[Milsurplus] RAK question

[Bruce Gentry]

The 876 ballast was called a "Barretter" tube by RCA. It has an iron 
filament and is filled with hydrogen under pressure, it gets blazing hot 
so it needs to be in a chimney enclosure of some sort or the glass will 
be strained and it will shatter- quite loudly. Some early AC powered 
entertainment receivers that had direct heated filaments used the 876 to 
protect the tubes from voltage surges. The tube is used in a highly 
inefficient "brute force" circuit where most of the power goes to the 
resistor in series with the tube and the power transformer in paralell 
with the resistor  just "goes along for the ride".  I had an RAK and RAL 
(which I very foolishly traded away), and  put a piece of fiber 
insulation under the center contact of the 876 after setting the switch 
to unregulated. I wanted to keep the tube in place for novelty and 
completeness of the power supply. Please do check the voltages in the 
power supply to see if today's 120 or more line voltage is too much even 
with the transformer taps set at their highest.  I have not yet seen a 
regenerative receiver that works as well and is as easy to control the 
regeneration as these. They may be archaic, but can be a very nice 
surprise.

       Bruce Gentry, KA2IVY

On 12/25/17 5:35 PM, Kenneth G. Gordon wrote:
> On 25 Dec 2017 at 22:07, Joe Connor wrote:
>
>> Ken, is the ballast the 38274, the 38593 or the 38276?
>   
>
> The 38276 is an 876 and is the ballast tube. It is quite tall, and has a long filament in it. It
> also has a mogul screw base like a big light bulb. It is surrounded on three sides by a
> reflective piece of metal. You must both unscrew that tube, and operate the switch in there
> which bypasses it.
>
>> Do I have to rewire
>> anything to take it out of the circuit or just remove it?
> No. No rewiring necessary at all.
>
> As I said, there is a switch in the power supply which bypasses the ballast tube. As I
> remember it, the switch is under the ballast tube, but I am not sure, no longer having any
> original power supplies. You do not have to do any rewiring. The power supply is all set up
> so you can simply switch the ballast tube out of the circuit.
>
> Both Al and I recommend completely removing the ballast tube since even when it is
> switched out of the circuit, it still remains "heated", uses unnecessary power and causes
> unnecessary heat.
>
>
> Ken W7EKB
>
> ---
> This email has been checked for viruses by Avast antivirus software.
> https://www.avast.com/antivirus
>
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>