Re: Drake TR-7 - Noisy transmitter
Almost one year since I parked the TR7 with the 'crackly audio' transmitter. How time flies!
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With the TR4310 now fixed, it was time to finish the TR7. Oddly, I had a couple of contacts on it with no trace of crackling. Then, during a third contact (after the radio had been powered up for many hours), the transmit audio went cracky, noisy, distorted and would not stop. Disconnecting the microphone and just shorting PTT to ground on the front-panel microphone socket with a screwdriver, I could vary the level of the crackling from zero to a good 50 W PEP, or more, using the mic. gain control. So, whatever was cracking, was before the mic. gain pot. In a TR7, there's not much active circuitry to consider - just a simple, two BJT amplifier.
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I could not see a way of having the Transmit Exciter Board on extenders at the same time as keeping the radio running using the Jumper Board to replace the DR7 / Display Board. Did I miss a trick here?
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Pulling the Transmit Exciter board, I noticed several low-value tantalum capacitors and, yes, two of them (C310 and C309) were in key positions coupling the transmit audio. In my experience, these were the most likely culprits, so I changed them. I did not bother changing C307, a 0.05 uF disc ceramic (coupling) capacitor. I can't remember ever finding a bad capacitor of this type in any of my vintage radio and took the risk that this case would prove no different. In addition, I changed several other tantalum capacitors, adjacent to the mic. amplifier circuitry, as I did not want to have to pull the board ever again. I also changed a quantity of electrolytic capacitors in key coupling and de-coupling positions in and around the balanced modulator an board generally.
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My attitude to parts replacement - especially capacitors - is hardening. I've never been fond of blanket / just in case replacement, but tantalums can cause a lot of collateral damage and undeserved misery when they go short-circuit. Generally, if I pull a capacitor out to test, these days, I replace with new regardless of the test results. In this case, I replaced old tantalum with new tantalum. If I had had low-value electrolytics to hand, I would probably have used those instead as it was an LF / audio application.
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Before re-installing the DR7, I changed the key electrolytic capacitors around the power feed in and the two 5 Volt regulators on this board.
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On test, the transmit audio is now clear and clean and got good reports on 40 m SSB. I've not checked way down to see if the 1 kHz low level artifacts (which seemed to be display multiplex related) have improved / gone, but will do so at some point.
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Almost time to put the covers back on. As part of doing that I have to do something about the 80% of the base plate screws a previous owner managed to break off in the PEM nuts. Will try drilling them out. If that doesn't work, push out the PEM nuts using a hydraulic press and try tapping the holes left behind in the chassis for some suitable metric screws.
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Regards,
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Mark, G4FPH.
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At last, the promised follow-up on the T-4XC which was sticking on tx. It turned out to be the relay switching tube (6FQ7 in this set).
On the tester (I have an AVO VCM Mk3) the original showed as slightly leaky/gassy, probably not enough to worry about in many applications but the T4 has high resistance feed into the grid and leakage of a few uA is enough to drag the 'off' bias voltage down to where the tube conducts enough for the relay to pull in.
It took an age for the replacement to arrive but all seems good now.
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I also looked at the relay, the PA switching contacts had a lot of debris around them and are well worn. I've suggested the owner starts saving to get a replacement (around $80 over here).
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Again, thanks for all the suggestions, great bunch of .people here.
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73, Steve G8GSQ
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Semiconductor List Closing
Hello, fwllow Drakesters...
I had a more-than-anticipated response to my semiconductor list.? This email hereby closes-off the request period.
I will now printo out all the requests and allocate accordingly.? My aim was to keep devices that are in common use stocked here for future use.? Example, MPF102 I need at least 5 to stay in invenroty here (as mentioned).? Rare devices like the UHF power transistors, I'd be happy to sell all of.
All requests from USA will have $5 added for shipping.? I figure I can get anything anywhere for $5, including any padded envelopes (I'll use my Amazon envelopes until they're gone).
Anything to Canada, if you can provide a USA mailing address, that would be GREAT.? Customs forms are now a major PITA and I avoid them like I'd avoid a jellyfish.
Hope to have final amounts over the weekend (life events, notwithstanding)...
73,
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
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That question might best be answered by YLs/XYLs.
I've moved several times in the past few years. And each time I pack stuff up and haul it to the next location, I look at everything and ask, "Do I REALLY need this?"
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I did this over and over again with the pile of test gear and cabling. Some things did not make the latest cut, like all those scraps of LMR400 that I was saving for "some day."?
