Frank,
I put an 76pa into service a couple of months ago - it also had some flaky
characteristics similar to what you mention. Turns out
it was what looked like cold and/or missing solder on some of the braid
connections at the bandswitch and also at the tube anode
caps.
Carl actually was the guy who suggested I look for it. Never seen it before
myself. But in closer checking, there were 2 spots on
the bandswitch soldering contacts and two of the 3 anode plate caps which
looked void of solder.
Never did figure out what caused the condition - but cleaning and resoldering
these contacts put the amps performance back on track.
It's been pushing out sweet watts since then with no complaints at all.
73, Jeff ACØC
www.ac0c.com
-----Original Message-----
From: Carl
Sent: Thursday, January 27, 2011 10:57 AM
To: VO1HP ; amps@contesting.com
Subject: Re: [Amps] Alpha 76CA Operation
The Ig doesnt tell us much without knowing the drive power.
That amp should do a comfortable 1500W out with 100W drive if :
The CA and PA also has a low and high drive option, with the original high
drive resistor pack it will be impossible to get 1500W with 100W drive but
the tube finals rigs used then could easily run 120-140W.
You can also get a decent idea of tube condition by removing 2 tubes,
stuffing paper towels in the holes and driving the remaining tube with
20-30W on 40M. Then repeat with the others. Input matching and tank Q will
be off but we are just looking for a relative comparison. Keep IG down to
25ma.
Carl
KM1H
----- Original Message -----
From: "VO1HP" <fdavis@nfld.net>
To: <amps@contesting.com>
Sent: Thursday, January 27, 2011 11:32 AM
Subject: [Amps] Alpha 76CA Operation
>I am helping a friend check out an Alpha 76CA ser # 69XX. I wonder if
> anyone can tell me what the typical CW output power should be for 700ma
> plate current and grid current in the 70ma range. We notice that
> while testing on 160M that the grid current will flop around a bit up
> down around the above figure. The amp has been in storage for about
> 20 years. We reseated the tubes and the various molex connectors.
>
> The amp tunes normally but the output seems low? On 160M we see
> about 700-800W and on 20M about 500W at above noted plate and grid
> currents.
>
> Amp is plugged into 120VAC line.
>
> 73 Frank VO1HP
> St.John's NL
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