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My L75 amp developed a problem on the meter. No longer responds.
Have checked it and the signal is reaching it.
The internal circuit on the meter is simply open.
Have look for replacements but no longer in production.
Any suggestions where could I find one?
Is this meter the same used on the L7? I don't have an L7 so no idea.
Last resource would be to buy a Chinese meter and install it on an external box. :-( sad option and the last.
Hate to modify equipment. Love to see things original and clean, in all its glory.
Open to ideas and suggestions.
Rob
YS1RS
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Rob, check on the meter face (at bottom) to see what the FS rating is. There¡¯s still a guy on eBay selling meters that definitely work with the L7. I replaced my plate meter recently with one of these and it works great.?
73,
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
On Wed, Jan 24, 2024 at 09:53, Roberto - YS1RS via groups.io < ys1rs@...> wrote: My L75 amp developed a problem on the meter. No longer responds.
Have checked it and the signal is reaching it.
The internal circuit on the meter is simply open.
Have look for replacements but no longer in production.
Any suggestions where could I find one?
Is this meter the same used on the L7? I don't have an L7 so no idea.
Last resource would be to buy a Chinese meter and install it on an external box. :-( sad option and the last.
Hate to modify equipment. Love to see things original and clean, in all its glory.
Open to ideas and suggestions.
Rob
YS1RS
|
Hola Steve.
This is. 200 uA. Meter
model is 83T
my amp is L75
I don¡¯t know if the bigger L7 also uses the same meter.
Do you remember the eBay sellers name??
Thanks and greetings from sunny YS country.
Rob
YS1RS
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That meter on eBay will work fine and fit perfectly. You will need to transplant the movement and shunt?to your old meter housing, which is easy but requires care. The new small resistor should be the same value as what you have.?
Look for ¡°Jewell 83T¡± and it should come right up.?
73,
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
On Wed, Jan 24, 2024 at 23:51, Roberto - YS1RS via groups.io < ys1rs@...> wrote: Hola Steve.
This is. 200 uA. Meter
model is 83T
my amp is L75
I don¡¯t know if the bigger L7 also uses the same meter.
Do you remember the eBay sellers name??
Thanks and greetings from sunny YS country.
Rob
YS1RS
|
I wonder what it is that makes these meters so prone to failure?
They certainly weren't cheap knockoffs.
John K5MO
|
Many thanks Steve.
Just ordered one.
Understood that open heart surgery will be required.
The shunt resistor that will come with it will have to be replaced by the value I have on the original one.
Better yet, use the old original resistor on the new one.
Hope to have it correct....
Thanks.
Rob
YS1RS
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Forgot to mention... yes, I will have to move everything from the new one to the old case.
That is the open heart surgery I was referring to...
Rob
YS1RS
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I found with mine that the terminal was shorted to one of the lamp sockets. My L7 is later production with the meter¡¯s shunt being external.?
So now I have two good meters.?
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
On Thu, Jan 25, 2024 at 09:25, John K5MO < johnk5mo@...> wrote: I wonder what it is that makes these meters so prone to failure?
They certainly weren't cheap knockoffs.
John K5MO
|
The resistors are the same value, so save yourself the work :-)
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
On Thu, Jan 25, 2024 at 09:39, Roberto - YS1RS via groups.io < ys1rs@...> wrote: Many thanks Steve.
Just ordered one.
Understood that open heart surgery will be required.
The shunt resistor that will come with it will have to be replaced by the value I have on the original one.
Better yet, use the old original resistor on the new one.
Hope to have it correct....
Thanks.
Rob
YS1RS
|
The new one is not FS=200uA but FS=50MV. The scale is from 0 to 300 DC Amps.
Have to check on that.
Rob
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In my limited experience with taut band meter movements the band usually lets go at one end or the other. A dead giveaway (no pun intended) is that the pointer won't move when you give it a gentle sideways shake. This applies to the W4 wattmeters and I have also seen it in AIE 920 deviation meters. They are said to be more rugged than pivot and jewel meters. I suppose that is true but when they let go they are gone. With pivot and jewel you might not notice the bearing deterioration over time until they just fail work right. They are all pretty old now in our Drakes so failures are to be expected either way. 73 -Jim NU0C On Thu, 25 Jan 2024 09:25:34 -0500 "John K5MO" <johnk5mo@...> wrote: I wonder what it is that makes these meters so prone to failure?
They certainly weren't cheap knockoffs.
John K5MO
|
Yep.? No problem.? It's the same meter (83T).? That movement gets configured differently in the equipment.? I'm guessing that your L75 has a shunt that is on the outside of the meter, since I believe the L75's were made around the same time as the later L7's.
