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141. Re: [Amps] 3CX3000A7 on 144 MHz (score: 1): Author: Steve <g8gsq72@gmail.com>; Date: Fri, 7 Feb 2020 18:09:17 +0000; What you say is true with respect to differences due to plate current but, from the grid's point of view, one end of the filament is at +7.5V with respect to the other end because of the filament PSU; /archives//html/Amps/2020-02/msg00070.html (10,560 bytes)
142. Re: [Amps] 3CX3000A7 on 144 MHz (score: 1): Author: Steve Thompson <g8gsq72@gmail.com>; Date: Sat, 8 Feb 2020 18:13:33 +0000; Looking at the constant current curves, DC filament supply with a centre tap probably won't be a problem, maybe 20% variation in emission from end to end. I still have some radios with 1.5V filament; /archives//html/Amps/2020-02/msg00078.html (10,076 bytes)
143. Re: [Amps] SB220 Meter blown (score: 1): Author: Steve Thompson <g8gsq72@gmail.com>; Date: Mon, 18 May 2020 09:59:52 +0100; Rich was talking about putting diodes across the current measuring resistor, not directly across the meter itself. Typically the resistor generates something in the region of 0.5-2V which the meter r; /archives//html/Amps/2020-05/msg00034.html (10,675 bytes)
144. Re: [Amps] SB220 Meter blown (score: 1): Author: Steve Thompson <g8gsq72@gmail.com>; Date: Mon, 18 May 2020 21:26:57 +0100; OK, I should have said the diode voltage could be 1.5-2V rather than 'will be', but I'm happy with the numbers. When adding something as protection and/or safety, I reckon it's good to work with wors; /archives//html/Amps/2020-05/msg00037.html (14,907 bytes)
145. Re: [Amps] RM Italy BLA350 (score: 1): Author: Steve Thompson <g8gsq72@gmail.com>; Date: Tue, 23 Jun 2020 08:23:32 +0100; There's been almost 300V p-p around the input circuits so I'd check D1-D3 as well, maybe other diodes too. Attenuator - it's difficult to predict what to expect depending on its internal configuratio; /archives//html/Amps/2020-06/msg00035.html (8,012 bytes)
146. Re: [Amps] RM Italy BLA350 (score: 1): Author: Steve Thompson <g8gsq72@gmail.com>; Date: Wed, 24 Jun 2020 10:59:29 +0100; Sadly you're right on both counts there. I can see there's some overdrive protection on the input which switches in 10ohms across the input to the transistors if the drive goes too high - but it does; /archives//html/Amps/2020-06/msg00037.html (8,156 bytes)
147. Re: [Amps] Hercules II With SD 1405 Bias Current Setting (score: 1): Author: Steve Thompson <g8gsq72@gmail.com>; Date: Mon, 24 Aug 2020 22:36:58 +0100; Mark, Can I suggest you check some other voltages? Looking at the schematic, with the bias pot at minimum the base voltage on the SD1405 should be equal to the voltage across the bias reference diode; /archives//html/Amps/2020-08/msg00054.html (8,736 bytes)
148. Re: [Amps] Looking for Alpha 87A expertise (score: 1): Author: Steve Thompson <g8gsq72@gmail.com>; Date: Sun, 14 Mar 2021 19:16:19 +0000; 2. Is a drop from 900V open-circuit to 730V typical when disconnecting/reconnecting the "R" bias lead at the HV board? I'm wondering if I have another leaky PIN diode or cap to ground that is loading; /archives//html/Amps/2021-03/msg00003.html (7,341 bytes)
149. [Amps] Drifting Power (score: 1): Author: Steve Thompson <g8gsq72@gmail.com>; Date: Sat, 16 Oct 2021 16:35:37 +0100; Inductor in the output side warming up slightly and shifting value as it changes size? Is the output tuning sharp? Can you tweak the output tune/load so it gives full output immediately (and then may; /archives//html/Amps/2021-10/msg00071.html (7,654 bytes)
150. Re: [Amps] 1:9 un-un for grid driven tetrode (score: 1): Author: Steve <g8gsq72@gmail.com>; Date: Mon, 25 Oct 2021 08:31:46 +0100; Core choice, wire length and winding style all play a part. https://cromwell-intl.com/radio/9-1-unun/ and https://g8jnj.webs.com/Balun%20construction.pdf might help figure out what's happening. Doesn; /archives//html/Amps/2021-10/msg00089.html (9,061 bytes)
