Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Baptiste on February 13, 2020, 12:27:14 pm
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Hi everyone,
It's m'y first post here, after much time reading stuff here and on other forums.
I plan to start building my first guitar amp this year, my goal is both to experiment and eventually end up with a nice amp. I don't have an extended experience in this, but I'm used to design and make stuff, and I've built my hifi tube amp some years ago.
So, before the questions, here is a first recap of the project, my current specs and design thoughts :
Volume
The starting point is the volume. I'm a strictly home player, live in a flat, practice often at night once the kids sleep...
I aim at around 60-85dbA (from just enough to be heard above the unplugged sound of the strings, to a loud acoustic guitar), not interested in more for this build.
So I think of something like this:
- 100mW to 1W power amp
- low efficiency 8" speaker (like Jensen p8r)
- VVR/L-pad... if needed
Style
I don't aim at cloning a specific sound signature, I just want to tweak up to something I like.
Style-wise, I'd like to go from clean to blues/rock to moderate gain hard rock (BoC, Black Sabbath).
Topology
I want to stay relatively close to conventional topologies, with 12a*7 preamp, and pentode power amp. Not interested in triode power stages.
I'm still hesitating between SE and PP, leaning towards SE for simplicity and epistemology reasons, and because I think if don't begin with an SE I might never try one out :-)
I plan to have an iterative breadboarding approach, starting with one tube (2 gain stages) for the preamp, then adding a second one. I guess a 4 gain stage preamp is totally enough saturation and trouble for me :-)
So, in the end, a single channel amp, something in the like :
G1(MB) > D1 > G2(MB/CC) > [D1 > G3(HB) > CF > TS] > D2 > SE > MV(VVR)
G= gain stage
D/V/MV: drive/volume/master vol. pot
MB/HB/CC : medium/hot bias, cold clipper
CF: cathode follower
TS: tone stack
[...]: bypassable sections
In the case of using VVR, I consider the VVR as MV, and the MV as a power amp drive.
I put twice D1 here, just an idea I might try, it's a stereo drive pot, like what Orange does (e.g. dark terror schematic). It seems interesting to get a wide range of clean to drive sounds on a single channel amp.
I'd also like to experiment on defeatable boost/OD/Tonestack sections.
Well, you get the idea, I want to see what I can do with 2 preamp tubes.
Now, the questions !
Question 1: overall topology concerns
The vast majority of SE amps use 2 gain stage champ-like preamps. Am I asking for trouble trying to put a higher-gain preamp on a SE amp ? Should I go for a PP instead ?
Other advices ?
Question 2: power tube choice
I've screened all low power amp topics I could find, here is the shortlist of tubes I found:
- 6AK6 (7pin): Pout ~1W
- 5902 (submini) : Pout ~1W
- 5672 (direct heating submini) : Pout = 80mW
- 3S4 (direct heating submini) : Pout=250mW
Low input tubes (4-5Vpp swing before cut-off) :
- 6au6
- 5654/6ak5
- 5840...
I feel the 6ak6 is a very sane candidate, it has been used in several projects. It's probably too powerful for my needs, but in SE+VVR it should be okay. If I decide to go PP, I'd rather select a lower power tube though, such as the 3S4 or 5672.
Any advice or considerations ? Is there any drawback/advantage to use lower input pentodes ? Sound-wise also, I have no idea how all those tubes would compare to conventional ones, and if I should avoid some of them...
Question 3: power supply topology
Most (very) low power output pentodes require a very much lower B+ than 12a*7. Typically 65 to 180V vs ~300V for the preamp. I couldn't find much practical answers for this, it seems everyone avoids to fall in this case.
Which PSU topology would be the best suited ? Pros & cons of those different solutions ?
2.a) Linear PSU ~300V B+, with dedicated fixed or variable voltage reduction for power section.
2.b) Linear PSU ~300V B+, with power section node at the end. Big dropping resistance.
2.c) Linear PSU, using two distinct secondaries and two separate rectifiers for preamp and power amp.
2.d) Linear PSU for preamp and heaters, separate SMPS for power amp
2.e) Separate SMPS for everyone. Heaters direct from 12v PSU.
2.f) Lower preamp B+ accordingly to the power amp restrictions. I'd like to avoid this.
2.g) replace 12a*7 with more suited tubes, such as 6112. I'd like to avoid this also, to stay closer to well known schematics.
Okay, that's more than enough for today, thanks to those who took the time to read everything ;)
Baptiste
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that is some laundry list for <1W :icon_biggrin:
build the PA section +PS make it work just the way you want, THEN make a preamp. the web has tons of lo-watt examples to steal from, re-inventing wheels went out of fashion just after the dark ages :icon_biggrin:
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... 100mW to 1W power amp
http://el34world.com/Forum/index.php?topic=5039.0 (http://el34world.com/Forum/index.php?topic=5039.0)
(https://i.imgur.com/Y1BJvIS.png)
(https://i.imgur.com/eYrhFvN.gif)
--
http://el34world.com/Forum/index.php?topic=6759.msg59501#msg59501 (http://el34world.com/Forum/index.php?topic=6759.msg59501#msg59501)
Franco
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low efficiency 8" speaker (like Jensen p8r)
SPL of this speaker is 91.8 dB. I.e., 1W (i.e. 2.83V) from amp into this speaker produces 91.8dB @ 1 M. This appears to exceed your stated design goal. For 85dB @ 1M, you need to cut the amp output in Watts in half twice; i.e., 250mW. Good tone probably requires pushing the amp to at least 1 or 2 0'clock on the vol dial. So you need a power tube to meet that criteria.
But, my shop vac does 85dB. Running that at night in a flat would not make my family happy.
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Thanks all for your quick replies
that is some laundry list for <1W :icon_biggrin:
build the PA section +PS make it work just the way you want, THEN make a preamp. the web has tons of lo-watt examples to steal from, re-inventing wheels went out of fashion just after the dark ages :icon_biggrin:
Sure, but why should I lower expectations because of the lower wattage ? :-)
I agree with your point, I don't mean to reinvent anything, but I still want to understand and appropriate what I do.
And to follow your advice, I still need to choose a power tube, and make sure my PSU will fit the later preamp section. Hence my questions.
@Kagliostro
Thanks for the links. I had forgotten about this one. I'll have another lol at the 6au6.
The scaling on Vg2 is interesting, however, I'd rather go for regular VVR on both G2 and anode. My understanding is that lowering only Vg2 completely shifts the whole balance of the power stage, because it makes the bias point more and more assymetric in regard to Va possible swing (closer to cutoff). In regular VVR you keep better proportionality, the full power tone shaping must be much better conserved.
