Please correct if wrong,
but if I remember correctly, as long as the mechanical bolt or mechanism holding the plates together is tight, NOT LOOSE, you are ok for that moment...
you takes your chances etc.
The rectification is based on sucessive passes thru each plate; loose connection equals hi temp, therefore toxic/heat failure...PLEASE be careful.
can't stress that enough...😱
but if I remember correctly, as long as the mechanical bolt or mechanism holding the plates together is tight, NOT LOOSE, you are ok for that moment...
you takes your chances etc.
The rectification is based on sucessive passes thru each plate; loose connection equals hi temp, therefore toxic/heat failure...PLEASE be careful.
can't stress that enough...😱
The selenium rectifier in this amp does not use any type of fastener to hold the plated together. This component is the size of a tootsie roll, and looks like an electrolytic capacitor, except for the fact that it has a large diode symbol on its case.
ANother note, I am having issues with the amp going red plate on a few of the tubes.
I have turned the bias voltage down on that particular channel, switched the tubes around, and the same tubes go red plate regardless of what channel they are in.
When I say red plate, the red on the plate is very dim (with the room lights on, you cannot see the red glow), but I hear that anyh plate color at all is not a good thing.
The red color gets brighter if I flog the amp.
The cathode resistors are ok, values right on the money.
My tube amp guy says that there isnt enough negative voltage on the control grid, makes sense.
At any rate, I havent had a chance to measure the voltage against the voltage indicated on the schematic, because I've been working with a cheap analog meter, and "somewhere between 25 and 50" doesnt cut it for precision.
What can I do to increase the negative voltage on the control grid?
I also was told that a screen resistor can be installed too.
Any ideas?
ANother note, I am having issues with the amp going red plate on a few of the tubes.
I have turned the bias voltage down on that particular channel, switched the tubes around, and the same tubes go red plate regardless of what channel they are in.
When I say red plate, the red on the plate is very dim (with the room lights on, you cannot see the red glow), but I hear that anyh plate color at all is not a good thing.
The red color gets brighter if I flog the amp.
The cathode resistors are ok, values right on the money.
My tube amp guy says that there isnt enough negative voltage on the control grid, makes sense.
At any rate, I havent had a chance to measure the voltage against the voltage indicated on the schematic, because I've been working with a cheap analog meter, and "somewhere between 25 and 50" doesnt cut it for precision.
What can I do to increase the negative voltage on the control grid?
I also was told that a screen resistor can be installed too.
Any ideas?
Changing out the selinium rectifier for a silicon diode will give you more bias voltage. In fact, you will probably have to insert a resistor in series with the silicon diode in order to drop the voltage to acceptable levels.
Also, if only one tube is glowing red, I would suspect that tube as being bad or the coupling cap attached to the grid of this tube. In fact you should change all 4 coupling caps to the power tubes as they are probably leaky. You really need to find out what the plate current is going through each output tube. Easiest way to do this is insert a 1 ohm resister between each output tube's cathode and ground.
Also, if only one tube is glowing red, I would suspect that tube as being bad or the coupling cap attached to the grid of this tube. In fact you should change all 4 coupling caps to the power tubes as they are probably leaky. You really need to find out what the plate current is going through each output tube. Easiest way to do this is insert a 1 ohm resister between each output tube's cathode and ground.
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Something new tonight.
I played around with my hunch some more tonight.
I tested some things:
In the bias supply loop from the power xfrmr, I am supposed to have 45 volts, I have almost 50.
In the control grid, (pin 5 on an EL34) I am supposed to have -40 volts. I have -31 volts. (across all tubes.)
I have 499V on the plate, and 499v on the suppressor suppressor grid, I am supposed to have 490, and 495 respectively.
I moved the tubes around a bunch, suspecting that it was a tube related problem, and I have since ruled out the tubes. I have Isolated the issue to the A channel.
Only the tubes in the A channel go red plate now, and it happens very quickly after the tubes come up to temp, they will not hold the bias. The B channel is happy now, no red plate at all. With the Bias voltage turned all the way down (with the factory adjustment knobs) it still runs away in that channel.
Now, are you saying that by replacing the selenium diode with a silicon diode, I would have more negative voltage on the control grid?
If so, I think that is my answer.
Now, the amp already has cathode resistors. I tested those and they are all right on the money.
Also- by coupling cap, are you referring to the caps on the control grid?? El34's have 3 grids.
If so, I have already replaced them.
I played around with my hunch some more tonight.
I tested some things:
In the bias supply loop from the power xfrmr, I am supposed to have 45 volts, I have almost 50.
