ok then, i will have to make the first stage the input and phase splitter then use capacitive coupling to the second stage still using ccs at cathodes, this way i will have more room to swing voltage, right?
I don't know that you need to go that route- after all, you still have effectively a 500V supply. I think you just need to draw your load line, understand that the tube's positive swings are more important than the negative swings (this IS an AB or B stage, right?), then pick a suitable operating point.
Just on a squinty basis, it looks to me that with a 75k load and effectively a 500V supply, 4mA will give you a plate to cathode voltage of 160-170V or so. It still doesn't look terribly linear... With a 5mA plate CCS and 180V plate to cathode, your upward swing looks a whole lot better. But I'm just talking off the top of my head, you'll want to spend some time with the plate curves, a ruler, and a pencil.
Just on a squinty basis, it looks to me that with a 75k load and effectively a 500V supply, 4mA will give you a plate to cathode voltage of 160-170V or so. It still doesn't look terribly linear... With a 5mA plate CCS and 180V plate to cathode, your upward swing looks a whole lot better. But I'm just talking off the top of my head, you'll want to spend some time with the plate curves, a ruler, and a pencil.
mikey115 said:
i got the stuff i needed from singapore expect 2 EH 6SL7 and 2 octal sockets. can you pick them up next time you visit martin?
now i need to locate some more parts. once i have most if not all parts i intend to start building.
also someone told me that i should start building from input to output. so the 6SL7 will be required before i start. meanwhile there are other parts to obtain. and remember i need 4 or 8 of each.
cogsncogs said:
Hey Wayne, I hope all went as well as it could go at the hospital. When you get some time I have lot os questions....see below...BTW I hope this is not too much.
Ok I understand R24 should be connected to the 4 ohm tap (in my case since i got 4 ohms speakers) and what should i expect if i connect it to the 8 ohm tap? I assume the 8 ohm tap would lower the ammount of feedback and act like some kind of low pass filter for the feedback. Warning: This may be a stupid question 🙂
What other HF compensation components would i require? I assume it would a a RC combition in parallel with R24? or just a cap in series with R24? I intend to use a 5K resistor in series with a multiturn 10K pot for R24. DMM and Scopes are nice but once i am done with that I'd like to tune by ear.
I am not a big believer in measurements except to make sure the ckt does to fry or explode. beyond that the ear is a far more sensitive tool. What say Mikey115? 🙂
Should/Could Q1 and Q2 be the same?
You mention Bias points at R11/12 but where are the bias pots. Should I replace R11 /12 with multi turn pots for bias adjustment?
Should I be measuring current between the bias point and ground? I think I could even meausre voltage across R11/12 and use that for bias right?
My idea is to include a small analog voltmeter into the chassis and the voltmeter would be connected to 4 points (4 way swtich) for the 2 channels. Or i could use 2 voltmeters (one for each channel and use a 3 way switch to switch between 2 bias points and the speaker output or something like that!
What do I use for D1 and D2? Can I use red or green or maybe even dual colour LEDs? if the last is true one can adjust for voltage and let the LED show if the voltage is ok.
All R would be 1W except R10 (0.5W) and R4, R5 (2W) and R24 (3W)?
What are the voltages on the caps? I dont get caps beyond 450VDC locally. so for C1, C3, C4 I would use 450DC ok? Also where is C2? and should all these caps be non polar?
lastly I have to order the power transformer and the guy who makes them would like to know what to make. Should I use R core?
Navin,
Does your OPT have a seprate windings for 4R and 8R taps? If yes then it opens up another very interesting possibility.
Does your OPT have a seprate windings for 4R and 8R taps? If yes then it opens up another very interesting possibility.
corbato said:
I think it just has 4 ohm and 8 ohm taps. I dont think there are seperate windings. I'd have to ask Steven Tay in Singapore and he does not use email!
you are thinking of using the 8 ohm winding for feedback or biwiring the speaker with the tweeter at the 8 ohm winding and the woofer at the 4 ohm winding?
