[TenTec] In praise of older technology

Thu Mar 6 19:31:30 EST 2014

I hate to be pedantic and off topic (but that won't stop me)... I don't 
think any helicopter tip are run supersonic because of huge efficiency 
losses. Here are numbers for the Bell UH-1 Iroqios (aka the Huey) 
helicopter. The rotor is 48 ft in diameter and max rotor speed is 324 
RPM. Add to that the max cruise of 135 MPH, and I get a max advancing 
tip speed of 1011 fps, about 100 fps shy of Mach 1 depending on 
altitude, temperature, etc. That still might make a fair bit of noise 
because there may be transonic shock waves on top of the tips.

One of the few aircraft parts I know of that will exceed (slightly) Mach 
1 are the tips of a North American AT-6. It has a two-bladed prop and 
the tips do slightly exceed the speed of sound at max RPM. The same 
engine and propeller are on the BT-13 and both are amazingly noisy 
because of that feature.

Tip speeds at an above Mach1 make for very inefficient propellers and 
are typically avoided assiduously.

Kim N5OP

On 3/5/2014 9:34 PM, Tony Lelieveld wrote:
> This is the same reason why a helicopter can be so noisy creating very 
> loud "whacking" noise.  As I was told, it is the result of the tips of 
> the blades exceeding the speed of sound.
>
> Tony, VE3DWI.
> ********************
>
> ----- Original Message ----- From: "Bob McGraw - K4TAX" 
> <RMcGraw at Blomand.net>
> To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
> Sent: Wednesday, March 05, 2014 8:57 PM
> Subject: Re: [TenTec] In praise of older technology
>
>
>> From an earlier commercial product which I was associated,  we 
>> learned that "tip speed" of the fan creates noise.  So less RPM 
>> larger and more blades mean lower tip speed for a given amount of 
>> air.  Plus sleeve bearing system is quieter than ball bearings 
>> although likely the sleeve bearings will need lubrication or fail 
>> sooner than ball bearings.
>>
>> 73
>> Bob, K4TAX
>>
>>
>>
>> ----- Original Message ----- From: "Rick - DJ0IP / NJ0IP" 
>> <Rick at DJ0IP.de>
>> To: "'Discussion of Ten-Tec Equipment'" <tentec at contesting.com>
>> Sent: Wednesday, March 05, 2014 3:30 PM
>> Subject: Re: [TenTec] In praise of older technology
>>
>>
>> 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 at 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 at DJ0IP.de>
>> To: 'Kimberly Elmore' <cw_de_n5op at sbcglobal.net>; 'Discussion of Ten-Tec
>> Equipment' <tentec at 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 at 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 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>
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