Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Dec Sun 17, 2017 3:32 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 28 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Oct Mon 30, 2017 9:53 pm 
Member

Joined: May Sun 28, 2017 9:08 pm
Posts: 201
Location: Whiteville, TN
Have no idea how long this kit has sat around before being put together on my bench. I am the third owner of this kit and the first to attempt to assemble! The problem at this point is a phase check is inconclusive because some out of spec voltages and the lack of audio response. Explaining some sysptoms, the white noise will come forth when the set is powered up just to fade to near silent in a very short time, one to two seconds max. It has about 11 electrolytics installed with one to go. I do not want to proceed until I get a satisfactory phase check 5 completed. It has two power bus circuits, 10 volt and 5 volt, both regulated. The 5v is for display and works. 10v is for the rest of the receiver and shows 10.2 volts and the regulater does not get hot. I am thinking one of the electrolytics has gotten a bit fuzzy and opening. What do all of you think and recommend?

_________________
Karl
KI4ZUQ


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Oct Tue 31, 2017 12:49 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 738
Location: Wayside, NJ Monmouth
If the kit has been sitting around for a long time. I would just go ahead and replace the electrolytics. Since they are low voltage types, they are inexpensive. If there are any Tantalums replaced they as well.


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Oct Tue 31, 2017 1:02 am 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 22134
Location: Somers, CT
Make sure none of the caps are installed backward.

_________________
Just because it can be done doesn't mean it should be done.


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Fri 03, 2017 1:40 am 
Member

Joined: May Sun 28, 2017 9:08 pm
Posts: 201
Location: Whiteville, TN
Boy, Pete, you really know how to hurt a guy! Trouble is you are right! I checked every electrolytic and I actually did get 'em right! You are right to hit the basics. I did check two electrolytics in the last section that would not pass the phase test but they passed. Put 'em back in and removed a filter upstream. Testing again was good indicating the problem is upstream of that. More later.

_________________
Karl
KI4ZUQ


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Fri 03, 2017 9:31 pm 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 22134
Location: Somers, CT
Karl, I built one of those for a magazine review. Believe me, I screwed it up a few times, including damaging a few controls during mechanical assembly!

Pete

http://www.americanradiohistory.com/Arc ... 998-09.pdf

_________________
Just because it can be done doesn't mean it should be done.


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Fri 03, 2017 10:13 pm 
Member

Joined: May Sun 28, 2017 9:08 pm
Posts: 201
Location: Whiteville, TN
Really good article, Pete! Progress checks at phase 4 were all good for me, it is phase 5 that has a problem. Rest assured, I will be CLOSELY examining the inductors! Those color bands could be confusing!

_________________
Karl
KI4ZUQ


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Fri 03, 2017 11:41 pm 
Member

Joined: Nov Wed 17, 2010 11:14 pm
Posts: 68
I have a 1254 and it worked well. Fun to put together and use. Sensitivity throughout most of the HF range was ~ 0.5 uV for 10 dB S/N. However, after about a year of operation the sensitivity degraded significantly. My suspicion is in the AGC loop where by Ten Tec controls the AGC via a front end series PIN diode. Its voltage is derived from the IF through a high beta Darlington device and I suspect its beta has substantially dropped. Ten Tec did indicate that issues were found with some of these devices. So if you are having issues at that stage, take a look at that area of the circuit on card. Alan


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Sat 04, 2017 9:51 pm 
Member

Joined: May Sun 28, 2017 9:08 pm
Posts: 201
Location: Whiteville, TN
Update: for Pete and Alan or anyone who has put one of these together. FL 2 now seems like the bad guy in that very little up stream seems to contribute to the noise or the lack of it. The part is CQ S455 IT which is very definitely a chinese part. The original was a Murata CFR 455 I which seems to be unobtainable. I will get circuit specific if desired. Mouser have some Murata IF filters but they are quite physically different. The board is configured for either chinese or Murata.

_________________
Karl
KI4ZUQ


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Sat 04, 2017 10:10 pm 
Member

Joined: Nov Wed 17, 2010 11:14 pm
Posts: 68
Thanks Karl for the heads up on the ceramic filter...Murata or otherwise. I'll take a look at the Filter on my unit and see what it uses. If I recall, their probably a couple kHz BW. Their attenuation floor is not too bad, about 40 dB or so. I think they were 4 pole and at one time I contemplated looking at putting in a 6 pole.

Yep, just looked at mine, black mono-block, definite not a Murata with CQ logo 455iT.

Would not surprise me if in my case I have the same issue. I was working around the IF and suspected either the AGC, the 1350 IF or ..... as I was loosing substantial signal level at that point. So you may have hit the nail on the head with a dying CF. I'll see what I have in the junk box and may be able to assist on the CF. Alan


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Sat 04, 2017 10:24 pm 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 22134
Location: Somers, CT
There should be no DC voltage applied to those ceramic filters... if there is, a DC
blocking cap is good insurance against eventual failure.

http://radiorepair.blogspot.com/2010/05 ... demic.html
http://sv8ym.blogspot.com/2010/07/myste ... lters.html

_________________
Just because it can be done doesn't mean it should be done.


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Sun 05, 2017 2:36 am 
Member

Joined: May Sun 28, 2017 9:08 pm
Posts: 201
Location: Whiteville, TN
Alan, drop whacher doin' and read Pete's links! That scratchy static-like noise is EXACTLY what I hear! Unless it fades altogether! Hmmmm, might just try to take that thing apart.....

