Dave,
I am going by the schematic that was referenced earlier in this post. Voltages to the 6AN8 is 285 volts in that one.
Link attached:
http://www.wdox.com/pics/aa151r.jpg
Would you have another schematic that is more accurate?
Heathkit AA-151
Message for DC
by Linn lover » Tue Mar 13, 2012 8:28 pm
- Linn lover
- Posts: 64
- Joined: Sun Jan 15, 2012 8:24 pm
- Location: Ottawa, Canada
Message for DR and DC
by Linn lover » Wed Mar 14, 2012 11:55 am
DR, Dave,
I have installed a 10k resistor as the first real resistor after the 60 uf input capacitor at the power supply.
Power supply voltages are now:
399 V at source
370 V before the 10k resistor (which replaced the 4.7k stock unit)
283.4 V after the 10K resistor (this one feeds the 6AN8).
Bias is now sitting at 15.32 volts over a 120 ohm resistor.
EL 84s: Pin #9 is at 367 V
Pin #7 is at 362V
Things thus far are looking good. I have a choke on order.
What follows is the voltage report for the 6AN8. If I follow the schematic and look at how things are installed in the amp, everything physically looks like it is properly setup. Now DR, brace yourself:
Pin #1 233 and 201 V (an improvement)
Pin #2 105 and 108 V (an improvement)
Pin #3 95 and 96 V (an improvement, but still lower than pin #2!
Pin #4, Pin #5 = 48 volts
Pin #6 45 and 77 V (don't shoot the messenger!)
Pin #7 50 and 40 v
Pin #8 0 and 0
Pin #9 1.4 and 1.26 volts
If I look at the layout, Pin #2 and Pin #6 are physically connected together via the 150K resistor across the tube socket underneath. From Pin #2, Pin #6 and Pin #7, various caps and resistors are tied in to GND, or, the 283.4 volts supply, etc...so all looks good.
Now what!
The amp plays. Lower power than before, but fine volume wise nonetheless. High frequency information is still lacking. Dave, anything I can do change the values of the resistors at the input to improve the high frequency content. Or, with me messing around with the amp, could I have fried the 6AN8s?
I can get the 6AN8s tested at work.
Now that I more or less have a handle on the source voltages, we need to get a handle on that 6AN8. Any suggestions appreciated.
Beethoven now running through the AA-151. Sounds solid, better, but not great yet! If the highs were present, it would be perfect!
I have installed a 10k resistor as the first real resistor after the 60 uf input capacitor at the power supply.
Power supply voltages are now:
399 V at source
370 V before the 10k resistor (which replaced the 4.7k stock unit)
283.4 V after the 10K resistor (this one feeds the 6AN8).
Bias is now sitting at 15.32 volts over a 120 ohm resistor.
EL 84s: Pin #9 is at 367 V
Pin #7 is at 362V
Things thus far are looking good. I have a choke on order.
What follows is the voltage report for the 6AN8. If I follow the schematic and look at how things are installed in the amp, everything physically looks like it is properly setup. Now DR, brace yourself:
Pin #1 233 and 201 V (an improvement)
Pin #2 105 and 108 V (an improvement)
Pin #3 95 and 96 V (an improvement, but still lower than pin #2!
Pin #4, Pin #5 = 48 volts
Pin #6 45 and 77 V (don't shoot the messenger!)
Pin #7 50 and 40 v
Pin #8 0 and 0
Pin #9 1.4 and 1.26 volts
If I look at the layout, Pin #2 and Pin #6 are physically connected together via the 150K resistor across the tube socket underneath. From Pin #2, Pin #6 and Pin #7, various caps and resistors are tied in to GND, or, the 283.4 volts supply, etc...so all looks good.
Now what!
The amp plays. Lower power than before, but fine volume wise nonetheless. High frequency information is still lacking. Dave, anything I can do change the values of the resistors at the input to improve the high frequency content. Or, with me messing around with the amp, could I have fried the 6AN8s?
I can get the 6AN8s tested at work.