@jjasilli
Yes I know, 1W in this speaker is plenty loud, but I couldn't find lower efficiency. Enters the VVR or power soak... Or a lower power pentode. And at night I'm fine with cleaner sound or no power amp distortion.
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I use an L-pad attenuation from Parts Express. Haven't used it for bedroom volume. Have you considered earphones?
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why should I lower expectations
no reason to, the PA section is the heart, the player, guitar n to some degree the pre are the soul. once you get the blood flowing, the player n guitar, then you add the missing spices, the pre. :icon_biggrin:
ps, still gotta do the #'s for filaments etc, I always pic 4 pre tubes - over head since I rarely use more than 3
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ECL84 tubes have a really good sound. I built a Plexi style amp several years ago with ECL84s in PP, and it probably put out 3-4 watts. Those tubes are true pentodes and have a surprising amount of bass. You could probably do something single ended and it would be a watt or so.
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I use an L-pad attenuation from Parts Express. Haven't used it for bedroom volume. Have you considered earphones?
I do use headphones, but find it cumbersome. I might add a headphone/line out tap though. And I consider L-pad to knock off just a few dB.
The PA section is the heart, the player, guitar n to some degree the pre are the soul. once you get the blood flowing, the player n guitar, then you add the missing spices, the pre. :icon_biggrin:
ps, still gotta do the #'s for filaments etc, I always pic 4 pre tubes - over head since I rarely use more than 3
Well, about the player... Let's say it's a work in progress :help:
And not sure if we say the same thing, but I meant maximum 2 tubes/4gain stage pre.
ECL84 tubes have a really good sound. I built a Plexi style amp several years ago with ECL84s in PP, and it probably put out 3-4 watts. Those tubes are true pentodes and have a surprising amount of bass. You could probably do something single ended and it would be a watt or so.
It's a bit more powerful, but very nice ! I overlooked pentode/triode combos.
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It's a bit more powerful
You could probably do something single ended and it would be a watt or so.
getting less from a SE isn't hard, more....trickyer
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Rob has a great 5E3 micro:
https://robrobinette.com/Deluxe_Micro.htm
Great directions even breadboard directions. PP or SE options. Various tube options. Output is in your range.
I agree with above, why invent a amp that are already out there. I f you want to build it and play amps exist. If you want to go your own, go for it, it is beyond my skill level and I will watch with interest. I have built a 1 watt amp but it is your basic champ with 3-5$ tubes, 6X4 rectifier, 6mc6 and 7732. It is a dirt simple amp that sounds great and could be built in a day.
I think you should start with what sound/tone you want and build it to that end, which you stated. Tubes can sound how you want by the parts connected to them.
Cheers Ron.
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Thanks Ron,
Rob website and micro amps projects are great, but he uses 12au7 (double triode) for the power section, either in PP or parallel SE. I really want to use pentode(s) instead.
Are you sure you meant 6mc6 ? I googled it, it's a high power (Pa_max=33W) pentode. I didn't know the 7732 too, that's another interesting one.
Tubes can sound how you want by the parts connected to them.
I'll try to keep this in mind ;-)
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Also, any advice concerning my initial questions #1 (SE vs PP for mid-gain) and #3 (PSU topology) ?
Those will help me decide on the power tube choice :-)
Thanks !
Baptiste
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Sorry double apologies.
1 I read past the pentode tube requirement.
2 A little dyslexic moment the tube is a 6CM6 it is a tetrode in the 6V6 "family". Other similar ones for future builds: 6aq5,6cw5,6005,7408,5992,7c5,12ab5,6p6s,6Ez5,6Cz5.
I will follow you build with interest, I find it great to see guitar amps come about with less "standard" tubes than in the commercially built amps.
Cheers Ron.
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... my current specs and design thoughts :
Volume
The starting point is the volume. I'm a strictly home player, live in a flat, practice often at night once the kids sleep...
I aim at around 60-85dbA (from just enough to be heard above the unplugged sound of the strings, to a loud acoustic guitar), not interested in more for this build.
So I think of something like this:
- 100mW to 1W power amp
- low efficiency 8" speaker (like Jensen p8r)
...
Have you heard and love the Jensen P8R?
Asking because a different and/or larger speaker is likely to be a more-satisfying sound, and your project is only gonna sound as good as the speaker you use. If it were my project, I'd start with the speaker choice then look to reduce amp-power to hit a suitable volume. And to some extent, low-volume playing will always be less-satisfying than high-volume playing (but is what it is for this project).
I've gotten some vintage amps over the past couple years, and in some cases the previous owners had swapped in new speakers to "preserve" the old ones. Because I don't really need to worry about blowing speakers, in every case I re-installed the original speakers. And in every case, the original speakers sounded better to me (or at least sounded like the amp's "authentic voice").
It also happened that I got a couple of mid-60's Celestion "silver" alnico speakers, and tried them in a 2x12 cab paired with a '65 AC10. I really liked the AC10's Elac speakers (better than the Webers the prior owner installed), but became an instant fan of the T1088 Celestions after trying them. Im fact, I liked them so much I got another pair, as well as a similar pair of T1656 Celestions. If I were to build an amp now, even a low-volume project (and these are probably 100dB speakers like the modern Celestion alnicos are rated), I'd go out of my way to use these speakers and reduce amp-power to hit the volume target.
Food for thought...
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any advice concerning my initial questions
#1 you want a rock solid, low ripple NO sag design similar to a SS PS. I build 10-20W xSE, I aim for <20mVac at V1 and <2vac at the PA tube. The OT is equally important, I like Edcor or Hammond UL rated 30 - 50% over Max plate I. at 25W though you need 2 ppl to carry it, so I fudge there
you'll have to do your own work on PP but anything that meets min requirements for the tube(s) you choose works, sag is a thing in some PP, higher ripple is acceptable because of the natural cancelation you get.
the tubes come 1st, without that data you can't know filament draw, max current, max V etc. to buy metal
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Have you heard and love the Jensen P8R?
Asking because a different and/or larger speaker is likely to be a more-satisfying sound, and your project is only gonna sound as good as the speaker you use.
[...]
Food for thought...
Thanks for the food HotBluePlates! You have a very good point, I didn't hear it in person, just some speaker shootouts on YouTube...
I'm not settled on anything yet, I'll take the time to reconsider the question.
My initial selection was based on those points :
- at such low power, why get bigger than 8 inch ? I often read that bigger speakers needed more watts to sound good. But It's so subjective, it's hard to filter what people say on the internet...
