KPA100 power on 20m/30m, update
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KPA100 power on 20m/30m, update
 
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This is a follow up to my own problem for the sake of complete Elecraft
archives. :-) A few weeks back I mentioned having slightly lower power on 30m. When the power knob was at its max, I had 97 W while all other bands were close to 120 W. What I forgot to mention is that on both 20 m and 30 m I always got the HI CUR warning, though the warning threshold was set to 3.5 A. I recalibrated the PA and then got 100+ W on 30 m. But a subsequent check a week or so later showed I was back down to 95 W into a dummy load. Not a big deal, really, but I didn't like the HI CUR message and spoke with Gary at Elecraft about it. He recommended changing the C80 & C81 caps. After doing so, I no longer get the HI CUR warning. In addition, I get slightly over 100 W on all bands rather than the nearly 120 W on most. Whether that it's due to new caps or better calibration, though, I don't know... I posted this followup because initially it seemed that a simple recalibration took care of the issue, but turns out I needed new caps like the other guys who were suffering from even worse side effects of their C80 and C81! 73, Mike AB3AP _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: KPA100 power on 20m/30m, update
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I had problems with HI CUR on 14 & 18MHz, 3.6 and 3.7 Amps respectively.
Changing C80 & C81 cured the problem, and I now have 2.9 and 2.4 Amps drawn. 73 Stewart G3RXQ On Wed, 22 Jun 2005 10:36:20 -0400, Mike Markowski wrote: > This is a follow up to my own problem for the sake of complete Elecraft > > archives. :-) > > A few weeks back I mentioned having slightly lower power on 30m. When > the power knob was at its max, I had 97 W while all other bands were > close to 120 W. What I forgot to mention is that on both 20 m and 30 m > I always got the HI CUR warning, though the warning threshold was set to > 3.5 A. > > I recalibrated the PA and then got 100+ W on 30 m. But a subsequent > check a week or so later showed I was back down to 95 W into a dummy > load. Not a big deal, really, but I didn't like the HI CUR message and > spoke with Gary at Elecraft about it. He recommended changing the C80 & > C81 caps. After doing so, I no longer get the HI CUR warning. In > addition, I get slightly over 100 W on all bands rather than the nearly > 120 W on most. Whether that it's due to new caps or better calibration, > though, I don't know... I posted this followup because initially it > seemed that a simple recalibration took care of the issue, but turns out > I needed new caps like the other guys who were suffering from even worse > side effects of their C80 and C81! > > 73, > Mike AB3AP > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Stewart Baker wrote:
> I had problems with HI CUR on 14 & 18MHz, 3.6 and 3.7 Amps respectively. > Changing C80 & C81 cured the problem, and I now have 2.9 and 2.4 Amps drawn. What value did you change them to? -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: KPA100 power on 20m/30m, update
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Vic Rosenthal wrote on 06/22/05 12:22 ET:
> Stewart Baker wrote: > >> I had problems with HI CUR on 14 & 18MHz, 3.6 and 3.7 Amps respectively. >> Changing C80 & C81 cured the problem, and I now have 2.9 and 2.4 Amps >> drawn. > > What value did you change them to? Apparently, all new kits will use 5600 pF, 5% caps for C80 and C81. Mike AB3AP _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: KPA100 power on 20m/30m, update
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Did you redo an alignment of the KPA100 after, or you just changed the 2
caps ? -----Message d'origine----- De : [hidden email] [mailto:[hidden email]] De la part de Mike Markowski Envoyé : 22 juin 2005 12:36 Cc : Elecraft Reflector Objet : Re: [Elecraft] KPA100 power on 20m/30m, update Vic Rosenthal wrote on 06/22/05 12:22 ET: > Stewart Baker wrote: > >> I had problems with HI CUR on 14 & 18MHz, 3.6 and 3.7 Amps respectively. >> Changing C80 & C81 cured the problem, and I now have 2.9 and 2.4 Amps >> drawn. > > What value did you change them to? Apparently, all new kits will use 5600 pF, 5% caps for C80 and C81. Mike AB3AP _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: KPA100 power on 20m/30m, update