Now that I more or less have a handle on the source voltages, we need to get a handle on that 6AN8. Any suggestions appreciated.
Beethoven now running through the AA-151. Sounds solid, better, but not great yet! If the highs were present, it would be perfect!
- Linn lover
- Posts: 64
- Joined: Sun Jan 15, 2012 8:24 pm
- Location: Ottawa, Canada
by dcgillespie » Wed Mar 14, 2012 12:54 pm
Linn -- You are referencing a Sam's schematic for the AA-151. I am referencing the Heath schematic for the unit, as published in the manual for the AA-151. In it:
1. The acceptable AC line voltage range is given as 105-125 vac, 50/60 Hz.
2. The B+ at pin 8 of the rectifier tube is given as 390 vdc.
3. The output tube plate voltage is given as 385 vdc
4. The output tube screen voltage is given as 390 vdc.
5. The output tube cathode voltage is given as 16 vdc across a 100 ohm cathode resistor.
6. The 6AN8 pentode plate voltage is given as 64 vdc.
7. The 6AN8 screen voltage is given as 55 vdc.
8. The 6AN8 pentode cathode voltage is given as 1.6 vdc.
9. The 6AN8 triode plate voltage is given as 235 vdc
10. The 6AN8 triode cathode voltage is given as 74 vdc.
11. The 6AN8 triode grid voltage is given as 64 vdc.
12. The B+ supplying the 6AN8 is given as 305 vdc.
The schematic you have supplied is identical to that of Heath's, regarding the power amplifier and power supply sections.
To know more regarding your performance issues would require performance tests to be performed: frequency response tests, power output tests, THD and IMD tests, as well as square wave testing as well.
It is very strange that you say you had good HF performance at one point, yet don't now even with all the work you have performed. About the only thing that can affect the frequency response of the power amplifier proper is the NFB circuit. The 150K/22K/56pf network at the triode grid of the 6AN8 intentionally rolls off the HF response of the basic amplifier block. This is necessary so that the amplifier will remain stable after the application of feedback, supplied by the 27K/33pf network connecting the 16 ohm output tap back to the pentode cathode of the 6AN8. The level of FB applied is such that within the 20Hz - 20 kHz range, the frequency response and power response will be basicly dead flat, for no boost or cut. The network between the 6AN8 sections then rolls off the supersonic frequencies only, to keep the final as designed circuit stable into various loading conditions. Therefore, if the NFB circuit has been compromised, removed, or altered, that would have a very big impact on delivered HF performance. Other than that, there is just very little within the circuit that can affect HF response within the audible range.
Confirming the integrity of all these components mention will go a long way to ensure that the HF performance of the amplifier is as it was designed to be.
Let me know!
Dave
1. The acceptable AC line voltage range is given as 105-125 vac, 50/60 Hz.
2. The B+ at pin 8 of the rectifier tube is given as 390 vdc.
3. The output tube plate voltage is given as 385 vdc
4. The output tube screen voltage is given as 390 vdc.
5. The output tube cathode voltage is given as 16 vdc across a 100 ohm cathode resistor.
6. The 6AN8 pentode plate voltage is given as 64 vdc.
7. The 6AN8 screen voltage is given as 55 vdc.
8. The 6AN8 pentode cathode voltage is given as 1.6 vdc.
9. The 6AN8 triode plate voltage is given as 235 vdc
10. The 6AN8 triode cathode voltage is given as 74 vdc.
11. The 6AN8 triode grid voltage is given as 64 vdc.
12. The B+ supplying the 6AN8 is given as 305 vdc.
The schematic you have supplied is identical to that of Heath's, regarding the power amplifier and power supply sections.
To know more regarding your performance issues would require performance tests to be performed: frequency response tests, power output tests, THD and IMD tests, as well as square wave testing as well.
