New 183 build

[Stephen1966]

So, just a little update here. I have most of my boards made up now and they are ready to go into the chassis.

I wedged matchsticks into the eyelets on the PCBs to prevent the lacquer fouling up the solder contacts. These photos show my preamp/PI board along with the relays, PS and relay filter boards. I have designed a new rectifier/bias board which I'm basing on the 124 rectifier for added over-voltage protection. That is, with three diodes in series on each of the HT rails. If there are any problems with noise from this rectifier which is going to fitted with the ultrafast 75ns UF1007s, I will return to the snubber circuit idea. I have a figure for the leakage inductance of the power transformer and when it's up and working I will be able to take a good scope reading of their performance. This, plus the data I've already gathered will help me to design an RC snubber using appropriate values for R and C. Let's burn that bridge when we get to it though

1673857701551.jpg

1673857701526.jpg

1673964557002.jpg

1673964556959.jpg

[Stephen1966]

Ever wondered why Sprague Atom capacitors cost so much?

Here's some data I collected when choosing the cathode caps for this build.

Cathode cap comparison.jpg

Different ways this data can be read... More common, standard production caps seem to be more uniform empirically. Spragues and Vishay BC appear more consistent whereas the branded "High-quality" caps like TAD Gold Caps and Weber Elytics and TTA show more deviation. 4 cap sets are not a definitive sample size, granted, but the deviation from stated values seems more marked in the branded high quality caps here. Looking at this data, I chose the Sprague Atoms for the cathode caps because of their lower Dissipation factor (D) / higher efficiency and lower ESR which suggests a greater handling of ripple current and reduced compression. The Atoms appear far less "lossy" than the others in the list, much closer to spec and with the highest Q, quality factor. It remains to be seen whether they actually sound good - that's where my ears are going to enter the equation and God help us, it may become apparent that an inferior cap (on paper at least) adds a dirty filtering of the sound that actually contributes to the magic of the amp. A test for later, when it's all biased up and dialed in and the subtle and perhaps not so subtle differences can be made out.

I haven't seen anyone collecting this kind of data on caps in the forum but I suspect MrD had an ear for these kinds of values, and we have to start somewhere, right? In the end, I put great store in the qualitative, subjective impressions we can gather over long experience building amps but with this kind of data collection we may be able to refine the component selection to a few modern counterparts more effectively. Demonstrably so!

[WhopperPlate]

my opionated findings : Bc caps in the cathode position have an overall very trebly emphasis, and feels pretty elastic . Least punchy. Illinois is kinda just meh, works well enough, punchier . Sprague is punchiest, but kinda grainy . Haven’t tried the others .

[Stephen1966]

my opionated findings : Bc caps in the cathode position have an overall very trebly emphasis, and feels pretty elastic . Least punchy. Illinois is kinda just meh, works well enough, punchier . Sprague is punchiest, but kinda grainy . Haven’t tried the others .

Appreciate the input. '...kinda grainy' - Interesting

[WhopperPlate]

my opionated findings : Bc caps in the cathode position have an overall very trebly emphasis, and feels pretty elastic . Least punchy. Illinois is kinda just meh, works well enough, punchier . Sprague is punchiest, but kinda grainy . Haven’t tried the others .

Appreciate the input. '...kinda grainy' - Interesting

Yeh, I don’t know if that’s the best word , but more specifically I guess you could call it not especially smooth in certain upper mid frequency range, and a bit forward , even though the top end overall was rather musical and nice .

I like to do like Marshall did : stick giant overrated caps on the cathode. They used the Phillips caps that were available in the correct value, which were obviously non polarized mustard caps , but electrolytic caps are benefited just the same IMO IME. Feels like it has better headroom overall , in fact you might find yourself having to adjust heavily elsewhere to compensate for the extra coming through. I have seen Cesar Diaz do this with the bias caps , which I also prefer at times .

[Stephen1966]

my opionated findings : Bc caps in the cathode position have an overall very trebly emphasis, and feels pretty elastic . Least punchy. Illinois is kinda just meh, works well enough, punchier . Sprague is punchiest, but kinda grainy . Haven’t tried the others .

Appreciate the input. '...kinda grainy' - Interesting

Yeh, I don’t know if that’s the best word , but more specifically I guess you could call it not especially smooth in certain upper mid frequency range, and a bit forward , even though the top end overall was rather musical and nice .

I like to do like Marshall did : stick giant overrated caps on the cathode. They used the Phillips caps that were available in the correct value, which were obviously non polarized mustard caps , but electrolytic caps are benefited just the same IMO IME. Feels like it has better headroom overall , in fact you might find yourself having to adjust heavily elsewhere to compensate for the extra coming through. I have seen Cesar Diaz do this with the bias caps , which I also prefer at times .

Again, interestng... do you think the cathode caps should offer a little compression, should have a higher ESR? Those TADs are billed as a cap that "...has been designed and manufactured with tube amplifiers in mind... [bringing] more brilliance to the sound when used in the cathode position." There's nothing on the Weber Speakers site about the Elytics, to suggest any fancy special qualities but they have a similar profile to the TADs. In any case, it's instructive - knowing WHERE to listen.

[rccolgan]

I would think the sound comparison of those caps in the cathode bypass position would be more from the capacitance value? Higher capacitance would allow more bass and increase the likelihood of distortion/grain? BC measuring low and Sprague measuring higher capacitance according to the chart.

¯⁠\⁠_⁠(⁠ツ⁠)⁠_⁠/⁠¯

It's a very small difference in the math for roll off between 5.0uf and 4.5uf but maybe it's enough in that position? Something to consider.

[martin manning]

Given the tolerances involved, I think measuring actual examples of the different brands of caps and combining that with listening tests would be the way to go. ESR and capacitance would still be confounded, but it might shed some light.

[ijedouglas]

I doubt you would be able to hear the 0.5uf difference on a cathode cap. I have experimented with multiple different caps (nichicon tvx/Nichicon tkb/Roe EB / Sprague tva /Sprague TE /Sprague 516D) and they all had a distinct sonic footprint.

Here is what I heard:

Nichicon tvx => overall balanced but pretty bright and can sound a little sterile
Nichicon tkb => similar to tvx but a little rougher/trashy on the top end
Roe EB => overall balanced / bright yet smooth and has a nice singing quality
Sprague tva => duller sounding and more bass
Sprague TE => bright, didn't care much for this

It's been a while so the memory may be a bit hazy. It's a really easy test to do and I recommend doing it. Use your bench tools to make sure they are in spec and the tools on the side of your head to see if you like them

[Stephen1966]

....Something to consider.

Higher capacitance would allow more bass and increase the likelihood of distortion/grain?

Are you sure? As I understand it, the higher capacitance would increase the gain of the bottom end, compared to the top end, but it would reduce the high frequency cut off. Decreasing the likelihood of higher frequency blocking and crossover distortion.

[Stephen1966]

Just to give the discussion some more context, this is an interesting thread:

https://ampgarage.com/forum/viewtopic.p ... 71#p121871

[Stephen1966]

...the tools on the side of your head ...

I like it Your're dead right though, any empirical testing and/or theory, can only give it context.

[bepone]

So, just a little update here. I have most of my boards made up now and they are ready to go into the chassis.

nice,
big like for epcos cans

[Stephen1966]

So, just a little update here. I have most of my boards made up now and they are ready to go into the chassis.

nice,
big like for epcos cans

Cheers! Have you used the Epcos? What do you think?

[Stephen1966]

Always an anxious moment, switching on for the first time

Relay system up and running...

1674334344813.jpg

And a couple of boards in...

1674334603780.jpg

1674334344770.jpg