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:
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>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
>
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