Sounds like a great project Derf - It's always great to hear of a homebrew work in progress.
Ron AC7AC From: Derf Mockford [mailto:d...@csldual.com] Sent: Wednesday, December 22, 2010 9:45 AM To: r...@cobi.biz; dpsa...@tx.rr.com; d...@w3fpr.com Cc: elecraft@mailman.qth.net Subject: K2 barefoot + ALS-600 Hi Ron, Phil & Don, further to your item below on the Elecraft reflector, I use the ALS600 with a barefoot K2. I appreciate that the required level of amp gain is illegal to supply in USA but customer mods are quite legitimate. The amp is ideal throttled-back for 400 watts max in UK. By removing the amp's 35 ohm input series resistor and the 33 ohm parallel resistor (3 x 100 ohms in parallel) that is across the amp's input transformer, the input impedance came down considerably. Using the K2 ATU, on 14.1MHz, 13 watts in = 600 watts out. The primary of the amp's input transformer was one turn only. It is Now re-wound with 3 turns as in the (almost identical) Communication Concepts EB104 amp. Input impedance is fairly close to 50 ohms for 1.9 to 20MHz. 6 watts in = 600 watts out. On 21 to 28 MHz, i/p Z is a bit off of 50 ohms, and up to 10 watts is required for full output. A 2db 50 ohm pi-attenuator was added on the input so that it is now a good match to the barefoot K2 and suits UK max power limits. I have no ALC connection from the amp to the K2, simply adjusting the K2 RF output to get the required RF from the amp. The amp is very stable and all mods took about 3 hours to complete. The ALS-600 includes the AD5X QSK mod. This was the first mod that I applied to the amp after purchase. Works perfectly. Phil, many thanks. To you all and to the many contributors to the Elecraft reflector, Merry Christmas. 73 Derf G8ZGK > > Subject: Elecraft Digest, Vol 80, Issue 42 > Message: 27 > Date: Mon, 20 Dec 2010 19:49:00 -0800 > From: "Ron D'Eau Claire" <r...@cobi.biz> > Subject: Re: [Elecraft] OT: modifying your amp for lower drive requirement > To: <d...@w3fpr.com>, "'Phil & Debbie Salas'" <dpsa...@tx.rr.com> > Cc: elecraft@mailman.qth.net > Message-ID: <000f01cba0c2$020458d0$060d0a...@biz> > Content-Type: text/plain; charset="us-ascii" > > Sure, but it's very easy to design a low-loss broadband matching network to > provide the required impedance transformation. > > One HB amp of mine used a 16:1 transformer at the input for just that > purpose. > > Ron AC7AC > > -----Original Message----- > Phil, > Your statement amplifies the difference between "ham assumptions" and > reality. > The data-sheet indications of gain do not consider the input impedance > (and loading of the driver), that parameter is quite important in actual > use -- if the amplifier does not provide a good load to the driving > transmitter, then "all bets are off". > 73, > Don W3FPR > > On 12/20/2010 8:28 PM, Phil & Debbie Salas wrote: > "It's very unlikely any solid-state amplifier uses an input attenuator: > Transistors and FET's just don't have that much gain." > > The Ameritron ALS-600 has about a 15 ohm input impedance. Then they put a > series 35 ohm resistor for matching and reducing gain. > Phil - AD5X ------------------------------ *********************************************************************** CSL DualCom Limited Registered Office: Salamander Quay West, Park Lane, Harefield, Middlesex UB9 6NZ Registered in England No. 3155883 This e-mail is only intended for the person(s) to whom it is addressed and may contain confidential information. Unless stated to the contrary, any opinions or comments are personal to the writer and do not represent the official view of the company. If you have received this e-mail in error, please notify us immediately by reply e-mail and then delete this message from your system. Please do not copy it or use it for any purposes, or disclose its contents to any other person. Thank you for your co-operation. *********************************************************************** ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
