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Old 16th Jul 2019, 11:07 pm   #1
Graham G3ZVT
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Default Tektronix 453 scope restored with Soviet help

Two of the 8393 nuvistors in this instrument had zero emission, so by swapping the good ones around I could either have dual traces with no triggering or a single trace with triggering.

The 8393 is very hard to find at any price, even a 13CW4 is rare, as is the once common 6CW4.

I was outbid on a single 13CW4 that came up recently, and anyway I need two.

What I hadn't realised is Soviet wire-ended nuvistors are in plentiful supply, and I ordered two 6C52H-B from a seller in Bulgaria they worked out at about £5 each including shipping.

There were three potential issues with these soviet nuvistors as I saw it:

The devices were "wire-ended".
6.3v rather than 12v heaters.
Higher mu than the originals.

I needed have worried about #1, yes they were wire-ended, but the wires are spot-welded onto pins, and the pinning is exactly the same as the 8393, 6CW4 etc. You lose less than a millimetre of pin if you snip them just above the welds. There is no locating collar, but I had no difficulty at all with that.

I had two choices with the heaters, either wire two in series and run them off 12v, or put a dropper in series with each, which, at 130mA, I calculated would be 47R 1W.

I was going to need access to the back of one of the major boards I decided that the sweep board at the top of the scope had the easiest access, especially after I realised that what I thought were spot-welds where the deflection power transistors were connected to the board, were in fact gold spring clips!
I was rather surprised at this method of construction, but who am I to criticise legendary Tek design?

So pop out the six leads, undo six screws and there is plenty of room to work on the back of the board.

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The triggering seems perfect on the modified scope, the sweep length was a bit short and could not be lengthened enough with the internal preset (1ms/div, 1KHz sawtooth).
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a 10K variable across the series resistor fixed that. (Note the clip-in nature of the power transistor leads).
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the X10 magnify feature could be adjusted correctly with its own preset at max.

I had already replaced four of the tunnel diodes with Soviet GI304A in a mistaken belief that they would be faulty, they certainly work, but I may put the originals back.

It's a profound thought that Soviet military components that were perhaps destined for an ICBM pointing westward, ends up in an American scope that was made in Guernsey.
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Old 16th Jul 2019, 11:39 pm   #2
MrBungle
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Default Re: Tektronix 453 scope restored with Soviet help

Nice job.

Last time I saw a 453 someone had actually swapped one of the nuvistors out for a 2N4416. Seemed to work just as well.
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Old 16th Jul 2019, 11:57 pm   #3
Graham G3ZVT
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Default Re: Tektronix 453 scope restored with Soviet help

Tek redesigned the 453 substituting FETs on later production instruments.
Mine is very early, perhaps Day One, SN 100007. The MSD "1" refers to the Guernsey factory.

These are cathode followers, I was surprised the higher mu seems to have reduced the overall gain of the x amp
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Old 17th Jul 2019, 8:24 pm   #4
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Default Re: Tektronix 453 scope restored with Soviet help

Years ago i removed the nuvistors (13CW4 I think) from the vertical and timebase of a TQ S54, and replaced them with FETs (maybe BFW10's?) I think I used zeners to drop about 80v with a cap across, and lower value "anode" resistors above the FETs. Worked a treat, no degradation of specs.
Later on, I tried the same thing on both the vertical and timebase modules of a Dynamco as I was trying to preserve my nuvistor stock. I tried everything, but had to give up in the end.I tried FETs with wildly different specs, but to no avail. A year or so later I saw an updated version of the scope where the manufacturers had converted to FETs, but no longer relevant.
Of course today I have a fair selection of nuvistors and likewise tunnel diods, quite a few of them new 4.7mA GE types.
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Old 20th Jul 2019, 6:46 am   #5
6AL5W-Martin
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Default Re: Tektronix 453 scope restored with Soviet help

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Originally Posted by rambo1152 View Post
Mine is very early, perhaps Day One, SN 100007. The MSD "1" refers to the Guernsey factory.
number 7 of Guernsey, that`s amazing, can be from the first day.
Take care for the instrument.

greetings from germany
Martin
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Old 21st Jul 2019, 5:55 pm   #6
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Default Re: Tektronix 453 scope restored with Soviet help

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Originally Posted by rambo1152 View Post
Tek redesigned the 453 substituting FETs on later production instruments.
Mine is very early, perhaps Day One, SN 100007. The MSD "1" refers to the Guernsey factory.

