B&W PT-2500A

[CollinsMan]

B&W PT-2500A 10 Meter Mod

I acquired one of these amplifiers the other day, and am really impressed with it. However, it has not had the 10 meter modification performed, yet.

Do any of you guys know what is required? I understand that B&W once supplied this information to licensed Hams, but the guys at that company tell me that they don't even know what the mod is as they no longer have that information on file. This makes sense, I guess, because that amp was made in the mid-80s. They didn't make a whole lot of them, either.

So, if anyone knows, I'd sure appreciate the info.!

 

[CollinsMan]

I did some poking around on the dark recesses of the Internet and think that I've found the mod. I'll post it, here, in case someone else runs across one of these amplifiers.

1. Remove the cover screws, then take off the top cover.

2. Remove knobs - this requires an appropriate hex wrench

3. Remove the 1 top (center) and 2 bottom screws from the front panel.
Leave the remaining 6 screws in place.

4. Carefully, using a thin shaft flat bladed screwdriver, back off (1-2
turns) the brass screws on the brass coupling holding the shafts of the
Tune and Load capacitors -- just INSIDE the front panel.

5. The front panel can now be pulled outward -- until the Tune and Load
cap shafts disengage their couplings -- then let forward and down
gently.

The front meter panel connector may be unplugged
from the power supply board to allow the front panel assembly to lie
down closer to flat.

10 Meter Modification - Only the input matching circuitry needs to be modified.

1. Carefully inspect the last clockwise setting (10m position) on the
band-switch, both front and back wafers. On some units, the fixed
contact on the 10m position may have raised, so as to prevent it from
making contact. If so, carefully restore it to its operating position. Use
an inspection mirror to view the back wafer switch, as its contacts --
on some units -- face the rear shield wall of the switch enclosure.

2. Add the single coil, described below, across the front and back
contacts of the 10m position of the band-switch. That is, from the
input front wafer of the band-switched 10m matching
filter to the output on the rear wafer.

3. Add a 133pF capacitor, described below, from the FRONT band-switch
wafer (input side of filter) to ground. Use the 15m position's ground
terminal to terminate the capacitor. It is to the immediate left of the
10m position.

*Coil is 18 gauge enameled wire wound on a 0.50" diameter form - 6 turns WIDE spaced

*Input Capacitor is 133pf: a 100pF and 33pF in parallel, both 500v dipped micas

 

[K4WHO]

B&W PT-2500A 10 Meter Mod

I acquired one of these amplifiers the other day, and am really impressed with it. However, it has not had the 10 meter modification performed, yet.

Do any of you guys know what is required? I understand that B&W once supplied this information to licensed Hams, but the guys at that company tell me that they don't even know what the mod is as they no longer have that information on file. This makes sense, I guess, because that amp was made in the mid-80s. They didn't make a whole lot of them, either.

So, if anyone knows, I'd sure appreciate the info.!

I have two of these amps, and was just curious if you still have yours? I have the mod on paper. Original manual also.