[Hallicrafters] HT-32B

[james.liles at comcast.net]

Hi Mike:

Switch the screen off to prevent plate current.

Wrap a sleeve around the 12BY7A but keep it separated from ground.

Solder a wire to the sleeve with silver solder so that it won’t melt.

Attach your RF probe or scope to the wire.  The wire is to prevent melting the plastic on your probe.

The 6146, depending on the version requires approximately 56vpp to fully drive in class ab1 mode.  Your 18v will not cut it.

You will measure about 56 volts if all is right with the shield probe setup and it will be non disruptive.  You can do a complete RF alignment with this setup.

If you are using the 6146B, set the bias for the stated idle current not 51v based on line voltage.  That 6146B tube requires more bias and more neutralizing feed back.

Good luck --- Kindest regards Jim K9AXN    






---------------------- ORIGINAL MESSAGE ----------------------------------
Message: 4
Date: Sun, 22 Jun 2014 21:47:41 -0500
From: "Langston, Mike" <MLangston at pricegregory.com>
To: "tetrode at googlegroups.com" <tetrode at googlegroups.com>,
"Hallicrafters at mailman.qth.net" <Hallicrafters at mailman.qth.net>
Subject: [Hallicrafters] HT-32B
Message-ID: <FD9D427B-E388-4523-B24A-3C06064E930D at pricegregory.com>
Content-Type: text/plain; charset="us-ascii"

The rectifiers have been SS already and the selenium rectifier has been replaced with a diode. The 5v FIL leads have been removed from the sockets.

Several quick replies steered me to the bias adjustment. Setting it at -51V (per the manual for my line voltage) reduces the plate idle current to 52 ma at 800V. 

Full rf drive now gets me 65 ma and 1 watt output but most importantly, the plate current is now steady. 

So I now assume all is stable and I just don't have enough drive. 

Does anyone have rf voltages for the various stages. My rf probe gives me about 18 V at the grids of the finals with the HV rectifier pulled. This peaks with the driver tune as expected. I have about 3 V at the grid of the driver. 

Thanks for the help.

Mike KL7CD

Sent from my iPhone