Martin,
You mentioned having to solder the 10 meter lead back to the switch or coil.
Regular 60/40 rosin core solder will work here since that is strap material and
a heavy connection. Just make sure the connetcions are good and clean, then use
a 200 watt gun to heat them with. Silver solder is generally used in high heat
applications where the temperature of the part can get hot enough to melt
lead/tin solder (3-500Z heater pins). If the 10 meter coil is wound with a
large enough conductor, it will not get hot enough to melt it. The coil which
can get hot is for the lower bands, especially a few turns behind the 10 meter
coil. This is because of the signifigant change in wire size between the two.
Some of these coils you can tell have turned dark for a few turns where they
get hot. If no turns are darkened, nothings been hot. If you use silver solder,
you'll need a heat source different than a standard iron like a small butane
torch. I think you'll find though, the original connections use standard 60/40
type solder. I have used it for years and never had a problem with it.
Best,
Will
----- Original Message -----
From: "Martin Sole" <msole@loxinfo.co.th>
To: amps@contesting.com
Subject: [Amps] Alpha 78 rebuild, some questions.
Date: Sat, 23 Jul 2005 19:57:13 +0700
>
> A short while ago I acquired 2 Alpha 78 amplifiers. Both were pretty dirty
> and in need of some serious attention. One of these amplifiers is now
> cleaned up and working, sort of, it puts out about 1300 watts with about 70
> watts of drive on 20m and below. I have yet to try 15 and 10 but before I
> try 10 I need to fix the broken strap going from the coil to the switch, I
> presume regular solder is not appropriate!
>
> I manufactured chimneys out of silicone rubber sheet and fitted an extra fan
> to the back of the power supply area. I can blow a sheaf of about 10 sheets
> of 80gsm paper off the top now. With just the internal fan I could barely
> move 2 sheets. My understanding is that the type of fan fitted has its speed
> controlled by the AC frequency, in this case 50Hz, giving a speed 20% less
> than it would be in the US operating on 60Hz, is this not significant?
>
> The Alpha 78 wires the fan across one of the 120VAC primaries together with
> a 25VAC buck winding setting the fan voltage to 95VAC, why would this be?
>
> I didn't check with the internal fan only but with both fans running and
> using my cheap Chinese multimeter with the supplied temperature probe taped
> to the top of the case in the airstream I get the following. Normal room
> ambient varies around 27 C depending on how much airconditioning is running.
> Amp on and in standby, after the 1 minute warm up about 30 C. Normal speech
> at about 1200 W out it goes to around 78 C and with the processor on I have
> seen about 95 C. Second question, can I relate these figures into something
> useful to know if or not the tubes have enough air through them?
>
> Thanks
>
> Martin HS0ZED
>
>
>
>
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