Re: Puzzling problem with the AGC in my R4-C
Thanks Jim.
I'll get them on order from Mouser.
I am curious what performance feature about these capacitors requires their use in the AGC circuit.
--
Bill N0CU
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Re: Puzzling problem with the AGC in my R4-C
I recommend these in the proper values:
Please don't order some chinese junk from amazon or ebay. Use these
from Mouser or Digikey.
73, Jim W7RY
On 3/12/2023 7:01 PM, Bill Leonard N0CU
wrote:
They are the two large caps on the AGC board. They are the size of
small electrolytic capacitors, but they are not polarized, so I
don't know what type they are:
C73: 0.22 uF
C74: 0.047 uF
--
Bill N0CU
--
Thanks and 73, Jim W7RY
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Re: Puzzling problem with the AGC in my R4-C
They are the two large caps on the AGC board. They are the size of small electrolytic capacitors, but they are not polarized, so I don't know what type they are:
C73: 0.22 uF
C74: 0.047 uF
--
Bill N0CU
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Re: Puzzling problem with the AGC in my R4-C
Any capacitor (especially an old one, even more so where it's in a
very hot environment all its life) can easily go bad.
What are the values of the capacitors?
73, Jim W7RY
On 3/12/2023 3:13 PM, Bill Leonard N0CU
wrote:
The receiver
seems to work fine when the AGC switch is set to S. However, in
the M position there is noticeable distortion on both noise and
signals. In the F position, the distortion becomes significant.
The distortion sounds like clipping, but none is seen on the
audio output with a scope. The S meter shows no difference with
the three settings. I am using the Sherwood audio amp and power
supply. I set up an HP sig gen to provide a pulsed RF signal.
What I see is the AGC pulse in response to that input signal
increases in voltage by x3 in the M position and by x7 in the F
position compared to the S position. The only changes to the AGC
circuit that I see when the delay is changed to the M & F
positions are the time constants (two RC networks). The
resistors in those networks check ok and to the limited extent
that I can check the two capacitors, they seem ok. What types of
capacitors are they and do they have a history of going bad? Any
suggestions would be appreciated.
--
Bill N0CU
--
Thanks and 73, Jim W7RY
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Re: TR7 Service Kit - Extender Boards Needed
Clean the push buttons for “Fixed XMIT” before you go in to extensive troubleshooting. Best to clean the “FIXED RCVR ?button and the “AUX Program” rotary switch as well. I think this will fix your issue.
Gary?
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On Mar 12, 2023, at 6:15 PM, John B <wb9fhl@...> wrote:
?I have a TR7 that I picked up at a local hamfest, it came with the matching power supply.? I've gone through the power supply, cleaned it up and tested it.? All is good there.? The TR7 receives but on transmit it does not lock on frequency, it just counts up. I would like to obtain a set of the extender boards (part of the Drake TR7 Service Kit) but it appears that there are none to be found anywhere.? If someone has a set they would like to sell or let me borrow for my repair effort I'd much appreciate it.? I would be happy to pay the round-trip postage.? ? John
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TR7 Service Kit - Extender Boards Needed
I have a TR7 that I picked up at a local hamfest, it came with the matching power supply.? I've gone through the power supply, cleaned it up and tested it.? All is good there.? The TR7 receives but on transmit it does not lock on frequency, it just counts up. I would like to obtain a set of the extender boards (part of the Drake TR7 Service Kit) but it appears that there are none to be found anywhere.? If someone has a set they would like to sell or let me borrow for my repair effort I'd much appreciate it.? I would be happy to pay the round-trip postage.? ? John
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Puzzling problem with the AGC in my R4-C
The receiver seems to work fine when the AGC switch is set to S. However, in the M position there is noticeable distortion on both noise and signals. In the F position, the distortion becomes significant. The distortion sounds like clipping, but none is seen on the audio output with a scope. The S meter shows no difference with the three settings. I am using the Sherwood audio amp and power supply. I set up an HP sig gen to provide a pulsed RF signal. What I see is the AGC pulse in response to that input signal increases in voltage by x3 in the M position and by x7 in the F position compared to the S position. The only changes to the AGC circuit that I see when the delay is changed to the M & F positions are the time constants (two RC networks). The resistors in those networks check ok and to the limited extent that I can check the two capacitors, they seem ok. What types of capacitors are they and do they have a history of going bad? Any suggestions would be appreciated.
