[ARC5] [Milsurplus] RAK question and RAL

[Peter Gottlieb]

Hydrogen gas has a high thermal conductivity. That is likely why it was used. 


Peter

> On Dec 26, 2017, at 1:04 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:
> 
>> On 25 Dec 2017 at 20:03, Bruce Gentry wrote:
>> 
>> 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 
> 
> You can say that again!
> 
>> so it needs to be in a chimney enclosure of some sort or the glass will 
>> be strained and it will shatter- quite loudly.
> 
> Hydrogen in air is explosive. And the RAK/RAL power supplies do have a chimney of sorts. 
> The 876 is mounted in the exact center of the power supply, facing the back and is centered 
> in a chimney of sorts.
> 
>> 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".
> 
> Yes. For OUR purposes, a total waste of power and a source of unneeded heat.
> 
>> 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.
> 
> And I completely agree with you. In my opinion, the RAL is the very best HF regen I have 
> ever used, and the RAK is excellent at MF and VLF too.
> 
>> They may be archaic, but can be a very nice 
>> surprise.
> 
> As I've said before, I used my RAL-7 for something like 12 years as my only station receiver. 
> My ONLY complaint with it was the frequency readout, which was essentially non-existent. 0 
> - 10 and 0 - 100.
> 
> Other than that, it simply sat there and always worked.
> 
> I turned it off after about 8 years to check the tubes, found nothing wrong with them, so I 
> turned it back on and left if.
> 
> It has a certain "transparent" sound to it, like you are directly connected to the RF spectrum 
> with nothing in between you and the stations you are working.
> 
> I only wish it wasn't quite so big.
> 
> Ken W7EKB
> 
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