The AM Forum

Hi Guy's,

Has anybody installed one of Dave's 6 Khz filters in there R390a or 75A4. If so what do you think of it and is it worth the $199 cost? Link is below.

http://www.ermag.com/index.cfm?v_link=product_detail&v_key=221

Steve,
WA2TTP

Steve,
I put his 9KC filter in my A4 and it works great. No problems at all.

Several years ago I purchased the 6 kc filter for one of my 75A4s.  I borrowed the stock Collins A4 filter from my other receiver and put them both in the same one.  Doing an A/B comparison, I could tell no difference in performance whatever - no better, no worse.

His mechanical  filters use modern-day Rockwell mechanical filters.  They are much smaller than their older predecessors, but are designed for solid state applications, so the input and output impedances are much lower.  The Dave Curry filters consist of the modern filter, with a stepdown transformer at the input and a step up at the output, to match the filter to the plate and grid of the tubes.  Filter, transformer and all are repackaged into a case that is identical in size and shape to the  original filter, with the same type of pin arrangement, making it a direct replacement.

The Curry filter has a resonance adjustment for minimum insertion loss and ripple.  Once set up, they work just as well as the original, and given that the original is 50 years old give or take a few, probably have a longer life expectancy.  And the price is comparable, if not lower, than an original Collins.

It is unlikely that you will ever again find original stock Collins A4 filters for $15 at the Dayton fleamarket, as once was the case.

Don,
I am in a retirement mode and don't have the free spirit of high finances. And even if I was still working, I can't see $200. I listened to a lot of good loud heavy Fred Flintstone music from WBCQ with the BW usually set at 8kc. and it was beautiful!! Reasonable high end and good pounding bass!!
It was a rare clear reception, free of selective fading that I would open it up to 16kc and that setting only made it slightly better, coz of International broadcast restrictions the audio was limited to 5kc. Mr Tron said that there was a slight leakage to 6kc to give some life back to the audio. The "brick wall" filters he was using were unforgiving to music. Towards the end of my "career" you could hear a little sibilence to the audio.
Listening to music on a local station in the 16kc position is great out of the diode load. I don't understand the ringing of the stock filters that people refer to. It's audible or do you need a piece of test gear to detect it?
Sorry for the chatter, I miss my Ham friends. I'm trying to get on the air more often.
There are some health issues on this side of the circuit. I need some prayers.
Fred

buy a soft rock 6 and convert it too 455 Khz and you will have variable bandwidth with the same performance at a wopping cost of $14 plus a buck for a color burst crystal.

Thanks to all for the information.

I also posted this question on the R390a email list and got a reply from WA0HQQ who referred me to a report he posted on this site. It is very detailed with nice graphs comparing stock R390a filters with Longwave products. Link is below.

http://www.r-390a.net/Collins-Curry-Study.pdf

From KH6U:

"I put a Dave Curry 6kc filter in one of my R-390As in place of
the 16 kc filter.  It works very well and I have been thinking of changing
the 2 kc filter to one of his 2.5 kc filters.  One of my 390As was free and
the other (a Rich Mich rebuild) was only $200 so I feel I can invest in
filters which are useful to me.  The 16 kc was often too wide and the 2 kc
filter is always too narrow for SSB at least to my ear."

73,
Steve

Steve, save yourself 20 bux on epay... I was thinking of buying one myself to fill the gap from 3.1 to 8 kc.

http://cgi.ebay.com/Collins-75A-4-6Khz-AM-Filter-BRAND-NEW_W0QQitemZ5880884346QQcategoryZ4673QQrdZ1QQcmdZViewItem

Sorry, what is "a soft rock 6"??

       _-_-  WBear2GCR

Frank said "buy a soft rock 6 and convert it too 455 Khz and you will have variable bandwidth with the same performance at a wopping cost of $14 plus a buck for a color burst crystal."

That is, of course, ignoring the $1000+ of computer hardware appendages it has to be tied to.