This is what I meant a 4s 4pk is described in the battery boys world .
Matt 2E0FGX
I got an Ft-891 to avoid the 817 plus amplifier issue and gain a newer receiver and 32bit DSP
So I can roll out 5 to 100 watts without any cables to worry about
Yes the current drain is more on receive but its worth it
Just pack a bigger battery
John ve3ips
Yes there cracking radios and the dsp work well . But I wanted a lighter radio with vhf as well as hf so was only feasible choice. Not done summits like snowdon yet but imagine that be a vhf activation
Matt 2E0FGX
That’s known as a 4S4P setup Matt. Yes, then it will have a capacity around 4x the single cell capacity.
…and lose 2m and 70cm! A pity, its such a tempting little radio.
I believe not - but it is worth remembering that the FT857D does have a built in compressor which I find very effective. Its one of those things that you tend to set and forget about, so beware of adding an external compressor too!
My wife and I are both participants in SOTA. She is strictly phone while I am primarily CW. We have had summits where she barely made the four contacts needed due to conditions.
I purchased one of the MX-P50M amplifiers and did a few bench tests. The device used for amplification is robust and capable of 100 watts at 900 MHz. The output is clean as long and you have the band switch set to the correct band. It functioned from 10 to 15 volts, the PA could take more voltage but I wasn’t sure about the rest of the circuit. The output power using 5 watts drive, varied from 35 to 45 watts, depending on voltage and bands.
We take it up on the hills and she now regularly makes 10 or better contacts. We use a 6 Ahr LiFePO4 12V battery, which seems to be all we need, so far we have activated three summits on one charge and the battery had plenty more to offer.
So far 70+ activations and no issues.
By the way, there is a SOTA Reflector thread with how to connect the FT817. FT817 + 45w Amp cable info needed
Lee N7LP
That’s the view from north of the border. 
My opinion is that they are a worthwhile buy. I use mine with both my FT-817ND and IC-703. The main problem with building your own amp is sourcing the components for the filters. Quite frankly I would rather spend my spare time on the hills, not trying to build an equivalent of this amp in so small a package with eyesight which is not what it used to be.
Well I found a UK source on eBay. I did note this is another thread some months back.
As for the power source, I run mine off a 4.2AH 4S LiFePO4 and at 2.5 watts drive I get around 30 watts out depending upon the frequency. That gives me at least 3 hours operating time. I agree with Malen that 30 watts out is the sweet spot for battery life / QSO’s. In practice it does actually make a difference when running SSB relative to an 817 barefoot and as Andrew says a speech processor is a worthwhile addition. The downside of running an external amp is the additional cabling. I also have the FT-857D which is a much neater solution, but it is less economical in terms of battery power.
If i need to do the vhf/uhf bands I pack the 817 or a handheld to use along with the 891. However, for car to summit then the weight is nothing to worry about and I can also bring a ladder and a picnic table.
If I was being a ultralight then I would use the 817 or the MTR3B and a handheld
Depends on the summit but why pack another amplifier and cable set
John ve3ips
Not very nice Brian, I might refer that remark to the Moderator.
CW was but one of seven approaches I suggested that I consider to be very much preferable to a linear amp. I think that’s a perfectly valid point. You even agree with one of my other suggestions but trust you won’t attract a similarly sneering remark!
A linear amp to me is extra weight, extra volume and extra expense, as well as denying oneself all the fun and satisfaction associated with each of my suggestions above.
For what it is worth I have had one of the amps for two years, and it does seem to make a difference. Having only been active in a period of low solar activity I struggled with SSB with 5w on HF. I tend to activate on 80/60/40 and using an FT817 feeding the amp at 2.5w I get good reports, and by putting in a speech processor too I seem to be able to make contacts despite the poor solar conditions. Had one poor report, think I was overdriving the amp by putting 5w in.
I am old enough to have the CW ticket - but never found it easy and despite occasional attempts am still reluctant to try it on an activation.
I use a couple of 4200mAH LiPo batteries with a voltage regulator to bring it down to about 13v and find that I am cold, or the dog is bored before the battery is flat!
I think SOTA is an individual challenge and quite how you make the contacts is up to you. Personally I don’t get much of a buzz out of a pair of running shorts and a 2m HH and I know I am nearer the “lucky anvil” end of lightweight operating but I enjoy it and that is probably quite important
PS Got my amp second hand off e-bay and never had a problem with it.
PPS Now the new challenges and the prospect of operating top band from the summit might be a bit harder as the amp does not go down to 160m - unless someone knows how to do it? ( Dont fancy operating without the right LPF to get rid of harmonics )
73 Paul
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That’s more than “Quite” important Paul, (IMHO) the enjoyment has to be the primary reasion for activating (or chasing for that matter)!
Good on 'Yer!
73 Ed.
You forgot to add the smiley, , which should have told you that it was light hearted in intent. Furthermore, it was more aimed as a gentle poke at Andy, who poked a “learn morse” comment at Matt when there had been no mention of mode in his post. Just to head off further discussion of an aside, I am perfectly happy to acknowledge the superiority of CW as a weak signal mode, furthermore I have learned morse code myself, can currently read at a speed in the middle teens and think that if we still had the 12 wpm code test I would be able to pass it. I just think that code and computer modes lack the charge that I get from the flavour of the human voice and choose not to use them at present, though I make no committments for the future - and anyway, I don’t have a key!
