Re: AC-4 Power Supply 10K Bias Trimmer Replacement
You can find about of the same make and size and move the insides to the old enclosure.?
I have done this with several different pots.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, Feb 8, 2025 at 20:07, Joe W7BWA via groups.io < W7BWA@...> wrote:
Thanks David.
Only that the holes are there and I wanted to replace it with what is there as the shaft is very short.
?
The main thing is finding a suitable replacement and Mouser seems stumped to one.
--
Joe - W7BWA
Custer, WA
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Re: AC-4 Power Supply 10K Bias Trimmer Replacement
A bit late to this thread.? Drake seem to use a lot of the CTS 450
series pots.? I would guess the pot in the AC4 is a CTS 450 series.?
You could get one of these from Mouser and swap out the wafer.?
???
Just be careful not to break any of the tabs securing the wafer when
you take the pots apart, replace the wafer on the short shaft pot
and put it back together.
73
Stan
KM4HQE
On 2/8/25 19:07, Joe W7BWA via
groups.io wrote:
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Thanks David.
Only that the holes are there and I wanted to replace it with
what is there as the shaft is very short.
?
The main thing is finding a suitable replacement and Mouser
seems stumped to one.
--
Joe - W7BWA
Custer, WA
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Re: AC-4 Power Supply 10K Bias Trimmer Replacement
I'll try that. Thanks!
--
Joe - W7BWA
Custer, WA
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Re: AC-4 Power Supply 10K Bias Trimmer Replacement
Thanks David.
Only that the holes are there and I wanted to replace it with what is there as the shaft is very short.
?
The main thing is finding a suitable replacement and Mouser seems stumped to one.
--
Joe - W7BWA
Custer, WA
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Re: Changes/alterations in early (S/N~18,300) R-4C IF
Kinda nice how spell-checker changes ¡°pentagrid¡± to ¡°pentagram¡±!
Gary
W0DVN
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On Feb 8, 2025, at 5:08?PM, Jim Shorney via groups.io <jimNU0C@...> wrote:
On Sat, 8 Feb 2025 16:00:31 -0600
"Gary Follett via groups.io" <xntrick1948@...> wrote:
the use of a pentagram converter tube That would be to allow operation on the Devil's Band.
--
73
-Jim
NU0C
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Re: Changes/alterations in early (S/N~18,300) R-4C IF
On Sat, 8 Feb 2025 16:00:31 -0600 "Gary Follett via groups.io" <xntrick1948@...> wrote: the use of a pentagram converter tube That would be to allow operation on the Devil's Band. -- 73 -Jim NU0C
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Re: Changes/alterations in early (S/N~18,300) R-4C IF
Gary, try putting the original screen resistor back and swap out tubes. It sounds like someone was chasing their tail over a gassy tube.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, Feb 8, 2025 at 17:00, Gary Follett via groups.io < xntrick1948@...> wrote: I am helping a fellow with his dead R-4C. I found the original problem, a puncture in one of the coax cables'
insulation pressing against the 12 volt line, pulling it to ground. Fortunately, this radio had been updated to a 7812 voltage regulator, which self-limited preventing its destruction.
However, someone had made other changes, among them the addition of a potentiometer in place of the 820 Ohm series resistor in the S meter zero circuit. It was poorly done and the pot was dangling in the air. I tried to revert back to schematic original, by putting in the 820 ohm fixed resistor where it belongs, but now I cannot zero the S meter. I determined a few things.
First, there was a 6BE6 in place of V5 (6BA6). Replacing this with a known-good 6BA6 improved the zero but not completely. I then determined that the screen resistor on V2 (6HS6) had been changed from 100K to 10K. This causes this end of the S meter bridge to draw too much current in a no-signal condition and this is the reason for the offset in the S meter (~S8).
Now I could just kludge in the pot again, but do a better job. I know it will zero with this change. I would like to know, first, if there is a good driving reason for there to be a change in the screen resistor value for V2 and also for the use of a pentagram converter tube (6BE6) in place of the pentode amplifier 6BA6 at V5.
Bob probably knows¡
Gary
W0DVN
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Good audio - T4XC and R4C
On 12m this morning, I received a good SSB audio report from MN.? I've had other good SSB audio reports.? I'm using a Shure 444.? My CW and SSB reception sound great as well.. maybe better sounding than my K4?? ?
Could it be that the absence of SRD,digitization, (etc)? and the presence of RF engineers on the T4XC/R4C design team were contributors?? 50-year-old radios.? Very cool.
73 Jay W6CJ
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Changes/alterations in early (S/N~18,300) R-4C IF
I am helping a fellow with his dead R-4C. I found the original problem, a puncture in one of the coax cables'
insulation pressing against the 12 volt line, pulling it to ground. Fortunately, this radio had been updated to a 7812 voltage regulator, which self-limited preventing its destruction.
