In Need Of A Ballast Tube

11/19/2009 10:50:36 PMCharles

I have a GE HJ905 that has a bad ballast tube. Where can I find one of these?

11/20/2009 8:31:38 AMSteve - W9DX

If none of your tube filaments are lighting, it's dead. The RR-782 ballast tube appears to have 3 sections noted on the schematic as R-16A with 19 ohms, R-16B with 90 ohms, and R-16C with 230 ohms. You should be able to replace the ballast with power resistors of the appropriate wattage. You may need to consider mounting them above the chassis since these babies are going to get really hot.
Steve

11/20/2009 9:29:36 PMThomas Dermody

AES and Radio Daze sell original style ballast tubes. While I'm usually all about originality, I do like the diode dropping method because it reduces heat. With a certain radio of mine a 6 pin ballast was missing, so I put a diode in series with the filament string, and then plugged a spare 25Z5 in the 6 pin socket to take up the excess. Worked out perfectly.

11/23/2009 6:46:14 AMEdd

Sir Charles. . . . .

I can certainly see that you might have some exxxxtreme problems coming up with that original RR782 ballas for your set.
That set used s o o o o , many tubes along with a mixing of different filament ratings, that they had to have two separate series strings of those tubes.

Usually there is but one series stringing arrangement of the tubes filaments, and then the need of a sole resistance value within the ballast tube to make up the voltage drop to match with line voltage, less the pilot lamp(s).

And then, there is another resistance value within the balllast to additionallly shunt the pilot lamp(s) filament , and end up with that arrangement also being inserted in the final series of the filament string.

Check out the referencing of your set below, and at the [ A ] perspective you will see the sets treatment of the ballast aspect.

The [ B ] portion is giving a break out and separation of the two different current strings.

Now with due consideration of initially checking out the universal series of ballasts . . . having optionally selectable resistance values . . . and seeing none that would even remotely match up with getting the desired resistance characteristics for this set. I then could only see the use of two ballasts, and EVEN that not being totally sufficient either. That would not justify an $18-36 investment for ballasts to experiment with.

The next consideraton of the use of power resistors was not looking to good from the perspective of an extra 8W + 13W + 6 watts of wasted power and extra heating floating about inside.

Soooooooo, if that was my set, and problem to be solved I would do as I have plotted out down on [ C ] perspective.

A circuitry run down:

I have assigned references [ A ]-[ T ] to the different filamental nodes. I have taken the [A]-[M] of the 150 ma tubes and then
" folded them over ", so that they ended up being paired off with each other to then place sets in parallel, with the exception of the 6N5 which needed a series resistor to make it an equivalency of a 12 volt filament tube @ 150 ma.

Since the 12SF5 was the tube that could be the most sensitive to stray hum pick up from its H-K internals, it remained at the very closest to ground potential for its filament source, this then made the "fold over" occur at the 12J5 pairs junction.

The other end leg was the 40 ohm leg at [M] which ties in to 12FS5's [A]. There was an option of two paralleled 36 volt strings of tubes, BUT, also from the induced hum perspective, the pairs were shunted at the [B-C-L-K] and [D-E-J-H] nodes.

With that string set up, then there is the need of the tie in to the " O-fish-ull " 300 Ma tubes by connecting [F-G] node to the
[N] node of the 25CG6 tube.

The end of the 300 mA string at [ T ] gets connected to the pilot light cluster which has received a shunting resistor of 220 ohms at 2 W metal film resistor along with two Zener diodes shunting the duo.

The shunt resistor makes the otherwise 250 Ma lamps conform with the 300 mA characteristics of the new filament string.
The Zener diodes take care of voltage hold down of the pilot filaments supply level.

Particularly, if the set is turned off, then flipped back on within a few seconds. (Did he just say what I think he said ! . . . like he was going to say it again ? )

The 6-8v spread spec of the series #44 lamps . . now at . . . 12-16 v, fall right in the high end of that 15V clamp level, yet those diodes presence, will be transparent, circuit wise, after the set fully warms up.

Final Info:

The original schematics RED x's signify the insertion points of the revised wiring to the old wiring of the set. The red bars designate the delineation points of the old ballast circuitry.

The assignment of the [A] - [T] designators is also coincident with their being properly associated with the 2 & 7's and the
7 & 8's sets of the tube filament connections, as they are NOT designated on the schematic, and only your chassis examination will reveal that.

When all logged down there, is very little chance of making a wiring error when consulting against them and then making a very final point by point check out .

Thassit . . . . .

Concurrent Referencing:

73's de Edd

11/23/2009 1:28:34 PMThomas Dermody

Regarding the zeners, you want them wired in series with eachother, not in parallel with eachother. If you wire them in parallel, the bulbs won't light at all, because depending on the direction of instantaneous current flow, one zener will always be shorting out the pilot lamps. When placing zeners across a lamp or tube filament, and when dealing with alternating current, you must select two zeners, each rated for the voltage you wish to drop, and then wire them back-to-back (+ to + or - to -). Wire the two zeners strung in series in parallel with the device (lamp or tube) you wish to protect.

...Also, if you decide to just use one zener in parallel with the device you wish to protect, the device will only light to about half brightness, for it will be the same as if it was being fed with an unfiltered halfwave rectifier. The zener will be shorting out half of the AC wave, and only regulating the other half. That is why it is necessary to wire two back-to-back.

11/23/2009 1:34:33 PMThomas Dermody

Also, upon looking at the schematic, since I originally did not, I realized that if you change all of the 12 volt tubes to 6 volt ones (300 mA), and then just wire the entire string in series, you'll come up with 111 volts, with little left to drop through a resistor. Although the set is interesting in design, it seems a bit gimmicky, with two rectifiers and only one output tube. Changing over all of the 12 volt tubes will certainly simplify matters.

11/23/2009 1:40:02 PMThomas Dermody

...And at 111 volts, you might not even need a dropping resistor, for the two pilot lamps require about 12 volts, so that'll give you an entire rating of about 123 volts, which should be fine. You will still need to protect the bulbs with zener diodes and a resistor, however. You can simply use zener diodes without a resistor if the diodes can handle over 300 mA, but it is best to include the resistance originally shown in the schematic, for it will protect the zeners should a bulb burn out, because the zeners might not like having a full 120 volts being applied to them.