CRT book by Keller

John Griessen

The coketron, a CRT made from a coke bottle, made me smile her in Albuquerque...
John Griessen -- building lab gear for biologists

Tektronix 492BP


Hi, I recently adquire this unit I had a diplexder and WG so to be able to increase the 21GHz frequency but this unit does not go over the 21GHz limit. It does not appear to have any options but it does has the external mixer connector and 1st and 2nd LO. Is there any way I can increase its limit?

2247A Is this normal?

Tim / N8TIM

Hello All
I have a 2247a and when I put it in the voltmeter mode and pick Peak to Peak the cursers are not touching the peaks of the wave form. Is this normal or do i need to get the service manual out?,,,20,2,0,0


Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?

Steve Goldstein

Hi Jared,

I was just going through the BOM at Digikey and encountered what may be a typo. C2, which you list as TBM1H105BECB, gives a non-existent part number error. Everything else so far seems to be OK.

I assume the LEDs are 20mA types as the fundamental design is pretty old.

BTW, you don't list a part number for the knob but Digikey PKG90B1/4 looks correct.

Re: T912 storage oscilloscope - No 2.7 KV high Voltage

Roger Evans


I am writing this on the phone and I can't easily get schematics at the same time - so no part numbers!

When you disconnect the diodes that generate the CRT cathode and grid voltages (-2.7kV) you effectively disable the negative feedback from the end of the focus resistor chain to the power transistors that energise T460. So the oscillator is running at maximum drive trying to generate -2.7 kV and in the same way is producing too high values for -120V and -220V. When running normally with negative feedback the transformer turns ratio ensures that if -2.7 kV is correct then so are the other voltages.

To me it looks like T460 is OK and so is the circuitry that drives the power oscillator. You have a problem with a failed diode or capacitor on either the CRT grid or cathode supply. If you replace just one of the supplies then the voltage across the two neons causes them to conduct and a fault on either supply will cause the oscillator to stop working.

I am afraid you may have check individual components to find the failure. Quite often a leaking diode or capacitor looks OK with a DMM but the leakage shows up with a high voltage around 1kV. I bought an insulation tester as used by electricians for checking house wiring.

I can go into more detail when back at a decent sized screen!

Best regards,


Re: 1s1 on ebay


Or figure out a solid-state replacement...

Re: T912 storage oscilloscope - No 2.7 KV high Voltage


Hi Roger,
the CR468 heats only with the C468 condenser connected, if I disconnect it the CR468 remains cold.
I wanted to add that I measured the voltages at pin 2 and pin 7 of the T460 transformer with respect to ground and I find very high voltages (on pin 2 there are 840 Vpp at 53 kHz and on pin 7 there are 484 Vpp at 53 kHz).
From pin 2 through the CR468 diode the - 120 Vdc are generated and from pin 7 through the CR467 diode the - 220 Vdc are generated, 840 Vpp to generate the -120 Vdc seem too many! I suspect an insulation problem in the T460 transformer (?).


Re: 1s1 on ebay

Dave Wise

?I have on my "to do someday" list, adjusting the heater current to acommodate 12AT7 and see if it's acceptable.

Dave Wise

From: <> on behalf of snapdiode via <>
Sent: Tuesday, January 12, 2021 10:54 PM
Subject: Re: [TekScopes] 1s1 on ebay

If you go by eBay prices, buying two 8416s will bring that "bargain" 1S1 in line with the 200$ range I see for 1S1s these days,

Re: T912 storage oscilloscope - No 2.7 KV high Voltage


Yes Max,
I disconnected the CRT socket, but without changes.



Re: The first International Mail was delivered today


Mine arrived today, Hertfordshire, UK

Many thanks Dennis.


Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?

Colin Herbert

Hi Larry,
Am I "CH *"? If so, I have sent you an email to your personal address, stating my interest, postal address in the UK and willingness to pay. Can you confirm that I am on your list? In which case I will send the money to you via PayPal as soon as I can.

-----Original Message-----
From: [] On Behalf Of Larry McDavid
Sent: 12 January 2021 22:10
To:; Tek500 Mail List (
Subject: Re: [TekScopes] I built a TM500 mainframe tester, and updated the design. Someone might find this useful?

Ok, folks, I now have finalized the cost of the board sets and domestic
packaging and shipping cost. Because the number of participants
increased, Jared and I were able to get the four-board set price reduced
to US$26; this is a significant improvement from the original estimate
of $38! And, these will be good boards with gold plating and
connector-edge chamfering on the main board, similar to what you see in
the YouTube video; the board color will not be black, as that is a cost

All I'm doing is aggregating requests for board sets and distributing
those board sets; no components are included in this group purchase.

So, the final price will be:

Board Set (four boards) $26
Packaging/Shipment CUSA $10
Total for CUSA $36

If you requested more than one board set, I can combine packaging and
postage for two sets only; if you requested more than two, plan for two
board sets per package.

For international, I have postage costs only for UK and Australia so far:

UK postage US$25 plus $5 packaging, total with board US$56
Australia US$28 plus $5 packaging, total with board US$59

I will have to check further for other international postage and I will
contact you individually.

Payment by PalPal Friends and Family, please! Use my email address as my
PayPal account name: lmcdavid at lmceng dot com. You should find my
email address in this message header.

There is too much cost here for me to place this board order in advance
so please pay now. In fact, there may be a conflict with Chinese New
Year so please pay promptly.

