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Justin, I have a couple of HF-2500 amplifiers I've used for many years and experienced the same failure of the meter lamps. The earlier HF-2500 (single meter) has two bulbs and the later (two meter) has four. I put up with no lamps for sometime and then just gave in to fixing the problem when another issue cropped up. I noticed that the plate voltage indicated on the front panel meter of the HF-2500 (dual meter) seemed quite low, and did not match the voltage read with a HV probe on the anodes of the PA tubes by over 500VDC. I decided to fix it, and replace the three meter lamps that were not lit. At the time I did not realize what a tall-order fixing the HV meter would be. Lamps first, I replaced the four incandescent lamps with 3800K Bright-Warm-White LEDs from a pinball supply company. These are in a #47 lamp form factor and are commonly used to replace lamps in boatanchor gear with 6.3VAC on the lamp. The current draw was something like 25mA each and I wired each meter pair in series. I also strapped a .001uf disc across each lamp to keep any RF out of the LED. There is also a published mod to the metering board where you replace the 7812 three terminal 12VDC 1A regulator with a 78S12 2A regulator. It solves the marginal current supply issue. The real pain was fixing the HV meter. As you may already know, the HV PS board is located under the RF deck. Nearly every part in the tank circuit must be removed to access the HV power supply board, as well as the front panel and more. It requires all this removal of "stuff" to take out a plate under the RF deck components that the HV board is mounted on. When I finally got the HV board out I found that the series resistors for the meter had gone way up in value. This probably was due to the dissipation in the three marginal wattage resistors, and the heat from all the bleeder resistors in the confined space. The air flow from the fan has about half of the air going to the right-hand tube closest to the fan, and the second half of the air passes through the HV compartment before it get to the left tube. So the left tube runs at a higher temperature. Go figure. While I was in the HV compartment I replaced all the filter capacitors with 105C types and replaced all the bleeder resistors and metering resistors with higher dissipation parts. I left the diodes as-is. Once reassembled, it worked great and the HV meter read correctly. After all this work I saw an ad from Palstar who apparently bought the Commander line and did a lot of upgrades on the already great amplifier. One significant change they made was to install a "door-plate" on the bottom of the RF deck to make easy access to the PS circuit board. If I ever have to do this again, I will cut a door in the bottom, hi! 73 Bill N4LG At 03:24 AM 4/11/2025, KG2RG via groups.io wrote: >[] >[] >[] >[] >[] >[] >[] >[] >[] >[] >[] > >Hello, >I have a Commander HF 2500. Have not had it to long. When I got >it, only 1 of the 4 meter bulbs was working. After about 3 month, >the bulb went dark. >I believe there is a 12V 1A regulator that >supplies the meter bulbs and the relay. I read the pulls are >Festoon type and need to be no more the 0.08A each so to not >exceed max current and cause the relay to no key. I finally got in >there and they are not the fuse looking type bulbs. They are >little bulbs with with short leads soldered to the meter board. > >i finally got in there because I had another Issue with the >standby switch. I think the standby switch was intermittent and a >relay was not keying sometimes. I started noticing the problem >when I would first turn on the amplifier after the short warm-up., >I placed the standby switch into operate and the amp would not >key. At first, I thought this issue may have been the regulator or >something else, but I started to notice the symptoms would often >happen after using the standby switch. I originally planned to >bypass the switch and see if the problem went away and then I >could replace the standby rocker switch. But when I got in there, >I noticed there was another set of poles th

