Before anyone tries to use the PT-2500A for serious work, they should
get in touch with me. I had 3 or 4 heartaches with this amp during
contests and found a number of design problems that can be easily
fixed. Not sure if the B&W version of this amp was any better.
Some highlights:
1. Screw goes down into windings of RF choke (use shorter screw).
2. HV on shaft of rotary switch when in 15 meter position (swap with cap).
3. Wattmeter is hopeless.
4. 160 meter load caps have poor Tc - use 8 10K pf micas in series.
5. Toroids for 80/160 break down - use an air coil.
Also, good idea to add cold start circuit. After making about 13 mods,
this amp is very reliable.
73 Tree N6TR
tree@contesting.com
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|