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TR-4C Problems with 28.0 and 28.5 bands
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I just picked up this TR-4C a couple of weeks ago and I'm going through it, everything is working fine except both the 28.0 and 28.5 bands do not work. I receive nothing and can't hear the CAL oscillator either. The 29.1 band is working OK but signals are weak. I thought it might be the Xtals so I swapped them around to see what happened. I put the 28.0 Xtal in the 29.1 band position and got nothing, same with the 28.5 Xtal. Then I put the 29.1 Xtal in the 28.0 band position and a tiny bit of signal by peaking the RF Tune but no CAL heard. When I put the 29.1 in 28.5 I got a little band noise I could peak but no CAL signal. I did check all the tubes and they are good.?
So? Does that sound like two bad Xtals or is something else bad?
Thanks in advance & 73, Dave KD5FX
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It could be crystals but it could also be that the 10m oscillator is out of adjustment.? Make sure that the 10m oscillator is peaked per the procedure. You can use either a VTVM or a scope for this.? Having two bad crystals makes me think ¡°check the oscillator first¡±. Steve Wedge, W1ES Time flies like an arrow. Fruit flies like a banana. Sent from for iOS On Thu, Jan 16, 2025 at 10:04, Dave KD5FX via groups.io <land.dave@...> wrote:
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I would start by inspecting all of the tabs on the rotary switches associated with the band selector rod to make sure they are not damaged and deox and clean them.? While you are under there inspect all of the wiring to the trimmers and make sure you don't have any opens like a capacitor leg that got separated or something.? T8 and T10 in particular are associated with the 10m band.? Tighten all the screws everywhere you can.? I doubt you have multiple bad xtals all for the same band.? Those xtals are more prone to drift but drift is just going to shift the frequency a bit.? My guess is something associated with T8 or T10 trimmers.??
On Thursday, January 16, 2025 at 09:04:18 AM CST, Dave KD5FX via groups.io <land.dave@...> wrote:
I just picked up this TR-4C a couple of weeks ago and I'm going through it, everything is working fine except both the 28.0 and 28.5 bands do not work. I receive nothing and can't hear the CAL oscillator either. The 29.1 band is working OK but signals are weak. I thought it might be the Xtals so I swapped them around to see what happened. I put the 28.0 Xtal in the 29.1 band position and got nothing, same with the 28.5 Xtal. Then I put the 29.1 Xtal in the 28.0 band position and a tiny bit of signal by peaking the RF Tune but no CAL heard. When I put the 29.1 in 28.5 I got a little band noise I could peak but no CAL signal. I did check all the tubes and they are good.?
So? Does that sound like two bad Xtals or is something else bad?
Thanks in advance & 73, Dave KD5FX
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You're referring to the 5-10 section, correct? Injection Crystal Oscillator adjustment. Thanks for the tip about using a scope instead of the VTVM, that worked much better for me. I was pretty close with the VTVM but got a better adjustment with the scope. So that is correct now and 29.1 is working (but weak signals on the CAL). But using my signal generator at 29.4 MHZ I'm getting an S9 which is the same signal I'm getting on my Flex Radio at that freq so I think the 29.1 band is working OK, there's just no signals out there to listen to on SSB, I do hear an FM signal at 29.620 which sounds like garbage of course on the Drake.?
So? Anything else I should check before ordering a Xtal?
73, Dave KD5FX
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¿ªÔÆÌåÓýLet¡¯s not get ahead of ourselves. ?Does the rig have the necessary crystals to operate on those two band segments? ?My TR4Cw came without them.Bill AE8EA On Jan 16, 2025, at 12:24 PM, Dave KD5FX via groups.io <land.dave@...> wrote:
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Ah, so the two lower crystals seem to be not working. Try baking them at about 350F for a few hours. ?Put them on tinfoil so that you don¡¯t upset any family member by soldering a cookie sheet¡ After they cool, try them again. Steve Wedge, W1ES Time flies like an arrow. Fruit flies like a banana. On Thu, Jan 16, 2025 at 12:24 PM, Dave KD5FX via groups.io <land.dave@...> wrote:
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Are you sure they are the RIGHT crystals?
