Pride Amp Series, Service Manual

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Copyright © 2004 CBTricks.com
Pride DX300 CHAPTER 4
4.4 Voltage Checks
As the voltages present on the DX-300 chassis are potentially lethal, the procedure below must be followed
when checking voltages.
1) Make sure that the unit is unplugged and has been off for several minutes to allow all voltages to bleed to zero.
2) Remove the top cover. Doing so will engage the safety interlock so never apply A.C. power when this cover is
removed.
3)
Loosen and remove the anode clamp from the 4CX-250B tube
(V1)
. Remove the tube, the ceramic chimney,
and the anode clamp from the chassis.
Make sure the parasitic suppressor
(Z2) is suspended away from any chassis parts.
4)
Replace the top cover on the amplifier.
5) Lay the amplifier on its side or top and remove the bottom cover.
Remember the tube must be removed or it will be damaged by the loss of cooling air when the unit is powered
without the bottom cover.
6) Apply A.C. power to the unit. WARNING: Extreme caution must be used when working with voltages of this
level. Always be cautious and alert while working on the live chassis.
7)
Refer to the individual circuit board pictorials for voltage readings and locations. Voltages on the tube socket
are as follows:
Pin 1
+350 VDC, ± 10%
Pins 3 and 7 6.3VAC, ± 10%
Grid Connection -82 to -64 VDC, depending on the setting of bias control and mods installed.
Caution:
When measuring the B+ supply (+2200 VDC), use only a meter, which is designed to measure 2kv
plus safety during operation at high voltage levels.
8)
Restore the unit to its original condition.
4.5 Preventive Maintenance
There are four circuit boards in the bottom compartment have all the wires attached to them with small spring-
metal socket contacts. Pull each of the socket contacts one at a time. If any of them that feel loose when you pull
on it should be GENTLY squeezed with a small pair of pliers so that it has some friction when you push it back
onto its circuit-board pin. Check for burnt components on each of the circuit boards replace as needed and look
for reason for failure.
Important
When you put the bottom cover back on check the seal and be sure that you put all the screws in.
Also be sure that the 3 screws on the back of the top cover are installed.
Now take a close look at that big copper hair-pin
(Z2)
that attaches to the tube clamp topside. If the resistors look
like toast, new resistors should be installed before you try to run it.
If the resistors look okay, and it has all 3 of them, leave it alone. If you replace them, we recommend using a 5-
Watt rated 100-ohm carbon-film or metal-film resistor. They will withstand more abuse than the original 2 Watt-
rated parts. DO NOT use wire wound resistors. Period. Both Mouser Electronics and Westgate Labs sell this
resistor.
Check the main fuse
(F1) in the back, and check the rating printed on it. The correct size is 10 Amp, 125 Volt or
250 Volt. A 32-Volt fuse is NOT the right type for this amplifier.