[Amps] Hard-drive Dive

[Gary Schafer]

Phil Clements wrote:
>>I am pretty sure that the choke is a National R175A. It has several pie
>>sections on it. I think it is 145 micro henries. One catalogue says 225
>>but a couple of reference say 145.
> 
> 
> The 175A is not a pi-wound choke.
> Describe yours a little further, and I'll run it down for you in the National
> catalog. I expect you have an R-152 or R-154.
> 
> The R-175A should not have resonances in the 160-80-40-20-15-10 meter
> bands unless it sits in an unusual environment in the amp.
> 
> Most of the old National chokes will not work on some WARC bands, or
> some even on 30 meters.
> 
> Over the years, construction articles using the R-175A choke had the
> builder removing turns due to layout and other resonance problems.
> If one of these is picked up used, it is a good idea to see if the form
> is full of wire to assure the old factory specs.
> 
> (((73)))
> Phil, K5PC
> 
> 
> 
You are right Phil. It is not pie wound. I used the wrong term. It has 
about 5 sections on the lower part about 1/2 inch in height each and 
about an inch in diameter. Then a tall section on the top about 3 or 4 
inches long and about 1/2 inch in diameter. The winding is a single 
layer. Each of the lower sections form individual chokes of around 10 
turns each (guess). Well, you probably know the R175A anyway. I am 
pretty sure that is what it is. It was quite a popular choke years ago. 
When I built that amp there were not any WARC bands. I think it was new 
so should have had all the turns.

I also have one in a pair of 4-400s amp that I haven't fired up yet.

73
Gary  K4FMX