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The bigger deal is the doubled current draw. I reckon it -highly- unlikely that a 300mA draw might kill a secondary but I'd be checking things to be sure.

Bill @ PEARL, Inc.

Bill,

Anita said someone had put in a power resistor to compensate for the reduction of the number 12V heaters. Voltage checks are/have will/been done to confirm the correct heater voltage across the remaining 12AU6s.

Mark

I'm away from home on a laptop and couldn't look at the schematic first (I have a cherry 575 BTW) but even so there must be some brainiac kludge to circumvent the problem, it's simply not that difficult.

The 12AU6 is a 150mA filament while the 6AU6 is 300mA and 8 is series drop 50.4v. So if the supply will handle that current it's a pretty simple problem; considered with no schematic that is :-)

Bill,
The heaters of the (8) 12AU6s are in series to the 100V supply. A 6V type will not work in this case.
Mark

Bill @ PEARL, Inc.

Bill,

The heaters of the (8) 12AU6s are in series to the 100V supply. A 6V type will not work in this case.

Mark

A 6AU6 is identical to a 12AU6 so why not sub in the 6 volt version and drop 6v across a zener or a resistor. It being a constant current load, either will work.

Shipping looks like it'll be about 1000yen, but customs is another matter..... I could pack it neatly and label it as 'New Stock' but that might not help depending on how ornery customs is... :D

However, the USB Gotek adapter is probably the best option as it eliminates the failure-prone mechanical floppy drive completely.


Jared

Hi!
Can someone please copy file C:\TekScope\calibration\calSPCConst.dat from DPO7254-DPO7354? And send it to me by email. (And console.txt, diag.txt from C:\TekScope\calibration\ )

Ed

Thanks for that info about Fetrons.
I had never heard of them, but I went and read up about them.
Pretty ingenious solution.

Menahem

Thanks Jaret, but I don’t think that will be needed for 2 reasons.

1st shipping form japan to Vietnam (my country) would probably cost more than the 30$ it would cost me to get the USB drive from aliexpress that you linked me.

2nd, Vietnam customs are really damn annoying. For some stupid reasons my country customs will refuse ANY used electronic.
I once had a buddy sent me a step attenuator for a spectrum analyzer from Australia. It got denied and held in customs for months before being sent back to Australia.

But I thank you for the kind gesture regardless.

I have found that bearings used in remote control cars are often good replacements in fans. Tamiya etc among other remote control brands are worth a look.
They are often high quality and can be purchased relatively cheaply. Sometimes even ceramic bearings are available.


Jared

If you need a disk drive, I have some spares that wouldn't be expensive to send as a 'small parcel'.
I'll be back in Japan just after new year, so I can test a couple and send you a working one for cheap.


Jared

Thank for the link to the replacement drive.
I re test with a bunch of different floppy disks, even a new sealed one. And it definitely seems like the drive is to blame.
I’ll order the replacement some time later.

I second the faulty floppy drive in the scope few of the scopes I've had on the bench were a bit flakey.


I recently converted my TDS784D and TDS794D to use the Gotek floppy adapters which work really well.
I purchased this exact one, which is a direct replacement with the FFC connector to use the original FFC interconnect cable:


Depending on the floppy drive you have (narrow or wide type) you may need to 3D print or otherwise fabricate an adapter bracket. I have designed one you can 3D print here (You'll also need an additional M2.5 x 10mm screw):


If you use one of these emulators, be sure to remove all jumpers on the Gotek floppy emulator except location S1 for proper operation.


Jared

Hi Barry,
My comment about 2N2219A vs 2N2219 was:
- "A" version is in the Tek replacement recommendation
- "A" version fT matches to original Tek part
- "A" version has higher Vceo of 40V. Plain 2N2219 has a Vceo of 30V and in my opinion it is too low for this application which will see 33V or above across CE.

I recommend 2N2219A. Mouser/Digikey has 2N2219A's. I don't use them often but Jameco also has them at a cheaper price although manufacturer is not reported so there is some risk.

Ozan

Ozan,

I see -32.5V across at the output

Q7042 was found to be bad when I started several days ago. I did not have one so I used a 2222A temoprarly. I have a couple "2N2219 PBFREE
Central Semiconductor 60Vcbo 30Vceo 5.0Veb / Bipolar Transistors - BJT" on on order from Mouser. I expect them on the 26th. I also have "5x 2N2219 MOTOROLA"on order from eBay.

I didn't read into the significance of your comment. Are you saying I need the 2N2219A part instead of the 2N2219 part?

Regards,

Barry

Thanks Siggi

That did the trick... works perfectly now.

John w.

Top and bottom in brass was about 85usd. (0.1mm, as milled).

On Tue, Dec 24, 2024 at 07:00 AM, Nick Stanley wrote:

Any idea why this is happening?

Assuming you have tried different discs my first choice would be
a bad drive, most likely the one in the scope.
If you can do GPIB you can get screenshots that way too.

/H?kan

Hey John,

Did you try the auto DC balance yet? Disconnect any probes or signals from
CH1/CH2, then press the input coupling for CH1 and CH2 up at the same time.
Wait and see whether this cleans it up.
Note that I believe DC balance is only available for CH1/CH2, so if this
also afflicts CH3/CH4, you have something else going on.

Siggi

On Tue, Dec 24, 2024 at 1:05?PM N7ZMG via groups.io <jwaldburger5377=
[email protected]> wrote:

Well I have replaced the U500 and the scope is triggering just fine.

However; when I changes Volts/Div scale without changing the input signal
the display jumps off center. If I recenter the display and measure the
amplitude and frequency it is accurate. If I switch scales again I have to
recenter the the display. This happens no matter which channel I am using.

I have tried to search the forum for possible answers but I am at a loss
as to what this is... Is it a problem with the horizontal or the vertical
calibration or the CRT or my eyes?

Any suggestions would be appreciated.

Its always something.

John w.

BTW, if that's not a secret, can you tell us how much JLCPCB charged you for your CNC'ed part?
Thank you.