Steve, The KPA100 will tolerate a 2:1 SWR with no problem. That is not uncommon with solid state amps. If you do have a HI SWR problem with the input circuit, it would likely indicate a defective component in the input circuit (most likely a capacitor).
My GLA1000 is not up and running either so I can't give you any 'tried and true' data. 73, Don W3FPR Stephen W. Kercel wrote: > Thanks to all who have replied. > > The amplifier that I have in mind is an old Dentron GLA-1000B that I am > restoring. It is a grounded grid sweep tube amplifier and uses fixed pi > networks (a different network for each band, selected by the band > switch) at the input. It is supposed to have a better than 2:1 SWR at > input. Back in the day, I used to run it with a Kenwood T-599D > transmitter whose output tank circuit was a wide range pi network, and > there never was a problem coupling the transmitter energy into the > amplifier. > > However, my K2 is much touchier about the range of loads it will tolerate. > > As the amp is not yet restored, I have not yet tried running it with the > K2. Thus, maybe I'll have a problem and maybe I won't. I did notice that > at least one poster to the list has had a problem the SWR seen by a K2 > looking into a cheap tube type amplifier. Thus, I'm thinking what I > might do if I run into the problem. > > If I do have an SWR problem, I see three possible solutions: > > 1) (If even possible) Change the values of the mica capacitors in the > amplifier input circuits to obtain a better match in the relatively > narrow CW segments in which I operate. > > 2) Insert an attenuator between the K2 and the amp. A 2 dB attenuator > would knock down a 2:1 SWR to 1.53:1. The down side is that I'd probably > need to construct the attenuator from thin film resistors. The other > down side is that I'd be contributing about 35 Watts to the Heat Death > of the Universe. The 63 watts (or so) coming out of the generator is > adequate drive for the amp to give me 400 Watts out. The up side is that > there is no tuning. > > 3) Insert a tuner (which do have on hand) between the K2 and the amp. > This is the cheapest solution, but it makes band changing take many steps. > > Regarding AD6XY's precautions: > > 1) This is a valve amplifier and not solid state. > > 2) I've never had a problem with amplifier oscillation in the past. It > is a grounded grid configuration and relatively low gain. It is not > impossible that it will oscillate, but it is less vulnerable than other > designs. > > 3) I have a very high quality KW dummy load for sush purposes as > adjusting amplifiers. > > Thanks agasin & 73, > > Steve > AA4AK > > > > > AD6XY wrote: > >> I would say something slightly different. Firstly I am assuming the PA is on. >> >> It might help to measure the input, especially if it is a valve amplifier. >> If it is solid state the input match is more likely to be RF power >> dependent, but if the match is really bad at low power it is not likely to >> get better at high power and such an amplifier would not be linear. A better >> way would be to measure at the power you intend to use but that requires a >> directional coupler. It is not ideal but an SWR meter connected with a very >> short lead would probably do. >> >> If the amplifier oscillates then there is a very high chance of damaging the >> analyzer, but if that were the case, then at least it did not destroy the >> rig. Make sure the amplifier output has a wideband matched load - definitely >> NOT an antenna. >> >> I don't think a blocking capacitor would be any use unless there is DC on >> the amplifier input line. If there is, there is probably a problem. >> >> >> Note: You can use an antenna analyser to initially measure matching circuits >> of a high power valve amplifier, but only when it is off. You need to load >> the anode with an appropriate impedance equal to the operational anode >> output load and tune and load for a good match at the output. It will not be >> spot on but it should be a good starting point. It is very hard to optimise >> the tank circuit in a valve PA any other way because of the high voltages >> both DC and RF. It does not tend to work so well with transistors as the >> impedances are so low and often dominated by the device capacitance. >> >> Mike >> >> >> >> WILLIS COOKE wrote: >> >> >>> I would say no to all three questions. The input impedance to the amp >>> will not be the same when it is not powered and driven. The SWR >>> indication on the driver will give you some idea of the input impedance. >>> It should not hurt the antenna analyzer if the amplifier is not powered, >>> but I don't think it will tell you anything useful. With power on the >>> amp, it might. >>> >>> Willis 'Cookie' Cooke >>> K5EWJ >>> >>> >>> >>> >> >> > > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > You must be a subscriber to post to the list. > Subscriber Info (Addr. 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