It is very strange that you say you had good HF performance at one point, yet don't now even with all the work you have performed. About the only thing that can affect the frequency response of the power amplifier proper is the NFB circuit. The 150K/22K/56pf network at the triode grid of the 6AN8 intentionally rolls off the HF response of the basic amplifier block. This is necessary so that the amplifier will remain stable after the application of feedback, supplied by the 27K/33pf network connecting the 16 ohm output tap back to the pentode cathode of the 6AN8. The level of FB applied is such that within the 20Hz - 20 kHz range, the frequency response and power response will be basicly dead flat, for no boost or cut. The network between the 6AN8 sections then rolls off the supersonic frequencies only, to keep the final as designed circuit stable into various loading conditions. Therefore, if the NFB circuit has been compromised, removed, or altered, that would have a very big impact on delivered HF performance. Other than that, there is just very little within the circuit that can affect HF response within the audible range.
Confirming the integrity of all these components mention will go a long way to ensure that the HF performance of the amplifier is as it was designed to be.
Let me know!
Dave
- dcgillespie
- KT88
- Posts: 399
- Joined: Sun Mar 08, 2009 5:34 am
- Location: Ball Ground, GA
DC Gillespie
by Linn lover » Wed Mar 14, 2012 2:10 pm
Dave,
Looks like I will need to raise the B+ to the 6AN8...I will remove the 10K in the power supply and install a smaller value. Calculations to ensue. Have 8.2 and 9.1k resistors to play with.
It is still weird about the voltages on pins #2 and #3. #3 should be higher than #2. And #2 should be the same as pin #6.....
I did install a new cap for the feedback resistors. I will double check them. I did not install new feedback resistors. But again, both channels are behaving the same way.
So check under way. I will double check the 56 PF and 33PF caps....they better be the correct values...or, if they are not, I found my problem.
Later!
Looks like I will need to raise the B+ to the 6AN8...I will remove the 10K in the power supply and install a smaller value. Calculations to ensue. Have 8.2 and 9.1k resistors to play with.
It is still weird about the voltages on pins #2 and #3. #3 should be higher than #2. And #2 should be the same as pin #6.....
I did install a new cap for the feedback resistors. I will double check them. I did not install new feedback resistors. But again, both channels are behaving the same way.
So check under way. I will double check the 56 PF and 33PF caps....they better be the correct values...or, if they are not, I found my problem.
Later!
- Linn lover
- Posts: 64
- Joined: Sun Jan 15, 2012 8:24 pm
- Location: Ottawa, Canada
Message for DC - good news!
by Linn lover » Wed Mar 14, 2012 7:08 pm
Dave,
Before I tell you the good news, here is the latest voltage report. I still don't know why the cathode of the triode is sitting higher than the grid, but in retrospect, things are improving. I will get both 6AN8 tubes tested again tomorrow.
Voltage report with 9.1k resistor in the power supply:
V in = 399V, 368 V prior to the first resistor and 299 V after. Very close to what is should be.
EL 84 - Pin # 9 is sitting at 366.5 V and pin #7 at 361.5 V. Bias is sitting at 15.17 volts over a 120 ohm resistor.
6AN8
Pin #1 229v 202V
Pin #2 108v 111V ?? Should be around 64 V
Pin #3 96v 90 (should be 74 v)
Pin #4 49 49
Pin #5 49 49
Pin #6 46.9 78 (should be the same as pin #2, around 64v) ??
Pin #7 45.9 50 Should be 55 VDC
Pin #8 0 0
Pin #9 1.424 1.34 (should be 1.6 vdc).
One experiment: While I was doing all these measurement I put a 20 pf cap between pin #8 and GND to see was capacitive loading would do to my sound. It was amazing - the highs went out the window even more. So capacitive loading on the input has a HUGE impact on sound!
And now for the good news (I think): You reference Pico farad in your email. I have 33nf and 56 nf. So If you confirm that they are indeed picofarad, then the mystery of the missing high frequencies would more than likely be resolved.
So thanks to your detailed accounts, I am able to resolve it if indeed I need pico and not nano.
DR - Once the tubes are tested, I will report back tomorrow. I am really at a lost to explain the differences in voltages between the plate of the pentode, the grid of the triode and it's cathode voltage.
