Interpreting "Horizontal Osc. Service"

[geezertron]

When I'm looking at a pentode's maximum ratings and it says "for Horizontal Oscillator Service" (which seems to mean something close to 15% duty cycle), where and how has this been factored into the values?

Specifically, if the plate is rated to dissipate 2.5W, has this value already factored in the average of the duty cycle? Put another way, would it dissipate 2.5W of DC without trouble?

Thanks.....

 

[BinaryMike]

Well, the short answer is YES, but there might be more to discuss because horizontal output tubes seem to be able to dissipate quite a lot more in audio service than what's specified for TV service.

 

[geezertron]

Thanks. In this particular case I'm looking at using the tube for a CCS, and all I really need to know is how much current can it pass at a particular voltage. Likely to never stress it in this usage, but I wanted to be sure.

 

[JMFahey]

all I really need to know is how much current can it pass at a particular voltage.

V*I=W
W<rated plate dissipation: fine
W>rated plate dissipation: bad

 

[DF96]

Anode dissipation can be averaged over a few seconds. Screen grid dissipation over a bit less than a second? Cathode emission averaged over a few microseconds? Hence a valve meant for pulse operation needs a big cathode, maybe grid2 coolers, but a normal size anode.

 

[Tubelab_com]

I worked on tube TV sets from the 60's through about 1973. Most horizontal oscillators that I encountered were half of a twin triode, usually a 6SN7 or 6CG7. Dissipation was not the issue, peak plate voltage is. The horizontal sweep drive is a sawtooth, ramp, or another more complex waveform in some color sets, with a huge flyback pulse that drives the horizontal sweep output tube to cutoff.

Which particular tube are you looking at? That may help us figure out what they meant.

 

[DF96]

Sometimes 'horizontal oscillator' is used in datasheets as shorthand for 'the whole line/sweep circuit' so this pentode may have been for 'line output/sweep' duty.

 

[geezertron]

The tube is a 6BH11 (spec attached). I'm playing around with the idea of using the pentode as a CCS with the two identical triodes on top as a LTP. This tube is one of the few twin-triode pentode compactrons where the triodes are identical.

 

[BinaryMike]

I used a 6BH11 successfully in my most recent power amp project: Bonseki 20/20. Here's the schematic.

 

[JMFahey]

I know those tubes were designed for exceptional performance in switching type circuits, fine, and under those circumstances high current narrow peaks make sense, same as narrow pulse dissipation averaging, pus they atre used at very high, fixed frequencies, so compared to them , even short time constants are long enough, cool, but since we are in DIY Audio and not in the Class D or SMPS area, I take the liberty to assume that we are talking analog audio, class A/AB (not Class C) and that sinewaves are useful test signals.
Under those circunstances, what I stated in post #4 should apply .

 

[Miles Prower]

Thanks. In this particular case I'm looking at using the tube for a CCS, and all I really need to know is how much current can it pass at a particular voltage. Likely to never stress it in this usage, but I wanted to be sure.

This won't be a problem if it's your intent to use the triodes as an LTP with the pent as a tail load. Horizontal oscillator is a small signal application, so if you don't bust any specs you'll be OK. The 2.5W P_D spec should present no problem for a small signal audio application.

As for how much current at some specific voltage: P= VI -- it really is that simple.

 

[Sch3mat1c]

The main difference is the peak voltage and current will be higher, for a variety of reasons.

If you compare the ratings between Class A and Osc/Amp service of typical examples (e.g., 6SN7, 6BX7, 6CD6, etc.), you'll see similar ratios; apply basically the same ratios elsewhere.

Tim

 

[Tubelab_com]

The tube is a 6BH11

I have played with that tube.....read this "secret" GE list. It tells you what's really inside the glass.....the 6BH11 is two triodes and a pentode stolen right out of the 6GH8.

The spec that is unique to "horizontal oscillator service" is the peak cathode current. You can suck 300 mA from that cathode for a very short period of time, followed by a cooling period that's nearly 6 times longer (15% / 85%). This spec is meaningless for a CCS. The 350 volts max, 20 mA max, and 2.5 watt max specs are the only constraints that apply here. Keep usage within all three (with some safety margin) and there will be no problems.