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Old 28th August 2003, 01:25 AM   #11
EC8010 is offline EC8010  United Kingdom
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Default Holy snivets! Where's the Bat-shark repellent?

Fascinating stuff. Thank you for the RCA reference, I will have to see if I can get it from my local library.
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Old 28th August 2003, 09:34 AM   #12
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Default snivets R us

Ha, I know what you mean!
In TV's with big pentodes used for horizontal deflection (Line output valves in UK tech), there was sometimes a Barkhausen phenomenon. It caused a thin watery line down the left hand side of the picture. It's amplitude and position could be changed by altering the valve's oprating conditions in any way - even puting a magnet nearby affected it.
Usually changing the valve cured it.
NB I seem to remember that if you bypassed the small choke in the top-cap lead, it would appear.

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Old 28th August 2003, 11:52 AM   #13
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Ah ha! So snivets are velocity modulation of the scan! Thanks for that, John.
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Old 28th August 2003, 04:07 PM   #14
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ITSR they're VHF/UHF oscillations that feed back all the way to the tuner section, and being in the same place each time in the horizontal system, it causes a vertical band.

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Old 28th August 2003, 04:31 PM   #15
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Default snivets on toast....

Quote:
Originally posted by EC8010
Ah ha! So snivets are velocity modulation of the scan! Thanks for that, John.
No. It's not velocity mod. That's something else, though the result is similar.
This is real RF! It gets picked up by the VHF or UHF tuner.

More precise description of phenomenon:
A thin vertical band, perhaps 1 to 2 uS wide, a number of uS from the active picture start.
It has some line-by-line positional instability, so appears liquid.
On UHF, when tuning up the band, the horizontal position changes, suggesting that the oscillation burst is in fact a sweep.

My memory is failing me to add any more there might in fact be some inacuracy in my recollection, but I hope you get the general idea.

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Old 28th August 2003, 04:52 PM   #16
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> section #1 of a 6CM7 dissimilar dual triode looks exactly like a 6FQ7 / 6CG7 / 6SN7 element

It probably is. There are thousands of tube types but they were assembled from only a hundred or so basic parts (grids, plates, etc). The small side of a V-sweep tube is just any ordinary triode. A lot of them appear to be 12AT7 parts, though some are more in the 12AU7 line.

The large side of the later V-sweep tubes seem to be unique, new in 1955. They are not small 2A3 nor 6080; nor do they look very much like large tuner-triodes, and most do not look like any beam-power type with missing grids. They may be descended from 6BX6(?) large octal twin triodes, but much cheaper.

They could be nice output tubes for a complete 1-watt amplifier on one bottle.

> Although section #1 is rated at 1.45 watts it is the same size as section #2 which is rated at 6 watts

It is possible the spec-writers wrote some reasonable number (V-sweep duty does not need a huge driver) but the production engineers had an ample supply of some bigger plate stampings.

OTOH, the big triode of these tubes has a very high rating for its size, and in TV duty would be worked right AT (and even past) that rating. Maybe if the big triode were idle (zero watts), the small triode could handle much more than 1.5 watts; but with the big triode working hard and hot the small triode can't take any more than its own 1.5 watts plus the several watts pouring out of one side of the big triode.
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Old 28th August 2003, 05:18 PM   #17
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Hi,

Quote:
They may be descended from 6BX6(?)
I think you mean the 6BX7 and family.

The 6CS7 has a raft of cousins if we stick with the noval series;

6CM7, 6DA7, 6CY7, 6DR7 and so on.

Most of these are useable for audio or regulators.

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Old 29th August 2003, 02:31 AM   #18
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Default Re: snivets on toast....

Quote:
Originally posted by dhaen
This is real RF! It gets picked up by the VHF or UHF tuner.
Gotcha. Thanks for the clarification. Now I see what you meant by the ferrite bead comment.
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Old 29th August 2003, 03:08 AM   #19
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Default scan of Figure 12

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Old 29th August 2003, 03:13 AM   #20
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Default Figure 13 scan

here is figure 13 from RCA "Electron tube design"
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