[Boatanchors] Hallicrafters HA-5 VFO

[james.liles at comcast.net]

Good morning Sandy:
Don’t think I would sub the 6U8A with a 6EA8A – it is simply a hotter tube with problems of its own. Try changing the 6U8A out --- could be the tube. 
Don’t write the Hallicrafters designers off as LO tech sandy; they built some of the most elaborate CTO VFOs of the analog era.
First, check that (C1A 11pf N1500) and (C1B 4pf N80) have been removed and replaced with (C1 15pfN750). If they have not been replaced do so it will fix the problem. There were 3 EC levels in the HA-5 089-002510, B, and C. Check your schematic and compare it to the “C” level. 
Next, attach a frequency counter to the output and measure the drift at three dial settings. Low, center, and high end. measure at 2 minutes, 15 minutes, and 1:15 minutes. These measurements will tell you if the temperature compensating components are working. If they are, you will find the lowest 15 to 115 minute drift near the CENTER dial setting. The drift at the LOW dial setting will be POSITIVE and less than 500 cycles for the first hour settling to wandering around a point of 20 to 50 cycles per hour. The HIGH dial setting will be NEGATIVE drift and less than 500 cycles for the first hour settling to wandering around a point of 20 to 50 cycles per hour.
During the first hour the drift may move up and down a bit but ignore that and take the 2, 15, and 115 minute measurements.
There isn’t a single mass produced VFO that cannot be improved with individual attention. 
Good luck and Kindest regards Jim K9AXN
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Date: Mon, 21 Jan 2013 01:06:30 -0600
From: "Sandy" <ebjr37 at charter.net>
To: "boatanchors group" <boatanchors at mailman.qth.net>
Subject: [Boatanchors] Hallicrafters HA-5 VFO...
Message-ID: <1CA88D1BA36F4899B024318ACD9FFC62 at SandysLaptop>
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Has any one replaced the 6U8 withy a 6EA8 or similar tube? Did this help the overall stability of the VFO?

Also looking for mods to slow down the drift of his beast! Looks like it would be good driver for the Drake 2NT if it could be stabilized! I hate trying to reinvent the wheel if someone else has already done it!!!

I can live with the lack of mechanical problems, as it is typically ?Hallicrafters? lo tech design. What I interested in is ?anchoring? the thermal drift to a reasonable rate!

Suggestions or practical solutions anyone?

73,

Sandy W5TVW