only way, in my opinion, to rectify this situation is for common sense, and rationality to prevail.
Roy


--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"

Re: 3.5mm connector for SD24 sampling head...

Leo Bodnar
 

You have probably all taken the lid off the sampling gate hybrid.
Has anyne else taken their amplifier module apart?
There are quite a few interesting design solutions in there.
http://www.leobodnar.com/files/Tek-hybrid.jpg
Leo

Re: 577 R300 pot

DW
 

I believe this connecting pattern will fit on the board best. There is 2 connectors coming out each side and down and then 2 connectors coming out towards the bottom and down, a total of 4 connectors. I know this is a 470k trimmer resistor so I will need to find a 100k

https://www.digikey.com/products/en/potentiometers-variable-resistors/trimmer-potentiometers/80?k=v24&pkeyword=&sv=0&sf=0&FV=ffed014c&quantity=&ColumnSort=0&page=1&pageSize=25

Re: Will super glue work?

DW
 

Thanks I will look into that

Re: Will super glue work?

Ken Eckert
 

There is a two part epoxy here called JB Weld, it is reasonably good at
that stuff

On Thursday, September 19, 2019, DW <wilson2115@...> wrote:

On the back of the 577 there is a metal cover that holds the regulator
board in place. There are about 6 metal fasteners that are secured to the
cover which you screw the regulator board onto in place. Anyways several of
them have come loose, they appeared to be pressed on but no longer holding
in place. I have used super glue before but perhaps there is a better way?
Thanks



Re: Morning fun - working scope with no tubes?

Roy Thistle
 

On Wed, Sep 18, 2019 at 07:13 PM, Jamie Ostrowski wrote:


I wish there was a way to find a way to keep the classic scopes out of the
hands of the tube harvesters.
Hi All:
The only way I found to do it was to offer more ( some times way more ) than what the tube hounds were willing to pay. Some people here are suggesting that solution.
In my experience, these tube harvesting guys are hard-bitten. And as far as I can reason, irrationally motivated by flummery they believe, or foist on their buyers.
Throwing money at the problem, will only be cause for asking for more money to be thrown.
I surmise, that the copious number of individuals willing to claim or believe, that brand X 12AX7 et. al. gives "a warm sweet chocolatey sound, with a hint of nutmeg" won't be deterred by the rational economic principle of diminishing returns. Quite the opposite: they will be thinking they are paying for a premium quality of sound that no one else has. The emperor is always willing to pay more for new clothes.
The only way, in my opinion, to rectify this situation is for common sense, and rationality to prevail.
Roy

Will super glue work?

DW
 

On the back of the 577 there is a metal cover that holds the regulator board in place. There are about 6 metal fasteners that are secured to the cover which you screw the regulator board onto in place. Anyways several of them have come loose, they appeared to be pressed on but no longer holding in place. I have used super glue before but perhaps there is a better way? Thanks

Re: 577 step generator troubleshoot

DW
 

1.7 ohms on the secondary for the winding that supplies power for the floating supply, I think the winding is okay and there is no shorts to ground. I also checked the rectifier with the multi meter it seems to be fine.

Re: 577 step generator troubleshoot

DW
 

CR712 is fine, hmm. No fuse appears to be blown, no voltage appears to be present, I hope the transformer is ok

Re: Morning fun - working scope with no tubes?

Chuck Harris
 

I am certain there is a reason for every person that
says no, rather than yes, to a higher priced 535.

Just as I may say no to a higher priced antique car.

My point is, that if you don't own it, you get no say
in what the person that does own it does with it.

Complaining about a tube harvester, harvesting tubes
because he sees a higher price for the tubes than
anyone is willing to pay for the scope as a whole,
seems fatuous at best.

If one doesn't like that the scopes get their tubes
removed and sold, one should offer a higher price for
the scope with tubes than the audiofools pay for the
tubes, without the scope.

The economic model will change to disfavor tube
harvesting almost instantly.

If you want to know what a reasonable price is, do an
inventory of the tubes in the scope, and check the sold
prices for the same tubes on ebay. Then make your offer
for the 535 be more than the sum of those tube prices
on ebay.

-Chuck Harris

Harvey White wrote:

Perhaps we don't have the money?

How much is a used 535 worth?

Firstly as a scope.

Secondly as a collector's object to be restored.

Thirdly a source of oh so valuable tubes.

Fourth as a source of spare parts for a working unit.

What would you suggest as "reasonable" prices we might pay....?

Harvey

Re: OT - Any members in Czechia or Poland who can help me with parts?

Tam Hanna
 

It takes a village.


The offer, of course, is also open to anyone else!

--
With best regards
Tam HANNA

Enjoy electronics? Join 15k7 other followers by visiting the Crazy Electronics Lab at https://www.instagram.com/tam.hanna/

Re: 577 R300 pot

DW
 

This is a good start, your help is appreciated!

Re: 577 R300 pot

Mlynch001
 

Digikey shows several similar to the original. Surely something there will be workable?

Not sure of the original PC Board drill pattern, however this series in particular catches my eye.

DIGIKEY # 1993-1196-ND PIHER # PT15NV02-104A2020-S

https://www.piher.net/piher-nacesa.com/pdf/14-PT15v03.pdf (DATA SHEET for this series)

Good Luck!

--
Michael Lynch
Dardanelle, AR

Re: 577 step generator troubleshoot

DW
 

Checking CR712 in circuit seems to be reading abnormal using my diode test feature on the multimeter, it indicates this diode is conducting both ways with a dead short. Bare to mind I have removed all the various connectors on this power supply board located at the rear of the instrument. I think I will pull it out to check it further. Perhaps if CR712 is bad that can cause some issues I'm having?

Re: 577 step generator troubleshoot

DW
 

F391 good

Re: 577 step generator troubleshoot

DW
 

F391, I will find and check

Re: 577 step generator troubleshoot

DW
 

I probed Q384 Q386 and found on the base of both transistors they are -1.2 volts, I see nothing on the collector or emitter of both transistors. Seems like the floating power supply maybe isn't putting out any voltage. Seeing as Q386 was accidentally shorted to the base perhaps a fuse is blown on the floating supply, well I hope at least there is not any serious extensive damage which might be the case? Yikes!

Re: 577 step generator troubleshoot

DW
 

My hope was replacing the thermal pad would at least have me with something I can work with. I should point out the step generator was partially working when Q386 did not have a thermal insulator pad. When I have thermal pads on both Q384 Q386 I am getting no indications of step generator function on the screen. This is weird that the step generator would show some forms of life on the screen with Q386 without a thermal pad