However, someone had made other changes, among them the addition of a potentiometer in place of the 820 Ohm series resistor in the S meter zero circuit. It was poorly done and the pot was dangling in the air. I tried to revert back to schematic original, by putting in the 820 ohm fixed resistor where it belongs, but now I cannot zero the S meter. I determined a few things.
First, there was a 6BE6 in place of V5 (6BA6). Replacing this with a known-good 6BA6 improved the zero but not completely. I then determined that the screen resistor on V2 (6HS6) had been changed from 100K to 10K. This causes this end of the S meter bridge to draw too much current in a no-signal condition and this is the reason for the offset in the S meter (~S8).
Now I could just kludge in the pot again, but do a better job. I know it will zero with this change. I would like to know, first, if there is a good driving reason for there to be a change in the screen resistor value for V2 and also for the use of a pentagram converter tube (6BE6) in place of the pentode amplifier 6BA6 at V5.
Bob probably knows¡
Gary
W0DVN
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T-4XC Bandswitch positions
T-4XC
Band switch waver positions?
On the T-4XC I purchased, the waver band switch is in the wrong positions.
crystal positions are fixed, the others may be wrong too!
After tuning only a small display on the meter.
Can someone help me and take photos of all waver positions, for example for 40m.
hm ?. . .?
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Re: T-4XC Final Cathode Resistors
One watt is enough. Modern carbon film will do fine, they do not drift. Metal film will also do fine. I think Garry used to recommend oxide coated film. Since the drop is part of the measurement of "plate" current (actually cathode current) the value is of some importance.
Old fashioned carbon composition resistors were never better than 5% because the heat of soldering them could cause that much drift.
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On 2/8/2025 6:24 AM, Craig W8CS via groups.io wrote: After updating my AC-4, I fired up the T-4XC and am dealing with all of the little usual issues after being dormant for a quarter century.
Checked the final Cathode resistors which are 15ohm/1Watt. They are running at 18/17.5 ohms, roughly 20% high.
* Is there a specific type of resistor composition that you prefer to
replace these with?
* Recommended to upgrade larger than 1W?
TIA
--
Craig/W8CS
Greenville, SC
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Re: T-4XC Final Cathode Resistors
Carbon film will run at red heat without damage. I spent some of my wasted youth working for a resistor manufacturer. We made established reliability metal film and mil spec carbon film resistors.
Otherwise I agree. There are oxide coated composition resistors which work well for this sort of application. There are very few virtues to old type carbon composition resistors. They were very widely used for a couple of generations because they were cheap to make. Laser trimming of carbon and metal film has reduced production costs to the point where they are now quite cheap.
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On 2/8/2025 9:58 AM, Steve G8GSQ via groups.io wrote: In general I'd say use metal film for everything. In this case, maybe consider carbon film and don't overdo the power rating. If the resistor burns out it might just save the tube; metal film can usually take a lot of overload.
The T4 I've just been working on had run just fine for years with 18ohm (2W metal film) resistors until operator error took them and the tubes out.
I think the exact value isn't critical. 2 x 33R 0.5W is a simple option.
Steve G8GSQ
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Re: T-4XC Final Cathode Resistors
In general I'd say use metal film for everything. In this case, maybe consider carbon film and don't overdo the power rating. If the resistor burns out it might just save the tube; metal film can usually take a lot of overload.
?
The T4 I've just been working on had run just fine for years with 18ohm (2W metal film) resistors until operator error took them and the tubes out.
?
I think the exact value isn't critical. 2 x 33R 0.5W is a simple option.
?
Steve G8GSQ
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Re: Drake TR-7 - Noisy transmitter
It is exactly as stated. The adjustment is an old school ceramic trimmer cap conveniently placed on the board in line with the key jack on the rear panel. Since you need key down CW to hear the side tone it becomes a one-handed adjustment to slide a small flat blade screwdriver through the key jack to both key the rig and adjust the trimmer. You do not need to have the drive turned up to do this. How you measure the 800 Hz audio tone is up to you. If you have a frequency counter that works well in the audio range that would be the obvious choice. Simply connect it across the rig's speaker. You could also use an accurate audio generator set to 800 Hz and connected to a small speaker to zero beat the CW side tone using your ears. Another option would be a Windows or Linux computer with the Fldigi digital mode software installed. You can accurately measure an audio frequency with Fldigi. Extreme accuracy is not required but I would suggest that you not go too far away from 800 Hz as that is the design center of the oscillator circuit. Which also makes the math easier. Drake's CW is a bit different than most other rigs. Modern rigs typically shift the RX frequency to hear a CW tone and the dial displays the zero beat (carrier) frequency. The TR7 is exactly the opposite. We shift the TX up 800 Hz and the dial displays the offset frequency. Your zero beat frequency is dial frequency +800 Hz. If you want to work someone on, say, 7010 you need to set your dial frequency to 7009.2 to be on his frequency. Re: a bench test jig, depending on the circuit you are troubleshooting you don't always need all the voltages to test a "naked" board. Much of the time you would only need +10. I have swept the IF filters from a couple of rigs using only +10 to turn on the desired signal path and negative volts from a 18650 cell to bias off the other signal paths. I used component lead clippings shoved into in the Molex connectors and alligator clip test leads to make the connections. A bit ugly but it worked FB. On Sat, 08 Feb 2025 06:48:58 -0800 "atlasstuff via groups.io" <g4fph@...> wrote: I tried to adjust the CW sidetone on the TR7, but could not understand the Drake procedure for this. Something about a screwdriver and the KEY jack! Are you able to shed any light here, please? -- 73 -Jim NU0C
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Re: Wanted Manual for AC4R power supply upgrade.