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So cut to my latest project; I'm bringing to life a C-Line (again) after 25 years of dormancy. And being that the AC-4 was original from 1977 with no mods, I knew I was living on borrowed time. I just did Mike's (Heathkit Shop) board upgrade, and I was thinking as I finished it, "Boy, sure would be great to have a Variac for the smoke test."?
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I did some digging in the attic and ....Son of a B...there it was. The Variac that I've been hauling around for the past 40 years. I had even forgotten that I still owned it.?
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Worked perfectly.?
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So for all of you wondering if you need all your stuff for "some day"...the answer is YES.?
--
Craig/W8CS
Greenville, SC
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I've moved several times in the past few years. And each time I pack stuff up and haul it to the next location, I look at everything and ask, "Do I REALLY need this?"
?
I did this over and over again with the pile of test gear and cabling. Some things did not make the latest cut, like all those scraps of LMR400 that I was saving for "some day."?
?
So cut to my latest project; I'm bringing to life a C-Line (again) after 25 years of dormancy. And being that the AC-4 was original from 1977 with no mods, I knew I was living on borrowed time. I just did Mike's (Heathkit Shop) board upgrade, and I was thinking as I finished it, "Boy, sure would be great to have a Variac for the smoke test."?
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I did some digging in the attic and ....Son of a B...there it was. The Variac that I've been hauling around for the past 40 years. I had even forgotten that I still owned it.?
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Worked perfectly.?
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So for all of you wondering if you need all your stuff for "some day"...the answer is YES.?
--
Craig/W8CS
Greenville, SC
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Has anyone successfully transplanted filters from a TR-4/4c into a TR-3? ?I have a nice TR-3 and a trashed TR-4 for a donor. ?
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Why do they sometimes use two caps in parallel on some amps? But others only have one?
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I¡¯m probably going to get this back together today if time permits. Getting more rigs in to repair for others so I have to get moving :-)
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Wed, Feb 5, 2025 at 21:05, KB9VY via groups.io < lcoblentz3@...> wrote:
You¡¯re most welcome Steve! ?73, de KB9VY.
On Wed, Feb 5, 2025 at 20:55, Steve Wedge, W1ES/4 via groups.io <
w1es@...> wrote:
Thanks to Lawrence Coblenz.?
I have confirmed that the transformer is original but the capacitors are not. The transformer was glued to the top of the weight bar in the bottom of the base.?
I¡¯ll be starting my testing with the caps removed. The element reproduces my whistling and voice as seen on an oscilloscope.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
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Re: Warning on the 7077 (and any plastic Astatic mic)
Thanks, Jim. Sometimes, I miss things.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Wed, Feb 5, 2025 at 21:02, Jim Shorney via groups.io < jimNU0C@...> wrote:
Again, the origial cartridge is a cheap low impedance dynamic.
On Wed, 05 Feb 2025 21:53:57 +0000
"Steve Wedge, W1ES/4 via groups.io" <w1es@...> wrote:
> I still don¡¯t know why anyone would have installed a low-Z element unless the original high-Z one had died and the low-Z element was what they had available.
--
73
-Jim
NU0C
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Re: Drake TR7, TX issue any ideas?
Agree Jim, have ordered batch of 6 so both will be replaced!
But I actually think you nailed it, situation improved with the PIN out of the circuit! Power consumption on 15Meters now dropped to ~24 amps from 31 Amps so great improvement! Also power output on 10Meters increased to ~30Watts from ~5Watts range, so I feel that good times are ahead :). New pin diodes and an Predrive / ALC alignment will probably improve the output. But let's see when the mailman drops by.
Again, Thanks for your time Jim, appreciate it!
?73's Michael.
I would replace both in the pair just to be safe. However you can see the results just by removing the bad diode from the circuit. It is only needed for the calibrator signal.
On Thu, 6 Feb 2025 08:17:36 +0100
"Michael Jensen via " <kavigal=[email protected]> wrote:
> Great Thanks! Jim, looking forward to replace the diode and see the result.
> I'll be back ;).
>
> 73's De Michael.
>
> On Thu, Feb 6, 2025 at 2:59?AM Jim Shorney via <jimNU0C=
> [email protected]> wrote:?
>
> >
> > Not quite. It is connected to the common signal path and will cause
> > problems if it has failed.
> >
> > On Wed, 5 Feb 2025 18:29:00 +0100
> > "Michael Jensen via " <kavigal=[email protected]> wrote:
> >?