These are cathode followers, I was surprised the higher mu seems to have reduced the overall gain of the x amp
On a related issue, I picked up a small single-trace Telequipment scope, as I wanted to see what British equipment was all about.
It looks like it uses a couple of Nuvistors as well.
The last RCA valve tuners used Hitachi Nuvistors.
Dave, USradcoll1.
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Old 21st Jul 2019, 8:39 pm   #7
MotorBikeLes
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Default Re: Tektronix 453 scope restored with Soviet help

USRADCOLL1, that sounds like the S54 I referred to earlier. One 13CW4 in each tail of the Y amp input and a third in the timebase section. In one scope I fitted a pair of 6CW4s in the Y amp, rewiring the heater base. I had a few 6CW4s, but no spare 13CW4 at the time.
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Old 22nd Jul 2019, 10:58 am   #8
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Default Re: Tektronix 453 scope restored with Soviet help

I have some spare boards for the FET version of the 453 if anyone gets really stuck.



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Old 22nd Jul 2019, 5:54 pm   #9
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Default Re: Tektronix 453 scope restored with Soviet help

Quote:
Originally Posted by usradcoll1 View Post
Quote:
Originally Posted by rambo1152 View Post
Tek redesigned the 453 substituting FETs on later production instruments.
Mine is very early, perhaps Day One, SN 100007. The MSD "1" refers to the Guernsey factory.

These are cathode followers, I was surprised the higher mu seems to have reduced the overall gain of the x amp
On a related issue, I picked up a small single-trace Telequipment scope, as I wanted to see what British equipment was all about.
It looks like it uses a couple of Nuvistors as well.
The last RCA valve tuners used Hitachi Nuvistors.
Dave, USradcoll1.
That's the one! I forgot the model number for the moment. The unit works somewhat.
I never seen a piece of equipment that had so many choices for mains voltage.
An interested USradcoll1, Dave.
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Old 22nd Jul 2019, 8:31 pm   #10
MotorBikeLes
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Default Re: Tektronix 453 scope restored with Soviet help

Another comment on the TQ S54. Nice little 10Mhz scope, but I did find at faster timebase speeds the display shortened. The output transistor of the unblanking circuit was "lazy", spec probably just not up to the job. Replaced with a video O/P transistor (BF258, BF458 or similar if I recall) cured that completely.
All the contemporary TQ scopes had similar wide voltage selection choices. fairly common on stuff "back then".
Les.
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Old 23rd Jul 2019, 9:39 am   #11
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Default Re: Tektronix 453 scope restored with Soviet help

Only tangentially related to this, I've just come across another Nuvistor application. The front end of my early HP 5261A video amplifier uses one. Later versions use a FET.

The Nuvistor, an 8056 low-voltage device, is PCB-mounted. The PCB is screwed to a brass block which then sits on a chunk of soft foam to isolate it from vibrations. The foam in my unit had completely disintegrated, so I replaced it with a bit of bath sponge stuck with carpet tape.

The circuit seemed a bit noisy, so I replaced all the highish-value carbon composition resistors with more modern ones. It didn't make much difference, to be honest, but certainly hasn't done any harm. The amplifier meets its spec comfortably, with the result that my frequency counter will reliably count signals down to about 700 microvolts - that's -50dBm, or about ten nanowatts at 50R!

Chris
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Old 23rd Jul 2019, 5:15 pm   #12
usradcoll1
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Default Re: Tektronix 453 scope restored with Soviet help

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Originally Posted by MotorBikeLes View Post
USRADCOLL1, that sounds like the S54 I referred to earlier. One 13CW4 in each tail of the Y amp input and a third in the timebase section. In one scope I fitted a pair of 6CW4s in the Y amp, rewiring the heater base. I had a few 6CW4s, but no spare 13CW4 at the time.
Les.
I should have read your earlier entry a bit more carefully!
There was a mast-mounted amplifier for an antenna that used a 13CW4 valve made many years ago by a US antenna maker. IIRC, It ran on a 24VDC source, using the same line as the signal.
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