IF can wanted

[w2amr]

I am restoring an old RCA CB rig. I found a short in one of the IF's and I can't fix it. Anybody have one laying around. It is 1650 KC's
14307

[N8YX]

Found this on eBay. Pricy but it'll work:

http://www.ebay.com/itm/Miller-1650-Khz-IF-Transformer-1732-Tube-Receivers-NEW-/361395778911?

[w2amr]

Found this on eBay. Pricy but it'll work:

http://www.ebay.com/itm/Miller-1650-Khz-IF-Transformer-1732-Tube-Receivers-NEW-/361395778911?
Tnx Fred, but the whole radio isn't worth that. The problem is, one of the flat silver mica caps in the bottom of the IF is bad. I have seen online where you can repair them by drilling out the rivet , bypassing the cap, then put a replacement mica on the leads under the chassis when the IF is reinstalled. Trouble is, I don't know what value to use , and it isn't marked on the schematic.

[N8YX]

Tnx Fred, but the whole radio isn't worth that. The problem is, one of the flat silver mica caps in the bottom of the IF is bad. I have seen online where you can repair them by drilling out the rivet , bypassing the cap, then put a replacement mica on the leads under the chassis when the IF is reinstalled. Trouble is, I don't know what value to use , and it isn't marked on the schematic.
Got access to a dip meter or network analyzer? LCR meter? Pull the old cap, measure the inductance of the coil with the slugs inserted halfway...then solve for "C" at 1650KHz. Get something close, tack it in then dip the tank and check resonance.

I've had to do this many times when adding WARC bands to older Kenwood and Yaesu rigs...build your own RF and IF stage peaking coils or transformers, VCO coils and whatnot.

Let me know what you need in the way of silver mica caps if your junk box is low on them.

[N8YX]

Did you see this, George?

http://www.surplussales.com/Inductors/Ind-SmAdjRF/Ind-SmAdjRF-1.html

[w2amr]

Got access to a dip meter or network analyzer? LCR meter? Pull the old cap, measure the inductance of the coil with the slugs inserted halfway...then solve for "C" at 1650KHz. Get something close, tack it in then dip the tank and check resonance.

I've had to do this many times when adding WARC bands to older Kenwood and Yaesu rigs...build your own RF and IF stage peaking coils or transformers, VCO coils and whatnot.

Let me know what you need in the way of silver mica caps if your junk box is low on them.Here is a close up of the caps Fred. they are flat wafers built into the bottom of the IF, held together with a rivet. 14308

[N8YX]

Is that cap showing shorted, George?

One other thing I found whilst cruising the 'Net for a solution...a good bit of 60s and 70s era gear used 1650KHz as an IF. Many Hallicrafters SX/S SW receivers, Lafayette CB rigs, Codan HF SSB maritime transceivers...know where any of these might be hiding?

ETA: Look here: http://www.ebay.com/itm/Hallicrafters-S-94-S94-Receiver-RF-IF-Transformers-Set-Good-Used-As-Shown-/252079372544?hash=item3ab119f900

Will those work? I don't have an S-94 schematic handy to check.

[w2amr]

Is that cap showing shorted, George?

One other thing I found whilst cruising the 'Net for a solution...a good bit of 60s and 70s era gear used 1650KHz as an IF. Many Hallicrafters SX/S SW receivers, Lafayette CB rigs, Codan HF SSB maritime transceivers...know where any of these might be hiding? Yeah, somehow it's shorting the top coil to the bottom one. If I can't fix this one, I'll have to keep an eye out for a junker that uses a 1650 IF. This is an RCA mark 7 which is almost the same radio as a Lafayette HE20. I have 3 Mark 7s now. One I restored and converted to 10 meters, the second one was my uncles who bought it new in 1960. I'm restoring that now for the CB. The 3rd one I just picked up on E-bay. It worked for about 15 minutes before the IF took a dump. Oh well, If I can't fix it , I'll have a good parts rig for the other two.

[K4PIH]

I have an old rca cb that I'll check and get back with you tomorrow eve. If I have a match you can have the whole radio. Pm your address if you want.

73 PIH

[w2amr]

I have an old rca cb that I'll check and get back with you tomorrow eve. If I have a match you can have the whole radio. Pm your address if you want.

73 PIHGreat, thanks!

[K7SGJ]

George, how did this turn out, or did it yet?