- I'll try to limit the cab size, so I could probably get away with a 10", but a 12" is a bit too much.
- at low volume, thanks to Fletcher Munson, I guessed an American voiced speaker would sound much better than British ones.
- I read reports that the P8R behaved very well at low volume. FWIW...
- It might be naive, but I considered if I tweaked the amp tone around the speaker, maybe the speaker choice wouldn't be that critical, provided it's a good quality one... Especially since I'm never going to get any cone breakup at 0.1W
It's a lot of assumptions, so I'd be very happy to have your view on it.
In the end, I might buy 2 or 3 and decide with my ears...
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A small speaker SOUNDS small at any power level. Your ear knows.
I've had hours of fun with a 12-inch RCA monitor and an amp that didn't make a whole Watt.
Yes, a Twelve and suitable box may be a bad fit in the bedroom.
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:icon_biggrin:
go with a 2 X12 and it doubles as a work bench
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any advice concerning my initial questions
#1 you want a rock solid, low ripple NO sag design similar to a SS PS. I build 10-20W xSE, I aim for <20mVac at V1 and <2vac at the PA tube.
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the tubes come 1st, without that data you can't know filament draw, max current, max V etc
Thanks for the figures!
About the tubes, even without settling for a specific model, I can say that the quiescent anode current will be lower than 15mA.
For anode and grid voltage, it will depend a bit more. 6au6 might be the highest at 250V max, but for the other tubes it'd be less than 180V.
For the preamp section, I'd like to stay on conventional B+ values, let's say around 300V.
Filament heating should be less than 1A for the whole amp, but I'd like to have some margin.
So, most probable scenario : very low current requirements for the PSU, and power amp B+ at half the preamp B+.
A small speaker SOUNDS small at any power level. Your ear knows.
OK, I'll keep this in mind, and maybe start negociating about cab size ;)
:icon_biggrin:
go with a 2 X12 and it doubles as a work bench
Haha, I have a workbench project I need to finish, I'll show you a picture the day I go back at it, you'll laugh. It's more of a 2X8 midget sized one :)
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Thanks for the food HotBluePlates! You have a very good point, I didn't hear it in person, just some speaker shootouts on YouTube...
I'm not settled on anything yet, I'll take the time to reconsider the question.
My initial selection was based on those points :
- at such low power, why get bigger than 8 inch ? I often read that bigger speakers needed more watts to sound good. But It's so subjective, it's hard to filter what people say on the internet...
- I'll try to limit the cab size, so I could probably get away with a 10", but a 12" is a bit too much. ...
I'm in the fortunate position to have a '63 AC30, a '65 AC10 (which I usually play through a separate 2x12 cabinet), a '64 Deluxe Reverb, a '67 Super Reverb, and recently sold a '66 Pro Reverb. All of those are amps with 12" speakers except the Super Reverb, but the large cabinet with 4x10" counts for this example.
I live in an apartment and sometimes play late into the night. Between the amp & guitar volume controls, I can keep the volume down so neighbors have never complained. But the added bass from big speakers & big cabinets help offset the fact your ear perceives low frequencies to be quieter at low volume.
Yes, all those amps will "sound better" at 105-115dB, but they all sound more satisfying than the Vibro Champ I have with its 8" speaker and small cabinet at the same low volumes. All of those amps are clean at these low apartment volumes, but I have pedals if I want distortion.
You really owe it to yourself to hear amps/speakers in-person to get a feel for what will work for you. Videos and sound clips online can give a misleading impression, and you won't really know what anything sounds like at the volumes you're trying to remain below without direct experience.
Or, make your best-guess but be prepared to spend more money later to get different speakers/cabinet if you find out reality doesn't match your assumptions.
- It might be naive, but I considered if I tweaked the amp tone around the speaker, maybe the speaker choice wouldn't be that critical, provided it's a good quality one... Especially since I'm never going to get any cone breakup at 0.1W
It's not just about "cone breakup" but the fact that every speaker has a different frequency response. Yes, you can try to modify the amp to suit, but if your speaker is "the right sound" from the start everything else falls into place.
For example, the Normal channel of the AC30 and either channel of a 1962 Deluxe basically do the same thing: they amplify everything in the "mid-band" and have some amount of bass roll-off and treble roll-off due to the circuit & tubes. They both feature 12" speakers, but they sound entirely different because their speakers sound entirely different. The Deluxe's Oxford 12K5 sounds nothing like the AC30's Celestion Blue alnico, and neither amp sounds "like itself" when used with some other speaker.
If you must stay with an 8" speaker, the Jupiter 8SC gets high praise from folks I'd tend to trust. However, it is louder than the Jensen 8" and probably is more expensive to get in the EU.
... So, most probable scenario : very low current requirements for the PSU, and power amp B+ at half the preamp B+. ...
Why does your preamp need to be over 150-200v?
If you're going to be using 6AK6, your preamp only needs to deliver ~9v peak to distort the output tube (when it is operating at 180v). The R-C chart on page 2 of this 12AX7 data sheet (https://frank.pocnet.net/sheets/093/1/12AX7.pdf) shows it will almost manage 9v peak with a 90v supply, and can manage more than twice what you need with a 180v supply.
- Pick your speaker so you know its sensitivity, and the true power output you need to hit your decibel target.
- Pick your output tube and design just an output stage (within the tube's constraints) to hit your power target.
- The output tube's bias voltage will dictate the amount of drive signal needed from the preamp for maximum output power & onset of distortion.
- Try to design the preamp using a supply voltage lower than the output tube supply voltage (should be easy), to make power supply design easier.
Or just build the PRR 1/3w amp. I've built one, and it's louder than what you can distort in a late-night/low-volume situation. The screen voltage "attenuator" works for small reductions in volume, but doesn't sound terrific at the bottom end of its range. Maybe make life easy and use a pedal for distortion when needed.
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If you want to play with low power pentodes I like EL91's. Proper audio power pentode, used as the audio amp in Eddystone receivers so loads of mil spec versions around on the cheap. My office noodling amp is a homebrew SE EL91 (actually switchable for the slightly beefier EL90). EF86 front end, 1 x ECC83 for gain/CF, tonestack, EL91. Also has another '83 for reverb. I have VVR in it which is useful. However I run it into a Boogie 1 x 12 fitted with an EVM12L. Don't think the EV even knows it's being spoken to at that power level! I can run it into power amp distortion at which point it's loud enough to annoy others in the house unless I turn down the VVR.