Now back, I hope, to the much more interesting discussion of linear amps.
Cheapest PA you can buy.
Is it? How much per hour is your time worth, and how many hours does it take to become proficient at Morse code? I can’t argue that it isn’t a worthwhile investment but it costs! FT8 is cheaper!
Ed
The power output from the MX50P is claimed as 50w and I never achieved quite that from mine. I found that more than 2.5w was too much drive and that would cause splatter - a wider than acceptable signal on SSB - and would waste power on CW.
Just a thought on the 70w/100w issue. PEP means the peak envelope power of a complex waveform but CW is a steady carrier. The peak power is equal to the average in that case. For a two tone test there is a standard relationship between the average power and the peak power over a modulation cycle. (Working from memory - can’t recall the number). For voice there is no standard, but the average power shown on an average reading meter is about 30% of the peak envelope power (on a sustained voice sound 
). Eg. on my Emtronics ATU the power meter usually indicates a peak reading of 20w when the radio is actually producing 100w peak. That’s normal and any higher readings will only occur with speech processing or overdrive.
I’d be suspicious of a power measurement so far above the rated power of the amplifier. Does it gel with the DC power being consumed and still have an efficiency of about 50%. (Power out divided by DC power consumed)… if not, check the power measurement device. Hope this helps…
Cheers
Andrew VK1DA/VK2UH
OK for Matt then if the MX50 tops out at 50 watts. I also made the point to be careful with drive levels. All these Chinese amplifiers seem to require only a low drive level (certainly not more than 3 watts) for full output. That is unless there is an attenuator on the input to drop the power of course.
I don’t have a PEP reading power meter. I have an SWR bridge with an “average” setting on it, but I wouldn’t trust that. When CW is generated correctly by inserting a carrier, the reading is as you say but if CW is created by generating an audio tone on one sideband - how does that relate to the power readings displayed?
In any case, whether an amplifier creates 40, 50 or 70 watts PEP output the difference in signal strength at the receiving end is only going to be marginal.
My amplifier kit (not sure about the MX-50) uses a pair of PA transistors in push-pull in AB1 mode I believe.
Heading out for an activation - wish me luck with the weather! (it doesn’t look good at the moment).
73 Ed.
I have one of those amps
The only mod I did was to change the PTT cable to a Phono as opposed to the one they supply, I did this as when on holiday, I take the 817, a small netbook and the Amp. If you use the amp you cant have CAT control for the 817, unless you buy/make one of these- Phono are more common than the supplied connector, so it offers greater flexibility
Now I can use it both for SOTA with no CAT or at home/on holiday with CAT Control
They get really warm on the full cycle modes like FT8, infact it is worrying how hot they get, but on SSB they’re fine.
I power mine with a 5ah 4cell Lipo- seems happy enough at 14.8v. The 817 is powered from a 2.2ah 3 cell Lipo
I use it on 60m, but make sure the 40m band is selected so as to negate any harmonics - I believe Allan GW4VPX does the same.
I also use the Speech Compressor from Germany that is built into the Microphone, I think you can buy one that goes inline with the Mic Connector. So I can get about 45 watts with some good punchy audio on the hill.
Having said all this, I still find myself on VHF more and more, tried the HF on SOTA and just saw it as a waste of the height!! If you’re up a hill, get on 2m with a beam and you will generally qualify and simplify the set up and speed of setting up!
73
Matt G8XYJ
Hi Ed, it all depends on the actual waveform. If there is a carrier on one frequency, even when achieved by inserting an audio tone, as long as the carrier and opposite sideband are suppressed sufficiently, the signal is near enough to a single frequency and the cw power reading can be taken as real.
I don’t think any current radios from the big three or four transmit cw using audio tones. That situation is more likely to occur when using an ssb mode to transmit some of the digital modes.
Apologies for hijacking the thread somewhat.
Andrew VK1DA/VK2UH
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Thank you all lots of great information in this thread . My idea is to use the linear for /p as well for sota activations . I got a holiday booked to go to lundy island in the bristol channel next summer and staying in a 1 man cottage . And will be taking radio kit as well as going exploring around the island . I have a 16ah lifepo4 golf cart battery which will use as well being able to charge during the day when the power is on .
This is the pack I have started to build a lifepo4 18650 pack from cells I had from a battery where the bms went wrong along with some of the cells .
Matt 2E0FGX
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Hi all,
I finally found the time to make a report on my build of the Chinese amplifier kit advertised as the “DIY 70W amplifier”.
I only had to pay for the amplifier kit, and the toroids for the LPF’s, the rest I found in my junkbox, total cost was below 20$!
I wanted to run it off a 3S6P Li-Ion battery pack I made (looks a bit like the one above), so I don’t get 70W … rather 40-50W, depending on band and battery voltage. But it works great, and it is linear(-ish) …
It lets me run my KX3 a lot cooler at only 2W drive power.
I hope to use it with the ATU-100 autotuner I described earlier on the Reflector.
If interested, read all the details here:
73
Luc, ON7DQ
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