I know V=IR, no prob. Although my DMM can't do Cap readings, I can do the R and V ones. I think it can also do current readings directly but never used that.
I'll probably ask you a lot of questions about where to measure.
Easiest thing for current readings is to measure each end of the resistor to get a voltage and then divide by the resistor value. For a DMM to do current readings it needs to be in series of the circuit in question....as you can imagine this is not practical.
This is why it is also important to understand what the voltage is on the cathode of the tube BEFORE the resistor as well. This can also be telling of an issue.
So you need to take 8 measurements.
Voltage from cathode to ground 12at7 section 1 - taken at the socket then to a ground point
Voltage across the cathode resistor 12at7 section 1
Voltage from cathode to ground 12at7 section 2 - taken at the socket then to a ground point
Voltage across the cathode resistor 12at7 section 2
Voltage from cathode to ground KT88 Left - same as above
Voltage across the cathode resistor KT88 Left
Voltage from cathode to ground KT88 Right - same as above
Voltage across the cathode resistor KT88 Right
Assuming your 12at7 resistor values are correct you divide your voltage readings by 220. It should be somewhere around 2.2V
Looks like you are using 560 ohm for the kt88 resistors so divide the dropping voltage by 560. Should be somewhere around 35-40V depending on B+.
then the last place would be the coupling caps and grid stoppers to make sure there is nothing impeding or blocking the signal. grid stoppers are usually from a couple hundred ohms to maybe 1k ohms...if you mistakenly have a 1megaohm resistor in there then it would likely block most of the signal. Yank the coupling cap out of the board and test for continuity on ohms if you dont have capacitance...at least there should be some continuity and not "open"...it will give you funny readings though.
This is why it is also important to understand what the voltage is on the cathode of the tube BEFORE the resistor as well. This can also be telling of an issue.
So you need to take 8 measurements.
Voltage from cathode to ground 12at7 section 1 - taken at the socket then to a ground point
Voltage across the cathode resistor 12at7 section 1
Voltage from cathode to ground 12at7 section 2 - taken at the socket then to a ground point
Voltage across the cathode resistor 12at7 section 2
Voltage from cathode to ground KT88 Left - same as above
Voltage across the cathode resistor KT88 Left
Voltage from cathode to ground KT88 Right - same as above
Voltage across the cathode resistor KT88 Right
Assuming your 12at7 resistor values are correct you divide your voltage readings by 220. It should be somewhere around 2.2V
Looks like you are using 560 ohm for the kt88 resistors so divide the dropping voltage by 560. Should be somewhere around 35-40V depending on B+.
then the last place would be the coupling caps and grid stoppers to make sure there is nothing impeding or blocking the signal. grid stoppers are usually from a couple hundred ohms to maybe 1k ohms...if you mistakenly have a 1megaohm resistor in there then it would likely block most of the signal. Yank the coupling cap out of the board and test for continuity on ohms if you dont have capacitance...at least there should be some continuity and not "open"...it will give you funny readings though.
If I wanted to build the amp with the PC board components all on one side and I wanted to use panel mounted sockets as opposed to PCB mounted sockets would the preferred method of wiring the sockets be to use jumpers soldered to the board on one end and the panel mounted sockets on the other end? Or can some sort of quick disconnect connector be used to make disassembly easier for experimentation easier?
With the associated voltages and currents direct solder only...not too much different than p2p wiring. A/C heater wiring needs to be tightly twisted to help reduce noise.
Short update:
Spent some time reading on the basics of tube amplifiers so that the circuit and terminology look less alien to me now, well worth it.
Additionally, re-tested the output of my source laptop, and it seems it's broken, so commissioned an old media player into action for further testing.
Will swap the drivers at output to check if the amp left + both drivers are OK.
Spent some time reading on the basics of tube amplifiers so that the circuit and terminology look less alien to me now, well worth it.
Additionally, re-tested the output of my source laptop, and it seems it's broken, so commissioned an old media player into action for further testing.
Will swap the drivers at output to check if the amp left + both drivers are OK.
Wired the old media player today and re-checked old drivers in initial position: OK for left channel, right channel still down, but mostly silent, no big rumbling, a little vibration if I touch the driver.
Swapped drivers, and the old right driver does function, so that's good as it means both my test drivers are still OK.
Noticed the Left Channel KT-88 has some blue glow near its base, but not the Right channel one, is that normal?
After just a minute of testing and then turning the amp off, the KT-88s are quite hot to the touch.
Swapped drivers, and the old right driver does function, so that's good as it means both my test drivers are still OK.
Noticed the Left Channel KT-88 has some blue glow near its base, but not the Right channel one, is that normal?
After just a minute of testing and then turning the amp off, the KT-88s are quite hot to the touch.
Triode no choke configuration
As I am checking out my wiring and comparing it to the Tubelab Triode and No Choke configurations, I get a little confused (bear in mind I have no choke):
1. George recommends a simple Triode config for initial testing as it's simpler, however this contains a choke:
Here, we are told for choke-less to see the next diagram and "use the OPT wiring from this diagram" - is it the one above or the one below?
Now, the second diagram to illustrate without choke actually also is Ultra-Linear as well as uses Cathode Feedback:
So my question is: If want a simple Triode, No Choke, No CFB, how is the wiring done?
I have mine currently with the OPT wired as #1 (recently changed) and I am not sure I got this right.
As I am checking out my wiring and comparing it to the Tubelab Triode and No Choke configurations, I get a little confused (bear in mind I have no choke):
1. George recommends a simple Triode config for initial testing as it's simpler, however this contains a choke:
Here, we are told for choke-less to see the next diagram and "use the OPT wiring from this diagram" - is it the one above or the one below?