I was swapping notes with PRR about low power amps when he sketched up the 1/3W as a suggestion. I tried that, sounds good, still quite loud when overdriven - probably not helped by the EV. He then added the screen grid voltage control. You can wind it right down with that. I found the 1/3W when clean was quieter than the acoustic sound from the strings.
My experience of 8" speakers is limited to a 70's silver face Champ I've just repaired for a friend. Whether it's the (original) speaker or the cab it just sounds small and boxey, particularly when driven into distortion. Not so bad clean. Probably fine in a band mix but if you're playing on your own at home I'd find irritating.
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looks like the data points are all there, out in the sticks where I live, the next step would be Shite or get off the pot :icon_biggrin:
plug in the weller n make smoke
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It's not just about "cone breakup" but the fact that every speaker has a different frequency response. Yes, you can try to modify the amp to suit, but if your speaker is "the right sound" from the start everything else falls into place.
If you must stay with an 8" speaker, the Jupiter 8SC gets high praise from folks I'd tend to trust. However, it is louder than the Jensen 8" and probably is more expensive to get in the EU.
Thanks for all the advices about speakers. Very much appreciated.
Why does your preamp need to be over 150-200v?
If you're going to be using 6AK6, your preamp only needs to deliver ~9v peak to distort the output tube (when it is operating at 180v). The R-C chart on page 2 of this 12AX7 data sheet (https://frank.pocnet.net/sheets/093/1/12AX7.pdf) shows it will almost manage 9v peak with a 90v supply, and can manage more than twice what you need with a 180v supply.
I just thought that by staying close to conventional values for preamp B+, it would be easier to reuse existing schematics of well known amps and stay close to the expected tone/behaviour.
I get your point, and it's reassuring to know I can go with that kind of voltages for the preamp. However, if I go for a VVR on the power section anyway, is there any point to try to keep voltages lower on the preamp ?
- Pick your speaker so you know its sensitivity, and the true power output you need to hit your decibel target.
- Pick your output tube and design just an output stage (within the tube's constraints) to hit your power target.
- The output tube's bias voltage will dictate the amount of drive signal needed from the preamp for maximum output power & onset of distortion.
- Try to design the preamp using a supply voltage lower than the output tube supply voltage (should be easy), to make power supply design easier.
That's pragmatic. I'm not going to choose the speaker immediately, but I'll make a not to constraining choice on sensitivity and go from there.
If you want to play with low power pentodes I like EL91's.
...
I found the 1/3W when clean was quieter than the acoustic sound from the strings.
Thanks JB for the input and feedback. I had not shortlisted EL91 because it was a bit higher output, but not so much indeed, and as Shooter already stated, it's easier to get lower power from a tube...
I found the 1/3W when clean was quieter than the acoustic sound from the strings.
I definitely need to put a VVR on this project. It will compensate for the wrong estimation I'm likely to make regarding clean vs overdriven volume.
About this, I have a very neophyte question : what kind of overdrive level do we get from the power amp at full swing, before clipping ? I know it's about 10%THD, but have no clue of what it translates to in regard to sound. Is it still a harmonically rich clean, or already overdrive territory ? And on the other side, is there a rule of thumb about what % of swing level is the limit a truly clean sound ?
looks like the data points are all there, out in the sticks where I live, the next step would be Shite or get off the pot :icon_biggrin:
plug in the weller n make smoke
Well, thanks for the help and for pushing me, but I don't know exactly when I'll start. It might take take a while on your Shooter scale ;)
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It might take take a while
just holl'r when it's up n you're ready to tweak it :icon_biggrin:
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Rob Robinette's Micro Bassman sounds really good, and it can be a micro JTM45 with just a preamp tube swap.
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Hi there,
I made a little table to quantify power VS clean/OD volume, and to estimate the kind of flexibility I could expect from a power amp section with VVR and post-OT attenuation.
I made a few reasonable assumptions in the parameters, I might be a bit off. Comments are welcomed.
It confirms without surprise that something around 1/4W would provide quite a lot of flexibility for my situation. Of course, it doesn't take into account the added flexibility of the preamp itself.
As a reference, here is an interesting video to illustrate what a 0.25W amp gives, with a Celestion V30 (100dB sensitivity), without any power scaling.
https://www.youtube.com/watch?v=8ZN4_kwi9gU&list=PLrJmIrbvx2T0STffCJtr2pW_ncq7K8nL1&index=7 (https://www.youtube.com/watch?v=8ZN4_kwi9gU&list=PLrJmIrbvx2T0STffCJtr2pW_ncq7K8nL1&index=7)
I'll try to document the math and the design choices as I progress on the conception, it might interest people like me who don't have much first hand knowledge but want to understand the underlying logic...
Cheers,
Baptiste
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Also, I began to check bias points and loadlines for the tubes we discussed.
There is something I don't understand on the 6au6 datasheets, such as this one :
https://frank.pocnet.net/sheets/093/6/6AU6A.pdf (https://frank.pocnet.net/sheets/093/6/6AU6A.pdf)
The typical operation values for Class A amplifier are totally off compared to the average plate characteristics figure.
typical operation @Vg2=150V : Ia = 10.6mA, Vg1 = -6.5V
It makes no sense to me, at Ia=10mA, Vg1 should be at -1.0V. -6.5V is not even on the graph...
What did I miss ?
Other question : G3 is not internally connected to the cathode, and the data provided suppose Vg3 = 0V. Does Vg3 have a noticeable impact on the graphs ?
Thanks,
Baptiste
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It sounds to me as if your objective is more "low volume" than it is "low power". I think it is important to make the distinction.
Have you considered going in a little different direction and building a tried and true moderate powered amplifier but using a variable efficiency speaker?
What is a variable efficiency speaker? One that you can modulate the magnetic flux and thus control the efficiency and overall volume output. In basic terms, instead of using a high power rare earth magnet with fixed field, you replace it with an electromagnet that you can control the current through and therefore the magnetic flux. In the old days this was a neccessity as permanent magnets were notoriously weak. They were called feild coil speakers back then.
Fluxtone is selling a modern version of field coils at an outrageous price. Not sure what magic they put in the box but it sure is expensive.
Might be worth playing with a homebrew version?
As for an output pentode... I have been playing with a little SE amp design that so far is pushing all our buttons the right way. It uses the 6AQ5. It can be played at bedroom level with one gain stage for very clean and a second gain stage for a nice distortion. Pick attack is very good and it is very dynamic, has great harmonics and is easy to get along with. It is a little sensitive to speaker selection though.
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You're right, I aim at low volume.
Low power is just the consequence.
