OK Kim, you convinced me. I won't use that transformer.
I understand why all of that is necessary but it is much too much work for
the little return of benefit in my case.
We're only allowed to run 750w here in DL.
The increased HV and lower current would mean better linearity on SSB, but I
mainly run CW so there is no benefit there either. Was just a spur of the
moment idea, since I was thinking of replacing the transformer anyway.
The biggest problem as I see it is the lack of space in the RF deck for
beefing up the coil.
If I am unable to silence the old transformer, I will just replace it with
the stock Ameritron transformer.
MFJ lists them for about $150.
The real problem with that amp is its horribly slow T/R relay.
They need up to 20mS to switch and that means a constant danger of burning
contacts unless you add some extra delay (which I do). So the relays goes
for sure. Once the transformer is out, it's simple to service the relay and
fan.
Thanks for the info. It was very interesting and sounds like you did a
great job modifying it.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Kimberly
Elmore
Sent: Wednesday, March 05, 2014 7:19 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] In praise of older technology
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@yahoo.com>
To: "cw_de_n5op@sbcglobal.net" <cw_de_n5op@sbcglobal.net>;
"tentec@contesting.com" <tentec@contesting.com>; "tentec@contesting.com"
<tentec@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>
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