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Nuvistors.

Dave
 

Found this in an idle moment...



Enjoy.

Dave B.

PS: Check the 'scope galery, Tek is well represented.
 

Ayup. I always wondered why Tek used the 8393, the 13 volt filament version of the 7586. Anyone?

Arden
 

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Phosphorphile posted
> Ayup. I always wondered why Tek used the 8393, the 13 > volt filament version of the 7586. Anyone?
I dont know what instrument Tek used the 8393 in, so cant comment on an actual TEK unit, ?but running? a13v volt filament on 12 v (provided the emission is high enough so the characteristics still suit the application ) will have two effects
1.?? All other things considered, it? can lengthen the???? ??? working life.
2.?? It will raise the input impedance much higher than when run at the specified filament watts.
?
I remember running 6.3 v fil?s at 4,0v to get hi Z inputs for electrometer applications in the distant past.
Cant remember the tube type now, maybe an EF37.
Underrunning filaments in this way was a common thing to do in high input Z applications, but you had to select the right tube that could handle it, without poisoning etc.
Special electrometer tubes were made with deliberately underrun filament voltages and some were specially selected types from a production run of normally 6.3 V filament units?tyen ?rebranded to a different type number.
The anode current was sigificantly reduced when this was done for the same grid base.
?
A somewhat parallel thing was done with the LM308A IC, which achieved a? 40Mohm Dc Zin by running in "current starved " conditions
?
But maybe TEK had a diferent reason?
Jojn Byers
 

Yes, it may be a 13 volt filament is easier to run at slightly lower voltage because perhaps the voltage being twice and the current being half of a 6 volt filament would make for a more constant current with line variations. Probably the way tungsten filaments work?

The 8393 was used in early 453's and later 503's, I know. Mebbe other models too.

Reducing heater voltage causes the cathode to produce a weaker electron cloud which reduces grid contact current. A positive voltage on the cathode sets plate current and normally blocks contact current with low DC resistance grid circuits but very high DC resistance grid circuits still suffer from grid current. I know for the 503 input 6DJ8's grid current was one of the selection criteria, too much produces diff amp balance instability.

308's were hot stuff when they came out but a little tricky to employ. Glad better types came out. Once ran into a PhD living in the past that thought a 308 was better than an OP27.

Arden

Phosphorphile posted
Ayup. I always wondered why Tek used the 8393, the 13 > volt filament version of the 7586. Anyone?
I dont know what instrument Tek used the 8393 in, so cant comment on an actual TEK unit, but running a13v volt filament on 12 v (provided the emission is high enough so the characteristics still suit the application ) will have two effects
1. All other things considered, it can lengthen the working life.
2. It will raise the input impedance much higher than when run at the specified filament watts.

I remember running 6.3 v fil s at 4,0v to get hi Z inputs for electrometer applications in the distant past.
Cant remember the tube type now, maybe an EF37.
Underrunning filaments in this way was a common thing to do in high input Z applications, but you had to select the right tube that could handle it, without poisoning etc.
Special electrometer tubes were made with deliberately underrun filament voltages and some were specially selected types from a production run of normally 6.3 V filament units tyen rebranded to a different type number.
The anode current was sigificantly reduced when this was done for the same grid base.

A somewhat parallel thing was done with the LM308A IC, which achieved a 40Mohm Dc Zin by running in "current starved " conditions

But maybe TEK had a diferent reason?
Jojn Byers
Don Lewis
 

My old HP-130C scope?has two 7586 Nuvistors in it, btw.
?
?
?
?

From: phosphorphile
To: TekScopes@...
Sent: Friday, January 20, 2012 12:30 AM
Subject: [TekScopes] Re: Nuvistors.

?
Yes, it may be a 13 volt filament is easier to run at slightly lower voltage because perhaps the voltage being twice and the current being half of a 6 volt filament would make for a more constant current with line variations. Probably the way tungsten filaments work?

The 8393 was used in early 453's and later 503's, I know. Mebbe other models too.

Reducing heater voltage causes the cathode to produce a weaker electron cloud which reduces grid contact current. A positive voltage on the cathode sets plate current and normally blocks contact current with low DC resistance grid circuits but very high DC resistance grid circuits still suffer from grid current. I know for the 503 input 6DJ8's grid current was one of the selection criteria, too much produces diff amp balance instability.