I've read about fluxtone speakers before, but they are crazy expensive. What do you mean about a Homebrew version ? It doesn't look like an easy task to convert a regular speaker...
I know 2 models of affordable variable sensitivity speakers : the eminence Maverick and reignmaker. They allow to adjust the magnet position (I think), and the sensitivity ranges from 91 to 100dB. Less range than fluxtone, but not bad. They are around 130€ in Europe.
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> -6.5V is not even on the graph... What did I miss ?
"Grid Voltage for Ib= 10 Microamps"
The Typical grid voltage is about -1. Do the math on Plate+Screen Current and Bias resistor.
If you want to turn the tube OFF, you will need about -6V.
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You're right, I aim at low volume.
Low power is just the consequence.
I've read about fluxtone speakers before, but they are crazy expensive. What do you mean about a Homebrew version ? It doesn't look like an easy task to convert a regular speaker...
I know 2 models of affordable variable sensitivity speakers : the eminence Maverick and reignmaker. They allow to adjust the magnet position (I think), and the sensitivity ranges from 91 to 100dB. Less range than fluxtone, but not bad. They are around 130€ in Europe.
3 options:
1. Find an old piece of gear that used a field coil speaker, salvage the speaker and the coil, and supply a current to the coil as your needs dictate
2. Remove the magnet structure from a speaker and replace it with a coil of wire to which you apply current as needed.
3. Wrap wire around the magnet and use it as a hybrid with the wire coil reducing the power of the magnet by reversing the field.
If you try this experiment, be aware that with a very inefficient speaker, there will be a temptation to turn the volume up and burn up the voice coil winding of the speaker rather than modulating the current in the field coil. You will need to create a safe guard to prevent this.
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"Grid Voltage for Ib= 10 Microamps"
The Typical grid voltage is about -1.
Of course !
I expected the bias voltage, overlooked the current information.
Oh, and I missed the line saying the suppressor grid is connected to the cathode also... It answers my other question I suppose.
This typical point of operation seems quite hot biased, isn't it? Is there a reason for this ? Other tube datasheets I have seen generally provide a neutral bias basis.
3 options:
1. Find an old piece of gear that used a field coil speaker, salvage the speaker and the coil, and supply a current to the coil as your needs dictate
2. Remove the magnet structure from a speaker and replace it with a coil of wire to which you apply current as needed.
3. Wrap wire around the magnet and use it as a hybrid with the wire coil reducing the power of the magnet by reversing the field.
Wow. I'm not ready for options 2 and 3, but I'll have a look at field coil speakers by curiosity.
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> This typical point of operation seems quite hot biased, isn't it?
DataSheets are normally *show-off* conditions. The 6AU6 is a radio IF tube where we need LOTS of gain to pull in weak stations. Except in all normal use, a "normal" station would overload the radio so the AVC system de-biases the IF tubes to a lower gain. How much AVC voltage might you need? Probably at-most roughly that "6.5V" which makes current (and gain) very-very-small compared to the "typical" (idle, no signal) 5mA-10mA condition. (However reducing gain in a tuned-circuit amplifier is very different from reducing gain in an Audio amplifier.) (The -6V might be a reference IF you were building a fixed-bias 6AU6 amplifier, say a push-pull Power amplifier, because that is about the most your bias supply needs to deliver.)
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It sounds to me as if your objective is more "low volume" than it is "low power". I think it is important to make the distinction.
Have you considered going in a little different direction and building a tried and true moderate powered amplifier but using a variable efficiency speaker? ...
Fun for thinking about, but very impractical for a sub-watt (or a "sub-80dB SPL") amp project.
Fluxtone products (https://www.fluxtonespeakers.com/product/model-3/) are extraordinarily expensive. A Fryette Power Station 2 (https://reverb.com/p/fryette-ps-2-power-station-integrated-reactance-amplifier) costs less than half-price. The Universal Audio OX (https://www.sweetwater.com/store/detail/OX--universal-audio-ox-reactive-amp-attenuator-with-speaker-modeling) is similar-price but can be used with any speaker, allows headphone-out, and is a recording/effect solution. The same money buys so much more elsewhere.
And Baptiste already mentioned the Eminence adjustable-magnet speakers (https://www.eminence.com/speakers/speaker-detail/?model=Maverick). Much more cost effective, but you get a 7dB range of adjustment; about the same as reducing amp-power to 1/5 its original value. 70dB SPL from a Maverick on the low-end of its sensitivity requires amp-power of ~5.5 milliwatts.
The end-result of this project may be finding that low-dB is unsatisfying, and requires a headphone output for quiet playing (that's pretty much where I landed). It may turn out that a reactive load is the best low-volume option (and perhaps most cost-effective, though building is usually more fun).
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The end-result of this project may be finding that low-dB is unsatisfying, and requires a headphone output for quiet playing (that's pretty much where I landed). It may turn out that a reactive load is the best low-volume option (and perhaps most cost-effective, though building is usually more fun).
Thanks for the feedback. I'm sure you are objectively right.
The thing is that I'm not used to playing loud, so I'm not convinced I have the same expectations as someone who would.
To rephrase my initial objectives, my goal is not as much to get nighttime full power amp distortion, as it is to make sure the range of usable volume fits as much as possible to my needs. If I built, say a 5W champ, I'd seldom get the opportunity to turn the volume up to any kind of sweet spot.
OTOH, with a 1/4W amp with VVR and attenuator, I should be in the ball park for day use. It's a best effort approach.
At night, well I'll see how it behaves. I can play cleaner, or with preamp only overdrive, or plug a loadbox/cabsim for headphones or to go straight to my hifi.
However, in any case, I need an amp to start with. Well, of course I don't need to built an amp, but I want to. And half of my goal is just to build it ;-)
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OTOH, with a 1/4W amp with VVR and attenuator, I should be in the ball park for day use. It's a best effort approach.
You need to aim higher and attenuate/VVR reduce power to 1/4W or less. If you ever want to play it clean, with the amp louder than your unplugged guitar, then 1/4W isn't enough.
I think you want minimum 1W and reduce from there. That could still be a 5W Champ and you'd be permanently running it at low HT. 6V6 (or EL90 miniature version like I use) will last forever like that.
Choose your output bottle, get yourself a suitable OT (Hammond 125A,B,C little single ended trannies are ideal for playing with a variety of low watt devices) and PT, build a basic pre-amp to drive it and play around from there. Starting with one small pentode and one 12AX7 in a Champ circuit with VVR will give you lots of information to move forward with your project.
