Thank you for providing a sound comparison with strong signals.
Two weeks ago, while on a SOTA hill, I compared together with @HB9HGQ the TX-500 with the KX3.
I was more interested in comparing weak signals, just some few dBs above the noise floor. But to be honest, we both could not really hear a difference between the two rigs while listening to faint SSB signals. The RX filter width of the TX-500 was set to 2.4kHz (300-2700Hz).
73 Stephan
There is a matching amplifier coming along for this radio. The 60W PA-500 has been in development for a while but now seems close to being available.
A UK supplier is now taking deposits for it although their website says it is now in stock. A cable is available to use it with the IC-705. The photos suggest it only does 10, 20, 40 and 80m but it does all the main bands and the LEDs change colour to show what is selected.
It needs a 13.8v supply but that can be easily done from a battery.
Hi John,
It looks nice and it supports all bands between 80m and 10m. But with the improving conditions, I’m fine with 10W, at least for now. Less weigth, and cables and no bigger battery needed. But indeed, it seems well engineered.
73 Stephan
I agree although for POTA/WWFF activations I can see the attractions. But for about the same money you can buy an FT-857.
True, but compared to a KX2 or TX-500 it will drain your battery even in RX in shorter time. But for these schemes you can more easily carry a bigger battery.
The good thing of an external amp is that you can stay lean when not using it.
As in live, several pros and cons.
This amplifier includes an ATU as well, and that is a pretty nice to have, even if you don’t plan to use the amp itself much.
To me the amp/tuner combo is very inefficient. Sure the TX500 on receive has a way lower almost 0A draw and a FT891 has 1.08A. Though on the other side of it these are the numbers I personally have experienced for FT891 TX 4.2-5.06A at 5W 4.8-5.3 at 10W 5.5-7.2 at 50w 7.5-10A at 100w. So for QRP yes the TX500 or other QRP radios are the clear winner TX500 set to TX 100% gives only a draw of 1.13A which is 9-12W on SSB depending on what you are saying. Looking at the numbers that Julian posted here https://oh8stn.org/blog/2021/10/14/diy-599-pa500-hf-amplfier-tx-power-measurement-40m/
Personally if I want more than QRP I will just use my FT891 sure it’s heavier but to me it’s more efficient on TX.
I don’t know if the amp/tuner combo will allow for tuner only operation. But if the tuner is more what someone is in the need for then buying an Elecraft T1 is a faction of the cost.
Maybe I’m totally wrong maybe I’m not, but Cost is a big factor to me also. FT891 only cost about $700 with shipping here in the US. This amp is going to cost more than that alone.
I think your figures are significantly wrong. 100W RF output is quoted at 23A by Yaesu and RX with signal present at 2A. Your figures don’t fit the reality of the circuit topology of radios like an 891. So either your meter is faulty, your measurement procedures are faulty or the laws of physics are different in your part of the world. 
Typically the PA will be about 45% efficient so 100W RF means 222W dc input which at 13.8V would be 16A ignoring the current for the synth, drivers, bias circuits, CPU, displays etc. etc.
I guess it is possible that my meter doesn’t work correctly but here is a clip I just filmed using my MFJ-4125 power supply.
My IC-7300 pulls 18-19A at 100W - according to the analog meter on my linear PSU. I don’t think the efficiency of any linear output stage can be much different - don’t forget the driver current is also significant.
If I measure with a cheap digital handheld meter it reads oddly because there is enough RF around to mess up the meter electronics. Same could be happening here
Rick
You are trying to measure current draw with a randomly varying voice waveform on a digital meter with a fixed sample rate uncorrelated to the waveform. Your measurements are complete and utter nonsense.
Use CW or FM and you will get near to the ballpark.
Just did it with FM and it’s only pulling 15.65A @ 100W. I am 95% SSB user with very little FT8 or JS8CALL. Though neither of digitalis do I plan on using with my TX500
Yaesu say 23A for 100W on an 891 and your meter says 15.5A. I know which I trust. 
The stated 23A is probably the max. current drain with some safety margin, but I agree that on 20m FM, transmitting against a dummy load, it will probably draw around 20A.
I know this meter you used, I bought it in a Chinese shop for a couple of bucks. And believe it or not, it’s rated for 150A! Probably Chinese 150A, hi. I never compared the current (it’s definitely in the ballpark), but the voltage it shows is surprisingly exact.
About the antenna tuner of the DIY-599: Some time ago, in the groups.io forum, I read that it’s not possible to use the tuner alone. Anyways, it’s more of a touch-up kind of tuner (small impedance range) and not comparable with the T1.
Update: In the DIY-599 quick start guide, the impedance range of the ATU is specified from 16-500 Ohms, which is more than I assumed.
The T1 manual specifies 10:1 or better (reduced range on 160 and 6 meters), which should correspond to about 5-500 Ohms.
73 Stephan
23A will be the maximum when the input voltage is at the low spec limit
SWR also makes a difference
Right, 23 A at low input voltage, full-carrier mode (like FM), and least efficient band, which is probably 6 m.
The ARRL Lab measured 18 A typical, 19 A max, at 13.8 V.
wunder
I agree! I have not yet ‘characterized’ my 891, but have with my 897 which also states 23 amps. Using FM I have measured 16 - 17 amps depending on band. 100% accurate - I doubt it; but accurate enough to determine battery size needs. In usage, used a 20 amp LFP for JOTA and ran all afternoon with capacity remaining in the battery.
Howard KE6MAK
Either way, I was not trying to derail this thread. In the few times I have used my TX500 I really liked it. Personally I’m good with the TX500 and the Elecraft T1. If I want more power I will just use my FT891.
I’m in the market for a TX-500. When first introduced, the MSRP was $789-ish. HRO currently lists them at $949. Anyone know why the price increase? I’ve read HRO was the only U.S. distributor.
This topic was automatically closed after reaching the maximum limit of 100 replies. Continue discussion at Discovery TX500 (Part 2).