Good evening folks.
Before I tell you the good news, here is the latest voltage report. I still don't know why the cathode of the triode is sitting higher than the grid, but in retrospect, things are improving. I will get both 6AN8 tubes tested again tomorrow.
Voltage report with 9.1k resistor in the power supply:
V in = 399V, 368 V prior to the first resistor and 299 V after. Very close to what is should be.
EL 84 - Pin # 9 is sitting at 366.5 V and pin #7 at 361.5 V. Bias is sitting at 15.17 volts over a 120 ohm resistor.
6AN8
Pin #1 229v 202V
Pin #2 108v 111V ?? Should be around 64 V
Pin #3 96v 90 (should be 74 v)
Pin #4 49 49
Pin #5 49 49
Pin #6 46.9 78 (should be the same as pin #2, around 64v) ??
Pin #7 45.9 50 Should be 55 VDC
Pin #8 0 0
Pin #9 1.424 1.34 (should be 1.6 vdc).
One experiment: While I was doing all these measurement I put a 20 pf cap between pin #8 and GND to see was capacitive loading would do to my sound. It was amazing - the highs went out the window even more. So capacitive loading on the input has a HUGE impact on sound!
And now for the good news (I think): You reference Pico farad in your email. I have 33nf and 56 nf. So If you confirm that they are indeed picofarad, then the mystery of the missing high frequencies would more than likely be resolved.
So thanks to your detailed accounts, I am able to resolve it if indeed I need pico and not nano.
DR - Once the tubes are tested, I will report back tomorrow. I am really at a lost to explain the differences in voltages between the plate of the pentode, the grid of the triode and it's cathode voltage.
Good evening folks.
- Linn lover
- Posts: 64
- Joined: Sun Jan 15, 2012 8:24 pm
- Location: Ottawa, Canada
by dcgillespie » Wed Mar 14, 2012 8:48 pm
Linn -- some points to continue pondering:
1. Yes, the values I listed are pf (or uuf, or mmf) values, and as such, are the correct units for the components in question. Heath uses the uuf designation on their schematic, whereas Sams uses the mmf. These are all the correct (and the same) unit designations for the values listed of 33 and 56 for the capacitors in question.
Frankly, I never made the switch to the new international units, so I like cps, mfd, micromhos, pf, and all the good old original units that this equipment was designed with. No slight against the newer units -- I just prefer, and continue to use, the old!
2. It is certainly possible that with such off value components installed in the all important stability locations, that the unit was very unstable. Connecting your meter leads into the circuit may have aggravated the issue even more. Therefore, this could lend to the strange voltage readings you are observing at the 6AN8. The readings may be bogus because of the very fact that you are trying to measure them in the first place.
3. I'm certainly going to assume that the meter you are using is a modern high input impedance type, and is in satisfactory operating condition. You'd never believe the error's caused when I've help some folks who I finally found out were using granddad's old 1000 ohm per volt vom!
It sounds like you've got it on the run now. This has been a bit of a bugger to figure out, but I think you'll be quite pleased when you're all through!
Dave
1. Yes, the values I listed are pf (or uuf, or mmf) values, and as such, are the correct units for the components in question. Heath uses the uuf designation on their schematic, whereas Sams uses the mmf. These are all the correct (and the same) unit designations for the values listed of 33 and 56 for the capacitors in question.
Frankly, I never made the switch to the new international units, so I like cps, mfd, micromhos, pf, and all the good old original units that this equipment was designed with. No slight against the newer units -- I just prefer, and continue to use, the old!
2. It is certainly possible that with such off value components installed in the all important stability locations, that the unit was very unstable. Connecting your meter leads into the circuit may have aggravated the issue even more. Therefore, this could lend to the strange voltage readings you are observing at the 6AN8. The readings may be bogus because of the very fact that you are trying to measure them in the first place.