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You need to aim higher and attenuate/VVR reduce power to 1/4W or less. If you ever want to play it clean, with the amp louder than your unplugged guitar, then 1/4W isn't enough.
I don't doubt your experience on this, but are you sure about the numbers ? If you take a non MV amp as a reference (such as a champ), it might be true because you quickly get a mix of preamp and power amp overdrive. It doesn't mean you can't get clean from a 1/4W amp with master volume.
Here is my calculation :
1/4W into a 95dB efficiency speaker gives 89dB with full swing at power amp input. Let's say I divide by 2 the input swing to stay clean. It's a 6dB knock off, I end up with 84dB of clean sound, which is a (very) loud acoustic guitar.
I might be wrong with the required input swing at power amp for clean sound, but even if I divide by 4 the voltage input, I get 78dB clean. Enough for me.
Choose your output bottle, get yourself a suitable OT (Hammond 125A,B,C little single ended trannies are ideal for playing with a variety of low watt devices) and PT, build a basic pre-amp to drive it and play around from there. Starting with one small pentode and one 12AX7 in a Champ circuit with VVR will give you lots of information to move forward with your project.
I totally agree with you on this. I'm shortlisting the tube choice right now, once I choose it and the corresponding OT I'll be able to follow this road.
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You need to aim higher and attenuate/VVR reduce power to 1/4W or less. If you ever want to play it clean, with the amp louder than your unplugged guitar, then 1/4W isn't enough.
I don't doubt your experience on this, but are you sure about the numbers ? If you take a non MV amp as a reference (such as a champ), it might be true because you quickly get a mix of preamp and power amp overdrive. It doesn't mean you can't get clean from a 1/4W amp with master volume.
I'm basing it on running PRR's 1/3W amp into my EVM12L (100 dB for 1W/1m). With the volume reduced until PA distortion stopped it was too quiet. I didn't measure power output though, may have been way under 1/3W.
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https://www.ebay.com/itm/6G6G-NOS-vacuum-tube-RCA-Victor/183847129586?hash=item2ace2491f2:g:fTcAAOSwRjxdAsa4 (https://www.ebay.com/itm/6G6G-NOS-vacuum-tube-RCA-Victor/183847129586?hash=item2ace2491f2:g:fTcAAOSwRjxdAsa4)
6AK6 descended from 6G6G.
as you already know, ≈1W with 10K load (hammond 125ASE) with 180V anode and g2 supplies. cool coke bottle octal - same pinout as 6V6. flip a switch makes ≈1/3W in triode mode. no need for VVR.
160-170V to preamps works better.
120V bias/filament PT w/ FWB would work well - ≈170V B+ or for slightly more a hammond 269AX. i'd probably go with the hammond 261C6 paired with a hammond 125ASE.
honestly for this stuff, a line6 pod and headphones...i do that (ducks and runs), even a 1/2W-1W op-amp rig would likely work and sound just as good with a lot less headache and bulk.
happy hacking! :icon_biggrin:
--pete
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happy hacking! :icon_biggrin:
he won't plug in a solder Iron, engineers :think1:
(disclaimer: tongue in my cheek :laugh:)
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OTOH, with a 1/4W amp with VVR and attenuator, I should be in the ball park for day use. It's a best effort approach.
You need to aim higher and attenuate/VVR reduce power to 1/4W or less. If you ever want to play it clean, with the amp louder than your unplugged guitar, then 1/4W isn't enough.
I think you want minimum 1W and reduce from there. That could still be a 5W Champ and you'd be permanently running it at low HT. 6V6 (or EL90 miniature version like I use) will last forever like that.
Choose your output bottle, get yourself a suitable OT (Hammond 125A,B,C little single ended trannies are ideal for playing with a variety of low watt devices) and PT, build a basic pre-amp to drive it and play around from there. Starting with one small pentode and one 12AX7 in a Champ circuit with VVR will give you lots of information to move forward with your project.
Really interested in this thread. I would like to build a Plexi style based around either EL91 or ECL84. Which tube would be closer in tone to an EL34? And does anyone have a schematic based on either of these tubes? Looking for a good 3-5 watt amp in push-pull mode.
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Look at the core series at ax84.com. There's a nice 2 watt pp amp. Plenty of preamps to mate with it or use your own design. Or use Doug's plexi preamp.
https://ax84.com/archive/ax84.com/coreprojects.html
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I’ve not tried ECL84. A pair of EL91’s will do about 4W. Check the data sheets, I think that’s at around 250V with 20K a-a load. I’ve tried lots of different preamp styles with them, currently a 5E3 arrangement.
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Thanks JB and DummyLoad for the feedback and references.
I was leaning towards 6au6, but thanks to JB I'm hesitating with 6AK6/6G6/EL91 on the other side (EL91 is about similar to 6AK6 at the same B+) :icon_biggrin:
So, here is a quick recap.
Option 1 - 6au6
About 0.3-0.4W at 160V B+ with a 20K (10K Hammond ASE with 8Ω speaker on the 4Ω tap) or 25K load (fender reverb tranny)
Pros
- power is close to my theorical needs, minus JB warnings.
- very easy to drive. Could be perfect for a passive effect loop. Might even be used without any preamp section.
- very large range of bias (compared to the other ones). Maybe not useful, but room for experimentation...
- very low current draw. Not very important, but makes VVR or fixed voltage reduction (to get a bit higher B+ for preamp) a non issue in terms of power dissipation.
Option 2 - 6AK6/...
As DummyLoad stated, about 1W at 180V B+ with 10K (Hammond 125ASE)
Pros
- more clean headroom
- more conservative load values => maybe better bass response ?
- higher B+, not much difference though.
Also, looking at the plate characteristics of both tubes, I have a feeling the 6au6 has more distortion than the 6au6.
Basically, I think the choice resumes to clean VS overdrive priorities.
It's probably not a big deal though, I could always change my mind after experimentation.
Also, if I go 6au6, is the 125ASE a good option for 20k load, compared to the reverb tranny ? The reverb tranny is cheaper and the 25k load is fine, but the Hammond is reusable for other tubes if needed...
The power transformer should not be an issue, there is at least one seller in France that makes low cost power transformers with bespoke secondary voltages.
he won't plug in a solder Iron, engineers :think1:
(disclaimer: tongue in my cheek :laugh:)
I will. But I have holidays coming first :icon_biggrin:
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I tried using a reverb transformer early in on low watt experiments. They have limited bandwidth. Go for a Hammond - sounds better, more loading options.
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Okay, I'll do that.
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6au6
built a 3SE outta those, get crunch, finicky, good volume.