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I repeated the procedures that dealt with adjustments on the board, but
skipped over things like the temperature calibration and current limit steps. Mike AB3AP Jean-François Ménard wrote on 06/22/05 12:56 ET: > Did you redo an alignment of the KPA100 after, or you just changed the 2 > caps ? > > -----Message d'origine----- > De : [hidden email] > [mailto:[hidden email]] De la part de Mike Markowski > Envoyé : 22 juin 2005 12:36 > Cc : Elecraft Reflector > Objet : Re: [Elecraft] KPA100 power on 20m/30m, update > > Vic Rosenthal wrote on 06/22/05 12:22 ET: > >>Stewart Baker wrote: >> >> >>>I had problems with HI CUR on 14 & 18MHz, 3.6 and 3.7 Amps respectively. >>>Changing C80 & C81 cured the problem, and I now have 2.9 and 2.4 Amps >>>drawn. >> >>What value did you change them to? > > > Apparently, all new kits will use 5600 pF, 5% caps for C80 and C81. > > Mike AB3AP Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: KPA100 power on 20m/30m, update
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In reply to this post by Vic K2VCO
On Wed, 22 Jun 2005 09:22:57 -0700, Vic Rosenthal wrote:
> Stewart Baker wrote: > >> I had problems with HI CUR on 14 & 18MHz, 3.6 and 3.7 Amps respectively. >> Changing C80 & C81 cured the problem, and I now have 2.9 and 2.4 Amps drawn. >> > What value did you change them to? New C80 & C81 = 5600pF 5%. No readjustments of K2 or KPA100 necessary. 73 Stewart G3RXQ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: KPA100 power on 20m/30m, update
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Thanks for the info, I'm waiting for my 2 caps.... ;-)
Le 05-06-23 à 03:57, Stewart Baker a écrit : > On Wed, 22 Jun 2005 09:22:57 -0700, Vic Rosenthal wrote: > >> Stewart Baker wrote: >> >> >>> I had problems with HI CUR on 14 & 18MHz, 3.6 and 3.7 Amps >>> respectively. >>> Changing C80 & C81 cured the problem, and I now have 2.9 and 2.4 >>> Amps drawn. >>> >>> >> What value did you change them to? >> > > New C80 & C81 = 5600pF 5%. > > No readjustments of K2 or KPA100 necessary. > > 73 > Stewart G3RXQ > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > ====== Jean-François Ménard / VA2VYZ ====== _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: KPA100 power on 20m/30m, update
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i just received 2 ka100 mod kits...... for both radios...
My question, should I be changing out the C80 & C81 while i messing in there... or do the changes in the "ka100 MOD kit" eliminate the need for a change. Looks like the R19 & R20 are changed in the 'mod' and are sitting right there. ??????? bill ny9h 1 k2/100 & 1 k2/qrp & ec2 KA100/KAT100 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: KPA100 power on 20m/30m, update
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Bill,
Yes, while you are monkeying around in there - removing the board from the heat sink and all, you may want to change C80 and C81. It may not really be necessary, because as I understand it, the problem only shows up if the 4700 pf caps are on the low end of their tolerance range. Elecraft is likely seeing the problem at this time because of one particular batch of caps obtained, but there is no harm in changing them 'just to be safe'. That should not be taken to mean that I am advocating changing them in a working KPA100 - just saying that while doing other work on it - why not change the caps. 73, Don W3FPR > -----Original Message----- > > i just received 2 ka100 mod kits...... for both radios... > > My question, should I be changing out the C80 & C81 while i > messing in there... > or do the changes in the "ka100 MOD kit" eliminate the need for a change. > > Looks like the R19 & R20 are changed in the 'mod' and are > sitting right there. > > ??????? > > bill ny9h 1 k2/100 & 1 k2/qrp & ec2 KA100/KAT100 > > No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.323 / Virus Database: 267.7.11/26 - Release Date: 6/22/2005 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Bill Steffey NY9H
Bill NY9H wrote:
