New 183 build

[WhopperPlate]

Connecting up the NFB and biasing it properly will make a world of difference, I'm sure.

I wouldn’t bother making any judgements whatsoever at this time .

Looking forward to hearing the real results!

[bepone]

congratulations!
fresh amp need at least 40 hours to settle down (midlle and high end harshness) , also connecting NFB will tame a lot of high end (now amp is in pentode mode, following speaker impedance curve, which is raising to high frequencies, so like result there is more highs then it is normal), also pentode characteristics are all but linear..

[Stephen1966]

Thanks guys for all your support. I do plan to burn it in for a period of time before I really start tinkering with different components and so on. I'll get it biased and tuned up as far as is possible first and then just let it run on a load while I get on with other things. Still have to make the pedal and the head shell. Loads still to do

[WhopperPlate]

congratulations!
fresh amp need at least 40 hours to settle down (midlle and high end harshness) , also connecting NFB will tame a lot of high end (now amp is in pentode mode, following speaker impedance curve, which is raising to high frequencies, so like result there is more highs then it is normal), also pentode characteristics are all but linear..

I tend to leave an new amplifier running for a few days before I change a thing . I have chased my tail trying fine tune an infant amp, only to go beck to exactly where I began as the amplifier finally began to break in . Don’t do it . Play it , put it on the shelf , play it again , put it on the shelf , and then start tweaking .

Even just leaving it unplayed for a month seems to homogenize something , I have walked away from amplifiers frustrated I couldn’t get the desired response only to revisit them later and realize they have matured for whatever reasons.

[Stephen1966]

congratulations!
fresh amp need at least 40 hours to settle down (midlle and high end harshness) , also connecting NFB will tame a lot of high end (now amp is in pentode mode, following speaker impedance curve, which is raising to high frequencies, so like result there is more highs then it is normal), also pentode characteristics are all but linear..

I tend to leave an new amplifier running for a few days before I change a thing . I have chased my tail trying fine tune an infant amp, only to go beck to exactly where I began as the amplifier finally began to break in . Don’t do it . Play it , put it on the shelf , play it again , put it on the shelf , and then start tweaking .

Even just leaving it unplayed for a month seems to homogenize something , I have walked away from amplifiers frustrated I couldn’t get the desired response only to revisit them later and realize they have matured for whatever reasons.

There's a lot to what you are saying... I've noticed a difference, just by turning the chassis around. I've spent the last few weeks peering at things from the back of the amp. I can't help but think it focuses the mind on particular aspects of the sound. Turn it around and you start to look at it from a different perspective, literally and sonically! I've heard differences as well, when a chassis goes into the cab, and obviously, when it's transported into a different space. I don't think I am losing my mind (truth be told, I lost it a long ways back) but I'm beginning to think it sounds different at night than it does during the day time

At the moment, it's nowhere near what I think it should sound like but it's encouraging that some of those elements - clear articulation and note delineation, a strong low-mid presence, sustain and bloom, a not too bright but a rich, singing top end - are there in a sense already, but they still need shaping and coaxing... out from the shadows.

I have a question for all of you have who have trodden this path before though. Where do you prefer to bias it? Where does it speak for you? With an average 70% bias or something a little cooler?

[WhopperPlate]

There's a lot to what you are saying... I've noticed a difference, just by turning the chassis around. I've spent the last few weeks peering at things from the back of the amp. I can't help but think it focuses the mind on particular aspects of the sound. Turn it around and you start to look at it from a different perspective, literally and sonically! I've heard differences as well, when a chassis goes into the cab, and obviously, when it's transported into a different space. I don't think I am losing my mind (truth be told, I lost it a long ways back) but I'm beginning to think it sounds different at night than it does during the day time

I have a question for all of you have who have trodden this path before though. Where do you prefer to bias it? Where does it speak for you? With an average 70% bias or something a little cooler?

You aren’t losing your mind. there are certainly a myriad of variable factors to consider . Interactions with other electronics with in the mains power supply from neighbors can influence voltage levels and introduce various noises within the ac voltage , and this can obviously depend on where you live and what time of day .

Certainly mounting it within a cabinet , especially a combo , can impact the vibrations going into the valves , but even a head cabinet mounted securely can change the way the whole chassis vibrates . Everything has a resonant frequency.

sometimes I will keep the head far away from the cabinet to isolate the vibrational interactions between the two.

Eric Johnson’s old pedal board is a testament to the layout of gear impacting the end tonal result . He would raise his tube driver slightly above the others , and each pedal has a specific positioning. This was discussed in his recent premier guitar rig rundown using his old rig . It’s become trendy generally call him crazy for hearing what others dismiss. I never understood how people feel this elevates themselves above another for showing an inability to discern …

All part of the rabbit hole of electronics…next thing ya know you are only using red wire because it sounds better… or only brand new Duracell 9 volts before they fall below 9.1 volts….

[brewdude]

As someone who enjoys the subtle differences to seemingly meaningless changes, I “get it”.

However, these nuanced tweaks tend to go unnoticed by the listener. Seems more OCD than science or art… then again, without a healthy dose of OCD, there might not be any truly great science or art.

[WhopperPlate]

However, these nuanced tweaks tend to go unnoticed by the listener.

The body of the listeners tend to notice things before the mind. My desire to play and my ability to long durations of high volume directly correlates with the quality of sound coming from the speaker. I will get tired and become disinterested in playing if the sound feels wrong . I noticed this growing up listening to a million shows , with good and bad bands with good and bad sound techs . some nights I would just get tired and fall asleep on the nearest chair mid set because it was so much ear fatigue.

The opposite happens when it sounds ideal. You play longer and harder and the audience responds and reciprocates the energy, and kids like me get up and dance . They may not notice why, but they notice .

