Solid State Amp in the Station

Choosing amps can be a dilemma. Tube amps tend to be clean (low distortion) but almost all require manual tuning and the tubes, although they can last many years in a newer product with protection circuits, are expensive to replace, if they can be found. Solid state amps are typically no tune and instant on, but tend to poor signal quality (IMD), and if the transistors fail they must usually be replaced by different ones since they are evolving (and improving) quickly.

I prefer tube amps for their reliability and clean output. That why I purchased an Acom 1500 a few years ago, and for its coverage of 6 meters and excellent protection circuits. The latter is critical for tetrodes just as it is for solid state amps.

Buying tube amps is becoming increasingly difficult to justify. Partly for the aforementioned reasons and also because of guest operators for contests. Many hams, even those licensed for decades, have difficulty tuning amps quickly and accurately in the midst of a contest. It's one of many things guest ops need to learn and deal with in an unfamiliar station. 

I have seen my amps poorly tuned or offline due to an unnoticed fault. The amp protection circuits prevent damage but contest effectiveness is impaired. There are tube amps with ATU (Acom 2000) or with preset tuning points (Alpha 9500) that make them almost (but not quite) no-tune, but they are very expensive.

When an opportunity recently arose to pick up a nearly new solid state amp with a good reputation, I bought it. It's an Acom 1200S. In the picture it is sitting atop the Drake L7 while I tested it. It is paired with the Icom 7600 (lower left) that I purchased last year.

Although the amp receives mostly positive reviews, nothing is perfect. Tubes fail and so do LDMOS and other solid state devices. Perhaps a better tell is that there are not many available on the used market. Skimpy used market data made it difficult to set a fair market value for the amp, which was necessary since I purchased it from the estate of a friend. Two of us have been testing and selling his equipment on behalf of the family.

I now have 3 kilowatt class amplifiers, and two of them include 6 meters. One of the three will become a spare. The Acom 1500 paired with the Icom 7610 will likely remain my daily amp. The 1200S will be amp for the second station, used primarily in contests (SO2R and multi-op). I might split the station for daily use, with one dedicated to HF and the other for 6 meters. I monitor 6 meters quite a lot in order to catch elusive openings.

Let me say a few words about the 1200S before returning to the topic of tube vs solid state amps in my station. I'll discuss the amp's pros and cons from the perspective of my interests. Those may differ from yours.

Pros: 

• Automatic band switching by measuring the input. That eliminates the need to split the CAT feed or to come up with a cable to connect the Icom/Yaesu/Elecraft/etc. band data to the amp. But it needs to a dit or similarly brief transmission, not jumping into normal operation. Hopefully guest operators will catch on.
• The protection circuits are fast and appear to be comprehensive. The one commonly encountered is too much drive for the SWR -- the higher the SWR, the lower the allowed drive and thus the forward and reflected power.
• It's light. That makes it easy to move around. I have accidentally pushed the amp backward by pressing the power button too firmly!
• Perhaps most important for contests, it's easy to use. No tuning, a large display and the colours tell you what you're doing wrong (or right).
• It's only a kilowatt. That makes it easy to stay legal per Canadian regulations, especially for CW, although it's a little light on PEP for SSB. Well, maybe that's just me since there are many that would see consider the power limit as a con.
  

Cons:

• The fan is always on and it isn't the quietest. It isn't loud but I expected it to be quieter when idling since there are no filaments. There are higher and noisier fan speeds when the temperature rises during hard use.
• The T/R relay is louder than I expected. It's louder than my Acom 1500 and the Acom 1000, but quieter than the L7 with its bulky 3PDT relay (I still use the original).
• There is only one antenna jack. Although I have my own hardware and software for automatic antenna selection, it would be nice to have a second port for 6 meters since that antenna is routed separately. For comparison, the 1500 has 3 antenna ports.
• The SWR limit can be a problem for many. In my station that is mostly the case for the non-contest HF bands since I have no resonant antennas for 30, 17 and 12 meters. On the contest bands it is rarely an issue since my antennas are optimized for CW, which I mainly operate in contests. On SSB the drive has to be reduced in a few cases, such as on 160 and 40 meters, and for the TH6. The reflected power must be below 100 watts or thereabouts. It is easy to forget to reduce drive when switching to an antenna with a higher SWR during a contest.
• I am a little uncomfortable with the higher IMD common to solid state amps, and LDMOS in particular. I wish more transceiver manufacturers allowed universal feedback loops for distortion reduction. For example, the DPD feature in the Icom 7610 uses a proprietary interface unique to their PW2 amp.
  

Considering the long list of cons, why would I purchase the 1200S? A solid state amp with more head room or an internal ATU like the RF2K-S or the PGXL (but no ATU) may be superior choices, but even those have their quirks and are substantially more expensive. I may take that step eventually, but not this year.

Every amp has its quirks, good points and bad points. I went into this purchase with my eyes wide open; I am not someone who rationalizes a purchase after the fact. There are better amps on the market and there are cheaper amps. At some point I may replace it with another. However, this one is pretty good and it was available. Time will tell whether I made a good decision.

Every modern amp is expensive. There is no getting around that. If you want cheap, go with a vintage tube amp (but check the tubes first!) and put up with its size, high replacement tube costs, lack of protection circuits and so forth. I sold two of those from the same estate at a recent flea market. There are no wrong choices, just wrong expectations. 

I could fill the blog with the endless rationalizations of hams who are eternally wedded to their amplifier choices. One non-buyer at the mentioned flea market looked over my table of amps and went on an on about the Mercury amp he bought. The same rationalization is also common for antennas, rigs, headphones, and other equipment. I have preferences but I can be persuaded by the performance and features of the unfamiliar or unconventional.

All that said, it is the amp for the second station. It may not see a lot of use. That is, unless another amp fails and I substitute it. Unlike the L7 with its glass envelope 3-500 tubes there is no need for periodic heating of the tubes to maintain the integrity of the seals. It may seem wasteful to have an two mostly idle amps but for my contest operating it is vital to have them ready to go. 

The connections to both the L7 and 1200S are identical and simple. There are just 3: key in, transmitter and antenna. Of course there's also the AC power plug; luckily the plugs on both amps are the same and compatible with my outlets. The amps can be swapped in a minute when they're stacked as shown above. 

If I get ambitious I will reconfigure the station so that one station can be used for monitoring 6 meters and the other for HF outside of contests. I have that flexibility with two 6 meter capable amps. I am sometimes reluctant to warm up the 1500 when a 6 meter opening opening is marginal or brief.

It's a shame that the 1200S doesn't have a second antenna port that I can use for 6 meters. I'll have to deal with it in other ways, such as manual coax switches. I have enough manual coax switches lying around since converting to automatic switching!

One thing I won't miss with the new amp is the post-it notes with tuning suggestions for each band and mode. There will be less stress or reluctance for guest ops when chasing mults and making frequent band/antenna changes.