Bill, "A man has to know his limitations" is a good rule to follow.? Working on HV power supplies is not rocket science but, like high altitude and the ocean, is very unforgiving of mistakes.? You want a clear?mind, no fatigue, and no distractions.??Even an undetected mistake while the power is off can have dramatic consequences when you power things up for the first time after a repair.? I've rebuilt a number of L4B and L7 supplies and if I can assist you with any questions that you have, please feel free to ask.
73, Evan, k9SQG -----Original Message----- From: Bill <[EMAIL PROTECTED]> To: drakelist@zerobeat.net Sent: Tue, 29 Jul 2008 12:24 pm Subject: Re: [drakelist] Drake L-4B Thanks! ? As soon as I get the amp I will look. I dont know how to work on 2500v power supplies and dont want to kill myself. Who is the L4B power supply guru that can check out the power supply and fix anything that needs fixing? ? Bill --- On Tue, 7/29/08, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: From: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Subject: Re: [drakelist] Drake L-4B To: drakelist@zerobeat.net Date: Tuesday, July 29, 2008, 10:28 AM Re: bleeders on L4B and L7 supplies. ? There are two sets of resistors that serve as "bleeders".? The first set is comprised of two 50 K resistors that are mounted to the transformer tabs on the top end of the supply; they are in series with a 5K 7wt resistor on the underside of the supply (for ALC purposes if one uses the ALC function).? This is the true bleeder string that has lower resistance than the "other" string. ? The other string is a series of 100K 2wt resistors, one each across each of the electrolytic capacitors.? They are designed to equalize the voltage across each of the capacitors but, indirectly, they do place a load on the supply that can also serve as a "bleeder" but are not as effective as the primary string; since these equalizing resistors have a resistance that is roughly 8 times higher than the primary string, they won't help as much with regulation and it will take them longer to bleed down the DC when the supply is turned off. I believe in keeping things as original as possible unless there is a known shortcoming.? Here too, it is a matter of preference in terms of which approach to use.? If one eliminates the two 50K resistors to save heat, then some other mechanism must be provided to provide 120 vdc for the ALC circuit.? When one/both of the 50K resistors opens, it can also affect the ALC circuit.? And when that 5k 7wt resistor opens, it takes out the ALC pot which hasn't been available for decades. -----Original Message----- From: Bill <[EMAIL PROTECTED]> To: drakelist@zerobeat.net Sent: Tue, 29 Jul 2008 9:32 am Subject: Re: [drakelist] Drake L-4B Evan and John, ? Thanks for the responses, I am not sure about the bleeders?this is what the guy who sold me the amp told me. ? Where are the bleeders located? and as soon as the amp show up if you could help me figure this out it and we will identify the harbach mod and then we can see if there are any other mods that need to be done. ? 73 Bill K9BUB --- On Tue, 7/29/08, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: From: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Subject: Re: [drakelist] Drake L-4B To: drakelist@zerobeat.net Date: Tuesday, July 29, 2008, 7:45 AM Bill, I'm not sure which Harbach mod(s) you are referring to.? There is a step-start for the high voltage, step-start for the filaments, replacement rectifier and capacitor board, and which sort of determines what else you might do.? When I rebuild supplies I replace just about everything except the power transformer, and with components that have better ratings than the original.? One important mod is to replace the 5K 7wt resistor on the underside of the supply with a 20 watt equivalent; your unobtainable ALC pot will thank you for it. I also place one or two fans on top of the supply.? I use a model that is 220v but will start and run reliably on 110v.? It is so quiet you can't hear it and it brings the case temperature down dramatically. 73, Evan, K9SQG -----Original Message----- From: Bill <[EMAIL PROTECTED]> To: drakelist@zerobeat.net Sent: Mon, 28 Jul 2008 10:56 pm Subject: Re: [drakelist] Drake L-4B I just found out the the L-4B?has the?Harbach mod and the bleeder resistors were removed to eliminate excessive heat. ? Is there anything else I need to do to the power supply? ? Thanks! ? 73 de Bill K9BUB --- On Mon, 7/28/08, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: From: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Subject: Re: [drakelist] Drake L-4B To: drakelist@zerobeat.net Date: Monday, July 28, 2008, 2:41 PM I would think 20A would be fine unless the run is long, then I'd opt for 30A.? Be aware that pin arrangements for the plug and socket change for the various ratings. Even if the PS is working ok with the amp, I always replace the 5K 7wt resistor on the underside of the supply with a 5K equivalent, 20 watt rating.? When the original resistor fails, it takes out the ALC pot that also contains the standby switch; these haven't been available for decades. -----Original Message----- From: Duane Calvin <[EMAIL PROTECTED]> To: drakelist@zerobeat.net Sent: Mon, 28 Jul 2008 2:34 pm Subject: Re: [drakelist] Drake L-4B I ran a 20A line for my Alpha 99.? Works great. ????????73,? Duane?? AC5AA At 01:23 PM 7/28/2008, you wrote: Just bought a Drake L-4B amp and while I am waiting for the amp to arrive I had the electrician over. He wants to know what everyone is running for their 240V line. 15, 20 or 30 amp service. ? Thanks! ? 73 de Bill K9BUB Duane Calvin, AC5AA Austin, Texas www.ac5aa.com The Famous, the Infamous, the Lame - in your browser. Get the TMZ Toolbar Now! The Famous, the Infamous, the Lame - in your browser. Get the TMZ Toolbar Now! The Famous, the Infamous, the Lame - in your browser. Get the TMZ Toolbar Now!