But I have holidays coming
what better way to relax than building an amp in the back-country :icon_biggrin:
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... Also, if I go 6au6, is the 125ASE a good option for 20k load, compared to the reverb tranny ? The reverb tranny is cheaper and the 25k load is fine, but the Hammond is reusable for other tubes if needed...
I tried using a reverb transformer early in on low watt experiments. They have limited bandwidth. Go for a Hammond - sounds better, more loading options.
Hoffman's reverb transformer is ~$18, where Mouser's Hammond 125ASE is $46. I thought the reverb trafo sounded great with my 6AU6 1/3 watt build.
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I thought the reverb trafo sounded great with my 6AU6 1/3 watt build.
+1
3tubes got me closer to 2W+ usable audio, 4W squared n screaming :icon_biggrin:
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Ok, first decision made, I'll go for the 6au6. A single one for now ;-)
If you have any recommendations about brands (preferred or to avoid), whether it's important or not... I'm listening.
Thanks for your feedbacks about the OT. It seems there is not really a wrong choice.
lf the Hammond has no other drawback aside from the price, I'll probably go for it for the added flexibility. In Europe it's about 34€, vs 17€ for the reverb one.
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Hi everyone,
I’ve been working a bit on my design.
Here is a first draft of the power section schematic (nothing fancy here), and the power supply (more interesting).
I didn’t know much about power supply design before this exercise, I learned quite a few interesting things in the process.
For those who seek some relevant tutorials about power supply design, here are the few I used :
- http://diyaudioprojects.com/Technical/Tube-Power-Supplies/ (http://diyaudioprojects.com/Technical/Tube-Power-Supplies/)
- http://www.valvewizard.co.uk/smoothing.html (http://www.valvewizard.co.uk/smoothing.html)
- https://dalmura.com.au/static/Hum%20article.pdf (https://dalmura.com.au/static/Hum%20article.pdf)
And I used the PSU designer 2 software from Duncan Amps:
- http://www.duncanamps.com/psud2/ (http://www.duncanamps.com/psud2/)
Design considerations:
- First design based on readily available transformers => 190-200V AC secondary voltage
- 150V DC for power stage
- 200-250V DC for preamp stage (12ax7 in mind)
- VVR for power stage
- Standard values for capacitors
I tried to factorize filtering between power and preamp stages, and to limit the size of the reservoir cap. Pretty easy considering the low current and voltage required for the power section. With the current values, it’s already quite overkill, but 10uF capacitors are cheap.
Ripple voltage is around 3mV for V1, 40mV for V2, 130mV for 6au6 anode, 100mV for G2.
Interesting fact is that it seems I can make a poor man’s VVR with a simple potentiometer, since I have very low power dissipation. It seems too simple to be correct. Did I miss something ?
Other noticeable fact is a heavy coupling between R3 (anode voltage drop resistor) and R8 (cathode bias resistor): due to the important value for R3, a tiny adjustment on current bias has a big effect on the 6au6 voltage.
I will review components values once I’ll be settled on a power transformer.
Any thoughts ?
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Looks like you will expect 14mA to flow through that 50K VR1 pot. The pot will have to dissipate 9.8 watts when set to max resistance. :huh:
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No, the current drops as the voltage drop increases on the pot. At 50k, there would be almost no current. 50k is probably too much btw, maybe 25 would be better, but it depends on the bias...
At 100v reduction through the pot, I would get only 3-4mA.
At 50v, maybe around 8mA.
Power dissipation is under 1W in any case :-)
I found 3W 500V Bourns pots that would seem to be well suited for this.
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> the current drops
Not enough for a low-price pot. The load is 150V at 14mA or like a 10.7k resistor. This will vary some at lower voltage but not a huge amount. Do the math. I figure the 50k extreme may need a $7 pot. But the worst-case is surely at part-turn where only PART of the track is taking the heat. Dart-boarding 13k (makes math easier) gives 0.6 Watts in 1/4 of the track. Conservatively this wants a 2.4 Watt pot. Yes, the mil-type "2W" part will handle it in non-critical duty (where you do not have 20,000 adoring fans to disappoint).
I'm no big fan of crystals in vacuum-state audio, but this does call for a MOSFET. (Heck, I've done it with a TV H-sweep NPN.)
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Let the idiot work the numbers. For these values, pot dissipation peaks at 18k which we could have figured from basic principles. However that heat is released in 18/50 or 0.36 of the pot track. So conservatively a 1/4W pot can take 0.25*0.36= 0.09 Watts. But it is dissipating more like 0.9 Watts in that third-track.
The advantage of the idiot is that it will do this a thousand times and make a plot. When we figure Watts divided by track-in-use, we find the per-area dissipation SOARS as we get toward zero Ohms. I bet at some point in here even a mil-spec pot will go "poof" and the first 1/10th turn is "dead".
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https://www.mouser.com/ProductDetail/CTS-Electronic-Components/026TB32R253B1B1?qs=sGAEpiMZZMtC25l1F4XBU7zZBtuyelZnQyjH9uc03iI%3D (https://www.mouser.com/ProductDetail/CTS-Electronic-Components/026TB32R253B1B1?qs=sGAEpiMZZMtC25l1F4XBU7zZBtuyelZnQyjH9uc03iI%3D)
RV4 (2W) would probably work, but heat up nice: you really need a wirewound pot. the above is a 5W WW, but only available up to 25K - use 27K 3W R in series. the next step up is a 10W rheostat that are available in 50K value, but fairly expensive and difficult to find stock.
--pete
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> 0.6 Watts in 1/4 of the track. Conservatively this wants a 2.4 Watt pot.
Indeed! I completely overlooked the fact that .
Many thanks PRR for the graph.
I searched for info about power dissipation of potentiometers, assuming it must be non linear, given the dissipation surface at disposal when the pot is full open.
https://www.bourns.com/pdfs/OnlinePotentiometerHandbook.pdf (https://www.bourns.com/pdfs/OnlinePotentiometerHandbook.pdf)
On this resource, it states (p44 of the pdf) that for metal-encased pots only, the admissible power dissipation is indeed non linear, and allow to dissipate ~50% of the power rating on 20% of the resistance (2.5 ratio). Asymptote at the beginning of the curve gives a power rating ratio of about 3.
This is not true for plastic encased pots.
If I consider PRR's calculations, with 14mA at 1ohm, it dissipates about 0.2mW versus 0.2 to 0.6 mW allowed for a 25k 5W pot.
