Is there a schematic here somewhere of a flor. ballast, two lamp. Two red, two blue and two yellow, with of course the feed. Iam curious as to how the coils are layed out internally.

Not yet, but four days ago Scott wrote: "I'll post some Ballast drawings ASAP...", so stay tuned.

habbbby,

Sounds like you are describing a Rapid Start - Hot Cathode Ballast for 2 lamps - typical of F40T12 lamps and HO/VHO lamps of 4' and 8' length.

Unless something changes between tonight and Friday, I will have a whole weekend off!!! Ya, Baby!.

Plan to post a few Audio Xover [passive] schematics, a couple simple motor drawings, and whatever I can draw/convert/post. I'll add a couple Ballast drawings - especially the RS hot Cathode Ballast you are asking about.

Your request is granted

Scott SET

cool!

yes that is the specific type I was asking about. Thanks, I will be looking for it!

Well, the Monkey wrench of time got thrown into the cogs of my "so-called" weekend off

Instead of getting things done like previously planned, only had Sunday off [thankfully ] - which gave me enough time to get 25% [1/4] of things done

Nevertheless, I have posted the Ballast Schematic in the new Technical Reference area, which habbbby was inquiring to.
It's under the subject F40 T12 2 lamp Ballast schematic type 1

I hope it's to your liking!!!

P.S. check out the speaker crossover schematics posted there too..

Scott SET

can the function of the 'heater' winding be explained?

It is a property of most materials that they will give up electrons much more easily when hot - meaning temperature. This was common nuisance with tube devices that had to be turned on to warm up for several minutes before they would begin working.

Cold cathodes typically employ a much higher discharge voltage so they can emit adequate electrons at typical room temperatures. Alas, this is much less efficient.

Hot cathodes have a heater (basically a little tungsten filament with a special coating) that emits lots of electrons to travel through the gas in the tube and make it glow.

Hot cathodes are quite a bit more efficient. About the only advantage of a cold cathode is the instant start..

thanks...
would this explain HO's ?

I just noticed your question. What is it that you wanted explained?

Hi again Steve.

Better late than never...

Well, Dspark covered the reasons for using Hot Cathode emission rather well, and the primary reasons for the heater windings in the ballast.

The older T12 Fluorescent lamps with Bipins will be continually heated [the cathodes, that is] during startup and during operation.
The Heater Windings found in the Ballast supply the lamp ends with around 1.0 amps at around 2.5 to 4.0 VAC. The current which the lamp uses to create light, flows through the Heater Windings without any Impedance [minimal Impedance], so during lamp operation, there's actually two separate currents flowing out the ends of a lamp.

Take notice to the series connection between the two lamps, via the secondary heater winding's taps [the yellow circuitry]. That's why when one lamp is removed, the other quits operation and just flickers. The flickering is due to some small lamp currents being able to flow into the secondary heater winding, or through Capacitive Coupling to the grounded conductor / ballast inputs.

As Dspark said, the Hot Cathode method is most efficient for Rapid Start Fluorescent lamps, operating at low frequencies [less than 1 KHz].
These lamps will produce/consume very near their rated wattage [40 watt lamp will come close to consuming 40 watts and producing a resultant light output to that 40 watts].

The T8 lamps are Cold Cathode Instastart lamps, connected in parallel [most of the time]. The frequency is close to 40KHz, so they run a little more efficiently than if at 60Hz.
They still only consume/produce 90% of their ratings [32 watt lamp will consume maybe 28 to 30 watts max, and produce light accordingly to the consumed power].
Their greatest advantages are no hot cathodes [no wasted power, longer cathode service life] and parallel connections [1 lamp fails, the rest can continue to operate].

To overcome the "dead" starting problem of cold cathodes, a very high starting, or open circuit voltage is used. It's like 2 times the OCV of the hot cathode emission lamps [750 VAC as compared to 300-450 VAC].

To answer your question regarding the HO / VHO lamps, this is the Ballast circuitry for the T12 size HO / VHO lamps.
The only difference is they draw 800 milliamps per each HO lamp, or 1500 milliamps per each VHO lamp, as opposed to 460 milliamps for a standard T12 lamp [such as F40T12CW].

Newer HO / VHO setups use the high Hz cold cathode electronic ballast circuitry, but they would be T8 sized lamps too [I believe...]

Let me know if this answered your Q's.

Scott SET