Manual has has been sent.
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On Feb 7, 2025, at 6:25 PM, George Cortez Jr via < ne2i@...> wrote:
I did email Mike also. Much appreciated!
Thanks
George NE2I
On Friday, February 7, 2025 at 05:59:42 PM EST, KB9VY via < lcoblentz3@...> wrote:
I have a paper copy I could scan for you. I can probably get it done this weekend. I¡¯m sure Mike Bryce probably has a pdf available ? ?Larry - KB9VY
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Re: Drake TR-7 - Noisy transmitter
Jim,
?
There have been several times I could have used a bench test jig for Drake boards. Just a simple thing with 5, 10 and 13 Volt supplies and some AF and RF generation and detection facilities. One day I might encounter a fault that will tip me into making one. I do have a surplus PBT / REF Board which I bought as 'untested' for no money (and only because it was no money). Of course, untested = does not work, so I should fix that at some point to turn it into a viable spare.
?
The Jumper Board has certainly proved it's worth while fixing the TR4310. A further useful service tool would be a small PCB that would plug vertically into the Translator Board, not covering anything else up, and programme it to work on some convenient band for testing. The deluxe version could have a DIP switch for range.
?
According to my Chinese tester, all of the tants. I removed are OK. My guess is that one of them, given applied operating voltage and time, started to breakdown when in circuit.
?
?
I tried to adjust the CW sidetone on the TR7, but could not understand the Drake procedure for this. Something about a screwdriver and the KEY jack! Are you able to shed any light here, please?
?
Regards,
?
Mark, G4FPH.
?
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T-4XC Final Cathode Resistors
After updating my AC-4, I fired up the T-4XC and am dealing with all of the little usual issues after being dormant for a quarter century.?
?
Checked the final Cathode resistors which are 15ohm/1Watt. They are running at 18/17.5 ohms, roughly 20% high.?
?
- Is there a specific type of resistor composition that you prefer to replace these with??
- Recommended to upgrade larger than 1W??
TIA
--
Craig/W8CS
Greenville, SC
|
Re: Drake TR-7 - Noisy transmitter
Hi Mark, On Fri, 07 Feb 2025 05:03:31 -0800 "atlasstuff via groups.io" <g4fph@...> wrote: 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? The trick is to power the board up on the bench from a 10V power supply. You can do a lot of troubleshooting this way. 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. Good detective work. I think I would have looked at the ceramic coupling cap first. They can go bad or become microphonic. Tantalums have an undeserved bad rap. They are very reliable unless they have been abused. High surge current, reversed polarity, and excessive soldering heat are the most common forms of abuse. It would have been interesting to find out if one of your tants is actually failing. 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. Some years ago I decided to completely re-cap one of my TR7s just to see if I could notice any difference. I did not. AFAIC the only "must replace" capacitor in the TR7 is C2108 on the power supply board. It WILL fail sooner or later and strange things will happen. 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. that probably won't work well. There was a reason Drake used PEMs there. Full disclosure, I detest PEMs. However with aluminum that thin your tapped threads will be very weak, if you can get any cut at all. Sheet metal screws would do better but would be easy to over-tighten and strip out. -- 73 -Jim NU0C
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Re: Wanted Manual for AC4R power supply upgrade.
I did email Mike also. Much appreciated!
Thanks
George NE2I
On Friday, February 7, 2025 at 05:59:42 PM EST, KB9VY via groups.io <lcoblentz3@...> wrote:
I have a paper copy I could scan for you. I can probably get it done this weekend. I¡¯m sure Mike Bryce probably has a pdf available ? ?Larry - KB9VY
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Re: Wanted Manual for AC4R power supply upgrade.
Ive looked around and have not found any.? Thanks
George NE2I
On Friday, February 7, 2025 at 06:07:13 PM EST, Richard Knoppow via groups.io <1oldlens1@...> wrote:
? ? Isn't it on line somewhere?? I have done two of the Heathkit Shop
upgrades but think I got only an instruction sheet with them. I don't
think he has changed the circuit any. Or have I missed something?
On 2/7/2025 2:55 PM, George Cortez Jr via groups.io wrote:
> I need the manual only. Does anyone have a pdf of it?
> Thanks....
>
> Yahoo Mail - Email Simplified <https://mail.onelink.me/107872968?
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
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Jim Shorney
Jay W6CJ
Craig W8CS