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Those Magnificent Television Tubes
Those Magnificent Television Tubes
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Old 3rd July 2017, 03:58 PM   #911
DIYBras is offline DIYBras  Brazil
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Default Red plate and current overload

The OTL amplifiers comes to mind about overload issue. Basically, the current emission overload destroy a tube in OTL amps. If red plate occurs in some occasions, without using all cathode emission capacity, no problem I think.
So I bet that TubeLab 500W amp will survive far more time than a OTL amp.
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Old 3rd July 2017, 06:11 PM   #912
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by DIYBras View Post
Coincidentally... This is actual number of PL509's I have in good conditions (funcional), but from several makers.
Still have to count all my used PL505/509/519, also from very different makers .

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Old 4th July 2017, 05:00 AM   #913
Miles Prower is offline Miles Prower  United States
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Quote:
Originally Posted by TonyTecson View Post
question: on power tubes that have several grid connections, is it required to connect grid stoppers on all of them? or just one?
You usually find multiple grid connects in tubes intended for grounded grid, VHF amplification. (Multiple cathode connections are seen in types like the 6AK5 intended for common cathode, VHF amplification to keep the ground returns of the plate and grid circuits separate.) At audio frequencies, it's not necessary to make more than one connection. It all depends on the type and how much it likes to make RF, the lay-out, construction practice whether you can float the unused grid pins and still remain stable.
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Old 4th July 2017, 09:56 AM   #914
TonyTecson is offline TonyTecson  Philippines
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Those Magnificent Television Tubes
thanks....
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Old 4th July 2017, 01:20 PM   #915
Kay Pirinha is offline Kay Pirinha  Germany
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Have a look at the 6KG6A/EL519 pinout diagram. Every grid, even the beam former 3rd grid, is brought out by two pins with large distances between both of them. I can imagine two reasons for doing it this way: Improved cooling, especially for the screen grid, and improved mechanical stability, which may ease manufacturing in the step when the envelope is pushed over the structure, prior to being melted to the glass bottom.

For normal or audio operation of a sweep tube *imho* it is not necessary to connect both pins.

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Old 4th July 2017, 06:22 PM   #916
nuvistordave is offline nuvistordave  United States
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Those Magnificent Television Tubes
A problem with the high gm tubes is their variability. Sweep tubes test run 250 plate 120 screen and -22 grid and see anything from 50 to 250 mA; and the gm varies as well. That is why I buy a lot of them and match. The different manufacturers don't matter as long as you match the sets. I usually run 1 bias adjustment per channel for single tubes and 2 if they are paralleled. All tubes on a bias adjustment need to be matched.
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Old 4th July 2017, 10:24 PM   #917
smoking-amp is offline smoking-amp  United States
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The 6HJ5 datasheet mentions that the extra pins for the grids are useful for cooling purposes if heavy wire leads are connected to them:

http://tubedata.milbert.com/sheets/084/6/6HJ5.pdf

I suppose that would entail a grid stopper on each pin if the wires go anywhere enough to pick up a Pos. Fdbk signal.
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Old 9th July 2017, 04:18 AM   #918
nuvistordave is offline nuvistordave  United States
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Those Magnificent Television Tubes
That lot of 14 42kn6 are on their way to me. $38. ;-) I use an outboard filament xfmr to run curves/match on my SOFIA. The MELOS chassis that I gutted and rebuilt is running Doubles (6KN6) on one channel and Singles (6KD6) on the other. The MC275 xfmr set is running 36KD6 labelled 42KN6 (Singles). Front end on both amps is compactron. The sound is most definitely not 6550's.
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Old 31st October 2017, 11:30 AM   #919
ballpencil is offline ballpencil  Indonesia
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Perhaps this has been covered before but i can't find it. What happens if we tie g1+g2 together and treat them as control grid? Do we simply end up with a beam triode; i.e high rp high mu triode like 6HV5, 6HS5?
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Old 31st October 2017, 02:25 PM   #920
Kay Pirinha is offline Kay Pirinha  Germany
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Have a search for »twin« or »crazy« drive.

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