Here’s Dennis:
INSPIRE 300B AMPLIFIER
I have not written up a formal manual for the new Inspire 330B amplifiers. Please read the following information below:
Make sure you insert the WE 300B tubes with the Western Electric logos facing forward. Large pins forward.
The 5U4 or 5AR4 rectifier tube is located to the far right up front of the power transformer. The 6SL7 driver vacuum tube is centered between the 300B output tubes
When first powering up from a cold start you may hear a slight hum in the loudspeakers as the
300B tubes auto bias up. This is normal.
You may notice the amps runs warm to the touch on the power transformer side. The heat generated is from a non-inductive power resistor dissipating the heat through the aluminum chassis. This resistor is part of the DC filament power supply. If you remove the bottom panel of the amplifier you will see the large aluminum resistor mounted to the side of the chassis near the power transformer.
The 1/4 inch jack located on the top of the amplifier behind the left facing 300B tube is for doing a simple, 300B cathode voltage check/reference. Your amplifier test voltage is:
10
vdc. Date: / 119 23
To calculate the plate current of the 300B output tube:
Simply plug in the 1/4" two circuit jack and hook the black lead to negative and the red to the positive of your DVM meter and measure the DC voltage of the output 300B tubes. Simply divide the DC voltage shown on the meter by 490 (auto bias resistance value) and this is the
plate current for both tubes operating. Example divided the indicated de voltage by 490 = Plate
current of both tubes then divide this total by 2. Now you will know the platte current to each
tube. 68 volts de divided by 490 = .138 divide by 2 = 69 ma. per 300B
To operate as a basic amplifier simply open up the front panel volume control to maximum.
These are the basics. Enjoy your new Inspire 300B amplifier and be sure to fill out the Western Electric 5 year warranty cards for the 300B tubes. List Inspire by Dennis Had as the distributor on the WE form.
Thank you and have a wonderful day
Dennis J. Had
78
490
=. 143=2 = 7/ ma each