_________________
Karl
KI4ZUQ


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Sun 05, 2017 2:51 am 
Member

Joined: Nov Wed 17, 2010 11:14 pm
Posts: 68
Yes! Thank you Peter for the heads up. The application of DC to a CF is a real heads up. Analogous to some of the mechanical filters. Apparently metal migration and the stress of applied voltage to a piezo device (in the case of the 1254 about 10 volts via T7) could very well be my problem. I will remove the CF and check it out and then begun the hunt through my junk box. Thanks again for the links and the warning! Alan W4AMV


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Sun 05, 2017 2:52 am 
Member

Joined: Nov Wed 17, 2010 11:14 pm
Posts: 68
Yes! Thank you Peter for the heads up. The application of DC to a CF is a real heads up. Analogous to some of the mechanical filters. Apparently metal migration and the stress of applied voltage to a piezo device (in the case of the 1254 about 10 volts via T7) could very well be my problem. I will remove the CF and check it out and then begun the hunt through my junk box. Thanks again for the links and the warning! Alan W4AMV


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Sun 05, 2017 3:26 am 
Member

Joined: Nov Wed 17, 2010 11:14 pm
Posts: 68
Hi Karl,

As you probably have already noted the outline on the TenTec card will accept the larger Murata filter as well as the smaller rectangular block. I have mostly the smaller 4 pole units and I believe what TenTec had in the 455 kHz position was a 6 pole. But I'll have to find my notes and catalog sheets. I have both Murata and NTK which manufactured CF units to compete. The 45 MHz first IF was 15 kHz BW. Need to look in the manual to see the 455 BW and see what is comparable and available today. Alan


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Sun 05, 2017 8:36 pm 
Member

Joined: May Sun 28, 2017 9:08 pm
Posts: 201
Location: Whiteville, TN
Checked the circuit schematic last night and there is NO capacitor on either end of that CF! Designer be shamed! Also studied the CQ filter itself and noted it is potted in tar or epoxy. Will have to study Pete's links again.....

_________________
Karl
KI4ZUQ


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Sun 05, 2017 9:00 pm 
Member
User avatar

Joined: Jun Sun 19, 2011 2:31 pm
Posts: 4812
Karl,

Thanks for starting the interesting thread on you 1254 receiver and I hadn't thought about the issue of applying DC to ceramic filters (and resonators) so your thread has been useful to more than just 1254 owners.

It also has me motivated enough to pull out my Ten Tec SP-325 (mil version of the RX-325) and put it on the bench because it only works when it wants to.

Rodger WQ9E


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Sun 05, 2017 9:22 pm 
Member

Joined: May Sun 28, 2017 9:08 pm
Posts: 201
Location: Whiteville, TN
Pete Bertini's first link sends up the balloon on recent and current receivers with these filters and designers that overlooked the capacitors. Let all know whatcha find!

_________________
Karl
KI4ZUQ


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Sun 05, 2017 10:31 pm 
Member

Joined: May Sun 28, 2017 9:08 pm
Posts: 201
Location: Whiteville, TN
Really great news! Update #2: Took existing chinese ceramic filter S455IT with a wire extension from pins 2,3 & 4 to ground, one each .1 pf capacitor from pins 1 and 5 to their respective spots. Looks bad, works good! Was able to get loud background hash noise from the speaker, increasing with probe touch on T6 and musical tones with the clarifier (fine tuning to you boat anchor boys!). Otherwords, a successful Phase 5.0 test! Now, I have to decide just exactly HOW I will incorporate two disc caps into this circuit so that it will be more or less reversible. The next question is what is the optimum cap value? Any suggestions?

_________________
Karl
KI4ZUQ


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Sun 05, 2017 11:32 pm 
Member

Joined: Nov Wed 17, 2010 11:14 pm
Posts: 68
Hi Karl. I would look at the pc traces in and out of the filter. I think there is enough room to cut the traces with an Xacto blade. You just want to create a GAP. Then use a surface mount cap, 0.1 uF should be fine at 455 kHz.

You will need to gently remove the solder mask on each of the traces, then pre tin the traces and good to go to place the SM cap. Pretty straight forward with an 0805 size cap. Alan


Top
 Profile  
 
 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Mon 06, 2017 12:01 am 
Member

Joined: Nov Wed 17, 2010 11:14 pm
Posts: 68
It is interesting to note, there is no mention that I see in the Murata or NTK filter data sheet on prevent applying DC to the filter. In many cases the matching of the filter, say 1500 ohm to the IF amp and a mixer is done with a simple L network, a series C to the filter with a shunt L from the filter port to ground. Hence, no DC on the filter. Of course, many cases that DO not use that arrangement. So is this a systemic problem or unique to this manufacturer?


Top
 Profile  
 
Post New Topic Post Reply  [ 28 posts ]  Moderator: Sandy Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: atwaterkentsrus, MDMcCool, Sandy, WoodchuckTN and 7 guests



Search for:
Jump to:  


















Privacy Policy :: Powered by phpBB