[Amps] Alpha 78 Problem

[Jim Barber]

Apologies for hijacking the thread, but speaking of the Alpha 77 bias, 
is there a preferred method for defeating the "active" part? I remember 
seeing somewhere that some revs had a pot for adjusting it that could be 
put at an extreme to continuously enable bias, but I don't believe 
either of my 77's has that pot.

Why do it? Probably not a good reason, but I've been asked maybe 2000 
times "Are you running VOX?" - I get tired of explaining how the active 
bias circuit in my amplifier would make it seem so. Unless the cooling 
system is otherwise inadequate, (and I don't believe it is) I'd rather 
just be done with it.

Thanks,
Jim, N7CXI

k8mlm at aol.com wrote:
> Isao,
> 
> The normal warm up time for the Alpha 78 is 3 minutes.  However, dur to the age of the caps and/or carbom comp resistors in the timer circuit the timer may not work or take a long tome to turn on.
> 
> I have an old Alpha 77 and have to overhaul (replace caps anr resistors) on the turn-on timer and active bias control boards to keep it operating properly.
> 
> Bob
> K8MLM
> 
> 
> -----Original Message-----
> From: isaonuma <isaonuma at cablenet.ne.jp>
> To: amps at contesting.com
> Sent: Tue, Dec 29, 2009 6:08 am
> Subject: [Amps] Alpha 78 Problem
> 
> 
> Hello all,
>  I have recently bought Alpha 78 and it's faily clean. I checked inside and
> eemed OK. So I connected 220V line and swithed on it. High voltage shows
> 500V+ at CW, 2000V+ at SSB mode. Air flow is OK and getting warmer little
> y little. But, not as mentioned in the manual there is no illumination of 
> ale
> ed or amber. I waited for 45-90 seconds, but there is any change of light 
> or
> ny click sound of relays. Maybe there's some failure on 28VDC line. 'Cause
>  didn't hear any sound from K2-Step start relay.
> ny comments, suggestions are appreciated.
> 73, Isao JH1ROJ/KG8XV near Tokyo, Japan 
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