-- Bill N0CU
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Yes, now that I have gone through this, testing of the shunt resistor on an unknown T4 should be one of the first things you do even before you apply power. It should definitely be replaced with a higher wattage rating. It seems Drake engineers were very good about not underrating parts. I wonder why they selected a 1/2W that carries 1/2W or possibly more as it heats. It is a recipe for failure.
I measure my shunt. It is about 9 ohms. I will be replacing with three 10 ohm 1/2W 5% in parallel. That should fix the problem. Then I can check the 15 ohm resistor values and measure the voltage to set the bias correctly and see what the resulting meter reading is.
I would expect, if the shunt was entirely open, it could cause meter damage. Perhaps back to back diodes across the meter or at the shunt would be in order. My guess is there are a lot of T4's out there not reading cathode current correctly, thus the bias is being incorrectly set, but since the current is always going to read higher than actual there would not be tube damage only signal distortion.
?Doug, WA3DSP
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Re: Cinch Jones connector identification
On Sun, Mar 12, 2023 at 11:54 AM, Jim Shorney wrote:
The RV75 works just fine without it
Thanks, Jim. Yes, I am aware the RV75 will work without the RIT cable but curiosity has the best of me and it appears to be an easy task. Rick K8EZB
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Re: Cinch Jones connector identification
Jones plug nomenclature on the web suggests P-3312-CCT. However, you only need this if you actually want to use RIT. The RV75 works just fine without it an honestly I have never missed it because I rarely use RIT anyway. 73 -Jim NU0C On Sun, 12 Mar 2023 11:37:35 -0700 "Rick Boswell" <frboswell@...> wrote: I recently acquired an RV75 to use in my 7-line station. The RV75 requires a cable from the RIT SWITCH phono connector on the rear panel to the ACCESSORIES connector on the rear panel of the TR7. This cable and CJ "adapter plug" wre not included in my purchase. Looking for the correct CJ part number for a plug compatible with the TR7 ACCESSORIES" connector in order to make the cable/adapter.
Thanks,
Rick
K8EZB
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Cinch Jones connector identification
I recently acquired an RV75 to use in my 7-line station. The RV75 requires a cable from the RIT SWITCH phono connector on the rear panel to the ACCESSORIES connector on the rear panel of the TR7. This cable and CJ "adapter plug" wre not included in my purchase. Looking for the correct CJ part number for a plug compatible with the TR7 ACCESSORIES" connector in order to make the cable/adapter.
Thanks,
Rick
K8EZB
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The Metal Body circular DIN connectors exist, BUT typical hobbyist & radio amateur will Constantly Complain about PRICE. These two (2) manufacturers are found through ALL Major Electronics Distributors:
RS (former Allied Electronics); Mouser; Newark; Digi-Key; Farnell (UK, EU); and Future. DELTRON COMPONENTS (North Lincolnshire, UK)
SWITCHCRAFT/CONXALL (Chicago area, USA)
DIN CABLE MOUNT
greg, w9gb
Conxall (military) division is in my neighborhood
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Doug:
Two resistors I ALWAYS check on a new-to-me T-4XC - R49 and R59 on the T/R relay board.? One of those is the 3.3 Ohm shunt resistor and the other is in the?+250V supply line.? Both are easy to swap for new.? They often show visible heat damage.
Also important for metering - clean the switch on the TUNE/LOAD control that changes the meter from Plate Current to relative RF OUT.
The meters are not high quality 'instruments" as you can see, so a first time bench check should include checking the bias setting by measuring the voltage drop across each 6JB6 cathode resistor and calculating the current through each one using its actual measured resistance.? Then see what the meter says for? a calculated 35 mA per tube.? Hopefully the meter is somewhere near the little tick?mark at 70mA!? If not....might?be a good idea to note that somewhere on the rear of the transmitter.? Or monkey with the meter shunt.