10meters is ripe for CB conversions.? Sometimes that doesn't work but the crystals may remain...
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Also, you will find most R-4x receivers with a lot of random crystals plugged in the extra crystal bank.
They are not right but they do give some extra coverage for some fun SWL operation. The 100KHz calibrator signals do not come up in the
right place but...
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73,
Gary
WB6OGD
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Time to bake.? Steve Wedge, W1ES Time flies like an arrow. Fruit flies like a banana. Sent from for iOS On Thu, Jan 16, 2025 at 22:30, Dave KD5FX via groups.io <land.dave@...> wrote:
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¿ªÔÆÌåÓýDid you tried to tweak L2? If not yet, give a try. Despite the instructions to set it up at 29.1MHz position, after that manual recommends that the level produced at the test point near V1 should be about the same at the 3 positions. It's a negative reading on an high Z voltmeter. On 10m positions I read -0,7V (-1,1V on 15 and -1,35V on 40m). I don't know how's the "health" of this 6EA8.73 Marcus (PY2PLL) Em 17/01/2025 00:30, Dave KD5FX via
groups.io escreveu:
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Good point, Marcus, and very easy to check. ?Try swapping the two 6EA8¡¯s if you don¡¯t have a spare. Steve Wedge, W1ES Time flies like an arrow. Fruit flies like a banana. On Fri, Jan 17, 2025 at 7:25 AM, Marcus PY2PLL <py2pll@...> wrote:
Did you tried to tweak L2? If not yet, give a try. Despite the instructions to set it up at 29.1MHz position, after that manual recommends that the level produced at the test point near V1 should be about the same at the 3 positions. It's a negative reading on an high Z voltmeter. On 10m positions I read -0,7V (-1,1V on 15 and -1,35V on 40m). I don't know how's the "health" of this 6EA8. |
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Look carefully for any signs of rework around the circuit.? I seem to recall that you said that some switch contacts looked ¡°funny¡±. Messing with switch contacts can ruin them. Check the resistances through the switch contacts for each of the two bands.? 73, Steve Wedge, W1ES Time flies like an arrow. Fruit flies like a banana. Sent from for iOS On Fri, Jan 17, 2025 at 20:37, Dave KD5FX via groups.io <land.dave@...> wrote:
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OK, more work done today! I did check and double check all the contacts on the band switch, especially those around the Xtal area. They are all good and tested good for continuity. There's a big contest going on today and I was able to hear some signals on the 28.5 band and the 28.0 band too! BUT they are very distorted, you can tell it's SSB but can't understand a thing (and yes, I tried both LSB and USB). Even the CAL signal is distorted. Not a pure tone, almost a buzz sound. All the other bands are working OK including the 29.1 band, I can hear the CAL signal fine there. Oh yeah,? I swapped another 6EA in there for V1, no change.?
Thanks for everyone's help so far, any other ideas??
73, Dave KD5FX
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Dave, I had a similar problem a number of years ago with a TR-4. The crystal oscillator will "free wheel" when the tuning is not exactly at the frequency of the crystal. The result was the same or similar to what you hear.? Try adjusting the proper coil (I don't remember which one) for the 10M band until the oscillator "locks" to the crystal. GL ES 73, Bob Loving K9JU Maryville, TN
On Saturday, January 18, 2025 at 03:24:19 PM EST, Dave KD5FX via groups.io <land.dave@...> wrote:
OK, more work done today! I did check and double check all the contacts on the band switch, especially those around the Xtal area. They are all good and tested good for continuity. There's a big contest going on today and I was able to hear some signals on the 28.5 band and the 28.0 band too! BUT they are very distorted, you can tell it's SSB but can't understand a thing (and yes, I tried both LSB and USB). Even the CAL signal is distorted. Not a pure tone, almost a buzz sound. All the other bands are working OK including the 29.1 band, I can hear the CAL signal fine there. Oh yeah,? I swapped another 6EA in there for V1, no change.?
Thanks for everyone's help so far, any other ideas??
73, Dave KD5FX
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Gary WB6OGD
Marcus PY2PLL
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