6L6: Thank you! Perfect timing; I just received my new variac so I'm gonna power mine up real soon 😀
So I powered one of my board up and there was little smoke 😱 but it turned out to be paint or something on the board. Anyways, it biases well however I cannot seem to get the offset below 0.5V, while maintaining a decent bias. The pot just runs out of room at about -0.9V offset when it is biased to 500mV. I am using 2200uf caps in place of the 1000uf at the moment just while I ensure it is working. Is it possible that this is the culprit? I don't completely understand their purpose to begin with.. Also, I am using the 9.1V zeners. Any suggestions?
I believe I found the problem. One of the zener diodes (P1, for offset) wasn't working properly and only had about 3.7V across it.. Replacing it now.
I am still curious about the function of the 1000uF caps if anyone cares to enlighten me. Why are they where they are and why 1000uF?
I am still curious about the function of the 1000uF caps if anyone cares to enlighten me. Why are they where they are and why 1000uF?
Use 6.2v zeners.
Using 9.1v zeners is stupid. They do absolutely nothing in the circuit unless the R7/8 is also changed.
6.2v zeners still allowes an bias adjustment range for more than 2A,,, which is nice.
C1/2 makes a DC separation to the outputstage for the tranformer socondary, but still allowes AC pulses to switch on the outputstage as ordered by the input signal, and so on...
Using 9.1v zeners is stupid. They do absolutely nothing in the circuit unless the R7/8 is also changed.
6.2v zeners still allowes an bias adjustment range for more than 2A,,, which is nice.
C1/2 makes a DC separation to the outputstage for the tranformer socondary, but still allowes AC pulses to switch on the outputstage as ordered by the input signal, and so on...
Thanks.. The stuff about the caps makes sense but regarding the zeners are you aware of any downsides to using 9.1V? You say it doesn't help but does it actually hurt?
The use of 9.1Volt zeners just gives one a greater range to select the voltage the IRF needs.
There's no problem with the 9V bias diodes, and they ensure that all output devices can be biased to the right point.
The capacitor value is not critical, and the quality is more important than the value.
Your problem may be that the resistor feeding the zeners is too large, causing too little current to flow in the zener diode.
I'd recommend a smaller resistor value, which will increase the zener current to ensure good voltage regulation for the bias.
For a 400mW 9.1V zener, this means a zener current of 3 to 9 mA is best. This about is 10% to 40% of the maximum 23mA zener current.
If we choose 6mA, then there is a total resistor current of (6mA plus 9.1/5k for the pot), or about 8mA. Then the dropping resistor
is (24V-9.1V)/8mA or about 2k. A 2.2k 1/2 W resistor should be ok. Note that the original value was 10k.
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It was just one of the zener diodes. I haven't had a chance to listen yet (I only have one channel complete anyway) but its been powered up for a couple hours. The bias remains stable at about 1.0A (470mV/R2) without creating too much heat and the offset stays within a couple millivolts. At this point I am fairly confident that the board works..
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With that piece of information, I'm glad I'm constructing an F6 instead of an F5.🙂
Hi, I'm building the F6 right now, I have 9.1v zener 100mA and also 28mA: considering that the current is 1.5mA, is it the 28mA type a better choice?
-Alex
Sent from my iPhone using Tapatalk
-Alex
Sent from my iPhone using Tapatalk
Yes, but consider reducing the 10k feeding it so there is 3-10 mA in the zener.
Remember there is about 2mA in the pot as well.
I love my F6. If someone tries to take my F6 I'll open a can of Fred Sanford whip ***.
I'm almost done with the 2nd channel but just listening through the one has given me peak of what to expect. My first impressions were "darn, this thing doesn't get very loud," but I had it hooked up to crappy speakers through a crappy preamp (my phone.) When I hooked it up to a better pre with more gain I quickly dismissed my concerns regarding power. It gets plenty loud (at least for me) when paired with a decent pre and efficient speakers, but you probably already knew that..
What really struck me on my first listen was the dynamic range and very coherent percussion. It just felt like the highs and lows had no limit; and I'm fairly certain that's actually the case (I recall someone, perhaps Nelson, commenting that the F6 is capable of amplifying everything from DC to around 50K, I would need to confirm that, though.) But at this point I don't think it would be fair to draw too many conclusions until I've had a chance to listen extensively through, you know, two channels..
What really struck me on my first listen was the dynamic range and very coherent percussion. It just felt like the highs and lows had no limit; and I'm fairly certain that's actually the case (I recall someone, perhaps Nelson, commenting that the F6 is capable of amplifying everything from DC to around 50K, I would need to confirm that, though.) But at this point I don't think it would be fair to draw too many conclusions until I've had a chance to listen extensively through, you know, two channels..
Does this comment pertain to the zener talk? There has been a lot of banter about which one is right and who is stupid for using this one or that one, could you please put this discussion to rest concerning the use of the zener for an amp using the IRF type output devices?
I already bought and installed the one I thought everyone had consensous with, but I would of course like the best choice before fireup. What IS the ideal choice for an Amp built with the IRF type mosfet outputs?
Thanks immensely in advance!
Russellc
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😛 Ok down to -3dB @ 1Hz according to the production specs, but I suppose you'd be the authority 😀 I admittedly have a relatively tenuous grasp on all this stuff being my first build and all.
I have to say though, its really cool that you are willing to share your circuits with the DIY community. I am building the F6 both because it is the latest iteration in the Firstwatt series but also because it is pretty simple in terms of components. At some point, though, I think I would like to build a more powerful amp capable of replacing my Adcom 555 mkII that I use 99% of the time. Do you think the F5T would be a good candidate? I was honestly a little put off when you commented that the F5 was relatively bright because I really don't like an overabundance of treble. Is it much brighter? Any comments (from anyone) would be appreciated.
I have to say though, its really cool that you are willing to share your circuits with the DIY community. I am building the F6 both because it is the latest iteration in the Firstwatt series but also because it is pretty simple in terms of components. At some point, though, I think I would like to build a more powerful amp capable of replacing my Adcom 555 mkII that I use 99% of the time. Do you think the F5T would be a good candidate? I was honestly a little put off when you commented that the F5 was relatively bright because I really don't like an overabundance of treble. Is it much brighter? Any comments (from anyone) would be appreciated.
On re-read I see the comment was to the "DC to 50" statement, if possible, I would still like to know Which zener?
Thanks Mr Pass, and everyone else too.
Russellc