73 Peter VE7PS
On Sun, Mar 12, 2023 at 7:39?AM Doug Crompton WA3DSP < wa3dsp@...> wrote: This is NOT a bias issue - read my original message. If anything, the bias is set too low due to an elevated shunt resistor value or opened shunt resistor. I am fairly confident that is the problem but I have to get back to the bench to determine that for sure. This apparently is a fairly common problem as the shunt resistor is underrated. I was wrong about the 2.7 ohms, not sure where I saw that, 3.3 ohms is the correct shunt value.
Scroll through this presentation and you will see the shunt replacement -
--
Doug, WA3DSP
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This is NOT a bias issue - read my original message. If anything, the bias is set too low due to an elevated shunt resistor value or opened shunt resistor. I am fairly confident that is the problem but I have to get back to the bench to determine that for sure. This apparently is a fairly common problem as the shunt resistor is underrated. I was wrong about the 2.7 ohms, not sure where I saw that, 3.3 ohms is the correct shunt value.
Scroll through this presentation and you will see the shunt replacement -
https://www.yumpu.com/en/document/read/43193420/drake-forum-presentation-3-of-3-wb4hfn-home-page
--
Doug, WA3DSP
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If the plate current is pegged, it is way too much.? It is also a good way to go thru your supply of 6JB6 tubes.? You need to pull out the book and set the bias.? It is the best ally to save the tubes.? The Plate current will be about 280 ma and the power out (tube condition dependent) will be 100 watts + output.? I would not suspect the metering just yet.? With these transmitters, tuning for max output is not necessarily?the best way to promote final tube longevity.? After all, there is little discernible?difference between 100 watts and 120 watts.
Sounds like you have a nice radio. Good Luck! David Assaf III W5XU, VP8RXU ?
On Sun, Mar 12, 2023 at 12:18?AM Doug Crompton WA3DSP < wa3dsp@...> wrote: Now that I have the AC4 rebuilt, I moved on to the T4XC. The transmitter was given to me probably 7 years ago by a now SK ham and has been stored by me since then. Probably not operated in over 10 years. It is a long story but he had two homes and he had to vacate one of them and his equipment ended up on the ground outside covered with a tarp outside. He called me and I got right over there and picked up the R4C/t4XC and MS4 as well as some other equipment. Fortunately, they had not been out there real long and were in fairly good shape. I would say good condition. The front panels are very good and the only sign of wear on both the RX and TX were that the chassis tops were discolored. Below chassis was very clean. This guy had an old pot-belly coal stove, and my suspicion is that the acids may have oxidized the chassis surface. It does not seem it did any other harm though.
So that's the backstory. I cleaned it, and deox'ed the tube sockets and controls/switches. First problem was the final filaments were out. Since they are series connected, I determined one of the 6JB6's had an open filament. Both tubes looked pretty beat so I replaced them with brand new 6JB6A's that I had. OK it now tunes up but since I have never had a Drake transmitter I have a few questions.
The bias was spot on according to the plate current meter. Surprising after the rebuild of the AC4 and sitting for all those years, but is the meter correct? Tune up on 80 meters gave good drive peak but the PA current does not seem right. The rig gives 100+ watts out but the PA meter is basically pegged at that power level.
The manual under CW tuning makes no mention of maximum PA current, but rather in section 3.12i says increase drive until there is no further increase in PA current. In my case that would be a pegged meter! I have not checked the meter shunt nor broken the PA voltage lead and measured actual current but I suspect the meter is not correct. Would 6JB6A's be any different than 6JB6's? I know I will need to check the neutralization but I don't think that is the issue here. Thoughts?
Doug, WA3DSP
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If your plate current t is pinning with the drive turned down, you may be losing your bias connection. Clean the blades of the Jones connector with DeOxIt and a Q tip.?
