There may be an interesting approach to this, in some situations where you have one 25k radio and one 8.33k radio and where the requirement is for just one radio, and where you are concerned that your national CAA requires the removal of any 25k radios (which would in itself be an outrageous position).
Referring to the phrase
“2.2 The requirement to convert 25kHz-spaced channels to 8.33kHz-spaced channels does not apply to frequency assignments:
(a) that will remain in 25 kHz channel spacing on the following frequencies:
(i) the emergency frequency (121.5 MHz);”
The last one means that you could retain the 25k radio, claiming it is solely for use on 121.5 
However, people closer to the UK CAA have reported that there is no proposal to remove 25k radios, so long as 8.33k capability (at least one radio) is acquired.
The Americans would love it if the European regulators did indeed come up with what would be an utterly idiotic requirement to remove 25kHz equipment. The US market would get flooded with thousands of items of gear, from KX155s, to a whole GNS480 radio+GPS whose capability is still unmatched in some respects.
Another thing is that an aircraft won’t need an 8.33 radio in airspace where the carriage of a radio is not mandatory, which is most (all – in theory?) of Class G. That will probably take care of most of the GA VFR fleet, for ever. They will be able to choose whether to spend a few k on an 8.33 radio to be able to get Class D etc transits, which is no big deal in the UK. The whole of the extensive French Class E will be in this category. More importantly, this conclusion means that ATC serving Class G won’t be able to move to 8.33!
It depends on the previous installation. The upper board GS and audio on the KX155A and GS OBS on the 165A.
If you install a KX165A in a 155A make sure that the audio pins arent connected (audio speaker amp board). In old days KX165 installed in KX155 the OBS scale on the KX165 would not work since its derived from the OBS board..
/Sam
Now that is really useful info… might explain a lot.
A KX165A/8.33, when put into my upper KX155A slot, failed to drive the KI525 HSI. So we put it into the lower KX155A slot.
Now, with the KI525 having been replaced with the Sandel SN3500, it will probably be OK because the lateral nav to the two 3500s from the KX radios is composite only.
Which audio pins are you thinking of? I have the IMs and MMs for these (they can also be found here) but both of my radios drive the PS7000 intercom, not a speaker directly.
Most installations with KX155 utilize only 4 pins on the top connector (glide/slope) all other remain unused since most people have an audiopanel which takes care of all audio.
Hmm KX155 is not normally used with an HSI such as the KI525. For this case we use the KX165.
The KX155 series are used in combination with indicators that have the VLOC converter buildt into the indicator such as the KI208/9(A), KI203/4.
To simplify things.. KX155 is identical to KX165. The difference is that KX165 has a OBS converter board installed. The KX155 MAY have the optional audio board in the same location…
In some cases people have installed a KX155 and a KN72 (external VLOR converte for driving a HSI. Dont ask me why…..
This was more “normal” in the KX175 days when everything was separate, used with KN77 (VLOC converter) and KN73 (GS receiver) and then connected to most likely a Century NSD360 HSI.
OK, apologies for leaving out a detail: the KX155A (COM1/NAV1) was driving the KI525 via a KN72.
Replacing the KX155A with a KX165A/8.33 stopped the KI525 working. I never spent time on it (the avionics engineer didn’t have any idea) but I suspected it was due to the 165A having some config for the LNAV signals, whereas the 155A doesn’t. I looked at the config pages in the 165A IM but could not see anything obviously relevant.
I also had a KX155A (COM2/NAV2) which drives a KI204 (composite signal only for LNAV, normal four GS signals for VNAV on the GS) only and that was successfully replaced with the 165A. That 165A now successfully drives both of the 3500 EHSIs, again via composite+GS, and of course the EHSIs decode the composite signal internally in firmware so there is no adjustment or calibration involved, although you can tweak it in the config menus to correct small errors (nice).
I thought a 165A was totally a pin compatible superset of the 155A…
I have no idea why Socata used a 155A+KN72 (155+KN72 in the older pre-GT TBs) rather than a 165A alone (or a 165 alone in the older TBs). A KN72 is about $1000 which is much less than the 155-165 or 155A-165A price increment, but the extra wiring to the KN72 (which is under the seat and taking up valuable space which could be used for something more productive) is a substantial amount of labour and is a big “detour” on the harness, for no good reason. The KN72 is also a piece of crap.
An article covering the original SN3500 installation is here.
I am really surprised about possible malfunctions after a replacement of a Bendix radio. I have just got a KX 165 A, 8,33, and I am planning to change it against a KX 155 A, which is connected to a HSI KL 525 as well to a KM 26 MKR. Before ordering the radio my avionics engineer told me that the exchange would be simple. Also the dealer in US confirmed an easy replacement due to same connectors. What is true ? Can the exchange harm the new radio, the HSI or any other avionics ?
Why would you like to change a KX165A for a KX155A ?
And… for all modifications that are done you will need (if you follow the rules) a EASA minor modification approval.
I see no point.. and one other thing.. the A series is a piece of junk chinese junk… same thing goes for the “new” KT76A with surface mount board.
The Cessnas had the King package as standard in early 2000’s… together with the KLN94 GPS… to bad they didnt go for Garmin my personal no #1 (GNS430 series).
/Sam
the A series is a piece of junk chinese junk…
I am not convinced it is junk. It has been out since the late 1990s and from what I hear the KX155A/165A are very reliable. I have had both opened up on the bench and the build quality is superb. Same with the KLN94 – same era.
Also, the non-A radios have a reputation for messing up GPS with the well known 11th and 13th harmonic problem (example) – see AC20-138 for the test procedures. Tune 121.20MHz, make sure it is quiet out there, and hold the PTT button for say 30 secs while watching the GPS satellite signal strengths… The “A” radios are a lot better – but still not good enough in some cases like mine.
Yes the KLN94 now looks a bad choice, especially with the European regulatory babble with PRNAV etc, but the GNS430 had only just come out when that decision was made, nobody could have known that Garmin would be bothered to produce the LoA for it while Honeywell would not be bothered, and the KMD550 has European VFR mapping quality which nothing from Garmin matches today.
The KLN94 has VNAV outputs so with different software etc (obviously planned) there could have been a fully LPV capable version, but the company melted down soon afterwards.
One has to laugh…
The question remains: why replacing a KX155A with a KX165A, in an installation which obviously must have a separate NAV converter (KN72 probably), doesn’t drive the KI525 HSI.
I am told that Trig are going to produce a slide in replacement for the KX155. The unit is to be half as tall at the 155 but will if required have a mounting to fitt the KX155 rack.
One more time Trig are set to steal the market from right under Kings nose !
I am not convinced it is junk. It has been out since the late 1990s and from what I hear the KX155A/165A are very reliable.
Both the non A and the A version have lots of display problems, as well as other Bendix/King avionics that uses these orange/red displays. It seems that aircraft outside suffer these problem the most. If you unable to read the display, the radio is worthless. I never seen this problems with other manufacturers.
One more time Trig are set to steal the market from right under Kings nose !
Would be good to have more choice, I think Trig products are good designs as well, and their support is good as well.
Garrecht from Germany, altough small, seems to have tought best about his avionics (transponders). The radio rack transponder had adapters to be useable for KT-76/KT-68 AND A & C versions, while compatition only did A & C versions. Same for the round hole transponder, his remote head could be screwed onto the transponder body, eliminating the need for wiring between head and body when their is enough panel space. Altough Trig’s products are good, they always require wiring between the head and body even if their would be sufficient panel depth available.
Garrecht for sure seems to have good practical ideas. His products don’t look to attractive unfortunatly, while it’s quality is good.
