[EICO] Eico 720 putting out an awful note

[shoppa_eico at trailing-edge.com]

> Well first I have to ask is the VFO/XTAL switch in the proper position?

Yep.

> What size choke did you put in to replace the burned out one?

A 2.5mH choke, the same inductance as the original.  But... the original
was 4 pi-sections around a ceramic former.  The new one (made by
Hammond) is 3 pi-sections around a ferrite former.

> Check out the 6AQ5 clamp tube if possible

Will check around it.  I'm hindered by my lack of understanding of
how the clamp circuit is supposed to work, but seeing as how it's
involved with keying as well it's probably worth learning about.

Another general note: this transmitter probably hasn't been on the
air in several decades.  I checked out all the resistors for correct
value and checked all the chokes but that's about it.

I'm used to seeing VR tubes (e.g. OA2) around the oscillator in
these simple transmitters.  I suppose it helps give a cleaner note.
I'll try scoping out the B+ and screen voltages and see what 60Hz
I see there.

Also, there's no neutralization adjustment on this radio.  (One
of the reasons I put a 6146 in place of the dubious 6146B).  Is
there some way of checking for proper neutralization and lack
of parasitics?  The output looks clean on a scope, I see some 60Hz
AM (a few percent) but it doesn't explain how bad the CW note is.

Tim.