[w2amr]

George, how did this turn out, or did it yet?I drilled out the rivet that holds the mica wafers together in the bottom of the IF. Then I took them out, reassembled the can, put it back on the chassis, and soldered the wires back on. Then I took a guess at the value and tacked a 120 PF cap across each coil lead. It receives, but not very well. I just have to find the right value caps to replace the micas.

[K7SGJ]

I have a bag full of Arco trimmers that might help you out. I can send you one of each if you like. If you find one that works, you could leave it in, or measure it and put in a fixed value that is close, and tweak the coil a bit. The nice thing about leaving the trimmer in, is that you can peak it at values that standard value fixed caps are not available in. Although I have a bunch of these, I think there are just 8 or 9 different values. Follow this link to find actual values. The ones I have are 400, 402, 407, 408, 469, 4613, 4614, and 4615. Shirley, one of them should get you there. Between the coil setting and capacitor setting, you should be able to get resonance with out too much trouble. The linked site is a bit hard to read, but you can get some idea of what's what. I'm sure there are sites with better resolution of the Arco page. Good luck, and let me know if you want me to drop these things in an envelope for you.

[w2amr]

I have a bag full of Arco trimmers that might help you out. I can send you one of each if you like. If you find one that works, you could leave it in, or measure it and put in a fixed value that is close, and tweak the coil a bit. The nice thing about leaving the trimmer in, is that you can peak it at values that standard value fixed caps are not available in. Although I have a bunch of these, I think there are just 8 or 9 different values. Follow this link to find actual values. The ones I have are 400, 402, 407, 408, 469, 4613, 4614, and 4615. Shirley, one of them should get you there. Between the coil setting and capacitor setting, you should be able to get resonance with out too much trouble. The linked site is a bit hard to read, but you can get some idea of what's what. I'm sure there are sites with better resolution of the Arco page. Good luck, and let me know if you want me to drop these things in an envelope for you.That's a great idea Ed. I think I may have some of those in the garage. I'll look for them tomorrow and let you know. Thanks.

[w2amr]

Good news guys, I found two arco #460 trimmers. internets say the values are 25-115 PF. I'll try them this weekend.

[w2amr]

I put the trimmers in and they worked fine. Trouble is, the radio only hears very strong signals. I must have issues somewhere else.

[N8YX]

I put the trimmers in and they worked fine. Trouble is, the radio only hears very strong signals. I must have issues somewhere else.
Bypass and/or coupling caps in the RF and IF amp stages? Could have more micas going bad, and any Orange Drops under that chassis are immediately suspect.

[w2amr]

Bypass and/or coupling caps in the RF and IF amp stages? Could have more micas going bad, and any Orange Drops under that chassis are immediately suspect. Could be. I think the next step is to check voltages at the tube sockets. But, I'm getting close Fred.

[K7SGJ]

Signal injection at this point is a good way to go on a receiver with the symptoms you have there, especially if the DC voltages are close. If you don't have a signal generator, often a noise generator can be helpful, and are easily and quickly built. Of course a grid dip meter can be used, as well as a DDs if you have one of those around. Measuring with a VTVM or DVM on a low ac scale, you can get an idea of stage gain. I would assume if you were to get 10db or better at each stage, it would be safe to assume it's working okay. With your current problem, I would try to look around the RF amp stage. If you tune to a signal you can hear, then that can be used to measure stage gain and even how well the RF amp is doing. Good luck. It looks like the final fix is just over the horizon, which reminds me of a story about the Fugowi Indians, but I digress...........

[w2amr]

Signal injection at this point is a good way to go on a receiver with the symptoms you have there, especially if the DC voltages are close. If you don't have a signal generator, often a noise generator can be helpful, and are easily and quickly built. Of course a grid dip meter can be used, as well as a DDs if you have one of those around. Measuring with a VTVM or DVM on a low ac scale, you can get an idea of stage gain. I would assume if you were to get 10db or better at each stage, it would be safe to assume it's working okay. With your current problem, I would try to look around the RF amp stage. If you tune to a signal you can hear, then that can be used to measure stage gain and even how well the RF amp is doing. Good luck. It looks like the final fix is just over the horizon, which reminds me of a story about the Fugowi Indians, but I digress........... Ok Ed TNX.