3. I'm certainly going to assume that the meter you are using is a modern high input impedance type, and is in satisfactory operating condition. You'd never believe the error's caused when I've help some folks who I finally found out were using granddad's old 1000 ohm per volt vom!
It sounds like you've got it on the run now. This has been a bit of a bugger to figure out, but I think you'll be quite pleased when you're all through!
Dave
- dcgillespie
- KT88
- Posts: 399
- Joined: Sun Mar 08, 2009 5:34 am
- Location: Ball Ground, GA
Up and running. Message for DC and DR
by Linn lover » Thu Mar 15, 2012 5:23 pm
DC,
I am using a fluke 79 (which also has a capacitance meter). I replaced the caps for the proper PF tonight. Amp is up and running fine! If you think I can get more bass by changing the power supply regulation, well, that would be great! Thanks for all your help.
DR,
Here is the voltage report. I think you will be more happy, but not completely satisfied. When I was measuring on pin #2 and #8, I had some noise that came through the speaker...the with high voltage on pin #2 and pin#8 from the voltage report. Comments?
EL 84
Pin #9 = 373
Pin #7 = 370
Bias = 14.26 volts over a 120 ohm resistor
Power supply: 403 volts in tonight
375V before the first resistor at the 60uf cap
298.7 volts after the first resistor (which is now 9.1k).
Pin #1 240 209
Pin #2 46.6 81.1 Noisy when measured
Pin #3 57.6 88.9
Pin #6 47 82.1
Pin #7 71.9 53.6
Pin #8 0 0
Pin #9 1.6 1.36
So, do I need new 6AN8 tubes?
Anything I can do to get these matched up would be great.
** The EL84 running are the old ones. They are old and tired except for one tube. I have a full new compliment. With the new tubes, would the voltage measurements on the 6AN8 change much?
I want to wait for the choke before putting the new tubes in.
Bottom line. Now sounding really good! I guess it will only get better from here on end. Thanks guys!
I am using a fluke 79 (which also has a capacitance meter). I replaced the caps for the proper PF tonight. Amp is up and running fine! If you think I can get more bass by changing the power supply regulation, well, that would be great! Thanks for all your help.
DR,
Here is the voltage report. I think you will be more happy, but not completely satisfied. When I was measuring on pin #2 and #8, I had some noise that came through the speaker...the with high voltage on pin #2 and pin#8 from the voltage report. Comments?
EL 84
Pin #9 = 373
Pin #7 = 370
Bias = 14.26 volts over a 120 ohm resistor
Power supply: 403 volts in tonight
375V before the first resistor at the 60uf cap
298.7 volts after the first resistor (which is now 9.1k).
Pin #1 240 209
Pin #2 46.6 81.1 Noisy when measured
Pin #3 57.6 88.9
Pin #6 47 82.1
Pin #7 71.9 53.6
Pin #8 0 0
Pin #9 1.6 1.36
So, do I need new 6AN8 tubes?
Anything I can do to get these matched up would be great.
** The EL84 running are the old ones. They are old and tired except for one tube. I have a full new compliment. With the new tubes, would the voltage measurements on the 6AN8 change much?
I want to wait for the choke before putting the new tubes in.
Bottom line. Now sounding really good! I guess it will only get better from here on end. Thanks guys!
- Linn lover
- Posts: 64
- Joined: Sun Jan 15, 2012 8:24 pm
- Location: Ottawa, Canada
by dcgillespie » Thu Mar 15, 2012 8:16 pm
Linn -- I would again emphasize to get the B+ supply to the 6AN8 correct, and get the component values associated with the tube correct. Then, let the actual terminal voltages be what they are. With the exception of the pentode's cathode voltage, the rest can vary widely and still be considered operationally good. Other types of tubes do not have this concern -- but it is well established that the screen and plate elements of small signal pentode tubes can -- and do -- vary widely. The published values should only be considered as a guide. Other manufacturers (like Dynaco for instance) actively state that measuring the plate and screen voltages of the pentode section (and therefore all of the elements in the triode section), is basically a pointless exercise, because the voltages can vary so widely, while still being operationally just fine.
