I know it's not mentioned much these days but I find it best to try loading the power supply with dummy loads before connecting the amplifier channels themselves - it's a simple thing and "one thing at a time" procedure is great for confidence.
Connect the power supply output rails to a couple of high power 16 ohm load resistors (or equivalent // units) that will draw about 1.5A per rail, the equivalent of one channel - you might need to dunk the resistors in a jug of water as they'll get hot rather quickly (ie 1.5A X 23 X 2 watts) but it's a realistic test at half load and will show if anything needs attention - if you have them, try some 8 ohm resistors that'll draw the full power load of about 3A from each rail.
A "Variac" would be also extremely useful too ...
Connect the power supply output rails to a couple of high power 16 ohm load resistors (or equivalent // units) that will draw about 1.5A per rail, the equivalent of one channel - you might need to dunk the resistors in a jug of water as they'll get hot rather quickly (ie 1.5A X 23 X 2 watts) but it's a realistic test at half load and will show if anything needs attention - if you have them, try some 8 ohm resistors that'll draw the full power load of about 3A from each rail.
A "Variac" would be also extremely useful too ...
Yee Haw
Look Ma, no smoke....
Props to 6L6's wonderful guide
The excitement is building; I have to remind myself to go slowly...
(The LEDs work. For some reason that pic didn't load, so I went with the pre-power-on pic. Also it shows everything better.)
Look Ma, no smoke....
Props to 6L6's wonderful guide
The excitement is building; I have to remind myself to go slowly...
(The LEDs work. For some reason that pic didn't load, so I went with the pre-power-on pic. Also it shows everything better.)
Attachments
Zero volts across 0.47 ohm bias resistor
Well, the B channel works. The bias and offset are good. The A channel does not. Zero volts across the 0.47 ohm resistor. The LED does not light up. However, it is oriented correctly. For reference I used the 6.2 volt zeners.
I could use some suggestions. Thank you, Bill
Well, the B channel works. The bias and offset are good. The A channel does not. Zero volts across the 0.47 ohm resistor. The LED does not light up. However, it is oriented correctly. For reference I used the 6.2 volt zeners.
I could use some suggestions. Thank you, Bill
Attachments
![20210410_213116[1].jpg](/community/data/attachments/855/855307-afebcaee4c0a8791b069d493b715bd39.jpg)
![20210410_213128[1].jpg](/community/data/attachments/855/855319-c4e50cac74f2fc20f9e7fc140c978303.jpg)
Well, I'm sure someone more knowledgeable than I will reply, but...
What are your rail voltages? If the LED is not lighting up and you really do have the cathode connected to R13 and the anode to ground, it's hard to imagine why it wouldn't be lighting up if there's voltage on the positive rail.
What's the voltage across the zener diode?
May or may not be relevant, but the orientation of your pots is opposite mine and I made sure to orient them so that turning the pot screw clockwise would increase bias (and offset). I installed them at 0 and it took a lot of turning before I started to see voltage across R2. I really thought something was wrong.
Hope this is of some use.
-- Thing
What are your rail voltages? If the LED is not lighting up and you really do have the cathode connected to R13 and the anode to ground, it's hard to imagine why it wouldn't be lighting up if there's voltage on the positive rail.
What's the voltage across the zener diode?
May or may not be relevant, but the orientation of your pots is opposite mine and I made sure to orient them so that turning the pot screw clockwise would increase bias (and offset). I installed them at 0 and it took a lot of turning before I started to see voltage across R2. I really thought something was wrong.
Hope this is of some use.
-- Thing
Yee Haw II
Successful power on of both channels achieved. F6 is up and running and sounds spectacular.
Only mod was replacing the zener diodes with 3 green LEDs in series and R7/R8 at 3.3k.
Rails at +23.3v/-23.3v with everything hooked up. Currently biased at 0.5v, offset at 0.000. Heat sinks are doing their job quite well.
Ramping up the first channel was a little nerve-wracking because I didn't realize how much I'd have to turn the pot screw (started at 0) in order to start to see voltage across R2. Then I semi-freaked out that my rail voltages seemed low until I remembered I still had the dim bulb cord in. But it all worked out in the end.
Still have to install pilot LEDs. The drill press I have access to for putting the appropriate holes in the front panel is an hour drive away, so that's a deferred project at the moment. Am also having some issues with chassis fit. The one piece of advice I'd have for other newbie builders is to assemble the whole chassis at the beginning of the build in order to see how it fits and make sure all the holes line up. Then take it apart as needed to build.
Any tips on doing that after the fact are welcomed.
Again, big thanks to 6L6 for the excellent guide, all those who have shared their ideas and experiences here, and of course Mr. Pass. Standing on the shoulders of giants.
I will be up late tonight, as I keep thinking of other music I can't wait to hear through this amp.
-- Thing
Successful power on of both channels achieved. F6 is up and running and sounds spectacular.
Only mod was replacing the zener diodes with 3 green LEDs in series and R7/R8 at 3.3k.
Rails at +23.3v/-23.3v with everything hooked up. Currently biased at 0.5v, offset at 0.000. Heat sinks are doing their job quite well.