Now, the second diagram to illustrate without choke actually also is Ultra-Linear as well as uses Cathode Feedback:
So my question is: If want a simple Triode, No Choke, No CFB, how is the wiring done?
I have mine currently with the OPT wired as #1 (recently changed) and I am not sure I got this right.
the choke and how you wire the OPT's are mutually exclusive.
A choke is used in the power supply section to help quiet the supply. You use either a high watt resistor or a choke - either way its just the PSU section only.
Now how you wire your primaries of your OPTs makes the difference between modes, UL, Triode etc.
Honestly for simplicity sake and safety sake I would wire up UL since the wire on the OPT for the UL connection will be hot, if you dont use it you need to tape it off and make sure it is "safe". May as well connect it up. Besides, I kind of like UL better than Triode anyways.
A choke is used in the power supply section to help quiet the supply. You use either a high watt resistor or a choke - either way its just the PSU section only.
Now how you wire your primaries of your OPTs makes the difference between modes, UL, Triode etc.
Honestly for simplicity sake and safety sake I would wire up UL since the wire on the OPT for the UL connection will be hot, if you dont use it you need to tape it off and make sure it is "safe". May as well connect it up. Besides, I kind of like UL better than Triode anyways.
My OPT Primaries are currently as in #1.
The OPT Secondaries are currently as in #1 too.
So, my configuration is correct as a simple SE Triode with no choke and no CFB, correct? Taping off of unused wires is already there.
This would mean the actual wiring diagram for this one is missing on the webpage and the instructions are slightly confusing for newbies.
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Checkout readings.
Here are today's fresh checkout measurements after making some new U-wires to fit in one Terminal (I really should get taller terminals because the current ones are way too small and making things difficult).
I followed the procedure by Ty Bower, starting with the Rectifier Pin 8:
Here are all the measurements. If there are mistakes labelling them they're mine, but I followed the illustrated checkout exactly as above. There was some low humming while the Power ON measurements were made.
(*): There was one reading which fluctuated when the probe moved around the pin or perhaps the pin itself moved and gave fluctuating readings and this is despite having reflowed the socket joints.
1. Rect P8: 76.3K
2. Driver P2: 221K
3. Driver P7: 218K
4. Driver P3: 222R
5. Driver P8: 219R
6. OutR P5: 219K
7. OutL P5: 219K
8. OutL P1: 550R
9. OutL P8: 551R
10. OutR P1: 550R
11. OutR P8: 551R
12. OutR P3-4: 101R
13. OutL P3-4: 101R
14. Driver P4: 6.8VAC
15. Driver P5: 6.7VAC
16. OutR P2: 6.7VAC
17. OutL P2: 6.7VAC
18. Rect P2: 5VAC
19. Rect P4: 393VAC (*)
20. Rect P6: 393VAC
These look normal, don't they?
Here are today's fresh checkout measurements after making some new U-wires to fit in one Terminal (I really should get taller terminals because the current ones are way too small and making things difficult).
I followed the procedure by Ty Bower, starting with the Rectifier Pin 8:
An externally hosted image should be here but it was not working when we last tested it.
Here are all the measurements. If there are mistakes labelling them they're mine, but I followed the illustrated checkout exactly as above. There was some low humming while the Power ON measurements were made.
(*): There was one reading which fluctuated when the probe moved around the pin or perhaps the pin itself moved and gave fluctuating readings and this is despite having reflowed the socket joints.
1. Rect P8: 76.3K
2. Driver P2: 221K
3. Driver P7: 218K
4. Driver P3: 222R
5. Driver P8: 219R
6. OutR P5: 219K
7. OutL P5: 219K
8. OutL P1: 550R
9. OutL P8: 551R
10. OutR P1: 550R
11. OutR P8: 551R
12. OutR P3-4: 101R
13. OutL P3-4: 101R
14. Driver P4: 6.8VAC
15. Driver P5: 6.7VAC
16. OutR P2: 6.7VAC
17. OutL P2: 6.7VAC
18. Rect P2: 5VAC
19. Rect P4: 393VAC (*)
20. Rect P6: 393VAC
These look normal, don't they?
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Looks OK
Measure voltage of each pin to ground of the 9 pin socket.
Some readings will look funny with no tubes installed...there really is no current flowing yet...like a dam holding all the water back....tubes cause the water/voltage to flow...hopefully the way you want or predict.
Are you using tube rectifier or solid state?
Measure voltage of each pin to ground of the 9 pin socket.
Some readings will look funny with no tubes installed...there really is no current flowing yet...like a dam holding all the water back....tubes cause the water/voltage to flow...hopefully the way you want or predict.
Are you using tube rectifier or solid state?
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Thanks for the feedback, and OK, I'll do that next. These would all be with the Amp ON, right? Additionally, what do you mean by the ground of the 9-pin socket? Where exactly? Thanks.
Mine is an all-tube implementation.
Put the tubes in amp on and very carefully black probe on ground red probe measure voltage at each pin on the 9 pin driver socket.
Only use one hand...use clips to attach black probe to ground point out of the way. Keep one hand behind back and probe with other hand...seriously.
You are measuring each pin voltage to ground is all.
Only use one hand...use clips to attach black probe to ground point out of the way. Keep one hand behind back and probe with other hand...seriously.
You are measuring each pin voltage to ground is all.
OK, I got it, that's the dangerous part. I'll wait for a time when my girlfriend is here and is willing to watch upon me while I'm doing it.
Question: For this, I should put all the tubes in? If so 'll need to reach 'underneath' the socket for readings, right?
Or did you mean I should put all the tubes except the driver one?