Hello, I have a Commander HF 2500. Have not had it to long. When I got it, only 1 of the 4 meter bulbs was working. After about 3 month, the bulb went dark. I believe there is a 12V 1A regulator that supplies the meter bulbs and the relay. I read the pulls are Festoon type and need to be no more the 0.08A each so to not exceed max current and cause the relay to no key. I finally got in there and they are not the fuse looking type bulbs. They are little bulbs with with short leads soldered to the meter board. i finally got in there because I had another Issue with the standby switch. I think the standby switch was intermittent and a relay was not keying sometimes. I started noticing the problem when I would first turn on the amplifier after the short warm-up., I placed the standby switch into operate and the amp would not key. At first, I thought this issue may have been the regulator or something else, but I started to notice the symptoms would often happen after using the standby switch. I originally planned to bypass the switch and see if the problem went away and then I could replace the standby rocker switch. But when I got in there, I noticed there was another set of poles that were vacant and likely never used so I decided to utilize it those and see how things went. I cleaned all of the contacts and the plugs on the wire wires with deoxIt, And then plugged the wires onto the never used terminals on the other pole. So far it’s been great for the past 24 hours. I’ll give it some time, but if the problem comes back, then I’ll try bypassing it and if the problem still persist during bypass, I’ll look to see other possible causes but so far things are good and my fingers are crossed. after messing around with the standby switch, I pulled the metering board out and surprise, it was not the fuse type bulbs. These bulbs had short leads soldered to the meter board. does anyone have a recommended replacement bulb suggestion? They likely need to be 12VDC at 0.08A. I should’ve used my caliber to measure the size so I’m not sure what size and what type of bulb or where I can source replacements. Any help would Be very appreciated! kG2RG

Fully operational and wired for 110V operation, has latest firmware version installed. $2500.00 shipped to any US destination (Buyer pays add additional insurance if desired) Includes a 6 month defect guarantee from my ACOM authorized US service/repair center which is now in the process of relocating due to a storm-water disaster emergency so tt this time can only accept a bank wire as Payment. The funds will expedite the relocation process greatly, thanks for looking. Steve Hearns KA2PTE Pending Honorary USMC Corporal Technotronic Dimensions [USA] WWW.TECHNOTRONIC-DIMENSIONS.COM E-Mail: Steve@...

I'm betting this will be an epic failure. I'll put money on it. BBI, in his infinite wisdom, is documenting the....'worlds biggest 11m amplifier' on his U tube channel. Using the 4CW-100,000E water cooled tetrode. Teaser video. 7 mins long. https://www.youtube.com/watch?v=jbD0wEPVv3s Here is part #1. It's 2 hrs and 27 mins long. https://www.youtube.com/watch?v=yUa54WgAzEI I found 5 x mistakes so far. This will be an epic failure. It's good entertainment though. 20 kw of drive for 500 KW output. Being built in Victoria Texas......in a welding shop.... by John De Luna and BBI. Here is the detailed Eimac spec sheet for the 4CW-100,000E https://www.relltubes.com/documents/Datasheets/4CW100000E.pdf IF they are gonna run it in GG, with both screen and grid bonded to the chassis, the 500 watt grid will burn up 1st. If it's gonna be grid driven, well have fun, esp neutralizing it. If it's gonna be cathode driven, like a Collins 30S1, have more fun. On the 30S1, the B+ supply, screen supply, and the bias supply are all in series, which means the screen and bias supply have max plate current flowing through em. I'm gonna assume 3 phase power to run it. With 500 kw pep out, it will suck 800-900 kva. Well he did parallel 4 x 2 uf @ 40 kv oil caps for the B+ filter. With 3 phase power, the raw DC from the 6 x leg rectifier assy has 5.2 % ripple. With 8 uf of filtering and 20 kv, total energy in the 4 x caps = 1600 joules = dick on a 770 kw DC input supply. Any hum will be 360 hz. (6F on 3 phase). The tube requires 20 gallons per minute at no more than 70 psi...... just for 100 kw CCS anode dissipation. My garden hose only does 4 gpm. I would be worried about distilled water purity, and resistance, and possible super heated steam explosions. 100 kw of diss = 341,000 BTU's of heat to get rid of. Do the maths, that will require one helluva BIG air cooled and shrouded radiator to dump that much heat. Eimac also warns of an X-ray hazard, when operated > 15 kv. The cavity needs to be lined with .020" lead sheeting. The folks building this amp are in for a rude awakening. They are talking about 250 kw CXR, and swinging to 500 kw....and pep output close to a megawatt. When tuned for close to a megawatt, the tank eff with just the 250 kw CXR will be aprx 25%. Anode diss = 750 kw. Tube rated for 100 kw diss. Calculate the RF current through the tank coil, and it's aprx 225 amps. Shit, even Kintronics doesn't make anything that big. 3" tubing would run hot. The RF current through the tune and load caps is beyond horrendous. 205 amps through the load cap. 102 amps through the tune cap. 80 amps into the TR relay + coax. You would have to parallel 3 x Gigavac G52 spst vac relays to handle that current. 5.7 kv peak across the connectors, load cap, and TR relay...and coax....with a 1:1 swr. Toss in sundry items like the plate block cap assy, which will have 100+ amps through it....... which in this case would have to be a fixed ceramic vac cap....and this will be end up being the project of the decade. This amp would work....if they backed down on the insane power levels. Dunno what they are gonna use for an ant, but if it's a gamma matched yagi with a vac cap, they will be in for more surprises. The rotor loop will be an engineering feat in itself. CM choke....good luck with that, not happening. IF they can pull it off, hats off to em. IMO, they have bitten off more than they can chew.

