[EdHolland]

Hi Folks,

Among my collection of HF receivers is a UK gem, the Lowe HF-225 which I have owned from new - bought from the manufacturer's showroom in 1992.

http://www.mds975.co.uk/Content/lowe3.html

Alas, all is not quite as it should be in the filter department, and I'll need to replace one of the crystal filter units if I can find a replacement. It is a radio I use most in sideband mode  and one filter has drifted off center frequency - basically giving a slightly mis-aligned IF, and an imbalance in frequency response between upper and lower sidebands. Useable, but annoying! The effects can also be heard in AM if one tunes carefully

This is a superb little set, built during what was arguably the best era for serious digital general coverage receivers. It can hold it's own against the contemporary Icom, Yaesu and JRC gear, yet at the time it cost significantly less. My aim is to keep it up to spec. No it' not a big recap project, but it is a special radio.

Cheers

Ed

[EdHolland]

OK! I found a source of Murata 4 kHz filters and ordered replacement parts. Hoping to have this set receiving properly again .

In part, this will be a tribute to a friend who passed away last week. A gentleman I never met, but with whom I established a great radio-centric friendship a number of years ago. He was an employee of Lowe Electronics, and wrote material for them in addition to technical work, including parts of their "Listener's Guide". We discussed restoration projects and other radio matters, and his knowledge, opinion and wit will be much missed.

Ed

[EdHolland]

I'm impressed. The part I needed were found from a small business run (I suspect) from the owner's home in the UK. The replacement 4 kHz filter arrived already!

The original filter has shifted center frequency by about 1 kHz, it is used in combination with the narrow SSB filter (to enhance selectivity). The shift means it is interfering with the passband of the narrow filter. Not really really serious, but quite noticable when switching from upper to lower sideband, rather like switching a heavy treble boost for one mode and bass boost for the other.

I'll probably take a quick diversion from the RCA to fix this at the weekend. Fortunately, the '225 is nice and easy to work on.

Ed

[EdHolland]

Hmm. Subtle difference in filter pattern. The permutations of designs are quite complicated! I could use one of these, but further searching seems to have found the correct part. Minimum order required, so I added some other fun radio parts - should have enough to scare up a crystal set project for my Son

[EdHolland]

Parts arrived for this at last. Finding time to tinker is another problem, as I can't resist fiddling with that RCA further up the board

[EdHolland]

Well, that did take a while! The new filter was an exact match for the original, which made the gamble of an international purchase worthwhile. Today I carefully desoldered the old part, taking care not to damage what are very delicate PCB traces. This wasn't easy to remove, as it has an odd 5 pin design. The new filter slipped neatly into the board once the holes were cleaned, and it was a quick job to solder up.

The radio is now working beautifully, and has correct filtering on the upper and lower sidebands. Although the faulty filter was 4 kHz bandwidth, not the 2.2 kHz narrow "sideband" filter, it is in circuit in narrow mode, to help reject adjacent channels. Unfortunately, it had drifted in centre frequency, so was clipping the narrow filter rather than complementing. This was cutting the bass on lower sideband, and treble on upper sideband (and vice versa) - it sounded really wrong.


Very happy to have this gem of a radio back in fine fettle. I've owned it since new, bought from the company showroom, back when they were a flourishing business in the UK.

Ed