[brewdude]

All good points.

[bepone]

I think is mostly because of main voltage variation, but to add more to this crazy subject

During the same amp setting, under sunny day and rainy day, amp becomes unplayable! I know for psychoacoustics, but i started to believe that speaker wave propagation or ear wave receiving under rainy day - under different atmospheric pressure - has different perception , mostly negative! So i quit with guitar or sound evaluation in those days

[WhopperPlate]

I think is mostly because of main voltage variation, but to add more to this crazy subject

During the same amp setting, under sunny day and rainy day, amp becomes unplayable! I know for psychoacoustics, but i started to believe that speaker wave propagation or ear wave receiving under rainy day - under different atmospheric pressure - has different perception , mostly negative! So i quit with guitar or sound evaluation in those days

You are correct. sound pressure changes with environment fluctuations. Sound waves move faster through the heat and slower through the cold. I remember reading a study that indicated a considerable deviation in pitch with a 20 degree Fahrenheit fluctuation . This combined with humidity plays all kinds of tricks , and the wood guitars themselves have their own susceptibility obviously .

[Stephen1966]

... in the meantime, I found a dry solder joint on one of the power caps and had to remove the board to fix it.

With all that okay now, I've been looking at the power nodes and voltages. There was a bit of pfaffing around with erroneous B+ voltages until it dawned on me; cooler bias = higher B+ and vice versa

I was curious to see how the tube town transformer performed with different primary voltages though. It has 120V, 230V and 240V taps. I was trying it out with wall voltage at 230VAC for the 230V primary and 240VAC for the 240V primary. I shouldn't be surprised, but the voltages are relatively consistent when the bias voltage is relatively the same.

Voltage - 230V and 240V primaries.jpg

The information in Tony's layout states the B+ was 465.5V, the voltages on pin 4 "after screen resistors" was 462VDC and the bias was 30.3mA and there are then some plate and cathode voltages for the preamp tubes and PI. I found the parallel of these voltages in my build was obtained with the bias voltage around -40V - that's a figure I seem to recall others have arrived at as well. This was just a rough test to try out the different PT primary options. Everything is in the ballpark but I might use a lower value resistor between B+2 (the screens) and B+3 (the PI), just to lift the voltages a little higher downstream of the power tubes. The resistor was originally a 3k/5W but with my built in FX loop to handle as well, I found a 4k7 that works okay to bring the PI and preamp voltages in line. Maybe a 4k2 there... we will see.

Anyway, I wanted a ballpark set of voltages to be getting along with and I've settled on the 230V set up now. Apart from the -40V bias voltage figure, I didn't record a cathode voltage in mA yet, it will be interesting to see if it comes out around 30mA.

Setting bias by voltage readings doesn't seem to make much sense on its own, but getting close to the voltages recorded in the original is probably the closest we can get to MrD's bias settings and the corresponding bias tone barring having the original on the bench, side by side. We can dream I will take the B+ as the benchmark and conduct my own tests on the biasing over the next several days. This video has an interesting method, injecting a signal late in the signal chain then modelling for a minimum of crossover distortion in the power tubes. It will all need to be evaluated by ear ultimately, but this looks interesting enough to try.



The next thing on the cards is the FET though, which has a ~6Vdd and ~1Vs bias now it's hooked up - this is with a B+7 voltage around 306.8V !!! I biased it up to 18V and 9V on batteries in series before I installed it and I expected some readjustment once it got wired to the B+ but this doesn't look promising. Maybe the jfet is fried - quite possible is suffered an electrostatic discharge from my Christmas jumper . At least I can test it separately as it's in a socket. Expensive fail if it has. Beware the Christmas jumpers.

[Stephen1966]

I've been thinking about the recorded figures in Tony's layout and conducting a couple of listening tests with various settings to get my bearings.

First thing worth mentioning is that I can bias to the B+ voltage of 465.5V and I get a pretty cool bias point or I can bias to 30mA but then my B+ comes in at around 460V. I can't get both. I put this down to the transconductance of the tubes and this is the to best of my knowledge, an unknown when it comes to the original. Biasing by the numbers though is a bit of a fool's errand because it all ends up with a listening test and a preference of the most subjective kind. So far, I am liking the higher plate voltage/cooler bias more. I heard more bloom in the notes in this range. I'm really interested in seeing the crossover distortion properties of these two different settings though, and if there really is a more pronounced notch in the lower B+ voltage area. If so, that would suggest greater odd order harmonic distortion and less headroom along with a harder driven PI. I know Aiken doesn't put much stock in the x-over distortion means of biasing an amp but as part of the learning curve here, it will be interesting to see an objective representation of what represents a sweet sound.

Playing with the PI trimmer here as well but purely by ear at the moment and in sub millimeter increments of turn but I am starting to detect some fine changes in the sound. The voltage difference between the triodes is around 8V, and it seems a well balanced tube. That said, better to arrive at a workable bias point before I go too far with phase balance. As the bias point changes, so too does the phase balance in relation to the bias. What worked in my 465.5V bias point, doesn't seem to work so well in my 30mA setting. Third harmonic and odd order harmonics may well be swamping out the more pleasant second and even order upper partials.

More fun with high voltages - more testing! Same old story - not enough hours in the day

[bepone]

First thing worth mentioning is that I can bias to the B+ voltage of 465.5V and I get a pretty cool bias point or I can bias to 30mA but then my B+ comes in at around 460V. I can't get both. I

this is because of transformer resistances in primary- secondaries, more current more voltage drop, this is all normal

[bepone]

More fun with high voltages - more testing! Same old story - not enough hours in the day

unfortunately agreed.......