1. Government Surplus equipment
Why consider using and modification considerations

2. Using Such Equipment Proven design Cheap
Availability is generally good
Documentation usually available
Components are top quality

3. Past equipment BC-457 (Command Sets) APX-6 BC-458 “ T-368 BC-458 “
BC-348A thru Q Models RT-68
R-389
R R-390A
AM-494
SCR-522

4. Popular 144-220-432 Equipment AM-494 AMP (2 X 4X150A)
SCR (2 meter AM 15 watts)
AM-6154/55
Modifiable to 2 – MC
AM=6155
350 – 400 watts All bands
Readily available
Reasonably priced – $ plus tube

5. AM-6155 Conversion data easily attainable High quality
Tetrode tube (lower drive requirements)
Cavity tank circuit design
Desk top unit
-heavy-
No special tools needed to complete mod.

7. A few evenings (Weekend timeframe to mod.)
In stock at Fair Radio Sales – Lima, Ohio
Numerous mod procedures on line
VE2ZAZ – W3RJW – K7XC
Plenty of assistance available
Can be made to appear as an attractive piece of table top amplifier.

8. AM-6155 AMP Must build a new grid input circuit
Must build a new grid negative voltage regulation circuit.
Modify AC input to operate on 220 VAC
Blower may be noisy
For tabletop usage install a god set of rubber feet
AC input connect may be modified

9. AM-6155 Improved Grid Bias Ckt.
Uses a LM-337T Negative regulator
Uses 9 parts
Can be mounted a small PC board
Construction not critical
Plenty of space inside to mount
Advise that you test first on the bench

10. Modification suggestions
Remove input coupling knob and shaft
Close front hole with a rubber plug
Remove black name plate from front of cavity unit.
Erase the unused lettering
Painting is optional
Use 4 good quality rubber feet
(remember the unit weighs about 80 pounds)

11. Tune up and operation Turn unit on – power light should come on
Check meter readings
Wait at least two minutes
Turn on high voltage switch – HV light should
Come on.
Again, check meter readings
Key unit via external pnono jack in rear of amp

12. Operation continue Key unit and adjust bias pot for 70 – 80 ma.
Check voltage on screen and HV
Screen 40 = 400 volts
High voltage = 20 or 2,000 volts
Apply a small amount of drive (2 – 5 watts) and adjust input tune for maximum Ip
Connect a watt meter to output and again adjust input tune, plate tuning and outputcoupling for maximum output.

13. Operation Cont.
NOTE: If another watt meter available place in the drive input so you can monitor the input and output power simultaneously.
Apply NO MORE than 10 to 13 watts.
Output, if all meter readings are with in limits should 275 to 350 watts.
Plate current (Ip) should not exceed 300 ma. For an 8930 – 350 ma. For a 4CX400A tube.