The movement itself seems a bit more damped than what was originally in my L7.? It also has a black needle, instead of red.? This is totally invisible when in use, as the bluish light makes the red look black.
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Thursday, January 25th, 2024 at 10:42 AM, Roberto - YS1RS via groups.io <ys1rs@...> wrote:
The new one is not FS=200uA but FS=50MV. The scale is from 0 to 300 DC Amps.
Have to check on that.
Rob
|
Have progress to share here.
Received the meter I bought from eBay.
Perfect fit as it was an 83T as the original.
The last one available. It was a 0-300 DC Amp. meter.
Came with an external resistor which I removed but guess what?
The original meter used by Drake for the L75 was 200 uA full scale.
The one received was 1 mA full scale. Tested it with a small circuit I put together and one amperimeter.
Opened it and couldn't find any internal resistor or anything like that inside the transparent meter.
Saw also a few improvements on the movement when compared with the original used on the Drake L75.
Looks like they corrected the issues that made the 83T model, fail on Drakes.
To make things brief...? the internal wire used on the internal meter coil was different than the one used for the 200 uA version.
As expected, all readings were pretty low, when installed it in the L75..
At the end of the day, I had to re-calculate all the meter section resistor network.
After installing the new resistors, went through the meter calibration process shown in the manual.
Have finished replacing all the resistors and now I have a fully functional meter that is a joy to see it working.
Previously, I was adjusting the Amp only by using an external Wattmeter. Actually, the Wattmeter is an Drake MN-2700.
Now, I can read Plate Voltage, Plate and Grid current and it matches what the manual says.
The Relative Output also matches perfectly.
Have written down on my notes the new values installed in case the XYL sells the Amp in the future LOL.
Anyway, wanted to share with you my experience.
Thank you all who helped me finding a solution to my Drake L75 problem.
Learnt a lot in the process.
73
Rob
YS1RS
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Sounds great, Rob! ?I didn¡¯t change anything with mine other than the scale. Mine said ¡°200uA FS¡± at the bottom of the scale. I didn¡¯t try calibrating it, as it appears to be showing the expected values.?
My amp is an L7, so that may be the difference. You probably don¡¯t need 1A readings at full scale.?
Glad it worked and glad you got one before they were gone!
73,
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
On Tue, Feb 6, 2024 at 22:15, Roberto - YS1RS via groups.io < ys1rs@...> wrote: Have progress to share here.
Received the meter I bought from eBay.
Perfect fit as it was an 83T as the original.
The last one available. It was a 0-300 DC Amp. meter.
Came with an external resistor which I removed but guess what?
The original meter used by Drake for the L75 was 200 uA full scale.
The one received was 1 mA full scale. Tested it with a small circuit I put together and one amperimeter.
Opened it and couldn't find any internal resistor or anything like that inside the transparent meter.
Saw also a few improvements on the movement when compared with the original used on the Drake L75.
Looks like they corrected the issues that made the 83T model, fail on Drakes.
To make things brief...? the internal wire used on the internal meter coil was different than the one used for the 200 uA version.
As expected, all readings were pretty low, when installed it in the L75..
At the end of the day, I had to re-calculate all the meter section resistor network.
After installing the new resistors, went through the meter calibration process shown in the manual.
Have finished replacing all the resistors and now I have a fully functional meter that is a joy to see it working.
Previously, I was adjusting the Amp only by using an external Wattmeter. Actually, the Wattmeter is an Drake MN-2700.
Now, I can read Plate Voltage, Plate and Grid current and it matches what the manual says.
The Relative Output also matches perfectly.
Have written down on my notes the new values installed in case the XYL sells the Amp in the future LOL.
Anyway, wanted to share with you my experience.
Thank you all who helped me finding a solution to my Drake L75 problem.
Learnt a lot in the process.
73
Rob
YS1RS
|
Thank you Steve.
It is a great satisfaction to have the L75 Amp working in all respects.
To see how the readings matches the manual and now it is easier to take care of it by reading the Plate and Grid mA.
Before, I was fully depending on the Wattmeter. Yes, that put me kind on the ballpark, but now I am certain of what is happening inside the Amp.
73
Rob
YS1RS
|
Yeah, I was doing the same thing. Fully-working is the best situation.?
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
On Thu, Feb 8, 2024 at 14:09, Roberto - YS1RS via groups.io < ys1rs@...> wrote: Thank you Steve.
It is a great satisfaction to have the L75 Amp working in all respects.
To see how the readings matches the manual and now it is easier to take care of it by reading the Plate and Grid mA.
Before, I was fully depending on the Wattmeter. Yes, that put me kind on the ballpark, but now I am certain of what is happening inside the Amp.
73
Rob
YS1RS
|
Roberto - YS1RS
Jim Shorney