> > > however I
> > > assume CR1402 has little to do with TX and only RX/Calibrator signal??
--
73
-Jim
NU0C
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Re: Drake TR7, TX issue any ideas?
I would replace both in the pair just to be safe. However you can see the results just by removing the bad diode from the circuit. It is only needed for the calibrator signal. On Thu, 6 Feb 2025 08:17:36 +0100 "Michael Jensen via groups.io" <kavigal@...> wrote: Great Thanks! Jim, looking forward to replace the diode and see the result.
I'll be back ;).
73's De Michael.
On Thu, Feb 6, 2025 at 2:59?AM Jim Shorney via groups.io <jimNU0C=
[email protected]> wrote:
Not quite. It is connected to the common signal path and will cause
problems if it has failed.
On Wed, 5 Feb 2025 18:29:00 +0100
"Michael Jensen via groups.io" <kavigal@...> wrote:
however I
assume CR1402 has little to do with TX and only RX/Calibrator signal?
-- 73 -Jim NU0C
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Re: Mini collection of DRAKE by SP3SWJ
I just wanted to show off my mini collection? of DRAKE radio.
35 years ago I fell in love with these radios .
15 years ago I started collecting them ;-)
?Well, this is the current effect:
One radio is fully working the others are waiting to be looked at, checked, started up. I jave some spare tubes and I have a meter to measure the tubes. Work in progress.
Jerry
SP3SWJ
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Mini collection of DRAKE by SP3SWJ
I just wanted to show off my mini collection? of DRAKE radio.
35 years ago I fell in love with these radios .
15 years ago I started collecting them ;-)
?Well, this is the current effect:
One radio is fully working the others are waiting to be looked at, checked, started up. I jave some spare tubes and I have a meter to measure the tubes. Work in progress.
Jerry
SP3SWJ
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Re: Drake TR7, TX issue any ideas?
Great Thanks! Jim, looking forward to replace the diode and see the result. I'll be back ;).
73's De Michael.
Not quite. It is connected to the common signal path and will cause problems if it has failed.
On Wed, 5 Feb 2025 18:29:00 +0100
"Michael Jensen via " <kavigal=[email protected]> wrote:
> however I
> assume CR1402 has little to do with TX and only RX/Calibrator signal?
--
73
-Jim
NU0C
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As shown by my photos. On Thu, 06 Feb 2025 01:55:56 +0000 "Steve Wedge, W1ES/4 via groups.io" <w1es@...> wrote: I have confirmed that the transformer is original but the capacitors are not -- 73 -Jim NU0C
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You¡¯re most welcome Steve! ?73, de KB9VY.
On Wed, Feb 5, 2025 at 20:55, Steve Wedge, W1ES/4 via groups.io < w1es@...> wrote:
Thanks to Lawrence Coblenz.?
I have confirmed that the transformer is original but the capacitors are not. The transformer was glued to the top of the weight bar in the bottom of the base.?
I¡¯ll be starting my testing with the caps removed. The element reproduces my whistling and voice as seen on an oscilloscope.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
|
Re: Warning on the 7077 (and any plastic Astatic mic)
Again, the origial cartridge is a cheap low impedance dynamic. On Wed, 05 Feb 2025 21:53:57 +0000 "Steve Wedge, W1ES/4 via groups.io" <w1es@...> wrote: I still don¡¯t know why anyone would have installed a low-Z element unless the original high-Z one had died and the low-Z element was what they had available. -- 73 -Jim NU0C
|
Re: Drake TR7, TX issue any ideas?
Not quite. It is connected to the common signal path and will cause problems if it has failed. On Wed, 5 Feb 2025 18:29:00 +0100 "Michael Jensen via groups.io" <kavigal@...> wrote: however I
assume CR1402 has little to do with TX and only RX/Calibrator signal? -- 73 -Jim NU0C
|
Thanks to Lawrence Coblenz.?
I have confirmed that the transformer is original but the capacitors are not. The transformer was glued to the top of the weight bar in the bottom of the base.?
I¡¯ll be starting my testing with the caps removed. The element reproduces my whistling and voice as seen on an oscilloscope.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
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I am in need of a VSWR set knob for the MN4C.
Anyone have one laying around or can tell me where to find one?
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See picture attached.
I'm good on QRZ.
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Thanks,
Ron WB4OQL
Clyde, NC
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Craig W8CS
Jim Shorney