Using the significant dropping resistance in the power supply, as well as the increased cathode resistance value is definitely reducing power output. With the reduced B+ you are now using, I would at least consider installing the proper cathode resistance value.
Increasing the capacitance values in the power supply (not the one at the rectifier cathode) will not increase the level of bass reproduction, but it will increase bass definition, which is always a worthwhile goal.
Glad you've got it on the run. Good luck with it!
Dave
Using the significant dropping resistance in the power supply, as well as the increased cathode resistance value is definitely reducing power output. With the reduced B+ you are now using, I would at least consider installing the proper cathode resistance value.
Increasing the capacitance values in the power supply (not the one at the rectifier cathode) will not increase the level of bass reproduction, but it will increase bass definition, which is always a worthwhile goal.
Glad you've got it on the run. Good luck with it!
Dave
- dcgillespie
- KT88
- Posts: 399
- Joined: Sun Mar 08, 2009 5:34 am
- Location: Ball Ground, GA
by DeathRex » Thu Mar 15, 2012 8:20 pm
I would go ahead and put the new EL84s in. With a single resistor to bias all of them, if 3 are weak and one strong, the strong one will really get hammered. Put them all in and see what your bias is. The EL84s right now are doing about 10.5 watts (one might be doing 20 watts). With that higher bias resistor you can move the B+ up or down, depending on what EL84s you get. 6P14P-EVs can take 400. Just take the bias voltage (14.26) divide by the bias resistor (120) equals total current (119ma) divide by the number of tubes on the resistor (4) equals about 30ma each tube. Multiply that by voltage dropped by the tube (370-14=356) gives you power dissipated by the EL84 (10.57 watts). EL84s are about 12 watts max, the 6P14Ps say 14 watts.
At first I wanted to be a ET. Now I are one.
-
DeathRex - KT88
- Posts: 1014
- Joined: Wed Nov 18, 2009 8:13 pm
- Location: Cortez, CO
Message for DC & DR
by Linn lover » Thu Mar 15, 2012 8:44 pm
Dave,
Noted about the correct value for the bias resistor. As a matter of fact, I have four 400 ohm resistors and 4 caps (I forget the value, but they are 50 volt units, and I think, 200 uf each) and am contemplating individually biasing the tube. I have the room to do it and thought it would be good to have them each on their own. But I can re-install the 100 ohm unit if I get lazy.
The choke will help further reduce the incoming voltage and I will make sure to re-adjust everything accordingly.
I have not changed any of the electrolytic caps in the power supply. I do have them, I just have to get to it sometime in the near future.
DR - I will install the new tubes and make a round of new voltage measurements to see if anything has changed or improved. I did notice that with the old tubes, some are running brighter than others.
DC - so if I read you correctly, I need to ensure I get about 235 V to pin #1 of the 6AN8 tube no matter what resistor value I put in...as long as I get to 235...so change the 36k resistor (R53 and R25) until I get 235v. Then I would need to ensure that Pin #9 of both pentodes are at 1.6 V.
I will tweak it to get it perfect. The strength of this amp for me at this time is the imaging. It does that very well. It's not the perfect amp, but tonight, it was sounding darn good.
I'll keep you posted. I'll try to load pics sometime....but if I had to do this all over again, I would strip it down and rebuild...seems simply that way.
Noted about the correct value for the bias resistor. As a matter of fact, I have four 400 ohm resistors and 4 caps (I forget the value, but they are 50 volt units, and I think, 200 uf each) and am contemplating individually biasing the tube. I have the room to do it and thought it would be good to have them each on their own. But I can re-install the 100 ohm unit if I get lazy.
The choke will help further reduce the incoming voltage and I will make sure to re-adjust everything accordingly.
I have not changed any of the electrolytic caps in the power supply. I do have them, I just have to get to it sometime in the near future.
DR - I will install the new tubes and make a round of new voltage measurements to see if anything has changed or improved. I did notice that with the old tubes, some are running brighter than others.
