HF2500 Amp Library

Welcome to our resources on the Command Technologies HF-2500 amplifier. Having owned a brand new unit since 2006 [Serial number #709], I’ve managed to collect a variety of useful information for owners. Included are also some modifications and parts information.

Command Technologies HF-2500 RF Amplifier [Front]

Command Technologies HF-2500 Amp The HF2500 is a real classic HF Amp which was produced by Pat Stein N8BRA
Download the ‘Hamradio Market’ review PDF by Bob Hutchinson N5CNN

Download the Original Command Tech PDF Schematic Here (16Mb PDF File)
Dedicated RF – the i6 [Next generation Commander amp but the project never happened. We had links to to the original site and it looked great – now the website is gone – link courtesy of www.qrznow.com]. PDF info sheet here.

Download the Palstar HF-2500 schematic PDF here
Download the Palstar HF-2500 Export schematic PDF here

HF-2500 ‘Festoon Bulb’ and Control Board Regulator Mod
The original bulbs (0.25a) are very low wattage and only seem available in North America.
After about 12 months use, they blow. I replaced them with European 3w versions and came across issues. See here what I did – But see the 2013 update below.

*2013 UPDATE* HF-2500 ‘More Bulb Problems’ G0UIH Modification
After 3 months of operating with only ‘2 Festoon Bulbs’.
There is still an intermittent issue which seriously affects the amp’s operation.
See my LED Mod here which seemed to have finally solved all the problems

Command Technologies HF-2500 RF Amplifier [Interior]

*2014 UPDATE* HF-2500 –  ‘Jim Smith W0MJY Offers an explanation on the bulb problem
Hi Steve, good to hear from you. I would suggest that you put a resistor in series with the lamps.  There is plenty of room and they will last longer, draw less current and do a good job for you. If the lamps have too low impedance it will draw the 13 volt down so the relays do not work.
– Happy Holidays 73 –  Jim W0MJY – Burghardt Radio Repair Inc (USA) – thanks Jim

*ONLINE INFO FROM TERRY KI7M – Confirms our suspicion regarding the regulator
Quoting Terry from his post on ‘Contesting.com’The 12VDC voltage regulator on the control board is only rated for 1A. The four original bulbs draw 0.25A each. It’s 1A for the light bulbs only. Everything else overloads the regulator. They often fail because of this. It’s best to use 6615F bulbs that draw only 0.08A each. You can also try to replace it with newer LED bulbs.

One day a huge bang erupted from the shack. The amp was not even key’d but suffered a big parasitic oscillation which caused the parasitic choke caps to fail. I ordered replacements here from Mouser.These are actually rated at 15kv rather than the originals which are 10kv. They are 2.5NF (2500z) caps from Vishay/Ceramite. Here’s the datasheet and see the problem here.

Command Technologies HF-2500 RF Amplifier [Rear]

The plate voltage meter is reading zero volts although the amp works normally. It just seems to be the meter that’s not playing ball (The plate current reads correct so I know the meter work ok). I have a feeling it’s the same issue as experienced by IC8POF with bad resistors. It’s not top priority as I’m very busy on the antennas but given a spare day or so, I’ll strip the amp down and check things out. As this looks like a trip into the PSU area I may well replace all the electrolytic caps in the PSU as the amp is now 15 years old. More on this to come. ** Ok it got delayed for quite a while – I’ll put a video on the site regarding this during 2022 [promise!] **

The internal relay of the HF-2500 is a solid state ‘CRYDOM’ relay. My own unit is working fine but on browsing the web I came across what seems to be a good replacement relay unit should the need arise. We think that the CWA2450 would make a good choice as it’s a higher spec than the original. Download the info sheet here.

Coming soon (Spring 2020) and a job that I should have done a while back. I have no reading on the ‘Plate Voltage’ meter on the front panel. The reason is well documented and the problem is the 2w carbon resistors in the PSU go bad, so I’ve got replacements for them using more modern components. At the same time, I’m going to replace the 8 electrolytic capacitors in the PSU which after 15 years are probably quite tired. The plan is to use some higher rated ‘381 Series Aluminium Capacitors‘ hardware by Cornell Dubilier. These caps handle 25% more ripple current than the originals and also have a higher temperature rating at 105C (rather than the 85C of the original Nichicons). I’ll put more info here when I do the mod and confirm the exact part numbers. A couple of guys in the US also say the reason the original caps fail so quickly is because of poor cooling in the compartment. I’ll look at a mod for this during 2022 and will do a video for the whole PSU refurbishment as it looks like a hands-on job.

The guys at Alpha Telecom take apart a HF2500 to work on the PSU control board [In Portuguese]

When I received my brand new HF2500 it came with the newer Eimac Pulse Rated Triodes 3CPX800A7 instead of the older 3CX800A7. The pulse rated devices are more rugged and you can see the original Eimac specifications here. ‘PULLS’ used to be available quite freely, but the 3CPX800A7 is now getting quite rare. Saying that, the standard 3CX800A7 seems to be trading here on eBay in the US but the prices are really high.