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first amp questions

Discussion in 'Amateur Radio Amplifiers' started by KA0RPU, Apr 6, 2021.

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  1. KA0RPU

    KA0RPU Ham Member QRZ Page

    I'm looking to get my first amp and have a few questions. First of all i'm only looking to get about a 600 watt amp. My old ts820s has been working fine for years barefoot, just have been wanting a bit more punch lately. My main two concerns are (1) tube or solid state- advantage and disadvantage of both would be nice and(2) transformer or switched supply, same concerns as previous.
    Mike Ka0rpu
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It seems like "most" HF amps in the 600W range have very delayed deliveries right now (check this, it probably changes) so a used amp may be easier and faster to find and obtain.

    If you decide a used amp is right for you, find one locally (SW MO, NW AR, NE OK or whatever) so you can watch it work and try it out.

    There is no shortage of used HF amplifiers, there are thousands out there and always hundreds for sale.
  3. W4HWD

    W4HWD Premium Subscriber QRZ Page

    Tubes are getting harder to find and more expensive when you find them. Solid-state amplifiers are plenty reliable and occupy less desk space. My KPA/KAT500 combo takes 55% less space than an AL-811 alone! The big advantage of the KPA500 is the built-in power supply; with the ALS-600 you need more room for the separate power supply. Here's my combo; amp on top, tuner on bottom, all inclusive:


    Solid state amps have instant bandswitching, meaning no tuning across bands or band segments. That's nice. I'm not a contester but I would imagine the no-tune stuff would allow Mr. High Score to get more points for not having to twist knobs.

    As for driving a solid-state amp with an old rig, it can be done. My KPA/KAT500 combo has RF sensing, which means that after you initially program the tuner, switching bands is done automatically by getting a whiff of the RF from any rig - all you need to do is set the proper drive level. Nothing could be simpler. The amp has RF sensing too, so you don't need the matching tuner, you can use a manual tuner if you want.

    An amplifier will NOT make your signal magically appear where it wasn't previously, but it will make your existing signal to whatever part of the world a bit stronger. It could mean the difference between logging that rare one or missing out. Once your antennas are as good as you can get them, add an amplifier if you want; 5-600 watts is a good range.

    I used to think that once I could afford a KPA1500 I was going to get one and "upgrade" to the legal limit. Well, now that I can afford it I don't want it. Why? The KPA500 is perfect for me and I can't see the point in spending $6000 for another 4.8dB.
    Last edited: Apr 7, 2021
    NQ1B, WA3GWK, K4MJA and 1 other person like this.
  4. K0OKS

    K0OKS Premium Subscriber QRZ Page

    The issue with any low drive amp (amp that you drive with less than 100W input, where you are likely to damage said amp with the full power ~120W from your Kenwood) is that you need to figure out his to reliably limit the output of your Keneood.

    Mic gain is Not the solution here. This puts the audio circuits at the bottom of their linear region (into non linear) causing distortion. You will need to look at building a circuit to apply negative voltage to the ALC to reduce output power.

    I would suggest you look for something like an AL80B or SB220 where this is less of a concern. (AL80B doesn’t like that much input power, but it has a good ALC circuit built in, and, unlike most amps, it works).
    W4NNF likes this.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Most of the "good" SS amps have various protection circuits that will shut them down (go from "operate" to "standby") very quickly if overdriven or overheated or if the load has SWR >3:1 (sometimes the trip point is lower than that), so they are reasonably self-protecting.

    However, for me that's also a bit of a pain since the amp can bypass itself on a single "dit" or syllable and then you have to figure out what the problem was.:p And often, there really wasn't any problem...the amp just thinks there is.:)

    In that regard, well-designed tube type amps can be more robust.

    But it's true power tube manufacturing is greatly limited today compared with what it once was even 20-30 years ago, and one day the tube sources may disappear.
  6. K0OKS

    K0OKS Premium Subscriber QRZ Page

    This protection is the issue when running the older, higher power gear (as I know you know). So your radio overshoots a tiny bit and the amp cuts out. Whereas a tube amp would keep on cranking, likely with no issues.

    No doubt the future is SS, but I am not sure if this is the best choice for use with an old Hybrid.
  7. K4MJA

    K4MJA XML Subscriber QRZ Page

    ditto on KPA500, love that piece of gear, easy to assemble and pleasure to operate. Has it paired with Icom 7300 and old Palstar AT Auto tuner (I have KAT500 mentioned above, too, its nice but extremely noisy).
  8. WG7X

    WG7X Platinum Subscriber Platinum Subscriber QRZ Page

    Tube amps? AL-80B Acom 1010. Both put out about what you want, but as mentioned, overdrive may be a problem with the Acom 1010. Not too much of a problem with the 80b
    KW6LA likes this.
  9. W4HWD

    W4HWD Premium Subscriber QRZ Page

    Mine was noisy when I first programmed it, as it clacked around looking for the best combination of L and C for each band/segment. Once set up no noise on band change.
  10. K4MJA

    K4MJA XML Subscriber QRZ Page

    that's true and but with my many antennas I often have to re-tune.

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