Verify your name initial is on the list below to be included. If your
name has an asterisk (*) beside it, I am missing information you must
provide very soon or risk being removed from the list. There are
additional requesters waiting for inclusion...

SM *
MH *
SC *
AAlt *
WS *
PMu *
GM *
CC *
BHe *
BK *
LR *
BG *
JK *
AAin *
PD *
BL *
CH *
DG *

The following have asked for inclusion in the group order after entry
was closed. If any of the above don't provide address info or don't send
funds promptly, the following will be offered the opportunity in the
order shown below.


Larry McDavid

On 12/31/2020 11:27 AM, Jared Cabot via wrote:
Hi all,

I have been accumulating TM500 modules and mainframes for a little while, so I recently finished building an 067-1201-99 TM500 mainframe tester from the Tek construction notes floating around.
I updated the design somewhat and designed it for simplified construction (Not a single wire to strip and solder!) and I thought someone here might be interested in taking a look or even building one themselves.
Here's a link to the youtube video:

And here's a link to the google drive with all the gerbers and schematics and stuff. I went so far as to rewrite the manual with the alterations and corrections included.

Direct link to the new manual:

Let me know what you think, and let me know if you see any errors that need correcting. :)


Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)

Re: T912 storage oscilloscope - No 2.7 KV high Voltage

Roger Evans


You say 'CR468 diode continues to boil', which implies that something is drawing too much current from the -120V supply. Which capacitor did you change? Can you measure the voltage across R469 and maybe check that the value of R469 is reasonably close to 1.2k? If this excess current is going to the storage board (rather than a leaking C469) then something will probably be very hot. It is not safe to touch components while the board is powered since there is 220V (and +335V!) in places but you can check that the -120V and -220V (and also +335V) have decayed a few seconds after the scope is turned off and then try touching a few components. I would start with Q942, Q944, Q946 and Q948.

Be very, very careful about not touching the parts which have high voltages (ie more than 50V) on them!



Re: T912 storage oscilloscope - No 2.7 KV high Voltage


Do you tried to disconnect the rear socket of CRT? Just to be sure there isn't some internal short.


Re: T912 storage oscilloscope - No 2.7 KV high Voltage


Greetings to all,
i replaced Q458 but nothing has changed.
I checked the voltage and frequency on the collector of Q458 with the HV diodes CR463 and CR465 disconnected: the frequency is 54 kHz and the voltage around 336 Vpp.
I also measured the voltage + 120V UNREG and it is +151 Vdc; on the collector of Q446 there are 5.3 Vdc, while on the emitter of Q454 there are 5.99 Vdc, the voltage + 8 V is + 7.98 Vdc.
On the output line from the T460 transformer I replaced a 0.1 uF capacitor towards ground but the CR468 diode continues to boil, if I remove the capacitor the diode remains cold and the voltage at - 140 Vdc (instead of -120 Vdc).
If I connect the HV CR463 and / or CR465 diodes there are no - 2.7 KV and the voltages of -120 Vdc and -220 Vdc drop to about - 14 Vdc.

I don't understand where the fault is, maybe it is the T460 transformer that is fault ?

Thanks for the attention


Re: Update on Domestic US Book Delivery Dates

Chris Wilkson

My copy arrived in Detroit 48206 yesterday. Thanks again, Dennis!

Re: The first International Mail was delivered today


On Wed, Jan 13, 2021 at 02:47 PM, Dennis Tillman W7pF wrote:

Another one is out for delivery this morning in The Netherlands.
Hello Dennis,
My book arrived this very morning, so NL is covered now...

Today is my birthday and .... when I told my wife several months ago about the book and that you were offering to send these books around the world, my wife offered to give one to me as a birthday present! Tell me about coincidence!

The book arrived in less than a week and is in as great shape as when sent, i.e. perfect. I like its beautiful, classic hard cover in maroon, black and gold.

I think a short expression of appreciation for the USPS is appropriate since they're having a rough ride and still succeed in delivering these books in a short time, both nationally and internationally. And no, I'm not forgetting Dutch Post (Post NL), for Leo's book and mine.

Thank you very much for all your efforts!


The first International Mail was delivered today


The first of the international shipments of Peter's books was delivered this
morning in The Netherlands.
Another one is out for delivery this morning in The Netherlands.
The one that went to Japan is waiting to clear Customs in Japan.
Two that were sent to the United Kingdom arrived in Heathrow yesterday.
Two that were sent to Australia are in Japan waiting for a connecting

Re: Tek 576 step generator problem

Dave S.


thank you very much guys for your help!
So it looks like my step-gen performs ok and like Michael Lynch said it seems to be normal that the waveform flickers a bit more @ 2, 4, 6, 8 and 10 steps.

Anyway i ran into another problem (or is it a problem?!) ... Maybe someone can do another (pretty easy) check/comparison
I shorted the C and E terminal, set the vertical range to 5uA and turned up the collector supply to have 2 divisions (10uA). When i change the vertical range now from 5uA to 10uA the reading is not 10uA but suddenly almost 75uA.
Is that normal due to internal change of measurement resistor?


10uA-Range without changing collector supply:


Re: 1s1 on ebay


If you go by eBay prices, buying two 8416s will bring that "bargain" 1S1 in line with the 200$ range I see for 1S1s these days,

Re: 1s1 on ebay


Woops, well that explains the price. I hope the buyer noticed.

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