[Drake] TR7 PA problem: part 3

[ltaft at charter.net]

You should have an increase in drive signal as the frequency increases.  The gain of the amp decreases with increasing frequency.

Using an oscilloscope on the input to the amp board I measured the following:

At 3.5 MHz
Input to amp board 1.6 volt peak to peak.
Output 120 watt output.

At 28 MHz
Input to amp board 6.2 volt peak to peak.
Output 85 watt output.  

73, Larry  K2LT
drakerepair.com
800-687-9161

> 
> From: "ik2bcp - Guido Tedeschi" <guido.ted at tin.it>
> Date: 2005/02/05 Sat PM 03:26:49 GMT
> To: <drake at mailman.qth.net>
> Subject: [Drake] TR7 PA problem: part 3
> 
> Maybe, the problem seems to be in the finals, already substitued because it 
> is a 2sc2879 pair.
> Disconnecting the bases of both final transitors and measuring the output of 
> drivers, across T2303 secondary, R2317 and C2306, the signal is regular with 
> about the same amplitude across the HF frequency range, when loaded with a 
> 2,3OHM load to roughly emulate the transistors bases load.
> When I reconnect the 2sc2879 bases, the driver frequency response returns 
> wrong with 12dB difference between 1.8 and 18MHz.
> I don't know what happened in the finals, it seems like the bases have 
> increased their capacity to very high values.
> With the bases not connected, the measurements with a multimeter of the 
> junctions gives as result two healty transitors...
> I'm now in a "cul de sac", before changing the PA transistors, has anyone an 
> explanation of what happened?
> Thanks and 73
> Ciao
> Guido, ik2bcp
> 
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