308's were hot stuff when they came out but a little tricky to employ. Glad better types came out. Once ran into a PhD living in the past that thought a 308 was better than an OP27.

Arden

> Phosphorphile posted
> > Ayup. I always wondered why Tek used the 8393, the 13 > volt filament version of the 7586. Anyone?
>
> I dont know what instrument Tek used the 8393 in, so cant comment on an actual TEK unit, but running a13v volt filament on 12 v (provided the emission is high enough so the characteristics still suit the application ) will have two effects
> 1. All other things considered, it can lengthen the working life.
> 2. It will raise the input impedance much higher than when run at the specified filament watts.
>
> I remember running 6.3 v fil s at 4,0v to get hi Z inputs for electrometer applications in the distant past.
> Cant remember the tube type now, maybe an EF37.
> Underrunning filaments in this way was a common thing to do in high input Z applications, but you had to select the right tube that could handle it, without poisoning etc.
> Special electrometer tubes were made with deliberately underrun filament voltages and some were specially selected types from a production run of normally 6.3 V filament units tyen rebranded to a different type number.
> The anode current was sigificantly reduced when this was done for the same grid base.
>
> A somewhat parallel thing was done with the LM308A IC, which achieved a 40Mohm Dc Zin by running in "current starved " conditions
>
> But maybe TEK had a diferent reason?
> Jojn Byers
>
Berj N. Ensanian KI3U
 

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Don Lewis wrote Fri, 20 Jan 2012 04:36:14 -0800 :

?
" My old HP-130C scope?has two 7586 Nuvistors in it, btw. "

A really fine rig. I read somewhere the HP-130C is regarded by some as the last good oscilloscope HP made.

By way of a little OT, mine after decades of routine use last year developed, upon warm-up, folding and contracting of the trace. The problem turned out to be transistor Q203 in the horizontal amplifier. The extend-its-life-fix was to put a 10-fins light sheet aluminum heatsink on Q203. I coated a light film of Desitin on the mating surfaces. The scope has been back to normal ever since. Desitin, which I read about somewhere on the net as a handy heatsink compound, is the baby rash creme found in supermarkets etc., it is much cheaper than the ZnO formulations marketed specifically as heatsink compound. Subjectively, I've had better luck with Desitin than the latter, perhaps because the Desitin is creamier and therefore easier to get on there as a thin film.

Berj / KI3U
 

Q203 may have developed more leakage over the years and will eventually have to be replaced. I'd look for a replacment just to be ready for when it does.

Arden

By way of a little OT, mine after decades of routine use last year developed, upon warm-up, folding and contracting of the trace. The problem turned out to be transistor Q203 in the horizontal amplifier. The extend-its-life-fix was to put a 10-fins light sheet aluminum heatsink on Q203.
Berj N. Ensanian KI3U
 

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r. Unfortunately Q203 is one of the more tedious-to-replace transistors in the HP130C, so at present it's put-off-today-what-you-can-do-later :), with the added excuse: experimentally lets see how long such a simple emergency fix is good for.

Berj / KI3U

To: TekScopes@...
From: gumbear@...
Date: Fri, 20 Jan 2012 18:29:40 +0000
Subject: [TekScopes] Re: Nuvistors.

?
Q203 may have developed more leakage over the years and will eventually have to be replaced. I'd look for a replacment just to be ready for when it does.

Arden

> By way of a little OT, mine after decades of routine use last year developed, upon warm-up, folding and contracting of the trace. The problem turned out to be transistor Q203 in the horizontal amplifier. The extend-its-life-fix was to put a 10-fins light sheet aluminum heatsink on Q203.


Egge Siert
 

Hi to All,

Tek used the 8393 Nuvistors in the Type 1A6 and 1A7. Look at the Circuit Description of both Plug-Ins and you know why. The so called differential adjustment of heater voltages. In addition lower heater current is lower hum/noise (the reason Tek used 8416's in the 1S1).

Egge Siert
Don Black
 

Perhaps it was just easier to provide a DC heater supply of 12 volts at half the current of a 6 volt tube in a tubes scope for hum reduction.

Don Black.