> i just received 2 ka100 mod kits...... for both radios... > > My question, should I be changing out the C80 & C81 while i messing in > there... > or do the changes in the "ka100 MOD kit" eliminate the need for a change. > > Looks like the R19 & R20 are changed in the 'mod' and are sitting right > there. I wish we could get an official statement from Elecraft on this issue. <begin MY OPINION> Apparently the metal-film resistors used in this application vary widely in inductance. Some resistors have an inductance that seem to resonate with the capacitors near the 30/20 meter bands, basically putting a parallel trap in series with the drive, and causing the driver stage to have to work harder. This shows up as high current and/or reduced output on 30/20 meters. Hence whether or not you need to change the capacitors and if so to what value depends on the resistors that you you have. Note that this depends on the physical construction of the resistor and it's (unwanted) inductance, not its resistance. <end MY OPINION> I guess the question is 'what capacitor value is appropriate for the resistors shipped in the mod kit'? -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Vic,
I agree with you, Vic. As perhaps the third to suffer this in recent kits, I have spent much time, with help from experienced guys at my club, investigating this. Increasing the caps (C80,81) cured most but not all kits at the recommended level (+900pF). My caps measured at 4600 & 4700pF on a Peak meter. Replacing them both with caps measured as closer to the design value did not 'cure' things. As a last resort I changed R19,20 with some British obtained items which happened to be from Vishay BC; 1.5 ohms was the only nearest value available. Imagine my surprise when all was cured. Today, in RADCOM there is an article on Low-inductance resistors as part of the 'In practice" series. This gave me some more insight into how metal film resistors are made. Apparently they can have from 1 to 10 helical turns cut into the metal film and can vary from manufacturer to manufacturer. You've guessed it - I sanded the coating off one of my original 1.6 ohm Elecraft resistors and a spare Vishay 1.5 ohm from the same strip of 10 that fixed my KPA100. The score - Elecraft approximately 6 turns and Vishay 1.25 turns. I just got lucky!! Moral - remember to take some sand paper with you when buying these type of resistors to be used for RF purposes in critical areas. Why not??? When we ran a small shop on the Grand Union Canal here in England, some folks used to poke or squeeze the bread to see how fresh it was!!! 73, Ted G7BQM K2#4732 On 23 Jun 2005, at 17:16, Vic Rosenthal wrote: > Bill NY9H wrote: >> i just received 2 ka100 mod kits...... for both radios... >> My question, should I be changing out the C80 & C81 while i messing >> in there... >> or do the changes in the "ka100 MOD kit" eliminate the need for a >> change. >> Looks like the R19 & R20 are changed in the 'mod' and are sitting >> right there. > > I wish we could get an official statement from Elecraft on this issue. > > <begin MY OPINION> > > Apparently the metal-film resistors used in this application vary > widely in inductance. Some resistors have an inductance that seem to > resonate with the capacitors near the 30/20 meter bands, basically > putting a parallel trap in series with the drive, and causing the > driver stage to have to work harder. This shows up as high current > and/or reduced output on 30/20 meters. Hence whether or not you need > to change the capacitors and if so to what value depends on the > resistors that you you have. Note that this depends on the physical > construction of the resistor and it's (unwanted) inductance, not its > resistance. > > <end MY OPINION> > > I guess the question is 'what capacitor value is appropriate for the > resistors shipped in the mod kit'? > > -- > 73, > Vic, K2VCO > Fresno CA > http://www.qsl.net/k2vco > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: KPA100 power on 20m/30m, update
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In reply to this post by Vic K2VCO
The "Trap theory" makes a lot of sense, and Don's comment about low
tolerance C80 and C81 capacitors would seem to support it. But if the resistors in parallel with C80 and C81 are the only "Inductors" that form the L part of the traps, I would have thought that by simply changing R19 and R20 to so called Non Inductive types would cure the 30/20 meter problem. But this might just move the problem to a higher band because of the inductance of leads AND PCB traces between C80/R19 and between C81/R20. But are these the only "traps"? Consider the low Q notch C80/R34 and C81/R35. If the "traps" are formed only by C80/R19 and C81/R20 plus lead inductance and the L of interconnecting PCB traces, yes increasing the values of C80 and C81 will shift the trap frequency down, but what happens if the