collins mechanical filter identification

[N3DRB The Derb]

round tube red label with  "F 455 Q 2 7T2" on it. It's 455kc of course but what's the bandwidth on it? It was JS installed into JN's 75A2, since taken out.

tanks fer info. 

[N3DRB The Derb]

found it!

455   F455Q-2     526-9309-00  2.0 @ 6 dB   5.6 @  60DB         Y


awful hard to get good AM sound out of a radio thats got a 2 KC wide slopbucket filter in it. 

I figured since the unknown bozo put in a product detector mod  that his choice of filters might not be the best for AM. I figured correctly.

I'm thinking it will sound a lot better next time I turn it on.

[K5UJ]

Hope U right.   That's the prob. with the stock 75A3.  That was the first ham rx collins made after developing the mech. filter.  It came with 800 Hz for cw and 3 KHz.  The 3 Kc was supposed to be used for SSB and AM.  For AM the manual instructs the user to carefully tune in the signal getting one sideband with the carrier just inside the skirt.  It works but you get only one sideband and even then you recover only 3 KHz of audio.  This was in the days of lots of AM and QRM and yellow stock rigs.   It's not acceptable now.  You have to get a wider filter or make up something to stick in the slot.

[KM1H]

You want to sell that filter?

Carl
KM1H

[N3DRB The Derb]

tis not mine to sell. Contact Mr. Johnny Novice directly and inquire.    I have the rx on a long term loan basis from him.


re: filters- That's why I'd rather have a A2 than a A3. no stupid filter to deal with. At least the A2 is good for about 5 KC stock. getting that 2 KC wide filter out of there is gonna be over half the battle on this one. 

[K5UJ]

tis not mine to sell. Contact Mr. Johnny Novice directly and inquire.    I have the rx on a long term loan basis from him.


re: filters- That's why I'd rather have a A2 than a A3. no stupid filter to deal with. At least the A2 is good for about 5 KC stock. getting that 2 KC wide filter out of there is gonna be over half the battle on this one. 

you mean 5 kc audio.  That's not too bad a compromise between fidelity and QRM.   I have a hunch the A3 is the least popular A line rx today.  I have no way of knowing if that is true or not.  Compared to the A1 and A2 it takes some work to make it provide good AM audio. 

[N3DRB The Derb]

well, 4.8 kc to be precise. It's enough because there's no way you are gonna get wide sound on it. single 6AQ5 and the outpoot transformer is crap. You just build it to make it usable without being yellowy.

The receiver was actually fatiguing to listen to, the audio was so pinched. After using it for more than 15 minutes or so I'd get a headache.

I liked the A-2 I had in the early 80's, it had no issues and ok quality. I did not like the 32V-2 transmitter.

[w3jn]

Actually there's a spec on the web that sez that's a 1.6 KC filter.

I had two of those 75A-2s at one point, bought from the same guy on eBay.  THe one Drb has had the mech filter mod, the other had a completely different front end.  I don't remember which is which - one has a 6BA7 first mixer and the other a 6BE6; believe one has a 6BZ6 first rf and the other a 6AK5.  The one with the 6BE6/6AK5 was a low serial number - like #32 or something.

Which one did you end up with Drb?  Now I have ANOTHER 75A-2 here that I bought at NEARFest for a hunnert bux, it's also one with a 6BE6/6AK5 front end.

[N3DRB The Derb]

this one is serial # 455. it's got a 6AK5, which was a lousy choice. It's got gain out the nutz, but it's a sharp cutoff tube. NG for a HF rx front end.

I'm just gonna make it the best I can. Getting rid of that damned tinny ass slopbucket filter JS will help a whole bunch.

heres some A-2/3 junk I found, gonna post em as they may help somebody. Will take stock of what I have after recapping. I need 2 (count them, 1,2) receivers to pair up with the future HB rigs.

hey, you got plans for that other one? bring it up with you when you come up and I'll do that one up too. always helps to have a model.

When ya want em they'll be tip top.

[w3jn]

Sure thang.  I powered it on some time ago and can't even remember what it did.  I have a cabinet for that one too (a bit rusty on top, but the radio's not in too bad a shape).

[KM1H]

If I remember, subject to correction  ,  the filter used with the 75A2 Collins kit was the 1st generation with lots of insertion loss and an oddball impedance. Not compatible with the later ones used in the A3 and beyond.

Carl
KM1H

[w3jn]

The one that was in there is from a KWT-6 or some other non-Art Collins-approved mod, Carl.  The ghost of Art Collins and the CCA are haunting whoever did that mod to the poor radio 

[Detroit47]

I don't know if you fellows are aware but some CB radios have 6kc Collins filters in them. I will provide some exact model numbers later, but as I recall. They are in Tram Titan 1 and 2 as well as Browning mark 2; they are for a 455 IF. The physical size is smaller than the one out of a 75 A2. I was able to mount one to a circuit board and it plugs it in with no mods on the receiver. I am happy with the results the Tram radios can be found a lot cheaper than an original 6 KC filter.
73 N8QPC

[N3DRB The Derb]

Sure thang.  I powered it on some time ago and can't even remember what it did.  I have a cabinet for that one too (a bit rusty on top, but the radio's not in too bad a shape).

groovy.     Well they will be shiny and bright when I get through with em. I got my sea legs back now and I gots to roll like that.

[w3jn]

You gonna do the obligatory PTO endpoint adjust on it, too? Did that in both those other A-2s.  Gotsta unslobber wires and pull the PTO and front panel to do it 

[WA1GFZ]

I bet it would be fairly easy to get a Racal 6.8 or 16 KHz filter working in an A3.

[N3DRB The Derb]

well. I'll check it out and see if it needs it, if it does I'll do it. I'll put em on teh production line.