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@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@cablenet.ne.jp>
> To: amps@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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