On 19-Jan-12 10:30 PM, phosphorphile wrote:
Yes, it may be a 13 volt filament is easier to run at slightly lower voltage because perhaps the voltage being twice and the current being half of a 6 volt filament would make for a more constant current with line variations. Probably the way tungsten filaments work?

The 8393 was used in early 453's and later 503's, I know. Mebbe other models too.

Reducing heater voltage causes the cathode to produce a weaker electron cloud which reduces grid contact current. A positive voltage on the cathode sets plate current and normally blocks contact current with low DC resistance grid circuits but very high DC resistance grid circuits still suffer from grid current. I know for the 503 input 6DJ8's grid current was one of the selection criteria, too much produces diff amp balance instability.

308's were hot stuff when they came out but a little tricky to employ. Glad better types came out. Once ran into a PhD living in the past that thought a 308 was better than an OP27.

Arden


Phosphorphile posted
Ayup. I always wondered why Tek used the 8393, the 13> volt filament version of the 7586. Anyone?
I dont know what instrument Tek used the 8393 in, so cant comment on an actual TEK unit, but running a13v volt filament on 12 v (provided the emission is high enough so the characteristics still suit the application ) will have two effects
1. All other things considered, it can lengthen the working life.
2. It will raise the input impedance much higher than when run at the specified filament watts.

I remember running 6.3 v fil s at 4,0v to get hi Z inputs for electrometer applications in the distant past.
Cant remember the tube type now, maybe an EF37.
Underrunning filaments in this way was a common thing to do in high input Z applications, but you had to select the right tube that could handle it, without poisoning etc.
Special electrometer tubes were made with deliberately underrun filament voltages and some were specially selected types from a production run of normally 6.3 V filament units tyen rebranded to a different type number.
The anode current was sigificantly reduced when this was done for the same grid base.

A somewhat parallel thing was done with the LM308A IC, which achieved a 40Mohm Dc Zin by running in "current starved " conditions

But maybe TEK had a diferent reason?
Jojn Byers


------------------------------------

Yahoo! Groups Links
 

It's not hum - the mainframe supplies regulated +75 DC for
plugin heaters. It's Coarse Balance. The beautifully simple
circuit Tek used is only possible with 8393's.

Dave Wise

-----Original Message-----
From: TekScopes@...
[mailto:TekScopes@...] On Behalf Of Don Black
Sent: Saturday, January 21, 2012 7:55 PM
To: TekScopes@...
Subject: Re: [TekScopes] Re: Nuvistors.

Perhaps it was just easier to provide a DC heater supply of 12
volts at
half the current of a 6 volt tube in a tubes scope for hum reduction.

Don Black.

On 19-Jan-12 10:30 PM, phosphorphile wrote:
Yes, it may be a 13 volt filament is easier to run at
slightly lower voltage because perhaps the voltage being twice
and the current being half of a 6 volt filament would make for
a more constant current with line variations. Probably the way
tungsten filaments work?

The 8393 was used in early 453's and later 503's, I know.
Mebbe other models too.
Don Black
 

That's what I was thinking; that they may have run the heaters off DC to prevent hum and it would be easier to supply 150mA heaters than 300mA in the tube era. Now it would be simple to use a three terminal regulator IC to provide 6.3 volts.

Don Black.

On 23-Jan-12 10:31 AM, David Wise wrote:
It's not hum - the mainframe supplies regulated +75 DC for
plugin heaters. It's Coarse Balance. The beautifully simple
circuit Tek used is only possible with 8393's.

Dave Wise

-----Original Message-----
From: TekScopes@...
[mailto:TekScopes@...] On Behalf Of Don Black
Sent: Saturday, January 21, 2012 7:55 PM
To: TekScopes@...
Subject: Re: [TekScopes] Re: Nuvistors.

Perhaps it was just easier to provide a DC heater supply of 12
volts at
half the current of a 6 volt tube in a tubes scope for hum reduction.

Don Black.

On 19-Jan-12 10:30 PM, phosphorphile wrote:
Yes, it may be a 13 volt filament is easier to run at
slightly lower voltage because perhaps the voltage being twice
and the current being half of a 6 volt filament would make for
a more constant current with line variations. Probably the way
tungsten filaments work?
The 8393 was used in early 453's and later 503's, I know.
Mebbe other models too.
------------------------------------

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