[TenTec] In praise of older technology

[Kimberly Elmore]

Yes, that's the one. As far as I know, I'm the only guy to ever buy one!

The mod isn't trivial. You'll need to change the filter capacitor stack and build a FWB rectifier instead of using the original FW doubler. If you raise the B+ you change the plate impedance and so will have to change the output tank a by adding some inductance. You'll also have to change the bias on the tube. For the output tank, the lower the frequency, the more inductance you'll have to add. 160 m is the toughest to tame; I made a powdered iron toroid inductor roughly equivalent to the one that's already in there for 160 m and placed it under the stock large air-dux inductor. It has very high RF voltages on it and so will need some serious insulation between it and the bottom the case. I used about 1/4" rubber sheet. You'll then need to move the taps for all the bands up through through 20 m. I did this by experimentation so that I had the load and tuning controls where I wanted them (they no longer strictly match the guide on the front panel). You'll
 also have to be very careful tuning it because the RF voltages are much higher, now. It must never be run lightly loaded as you are certain to flash over the band switch. Once I figured it out and put stick-on markers for tune and load pointers, it was easy

I upped the bias on the tube based on the Eimac spec sheet. Failure to do so will cause the tube to dissipate more than 500 W in an idle condition. I've forgotten what the new Zener value had to be, but it was a stock value and the idle bias is set to be (I think, it's been a while) about 60 mA. The primary requires 240 VAC -- you'll no longer be able to run it on 120 VAC.

Kim N5OP


________________________________
 From: R. Eric Sluder-W9WLW <resluder at yahoo.com>
To: "cw_de_n5op at sbcglobal.net" <cw_de_n5op at sbcglobal.net>; "tentec at contesting.com" <tentec at contesting.com>; "tentec at contesting.com" <tentec at contesting.com> 
Sent: Wednesday, March 5, 2014 11:35 AM
Subject: Re: [TenTec] In praise of older technology
 

That explains the upgraded Peter Dahl transformer you can still buy for the AL-80a.  I've considered swapping my transformer out because it looks a little weary for its age and such.  I fear a short could be in its windings in the not to distant future.  My amp I believe came from a moist environment, and that is why I have the concern over a short.  The outer paper layers don't look their best.<br/><br/>Eric<br/>W9WLW<a href="https://overview.mail.yahoo.com?.src=iOS"><br/><br/>Sent from Yahoo Mail for iPad</a>
_______________________________________________
TenTec mailing list
TenTec at contesting.com
http://lists.contesting.com/mailman/listinfo/tentec