[Amps] AL-1500 pi-network capabilities

[Will Matney]

Rob,
I almost didn't catch your question below about the low frequency coil 
in tank circuits. Yes, the type of core used on the coil can cause a 
coil to heat up. Preferably, this should be a true air coil. The form is 
used to keep the coils conductors spaced evenly from turn to turn. 
However, I prefer Air-Dux coil for this or a similar material. The 
reason being is the air flow being able to cool the coil easier. The use 
of solid cores block any air flow to the wire. Air-Dux was designed for 
this specific reason. Some manufacturers wind their own low freq coils 
and don't use anything to space the windings. This spacing really 
doesn't need to be 100% accurate. The thing is, a long coil of smaller 
diameter wire will "droop" under its own weight. Generally coils wound 
with no type of form use a heavier wire for this reason. One example of 
this is inside a QRO amplifier. They use coils they wind themselves, 
generally to save money over buying Air-Dux as it would be more 
expensive. Low freq coils can be wound easily using tinned "buss wire". 
The use of a small lathe makes winding even coils easier too (making one 
right now =)). B&W (and Cardwell I think) still makes Air-Dux coil and 
the clamps for the taps. They have a listing for it on their website. 
You can also get Air-Dux wound with flat wire. This was used on both 
fixed and some rotary inductors though most rotary use round conductors. 
A rotary inductor is about the only application where I would use a 
solid tubular form and would be a must. The reason I think some use 
tubular cores is its mounting features. Most of these forms have a set 
of holes to mount the core on standoffs. One thing about the taps, I 
prefer to use soldered connections directly to the coil, and not use a 
clamp because of corrosion.

If you take a look at that Ten-Tec coil, It shows a blue discoloration 
at the topmost coils of wire. This is a sure sign it was hot. The high 
freq coil has some discoloration but this is from the plating itself.

Will Matney

Rob Atkinson, K5UJ wrote;

Hi Will,

> thanks very much for these observations.  I apologize for not giving 
> more information.  I naively thought the photos would be enough.  
> interesting what you said about the low frequency coil, as I have 
> heard that having it wound on a solid cylinder form may be a problem 
> (heat buildup?).
> I wish I had one of the original h.v. transformers.  I would be glad 
> to send it to you but I guess the shop kept it.  your comments about 
> coil tube thickness and plating very interesting also.
> Why don't these amp manufacturers just bite the bullet and make us an 
> amp with the needed monster coils?