151. Re: [Amps] 1:9 un-un for grid driven tetrode (score: 1): Author: Steve Thompson <g8gsq72@gmail.com>; Date: Mon, 25 Oct 2021 17:33:15 +0100; What's the impedance of a parallel tuned circuit at frequencies well below resonance? Steve G8GSQ _______________________________________________ Amps mailing list Amps@contesting.com http://lists.c; /archives//html/Amps/2021-10/msg00093.html (8,151 bytes)
152. Re: [Amps] Alpha 76PA Conversion - Drive Issue (score: 1): Author: Steve <g8gsq72@gmail.com>; Date: Thu, 2 Dec 2021 22:17:41 +0000; Somewhere I have a copy of an early release data sheet for the 3CX800 - before it was re-rated to 750W (so a pair = 1500W) to fit in with FCC rules about output specifications. From memory it has 250; /archives//html/Amps/2021-12/msg00020.html (8,678 bytes)
153. [Amps] 8874s for sale (score: 1): Author: Steve <g8gsq72@gmail.com>; Date: Wed, 8 Dec 2021 15:31:36 +0000; Not by me, UK seller: http://pub29.bravenet.com/classified/show.php?usernum=2477864602&cpv=1 and page down until you find it. Posted 7 Dec - ads often get deleted if sold so check posting dates if yo; /archives//html/Amps/2021-12/msg00066.html (6,427 bytes)
154. Re: [Amps] Modern Op-Amp shunt stabilizator power supply (for tetrodescr (score: 1): Author: Steve Thompson <g8gsq72@gmail.com>; Date: Thu, 3 Mar 2022 13:35:38 +0000; A while ago I breadboarded a screen regulator supply with some similarities to Jim's design. One of these was that the 'pull down' transistor could act as a clamp if there was a flashover to the scre; /archives//html/Amps/2022-03/msg00002.html (8,520 bytes)
155. Re: [Amps] Why does power output increase? (score: 1): Author: Steve <g8gsq72@gmail.com>; Date: Sun, 5 Jun 2022 16:41:35 +0100; Tack a 10k resistor to each filament pin, 10nF decoupling between the loose ends then twisted pair out to your DVM. Should filter out the rf and you don't have to worry about shorting the wires toget; /archives//html/Amps/2022-06/msg00039.html (8,885 bytes)
156. Re: [Amps] Measuring filament voltage (score: 1): Author: Steve <g8gsq72@gmail.com>; Date: Sun, 5 Jun 2022 19:29:49 +0100; Good additional and practical points from John. Higher value resistors might suit in some situations - don't forget to allow for the error introduced by the 'pot down' of the resistors against the DV; /archives//html/Amps/2022-06/msg00050.html (8,171 bytes)
157. Re: [Amps] Measuring fil V (score: 1): Author: Steve <g8gsq72@gmail.com>; Date: Tue, 7 Jun 2022 23:08:02 +0100; Good points, Jim. I stick with resistors as it avoids embarrassment if/when the meter wires get shorted. Been there, done that..... :-) Steve G8GSQ Be careful if using a 10 kw resistor hanging off ea; /archives//html/Amps/2022-06/msg00073.html (8,227 bytes)
158. Re: [Amps] Average anode dissipation using SSB ? (score: 1): Author: Steve <g8gsq72@gmail.com>; Date: Mon, 15 Aug 2022 19:27:04 +0100; Rule of thumb - for a class AB amplifier, device dissipation is roughly constant from 10-100% output power. Steve G8GSQ Average anode dissipation using SSB ? Ok, this in reference to average anode di; /archives//html/Amps/2022-08/msg00015.html (8,410 bytes)
159. Re: [Amps] B&W PT2500 (score: 1): Author: Steve <g8gsq72@gmail.com>; Date: Sat, 27 Aug 2022 18:20:27 +0100; For clarification, adding an attenuator doesn't guarantee a 50ohm load to the rig regardless. An attenuator makes VSWR lower, the amount of improvement related to the value of the attenuator. For exa; /archives//html/Amps/2022-08/msg00052.html (9,342 bytes)
160. Re: [Amps] 2m GS35B Amplifier (score: 1): Author: Steve <g8gsq72@gmail.com>; Date: Sun, 2 Oct 2022 14:12:50 +0100; You mention adding 'the ability to adjust output loading'. What was added and where? The original circuit does allow the loading to be altered, just not in the way that you might be used to with 'tun; /archives//html/Amps/2022-10/msg00007.html (10,793 bytes)

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