DC - so if I read you correctly, I need to ensure I get about 235 V to pin #1 of the 6AN8 tube no matter what resistor value I put in...as long as I get to 235...so change the 36k resistor (R53 and R25) until I get 235v. Then I would need to ensure that Pin #9 of both pentodes are at 1.6 V.
I will tweak it to get it perfect. The strength of this amp for me at this time is the imaging. It does that very well. It's not the perfect amp, but tonight, it was sounding darn good.
I'll keep you posted. I'll try to load pics sometime....but if I had to do this all over again, I would strip it down and rebuild...seems simply that way.
- Linn lover
- Posts: 64
- Joined: Sun Jan 15, 2012 8:24 pm
- Location: Ottawa, Canada
by dcgillespie » Fri Mar 16, 2012 12:01 pm
Linn - - My intention was to have you get the 305 vdc B+ rail that supplies the 6AN8s to the correct level, as well as the values of the components associated with these tubes. Then, the actual terminal voltages at the 6AN8s will be what they will be.
Dave
Dave
- dcgillespie
- KT88
- Posts: 399
- Joined: Sun Mar 08, 2009 5:34 am
- Location: Ball Ground, GA
Message for DC & DR
by Linn lover » Fri Mar 16, 2012 9:14 pm
Dave,
Do you think a new set of 6AN8s would help my amp at all. I have not yet re-tested the tubes. They were ok (not great) when I tested them about 1 month ago.
My next step will be to replace the remaining electrolytic caps in the power supply.
After that is complete, I am most likely going to install one bias resistor and cap for each tube. I am not sure if that will help things, but at least one weak tube would not be hard on the remainder of the lot....but then, how do you keep them balanced when you replace just one tube. I would need to have an adjustable bias resistor. Seems like a lot of work. I gotta think this through.
I'll report back with new voltages once the power supply is completed.
Do you think a new set of 6AN8s would help my amp at all. I have not yet re-tested the tubes. They were ok (not great) when I tested them about 1 month ago.
My next step will be to replace the remaining electrolytic caps in the power supply.
After that is complete, I am most likely going to install one bias resistor and cap for each tube. I am not sure if that will help things, but at least one weak tube would not be hard on the remainder of the lot....but then, how do you keep them balanced when you replace just one tube. I would need to have an adjustable bias resistor. Seems like a lot of work. I gotta think this through.
I'll report back with new voltages once the power supply is completed.
- Linn lover
- Posts: 64
- Joined: Sun Jan 15, 2012 8:24 pm
- Location: Ottawa, Canada
by dcgillespie » Sat Mar 17, 2012 8:57 am
Linn -- It is the triode section of the 6AN8 that is worked the hardest in the circuit. The pentode section is hardly worked very hard at all.
Against this, the output stage in this amplifier requires little drive to develop full power output. Therefore, even mildly weak triode sections will still deliver very good performance in this design. This is opposed to say the original Dynaco MK III design, wherein again, it is the triode section that is driven the hardest, but in this case, it is driven much harder, and required to deliver significantly more drive to the output stage to develop full power output. As a matter of fact, it is not all that uncommon to go through more 6AN8s in a stock MK III, than it is output tubes!
All you can do is try it and see. From a designed performance standpoint however, this design is very forgiving of the 6AN8s actual condition.
Dave
Against this, the output stage in this amplifier requires little drive to develop full power output. Therefore, even mildly weak triode sections will still deliver very good performance in this design. This is opposed to say the original Dynaco MK III design, wherein again, it is the triode section that is driven the hardest, but in this case, it is driven much harder, and required to deliver significantly more drive to the output stage to develop full power output. As a matter of fact, it is not all that uncommon to go through more 6AN8s in a stock MK III, than it is output tubes!
All you can do is try it and see. From a designed performance standpoint however, this design is very forgiving of the 6AN8s actual condition.