value of the new caps is at the high end of their tolerance range? Does the problem start to affect 40m? (Slide rule warming up).Probably not. The same thought about the notch circuits. So I am not totally convinced that the C80/R19 and C81/R20 is all that there is to it, I hope that I am wrong, but I do wonder about the stack of bypass capacitors at the centre tap of T1 as well, and the other 2W resistors for starters. Increasing the value of C80 and C81 will also affect the amount of feedback around the finals Q1 and Q2 to some extent, but without doing the sums for the parallel tuned trap situation, I think only by a small amount IF T1 and the bypass caps at T1's centre tap are well behaved. The effect of a series resonant notch would be different. The behaviour of C58, C59 and C83 also need to be checked. A measurement of the gain of the PA between 3.0MHz and 30MHz when driven from a pure resistive source, with everything to the left of R34 and R35 disconnected except bias, would tell much. Dummy load at T2's output. No doubt Elecraft already have this information. So I can understand why Elecraft have not yet issued an official statement. There are several "spurious" resonant circuits to be considered IMHO. Some thoughts. 73, Geoff GM4ESD P.S. Welcome home Vic! ---------------------------------------------------------------------------- ----- Vic Rosenthal wrote: > I wish we could get an official statement from Elecraft on this issue. > > <begin MY OPINION> > > Apparently the metal-film resistors used in this application vary widely > in inductance. Some resistors have an inductance that seem to resonate > with the capacitors near the 30/20 meter bands, basically putting a > parallel trap in series with the drive, and causing the driver stage to > have to work harder. This shows up as high current and/or reduced > output on 30/20 meters. Hence whether or not you need to change the > capacitors and if so to what value depends on the resistors that you you > have. Note that this depends on the physical construction of the > resistor and it's (unwanted) inductance, not its resistance. > > <end MY OPINION> _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: KPA100 power on 20m/30m, update
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Geoff,
These are not intentional traps, but are a parallel RC circuit to adjust the base drive with frequency (at low frequencies, the resistors are the main path, at higher frequencies, the capacitors pass more RF). This is done to compensate for the gain vs. frequency characteristics of the transistors. The inductance of the resistors is just an unfortunate by-product (but must be considered just the same in the design). 73, Don W3FPR > -----Original Message----- > > The "Trap theory" makes a lot of sense, and Don's comment about low > tolerance C80 and C81 capacitors would seem to support it. But if the > resistors in parallel with C80 and C81 are the only "Inductors" that form > the L part of the traps, I would have thought that by simply changing R19 > and R20 to so called Non Inductive types would cure the 30/20 > meter problem. > But this might just move the problem to a higher band because of the > inductance of leads AND PCB traces between C80/R19 and between > C81/R20. But > are these the only "traps"? Consider the low Q notch C80/R34 and C81/R35. > > No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.323 / Virus Database: 267.7.11/26 - Release Date: 6/22/2005 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: KPA100 power on 20m/30m, update
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Hello Don,
Yes I understand the purpose of the RC compensation circuit in the drive path to each transistor to offset their decreasing gain as the working frequency increases, and which cannot be fully dealt with by the RCL network in the primary circuit of T1. As you say say they are not intentional traps, which is why I use the term "spurious resonant circuits". The possibility of unwanted resonances in the feedback networks eg R39, C59, R35 is very real. If for example R39 and C59 were to be a series resonant circuit at X MHz, the in-circuit gain of Q2 would decrease at X MHz. RF design is an unforgiving mistress!! 73, Geoff GM4ESD ----- Original Message ----- From: "W3FPR - Don Wilhelm" <[hidden email]> To: "Geoffrey Mackenzie-Kennedy" <[hidden email]> Cc: "Elecraft Discussion List" <[hidden email]> Sent: Thursday, June 23, 2005 9:58 PM Subject: RE: [Elecraft] KPA100 power on 20m/30m, update > Geoff, > > These are not intentional traps, but are a parallel RC circuit to adjust the > base drive with frequency (at low frequencies, the resistors are the main > path, at higher frequencies, the capacitors pass more RF). This is done to > compensate for the gain vs. frequency characteristics of the transistors. > The inductance of the resistors is just an unfortunate by-product (but must > be considered just the same in the design). > > 73, > Don W3FPR > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Geoff, Don,