So, a pot such as the one DummyLoad proposed should be compatible, but without much power margin. And the 25k max value is a bit limiting (ideally I'd prefer to have ≥35-40k)
Other options :
- Mosfet based VVR => I'll go this way if needed, but I'd rather try the simpler options first.
- Switchable resistance instead of VR1 => I don't need fine tuning of the voltage reduction, so a single switch or a 3/4 position rotary selector would be enough.
I think I will go for a switchable resistance, cheaper, more reliable and not limited to 25k.
I suppose the voltage/current discontinuities when switching the resistor will be handled by the RC filter capacitor.
Do you think of other caveats with this solution ?
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Let the idiot work the numbers
:laugh:
it was a crayon night, but I felt embolden so I used a pencil :icon_biggrin:
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> switchable resistance
Makes sense. How often will 0.33W be spot-on but 0.32W or 0.34W gets you thrown out of the club (bedroom?)? Taking 3dB-4dB steps over a 15dB-20dB range (all a single tube can cover) suggests a 6-way switch which is about $2. (You are over the voltage rating, so buy a spare, and don't switch directly into a capacitor without some series resistance.)
I think you have 'mW' a few places in #57 which should be 'W'.
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https://www.ebay.com/itm/De-Jur-Amsco-Radio-Rheostat-50K-Spec-No-KS-9004-NOS/293468475051?hash=item4454158eab:g:z5kAAOSwYpxeQIOT
--pete
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You are over the voltage rating, so buy a spare
There shouldn't be much over 100V across the selector. Or do you mean the absolute voltage if the (plastic?) selector is grounded ? I could start with putting it after the dropping resistor to lower the absolute voltage at 150v.
don't switch directly into a capacitor without some series resistance.
Could you explain a bit further, I'm not sure to understand ? Is it to limit peak current when switching ? I have the dropping resistor in series with the switch already. Is it enough ?
I think you have 'mW' a few places in #57 which should be 'W'.
No that's what I meant. 14mA across 1 ohm gives 0.2mW, versus 1/25000*5W = 0.2mW theorical power limit. Values are ridiculously low at such resistance values.
(BTW, I can't picture burning a 5w pot with such a low power, even if it's only across 1/25000 of the resistor...)
https://www.ebay.com/itm/De-Jur-Amsco-Radio-Rheostat-50K-Spec-No-KS-9004-NOS/293468475051?hash=item4454158eab:g:z5kAAOSwYpxeQIOT
--pete
Impressive beast ! I won't go that route, but good to know it exists, and at such prices ;-)
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Hi everyone,
Time flies, isn't it ?
I've been quite occupied with other topics these last months, but I found some time to buy the components for my project, and I did the first build. So here is a recap !
So, I made a quick prototype based on the power supply and 6AU6 power section schematics I posted earlier, with a champ 5F1 preamp, to have a simple first working version. I only use 3 knobs : volume, master volume, power scaling. The 3 others are for the future tone stack.
(https://i.imgur.com/ha8gUoN.jpg)
I'm quite happy, it worked straight away, despite the quick and dirty method I used for prototyping. It's a bit buzzy, not a big surprise given how I did not care about lead dress (except for heaters). It's still perfectly usable at low volumes though, and it didn't bother me enough to redo it yet.
PSU and power scaling design
So far I'm very happy about that, the PSU works fine, and the SE 6AU6 seems to be the right power for my needs. I used a 6 position selector for power scaling, which changes the dropping resistor for the power section only (anode and G2).
The range of values I selected give me from 50V to 150V for the 6AU6 anode. At max voltage the 6AU6 provides about 0.4W, and I have enough headroom for my needs. At lowest voltage, It gives around 50mW, perfect for late night practice.
I did not try to get lower in voltage, maybe I could go down to 40V, but I suspect I might be near the reasonable limit, because at 50V I'm already really low on grid bias (-0.55V, versus -1.8V @150V).
Given the very low output power, the dropping resistor handles the power dissipation by itself, and I don't see the need for any voltage regulator.
There is a caveat though with the "dropping resistor power scaling" that I didn't expect: at startup, the dropping resistor is uneffective, because the 6AU6 draws no current while it's still cold. For 10 seconds, the tube sees the full PSU voltage on anode an G2, about 315V (which is much higher than what I expected).
From what I read, over-voltage at startup seems like no big deal for most tubes, but I don't really know for the 6AU6, it's twice the maximum voltage for G2. Anyway, the mighty 6AU6 survived a couple hard starts, and since I have my 6 position selector at hand, I decided to use the first position as a standby switch. This standby only affects the power tube and it works fine.
About the build
At first, I wanted to fully breadboard the amp, with a convenient way to test and change conponents and connections. I searched for ideas, and I found these Chinese spring connectors:
https://a.aliexpress.com/_dTbctRZ (https://a.aliexpress.com/_dTbctRZ)
I first planned to use them flat on a large wooden panel, along with the transformers, tube sockets... I changed my mind, thinking it would be safer and faster to use a real chassis. For the sake of simplicity, I used a small pre-punched chassis from Tube-Town.net. I think it was the right move, it took me maybe 4 hours to fasten everything mechanical (spent some time on a plexiglass support for the knobs), and 2 evenings to prototype and power on.
(https://i.imgur.com/2rvtFMW.jpg)
spring connectors
(https://i.imgur.com/hSiCIeb.jpg)
soldered ground bus
In the end, I'm a bit mitigated with this connectors approach, mostly because I didn't tweak much components values after the build. However, I think it could be useful for people prototyping a lot. Here are my thoughts about it:
Pros:
- allows prototyping without soldering (useful if you want to advance your breadboarding with young kids around...)
- robust connections so far. Didn't have any connection problems.
- same spacing as the turret board I plan to use after.
- dirt cheap. A few bucks for 100 connectors.
- easier to switch components or correct mistakes, or redo everything.
Cons:
- not much faster than soldering. Might even be slower
- wires must be the same size if you want to put several together
- grounding bus needs soldering anyway (it's a PITA to daisy chain small wires with the connectors without soldering)
- larger than an optimized turret board design => hard to fit in a small chassis.
Next
At first I wanted to experiment with various 3 to 4 gain stage preamp topologies and tweak my own resulting schematic. However I have to admit I don't have the time for this, so I'll try to focus on a more straightforward solution.
I'd like to go for a well known and versatile 4 gain stage topology, make a clean build for it, and limit myself to minor tweaks after. I spent some time looking for schematics a few months ago, found quite a few here and elsewhere. I'll make a recap, I'd like to have your advice on these options. If you have any preamp schematic in mind, dont hesitate to share !
Thanks for reading me,
Baptiste