In the control grid, (pin 5 on an EL34) I am supposed to have -40 volts. I have -31 volts. (across all tubes.)
I have 499V on the plate, and 499v on the suppressor suppressor grid, I am supposed to have 490, and 495 respectively.
I moved the tubes around a bunch, suspecting that it was a tube related problem, and I have since ruled out the tubes. I have Isolated the issue to the A channel.
Only the tubes in the A channel go red plate now, and it happens very quickly after the tubes come up to temp, they will not hold the bias. The B channel is happy now, no red plate at all. With the Bias voltage turned all the way down (with the factory adjustment knobs) it still runs away in that channel.
Now, are you saying that by replacing the selenium diode with a silicon diode, I would have more negative voltage on the control grid?
If so, I think that is my answer.
Now, the amp already has cathode resistors. I tested those and they are all right on the money.
Also- by coupling cap, are you referring to the caps on the control grid?? El34's have 3 grids.
If so, I have already replaced them.
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Old amp-red plating-replace the coupling caps, at least that what I remember on this site or another. I looked at a schematic to verify that if the all of the voltages to the EL84 or El34 are close to spec, a bad coupling cap makes the most sense. Besides, Russina PIO K40Ys or Sprague "Orange-drop" seem to commonly reported to dramatically improve the sound over those old coupling caps. I can't comment on orange drops for coupling caps; the Russian K40-Y make a huge improvement when I install them.
If you have the schematic, measure the resistors to see if you should replace any while in there.
I played around a lot with HeathKit integrated PPEL84 and found that the RCA white lettering 6AN8 sounded the best, May be it was Eli that suggested them?
Best from Tucson
Bob
If you have the schematic, measure the resistors to see if you should replace any while in there.
I played around a lot with HeathKit integrated PPEL84 and found that the RCA white lettering 6AN8 sounded the best, May be it was Eli that suggested them?
Best from Tucson
Bob
I see your coupling caps are 600V .047uF.
The old notation of uuF, micro, micro is now call picoFarad
I recently bought some HeathKit monoblock using 6L6GCs and 6SN7G and discovered I drive them with an MP3 and my Dynaco FM-3 stereo tuner that has a volume control--no preamp necessary!
Best from Tucson
Bob
The old notation of uuF, micro, micro is now call picoFarad
I recently bought some HeathKit monoblock using 6L6GCs and 6SN7G and discovered I drive them with an MP3 and my Dynaco FM-3 stereo tuner that has a volume control--no preamp necessary!
Best from Tucson
Bob
I replaced the bias rectifier today with a new one. I have the proper voltage on the control grids now.
I've been playing it for some time now and the tubes seem to be under control.
I'll get a set of coupling caps anyway.
I am going to ditch the "surgister" and replace it with a standby switch on the center taps for the OPTxfmrs.
That'll remove the issue there.
I now need to find a switch that can handle >500VDC.
I've been playing it for some time now and the tubes seem to be under control.
I'll get a set of coupling caps anyway.
I am going to ditch the "surgister" and replace it with a standby switch on the center taps for the OPTxfmrs.
That'll remove the issue there.
I now need to find a switch that can handle >500VDC.
I use Mouser and Digi.
I can't help with the value of the coupling caps since yours are quite different from the .1 to .3uF I've encountered, seen as suggestions.
While in there, I would replace the resistor between the coupling cap and the El34 grid and the cap paralleling it.
Best
Bob
I can't help with the value of the coupling caps since yours are quite different from the .1 to .3uF I've encountered, seen as suggestions.
While in there, I would replace the resistor between the coupling cap and the El34 grid and the cap paralleling it.
Best
Bob
IIRC, Heath's power trafo can't take surges. That's exactly what will happen, when you apply power. Put a NTC inrush current limiting thermistor in, as a replacement for the surgistor. It is probably a good idea to put a pair of CL90s on the rectifier winding too, just like McShane puts on the Cit. 2's rectifier winding.
I am still having some issues darnit. 
One tube in my A channel is still going a very dim red plate.
I retested all of my control grid voltages, and they are right on the money.
I am about to order a set of coupling caps (if I can find them)...
Would leaky coupling caps also cause a 60 cycle hum?
Iunno... I ran the amp for a couple of hours tonight, and the 60hz started out pretty quiet, almost silent. After the TV show/concert we were watching was over and the sound went quiet, the 60hz sound sounded like a guitar amp.
I am going to replace the coupling caps and see where I get with that i guess....
Damn, I thought I had this thing nailed down.
