From: Ron Wagner 
Subject: RE: [drakelist] AC-4 rebuild ???


Ron Wagner  made an utterence to the drakelist gang
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Dave,
The loss of the bias on any amp with it keyed would do some major damage. 
Think about it a minute, the bias is a negative voltage that is designed to 
"hide" the large positive plate voltage from the cathode.  Without that 
negative grid "hiding" the plate, the tube goes into full conduction.  As 
much power as the power supply can produce will be run into the 6JB6s. 
Keep in mind that the AC-x supplies could provide well into the 300+ watts 
input into the rigs finals.

A 3-500 going "full bore" without bias would "blow up"
fairly quickly too. 
It is that the loss of bias also keys the rig in the Drakes.  That turns 
the 6JB6s on full and very quickly turns the tubes bright red and then 
crack, or implode.

I have not really paid a lot of attention to any tube radio other then 
Drake, so I am going out on a limb here.  I would think the same kind of 
thing would occur to a Heath, Kenwood, Yaseu, Collins ....... if their 
bias supply shorted and did not get their plate voltage shut down (ie 
blown fuse).

73,
Ron

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Visit my astronomy home page.   http://www.dma.org/~wagner
Amateur Radio Station: WD8SBB - Ron  and  KB8NRP - Joann
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On Wed, 2 Feb 2005, Dave Meadows wrote:

>
> "Dave Meadows"  made an
utterence to the drakelist gang
> ----------------------------------------------------------------------
> Keith:
> Thanks for asking what I've been asking in the back of my mind.  I've heard
> that if the bias supply goes the radio fries and other such dire
> predictions.  I've worked on lots of vintage gear and have had power supply
> filter caps short out and over heat transformers and take out a resistor or
> two but never had the actual "working" part of the gear
harmed because of
> it.  Maybe there's a first time for everything.
> Dave Meadows - K4LDI
>
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