73,
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
Sent from Proton Mail for iOS
On Sun, Mar 12, 2023 at 01:18, Doug Crompton WA3DSP < wa3dsp@...> wrote: Now that I have the AC4 rebuilt, I moved on to the T4XC. The transmitter was given to me probably 7 years ago by a now SK ham and has been stored by me since then. Probably not operated in over 10 years. It is a long story but he had two homes and he had to vacate one of them and his equipment ended up on the ground outside covered with a tarp outside. He called me and I got right over there and picked up the R4C/t4XC and MS4 as well as some other equipment. Fortunately, they had not been out there real long and were in fairly good shape. I would say good condition. The front panels are very good and the only sign of wear on both the RX and TX were that the chassis tops were discolored. Below chassis was very clean. This guy had an old pot-belly coal stove, and my suspicion is that the acids may have oxidized the chassis surface. It does not seem it did any other harm though.
So that's the backstory. I cleaned it, and deox'ed the tube sockets and controls/switches. First problem was the final filaments were out. Since they are series connected, I determined one of the 6JB6's had an open filament. Both tubes looked pretty beat so I replaced them with brand new 6JB6A's that I had. OK it now tunes up but since I have never had a Drake transmitter I have a few questions.
The bias was spot on according to the plate current meter. Surprising after the rebuild of the AC4 and sitting for all those years, but is the meter correct? Tune up on 80 meters gave good drive peak but the PA current does not seem right. The rig gives 100+ watts out but the PA meter is basically pegged at that power level.
The manual under CW tuning makes no mention of maximum PA current, but rather in section 3.12i says increase drive until there is no further increase in PA current. In my case that would be a pegged meter! I have not checked the meter shunt nor broken the PA voltage lead and measured actual current but I suspect the meter is not correct. Would 6JB6A's be any different than 6JB6's? I know I will need to check the neutralization but I don't think that is the issue here. Thoughts?
Doug, WA3DSP
|
I am sorry but I can't remember the exact value. It is important mainly in setting the idle bias. Again you can check the current at the 15 ohm cathode resistors.? They tend to go high .?? Unfortunately my lap top died so I have lost a lot of references.?
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-------- Original message -------- From: Doug Crompton WA3DSP <wa3dsp@...> Date: 3/11/23 11:46 PM (GMT-08:00) Subject: Re: [DRAKE-RADIO] T4XC help
OK, did a little further research. I have not checked it yet but the cathode current meter shunt is 2.7 ohms 1/2W. I see a replacement in a WB4HFN slide show uses three parallel 10 ohm 1/2W resistors. I suspect (and hope) this is the problem, since it is an easy fix.? Is the 3.3 ohms a compromise, or should I parallel to get closer a measured 2.7 ohms as shown on the schematic? -- Doug, WA3DSP
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OK, did a little further research. I have not checked it yet but the cathode current meter shunt is 2.7 ohms 1/2W. I see a replacement in a WB4HFN slide show uses three parallel 10 ohm 1/2W resistors. I suspect (and hope) this is the problem, since it is an easy fix.? Is the 3.3 ohms a compromise, or should I parallel to get closer a measured 2.7 ohms as shown on the schematic?
--
Doug, WA3DSP
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Two sites to bookmark. K4AOH. Order Garry barrell's ca for the C line. Available from his wife. You can download them.? Not expensive.? ?WB4HFN. Has tons of stuff.
Study the metering circuit.? Note that each tube has a 15 ohm cathode resistor.? Measure these to make sure they are accurate.? Replace if not.? Use thick film resistors.? The tube current can be measured as the drop across these.? Meter measures total current,? that is the combined plate and screen current. Check all other resistors in the meter circuit. ?Make sure you understand the tune up procedure.? ?It is relatively conventional.? Drive must be peaked at a.low level. Then tune plate for a dip and peak the load for maximum output on the rf meter or external watt meter. Alternate between plate dip and load peak until output is maximized,? then increase drive and do it again. At maximum output you should have about 300ma plate current ( I am going by memory, check the book).? Tune up in TUNE you can push out a few more watts in CW but it's not good practice. Plate load should be set a little below maximum output.? _ALWAYS_dip the plate last.? HV will be around 650V.? Maximum output depends on frequency and condition of tubed, max around140 watts at 40 meters.? In SSB? the ALC limits output to around 125 watts.? The plate meter should never pin in normal operation.? Read the material referred to.? My memory is getting old.?