ANother thing:
The coupling caps I currently have are electrolytics. The only ones I can find at the proper values are poly pros (they look like orange drops). Is a cap a cap in this case? Do I have to be picky about what kind it is as long as the values are kosher?
One tube in my A channel is still going a very dim red plate.
I retested all of my control grid voltages, and they are right on the money.
I am about to order a set of coupling caps (if I can find them)...
Would leaky coupling caps also cause a 60 cycle hum?
Iunno... I ran the amp for a couple of hours tonight, and the 60hz started out pretty quiet, almost silent. After the TV show/concert we were watching was over and the sound went quiet, the 60hz sound sounded like a guitar amp.
I am going to replace the coupling caps and see where I get with that i guess....
Damn, I thought I had this thing nailed down.
ANother thing:
The coupling caps I currently have are electrolytics. The only ones I can find at the proper values are poly pros (they look like orange drops). Is a cap a cap in this case? Do I have to be picky about what kind it is as long as the values are kosher?
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Upon further research, the supplier that heath used for coupling caps was kind of an oddball.
They are in fact polypros (but look like electrolytics?).
I ordered the caps today.
They are in fact polypros (but look like electrolytics?).
I ordered the caps today.
If all 4 of your control grid voltages are right on the money then you have a bad output tube or that one tube is way out of spec (bad). Switch the 2 "A" chanel output tubes and see if the same tube glows red.
Do you have a tube tester? Don't assume that new tubes bought from a dealer are automatically good. Things happen...
You really need to test for current going through each output tube. There should be no more than 0.3 volts going through each 6 ohm resistor on the cathodes of the output tubes. 0.3 volts = 50ma = 25 watts per output tube. Measure the voltage at each 6 ohm resistor and see what it is.
Do you have a tube tester? Don't assume that new tubes bought from a dealer are automatically good. Things happen...
You really need to test for current going through each output tube. There should be no more than 0.3 volts going through each 6 ohm resistor on the cathodes of the output tubes. 0.3 volts = 50ma = 25 watts per output tube. Measure the voltage at each 6 ohm resistor and see what it is.
If I were to measure current directly, would I not put the electrodes from my DVM across the center tap (red) and the plate?
I played with it some more tonight. I removed the resistors in the bias supply by the rectifier diode to give me a few more negative volts on the grid. The spec says I should have -40 on the grid and 490 on the plate, well I have 499 on the plate and had just above -40 on the grid(-38 to -39.5), now I have -45 and it seems to have helped it stabilize. I put the tube that was glowing in the B channel and that was the only tube that was mis behaving tonight.
I have an RA in with the tube supplier and a new set of tubes on the way, along with a set of coupling caps.
I played with it some more tonight. I removed the resistors in the bias supply by the rectifier diode to give me a few more negative volts on the grid. The spec says I should have -40 on the grid and 490 on the plate, well I have 499 on the plate and had just above -40 on the grid(-38 to -39.5), now I have -45 and it seems to have helped it stabilize. I put the tube that was glowing in the B channel and that was the only tube that was mis behaving tonight.
I have an RA in with the tube supplier and a new set of tubes on the way, along with a set of coupling caps.
NEGATIVE! A current measuring device gets inserted in series with the line. Do you really want to break the wire between the plate and the O/P trafo? 🙁 A voltage measuring device gets connecting in parallel with the line. Measuring the voltage drop across the cathode resistor and using Ohm's Law to compute the current is THE way to go.
Heathkit AA-141 schematic or manual??
Hello all --
Saw this thread on a web search -- Do any of you have a copy of the AA-141 manual/schematic by any chance?? thx much!!
Hello all --
Saw this thread on a web search -- Do any of you have a copy of the AA-141 manual/schematic by any chance?? thx much!!
^^^
I do have the 141 schematics, but not in a digital format.
Perhaps I can fax them to you?
A new issue- my filter caps are starting to leak white stuff from the bottom of them onto the floor of the under chassis.
Time to get new ones. But--- I cant find them.
I need Multiple anode Single cathode single section caps.
2 each of 150uf at 300V and 200uf at 300v
They say "type EY" on the caps, made by Astron.
They also say B-25-50 on the 150uf caps and B-25-51 on the 200uf caps.
I do have the 141 schematics, but not in a digital format.
Perhaps I can fax them to you?
A new issue- my filter caps are starting to leak white stuff from the bottom of them onto the floor of the under chassis.
Time to get new ones. But--- I cant find them.
I need Multiple anode Single cathode single section caps.
2 each of 150uf at 300V and 200uf at 300v
They say "type EY" on the caps, made by Astron.
They also say B-25-50 on the 150uf caps and B-25-51 on the 200uf caps.
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