As an ex sufferer of this disease, my 2p worth. My investigations, admittedly only with the limited kit available to me including 20MHz scope and 2 or 3 different wattmeters, I think it was, showed that the output across all the bands up to 21MHz was remarkably constant for a given Q1,2 base voltage (and attempt at current calculation). However, there was a very marked voltage (estimated current) loss across the base drive circuits on the affected bands (C80,81/R19,20). Readings prior to this in the RF line merely confirmed the high drive requirement as did the Hi Cur on 20/30m. With much help and advice from guys at my club, we too considered the possibility of other spurious resonant circuits but could find no evidence for these in my kit at a level that affected performance. 73, Ted G7BQM K2#4732 and first year RF engineering student! On 24 Jun 2005, at 02:31, Geoffrey Mackenzie-Kennedy wrote: > Hello Don, > > Yes I understand the purpose of the RC compensation circuit in the > drive > path to each transistor to offset their decreasing gain as the working > frequency increases, and which cannot be fully dealt with by the RCL > network > in the primary circuit of T1. As you say say they are not intentional > traps, > which is why I use the term "spurious resonant circuits". The > possibility > of unwanted resonances in the feedback networks eg R39, C59, R35 is > very > real. If for example R39 and C59 were to be a series resonant circuit > at X > MHz, the in-circuit gain of Q2 would decrease at X MHz. > > RF design is an unforgiving mistress!! > > 73, > Geoff > GM4ESD > > >> Geoff, >> >> These are not intentional traps, but are a parallel RC circuit to >> adjust > the >> base drive with frequency (at low frequencies, the resistors are the >> main >> path, at higher frequencies, the capacitors pass more RF). This is >> done > to >> compensate for the gain vs. frequency characteristics of the >> transistors. >> The inductance of the resistors is just an unfortunate by-product (but > must >> be considered just the same in the design). >> >> 73, >> Don W3FPR >> _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: KPA100 power on 20m/30m, update
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Hello Ted,
At the risk of continuing this thread for too long, brief comment. IMHO you hit on the main culprit causing problems on 20m / 30m - the inductance of R19 and R20 as supplied. If you like, I can go off list to discuss with you your other comments. I am not surprised that you could not find evidence of other resonances, but there are ways to expose them and they are an important part of a designer's 'toolkit'. The important thing is that your problem has been solved. 73, Geoff GM4ESD ----- Original Message ----- From: "Ted Turk" <[hidden email]> To: <[hidden email]> Sent: Friday, June 24, 2005 7:17 AM Subject: Re: [Elecraft] KPA100 power on 20m/30m, update > Geoff, Don, > > As an ex sufferer of this disease, my 2p worth. > > My investigations, admittedly only with the limited kit available to me > including 20MHz scope and 2 or 3 different wattmeters, I think it was, > showed that the output across all the bands up to 21MHz was remarkably > constant for a given Q1,2 base voltage (and attempt at current > calculation). However, there was a very marked voltage (estimated > current) loss across the base drive circuits on the affected bands > (C80,81/R19,20). Readings prior to this in the RF line merely > confirmed the high drive requirement as did the Hi Cur on 20/30m. With > much help and advice from guys at my club, we too considered the > possibility of other spurious resonant circuits but could find no > evidence for these in my kit at a level that affected performance. > > 73, > Ted G7BQM K2#4732 and first year RF engineering student! > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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