Kim, that is interesting about the fan.
I was unaware of that.
I have built a few amplifiers, long ago, and always used AC fans.
I was actually considering a d.c. fan this time around but you just talked
me out of it.
I have had good experience with the Pabst fans, but they cost about twice as
much as most other boxer fans.
I think I'll stick with what I know works.
What kind of material is hardware cloth shield made of?
I used to put just ordinary screen, like window screen, in front of all of
my fans.
Helped keep the garbage out.
Of course this particular amp has the fan inside and in the middle of the
box so it won't help in that respect.
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 10:17 PM
To: 'Discussion of Ten-Tec Equipment'
Subject: Re: [TenTec] In praise of older technology
That makes perfect sense, Rick and I agree completely. It's a fair bit of
work for, frankly, not a lot of return, even with the 750 W limit. I learned
a LOT by doing it, so in that regard, I got my money's worth out of it. I
was intrigued by the Eimac ratings for the tube that say at 4 kV we'll get
something like 1100 W out of it and so I decided to find out. The sweet spot
for the amp is 40 m, and that;s where I can get that kind of power out,
though I have to exceed the 400 mA plate current limit a bit to do it. It is
most certainly *not* a CCS amp when run that way.
I, too replaced the fan in mine. It originally an AC fan the AC "singing"
was very apparent and pretty annoying. So, in my infinite wisdom, I chose
to replace it with a DC fan with a bit more air flow. That fan is much
quieter. It got even more quiet when I tuned the amp up on 20 m. In fact,
the fan became silent because the fan stopped. DC fans aren't truly DC: they
have inverters in them that generate something like 20 kHz AC, and this is
what runs the brushless motor. Unfortunately, when exposed to that much RF,
the inverter stops. The fan is certainly quiet, because it's not fanning.
So, I had to put a hardware cloth shield between the fan and the RF deck.
The problem went away with that final mod and I learned something new in the
process.
It's a very fine "one-holer" amp now, and almost certainly one-of-a-kind.
Kim N5OP
________________________________
From: Rick - DJ0IP / NJ0IP <Rick@DJ0IP.de>
To: 'Kimberly Elmore' <cw_de_n5op@sbcglobal.net>; 'Discussion of Ten-Tec
Equipment' <tentec@contesting.com>
Sent: Wednesday, March 5, 2014 1:41 PM
Subject: RE: [TenTec] In praise of older technology
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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