Ramping up the first channel was a little nerve-wracking because I didn't realize how much I'd have to turn the pot screw (started at 0) in order to start to see voltage across R2. Then I semi-freaked out that my rail voltages seemed low until I remembered I still had the dim bulb cord in. But it all worked out in the end.
Still have to install pilot LEDs. The drill press I have access to for putting the appropriate holes in the front panel is an hour drive away, so that's a deferred project at the moment. Am also having some issues with chassis fit. The one piece of advice I'd have for other newbie builders is to assemble the whole chassis at the beginning of the build in order to see how it fits and make sure all the holes line up. Then take it apart as needed to build.
Any tips on doing that after the fact are welcomed.
Again, big thanks to 6L6 for the excellent guide, all those who have shared their ideas and experiences here, and of course Mr. Pass. Standing on the shoulders of giants.
I will be up late tonight, as I keep thinking of other music I can't wait to hear through this amp.
-- Thing
Attachments
Congratulations and we expect nothing less than spectacular!
Have fun!
Run your DMM set to continuity along the A-F path. A to B, C to D, and E to F. The flat side / cathode goes to "the most negative" side.
If one channel is working, then your PSU is working.
You have power to the board and no smoke, which is good. Trace voltages through the circuit. Or... you can keep turning P2. How far did you get? See previous post re: surprise how many turns it took before they saw a voltage.
Edited to add - check voltage across R1 too.
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@chanthing and @ItsAllInMyHead
Success!!!!. Did continuity checks. Figured out that I kept the 10k LED resistor with a red LED. Doesn't work of course. All I had left was a red LED.
Next, I checked the pot values on the B channel and duplicated that on the A channel. As mentioned, it took a lot of twisting to set channel A. When I fired it up, it was darn near right on. Yipeeeee. Need to let it cook with the cover on and install the feet, etc. Thank you, Bill
Success!!!!. Did continuity checks. Figured out that I kept the 10k LED resistor with a red LED. Doesn't work of course. All I had left was a red LED.
Next, I checked the pot values on the B channel and duplicated that on the A channel. As mentioned, it took a lot of twisting to set channel A. When I fired it up, it was darn near right on. Yipeeeee. Need to let it cook with the cover on and install the feet, etc. Thank you, Bill
System is Paul Carmody designed Speedster speakers and an M&K Volkswoofer subwoofer on the output side. Since the nuTube in my B1 recently crapped out, the F6 is currently being driven by an Advent 300 receiver in preamp mode. Sources are a Thorens turntable with Ortofon 2M Red cartridge and moodeaudio running on a Raspberry Pi with a HifiBerry DAC+ board.
Previous amp setup was a pair of ACA's configured as monoblocks. Also briefly tried a B&K ST-140, which I didn't like at all.
The biggest improvements with the F6 are firmness of bass and a much more detailed sound all around. Very engaging. I find it difficult to write about audio without lapsing into cliche', but all the edges are much sharper, without being annoyingly so.
Probably will stick with the Model 300 even after I replace the nuTube in my B1 and relegate that to my bedroom system with the ACAs. I really like the phono preamp in the Advent and it's less fussy with hum than my outboard phono preamp. Seems to match well with the F6.
-- Thing
Added a few mods to my F6 while checking the bias/offset today.
Replaced bolt on bridge rectos with standalone devices utilizing the stores UPS PCB. While at it I added the secondary snubbers for my Antek 400VA transformer.
Also added a soft start circuit, PCB courtesy of the store. Not much of a delay in “human time” but I guess electrically it’s doing what it needs to do.
Honestly I’m not sure if I hear a difference lol, I don’t have the best ears and I can’t A/B the changes. Oh well, I can sleep well at night. What an amp!
Replaced bolt on bridge rectos with standalone devices utilizing the stores UPS PCB. While at it I added the secondary snubbers for my Antek 400VA transformer.
Also added a soft start circuit, PCB courtesy of the store. Not much of a delay in “human time” but I guess electrically it’s doing what it needs to do.
Honestly I’m not sure if I hear a difference lol, I don’t have the best ears and I can’t A/B the changes. Oh well, I can sleep well at night. What an amp!
Attachments
Ok. Back to it.
New pots. set to midrange.
6.8 Zeners
Retested PSU with dim bulb. Passed. 24.1 on both channels
Now using a Variac.
R7 & R8 are 3.3K.
I had the Variac at around 60 volts
Not much action on the bias pot.
But the offset pot DMM shows mV rapidly climbing to OL.
I removed that trimpot and it was set in the middle.
I replaced it with a new one set to the middle.
But before I try things again, I believe I'm missing something with the offset pot.
I appreciate some fresh eyes looking over this. So far nothing has smoked, I guess thanks to the Variac.
New pots. set to midrange.
6.8 Zeners
Retested PSU with dim bulb. Passed. 24.1 on both channels
Now using a Variac.
R7 & R8 are 3.3K.
I had the Variac at around 60 volts
Not much action on the bias pot.
But the offset pot DMM shows mV rapidly climbing to OL.
I removed that trimpot and it was set in the middle.
I replaced it with a new one set to the middle.
But before I try things again, I believe I'm missing something with the offset pot.
I appreciate some fresh eyes looking over this. So far nothing has smoked, I guess thanks to the Variac.
Attachments