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-------- Original message -------- From: Doug Crompton WA3DSP <wa3dsp@...> Date: 3/11/23 10:18 PM (GMT-08:00) Subject: [DRAKE-RADIO] T4XC help
Now that I have the AC4 rebuilt, I moved on to the T4XC. The transmitter was given to me probably 7 years ago by a now SK ham and has been stored by me since then. Probably not operated in over 10 years. It is a long story but he had two homes and he had to vacate one of them and his equipment ended up on the ground outside covered with a tarp outside. He called me and I got right over there and picked up the R4C/t4XC and MS4 as well as some other equipment. Fortunately, they had not been out there real long and were in fairly good shape. I would say good condition. The front panels are very good and the only sign of wear on both the RX and TX were that the chassis tops were discolored. Below chassis was very clean. This guy had an old pot-belly coal stove, and my suspicion is that the acids may have oxidized the chassis surface. It does not seem it did any other harm though. So that's the backstory. I cleaned it, and deox'ed the tube sockets and controls/switches. First problem was the final filaments were out. Since they are series connected, I determined one of the 6JB6's had an open filament. Both tubes looked pretty beat so I replaced them with brand new 6JB6A's that I had. OK it now tunes up but since I have never had a Drake transmitter I have a few questions. The bias was spot on according to the plate current meter. Surprising after the rebuild of the AC4 and sitting for all those years, but is the meter correct? Tune up on 80 meters gave good drive peak but the PA current does not seem right. The rig gives 100+ watts out but the PA meter is basically pegged at that power level. The manual under CW tuning makes no mention of maximum PA current, but rather in section 3.12i says increase drive until there is no further increase in PA current. In my case that would be a pegged meter! I have not checked the meter shunt nor broken the PA voltage lead and measured actual current but I suspect the meter is not correct. Would 6JB6A's be any different than 6JB6's? I know I will need to check the neutralization but I don't think that is the issue here. Thoughts? Doug, WA3DSP
|
Now that I have the AC4 rebuilt, I moved on to the T4XC. The transmitter was given to me probably 7 years ago by a now SK ham and has been stored by me since then. Probably not operated in over 10 years. It is a long story but he had two homes and he had to vacate one of them and his equipment ended up on the ground outside covered with a tarp outside. He called me and I got right over there and picked up the R4C/t4XC and MS4 as well as some other equipment. Fortunately, they had not been out there real long and were in fairly good shape. I would say good condition. The front panels are very good and the only sign of wear on both the RX and TX were that the chassis tops were discolored. Below chassis was very clean. This guy had an old pot-belly coal stove, and my suspicion is that the acids may have oxidized the chassis surface. It does not seem it did any other harm though.
So that's the backstory. I cleaned it, and deox'ed the tube sockets and controls/switches. First problem was the final filaments were out. Since they are series connected, I determined one of the 6JB6's had an open filament. Both tubes looked pretty beat so I replaced them with brand new 6JB6A's that I had. OK it now tunes up but since I have never had a Drake transmitter I have a few questions.
The bias was spot on according to the plate current meter. Surprising after the rebuild of the AC4 and sitting for all those years, but is the meter correct? Tune up on 80 meters gave good drive peak but the PA current does not seem right. The rig gives 100+ watts out but the PA meter is basically pegged at that power level.
The manual under CW tuning makes no mention of maximum PA current, but rather in section 3.12i says increase drive until there is no further increase in PA current. In my case that would be a pegged meter! I have not checked the meter shunt nor broken the PA voltage lead and measured actual current but I suspect the meter is not correct. Would 6JB6A's be any different than 6JB6's? I know I will need to check the neutralization but I don't think that is the issue here. Thoughts?
Doug, WA3DSP
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Doug Crompton WA3DSP
Jim Shorney
Greg W9GB
David