Blowing Fuses. Dennis Had Inspire 300B SET

My lack of knowledge. I plugged a Cary Bias Meter into the jack hole on top. It measures plate, not bias. My bad… bias meter went arrow to the right… yet the amp continued to run for weeks thereafter. 

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

Yes. Thanks. I did, and it toasted another one, stopping the others I guess from warming up. It is self-biasing amp. 
 

to be honest, I have two tube amps, and it’s the first time I’ve ever been listening in the middle of a session and for the first time with this Dennis had amplifier, that the amplifier failed or any amplifier turned off so I guess that’s the way it works when that happens. 

I am not sure about the 2amp fuses? Is it right to have a SLOW BLOW fuse as the main fuse? It looks like that is what was present since I bought it used?

  I am happy to report that Dennis Had got back to me and told me after asking what type of rectifier tubes I had, to buy from Tube Depot, and to purchase a JAN Phillips Military rectifier…. also that I needed a slow blow 2 amp fuse, and if this does not work that he would take a look at it for me.

I want to say that you are all very helpful and I want to thank you for all chiming in on this one! Merry Christmas

Plugged in. Turned on without tubes. Fuse is stable. Waiting on tubes now. 

After getting the rectifier tube, the problem still remains as a blown fuse continues and the replacement of the blown fuses continue. The only tube that was able to get warm was the rectifier tube and my Western Electric 300 bees showed signs of life before the fuse did its job. I have contacted Dennis Had and hopefully he will help me. 

Fed Ex has it now, (I think).
 

Shipping with them is 3rd World it seems, at times. 

it didn’t blow fuses with NO Tubes, turned on… with tubes, only the rectifier got warm, as it blew a fuse. 
 

Dennis awaits the shipment. Thanks for your interests!

To Dennis I gave my apologies. I blew up the electrolytic capacitor. I inserted a Cary Bias meter into the jack inlet on board the amp, purely no knowledge on the consequences of THAT action! 
 

Dennis took it back, and repaired it, scratching his head on how it could have happened, until we spoke on the phone.