Dave
- dcgillespie
- KT88
- Posts: 399
- Joined: Sun Mar 08, 2009 5:34 am
- Location: Ball Ground, GA
Message for Dave (AKA DC)
by Linn lover » Sun Mar 18, 2012 8:27 pm
Dave,
I have been listening to the heathkit all weekend. Runs great. I powered my other 8 ohm speakers, my Totem Sttafs. Originally, the AA-151 could not muster the gusto to make semblance of decent sound. With the new components and tubes, it actually sounds ok. Totems, generally speaker, require lots of power to sound good.
The next step to refurbish the amp is that I want to install new electrolytic caps. Here is what I have at my disposal:
1
New JJ can cap - 500V, 50 + 50 micro farad
I was thinking of using this as the first cap off the power supply = C1. Original spec is 60 microfarad: all I could find is 50. Good enough?
I also have an axial 50 uf 500 V cap...depending how well the physical install goes.
2 the second cap in the power supply (C1) is specified at 25 microfarad. I was thinking of using the second half of my can cap: the 50 microfarad 500 V unit. Comments?
Plan B: I also have a 25 microfarad unit (450V) axial unit if I really do need to stick to 25 (instead of 50)
I do have two 30 microfarad units for C2 (axial units). So good there.
Cheers.
I have been listening to the heathkit all weekend. Runs great. I powered my other 8 ohm speakers, my Totem Sttafs. Originally, the AA-151 could not muster the gusto to make semblance of decent sound. With the new components and tubes, it actually sounds ok. Totems, generally speaker, require lots of power to sound good.
The next step to refurbish the amp is that I want to install new electrolytic caps. Here is what I have at my disposal:
1
New JJ can cap - 500V, 50 + 50 micro farad
I was thinking of using this as the first cap off the power supply = C1. Original spec is 60 microfarad: all I could find is 50. Good enough?
I also have an axial 50 uf 500 V cap...depending how well the physical install goes.
2 the second cap in the power supply (C1) is specified at 25 microfarad. I was thinking of using the second half of my can cap: the 50 microfarad 500 V unit. Comments?
Plan B: I also have a 25 microfarad unit (450V) axial unit if I really do need to stick to 25 (instead of 50)
I do have two 30 microfarad units for C2 (axial units). So good there.
Cheers.
- Linn lover
- Posts: 64
- Joined: Sun Jan 15, 2012 8:24 pm
- Location: Ottawa, Canada
by rmyauck » Sun Mar 18, 2012 11:35 pm
Congrats on getting it working nice!
Actually that first cap 60 uF should be close to 30 uF . Some manufactures just used what they had without a care for tube life. Caps down the line however can be increased.
If you don't have a lower value cap and have Two 50 or 60 uF caps you can use them in series and they will end up giving you Half the uF value. Voltages are additive so if each cap is say 250V you will have a nice safe 500V. It's a good idea when you do this to run 2 resistors in series also in parallel with the 2 caps to equal out any differences there may be in caps.
A pair of the same 100-220K 1W would do nicely/
Diode mod is good for helping new and old rectifier tubes last. UF4007 best for a few cents more. Doesn't hurt sonics.
http://dynacotubeaudio.forumotion.com/t ... -diode-mod
Regards,
Randy
Actually that first cap 60 uF should be close to 30 uF . Some manufactures just used what they had without a care for tube life. Caps down the line however can be increased.
If you don't have a lower value cap and have Two 50 or 60 uF caps you can use them in series and they will end up giving you Half the uF value. Voltages are additive so if each cap is say 250V you will have a nice safe 500V. It's a good idea when you do this to run 2 resistors in series also in parallel with the 2 caps to equal out any differences there may be in caps.
A pair of the same 100-220K 1W would do nicely/
Diode mod is good for helping new and old rectifier tubes last. UF4007 best for a few cents more. Doesn't hurt sonics.
http://dynacotubeaudio.forumotion.com/t ... -diode-mod
Regards,
Randy
- rmyauck
- Posts: 89
- Joined: Thu Dec 09, 2010 5:13 pm
- Location: Canada
Who is online
Users browsing this forum: No registered users and 43 guests