Hello Could you help me validate the attached schematic? The goal is to negatively bias the 3-500Z grid using a Zener diode, without passing the cathode current through the Zener diode. The components added to the original schematic are shown in red. The biased wires in the diagram have already been set up in a previous experiment to bake the anodes under low anodic voltage. With the original zero bias wiring, I observe, at rest, 250 mA under 2400 V (2x300 W) which seems exaggerated to me. I'd like your opinion on this schematic before I do something stupid. Could you add to the diagram the diode(s) to be installed in order to limit the effects of an arc which is always possible in a 3-500Z. -- F1AMM Fran?ois

Hello On my Drake amplifier, I would like to install additional hardware using existing threaded rods (3-500Z support spacers). If I measure the thread diameter, I get a reading of 3.3 mm (1/7 inch). The existing nuts measure 6.1 mm (1/4 inch) across the flat. Can you tell me the US thread size for this type of thread? -- F1AMM Fran?ois

I'm going to bore you again with my L-7. The 4 lamps that light the two galvanometers are out of order (strange). They are powered by the 5 volts (alternating current) of the filaments of the 3-500Z. Have you replaced these fairly classic bayonet lamps? by LED lamps? -- F1AMM Fran?ois

Hello Now that both of my 3-500Zs have been de-gassed, I have a new question. · In the L7 (Drake) the bias is at 0 volts · In the Kenwood TL-522 it is -7.5 V as shown in the following diagram We read a bit of everything http://amfone.net/Amforum/index.php?action=printpage;topic=46759.0 The objective is to put the L-7 into operation in SSB at medium power. -- F1AMM Fran?ois

Hello I am in the process of putting a Drake L 7 amplifier back into operation. I was advised on this forum to bring the anodes of the 3-500Z to red to maintain the quality of the vacuum. After removing the screens to check the equipment and the filaments, I realize that once the screens are put back, there is no way to observe the anodes of the 3-500Z; everything is shielded (no window). How do you observe these anodes? -- F1AMM Fran?ois

The output relay in my Ameritron AL-1500 needs to be changed. I checked with MFJ since they are still selling some Ameritron replacement parts, but no luck. From the user manual, this is "RLY1" and its Ameritron part number is 408-6139. This is a 3PDT, 10A, 12V DC through hole PCB mount relay. Two of the poles are used for RF switching and the third is used for another function. I've searched on Mouser, Digikey, Allied, Newark and E-bay websites without finding anything that might be a satisfactory replacement. Ideally, an original replacement part would be found. This would allay my concern about the contact materials which should be gold or gold plated for the two NC RF contacts to ensure good contact when receiving. Suggestions would be appreciated. 73 de Riki K7NJ