Meanwhile let me know if 6SL7 are available on your side of India. I need 2 along with 2 octal sockets.
BTW since you ahve seen the ckt Wayne posted (6SL7-6SN7) do you think it is capable of accepting KT88 or 6550 tubes as well.
Why not. But for completeness sake, I may consider an additional driver stage after the splitter. You will need to rework the values of some components. I will also split the Rk at the input valve and inject the R24 at the junction. I am off to Auto Expo tomorrow and once back send you a few schematics.
6SL7’s are available, though I will prefer a Pentode at that place. Lately I’ve re-discovered the 6SJ7. This ubiquitous valve is an excellent to alternative to the expensive EF86.
Wayne has, inspite of the personal issues, put up some excellent illustrations so start building NOW!! At the risk of repeating myself, please, as a starter, get a simple 6SL7>6SN7>EL34 plot fired up. All these SS calls for a fair amount of experimentations at the Breadboard. Once you know what to expect, you will be in a better position to tackle the CCS, Delays, Regulations etc, involving SS device and such.
Having said that an LM334Z would be more straightforward choice for the current sink at the tail. National should be happy to send you a few sample if you ask nicely enough using your work email ID. 😎
6SL7’s are available, though I will prefer a Pentode at that place. Lately I’ve re-discovered the 6SJ7. This ubiquitous valve is an excellent to alternative to the expensive EF86.
Wayne has, inspite of the personal issues, put up some excellent illustrations so start building NOW!! At the risk of repeating myself, please, as a starter, get a simple 6SL7>6SN7>EL34 plot fired up. All these SS calls for a fair amount of experimentations at the Breadboard. Once you know what to expect, you will be in a better position to tackle the CCS, Delays, Regulations etc, involving SS device and such.
Having said that an LM334Z would be more straightforward choice for the current sink at the tail. National should be happy to send you a few sample if you ask nicely enough using your work email ID. 😎
corbato said:
Gee thanks. One more stage. Why? do we need so much more gain? BTW anty advantages a pentode has ove a triode given todays high level sources and a 50K volume pot?
1. I dont have the 6SL7 yet. I have to get them. So I await these tubes. At this stage all I have are the 2 6922 (for the crossover) the 4 6SN7 and the 8 EL34 so I am willing to consider any other tube at the input. However I hate to see so much of Wayne's work go to waste. He has also posted a ckt using another input tube (I forget which). He has done a fantastic job. So I am inclined to follow his advice and schematics blindly. Wayne has so much knowledge that my fear is that if I start thinking I will screw up somewhere. Better to build his ckt like I was building a kit.
2. I thought one needs to have such things such as the rectification and CCS and power transformer to start building. I was hoping to build one stage at a time and check voltages and current before building subsequent stages.
3. All I can build right now is the Steve Bench Crossover but I was wondering if this tube could not be inorporated into the power amps themselves and have a purely passive control amp. Just wondering mind you!
Till I get the input tube I have time to consider options.
This is my first tube amp build. I have built some SS stuff though (EQs, Power amps, Pre amps, Metal Detectors, Radio Remote controls etc..). I realise I have to be very careful of the high DC voltages - that is one issue I have not dealt with before.
The object here is to build a tube amp that suits the speakers and room. As stated before I am doing research while collecting parts and as soon as I have enough parts to start building atleast the input stage I will start. It might lead to more stupid questions though.
These days, a pentode input stage offers no real advantage and the definite disadvantage of higher noise.
SY said:
this is what i was told but wanted someone smarter to post. 🙂 I dont know enough about tubes (I dont know jack about tubes) to defend this argument either.
poobah said:
Because you don't need better than 2V sensitivity to match today's signal sources and because pentodes have partition noise that triodes don't.
SY?????????
Nah, that one was too easy.
In the few situations where very high sensitivity is needed, a cascode can give similar gain to a pentode, but without the partition noise.
In the few situations where very high sensitivity is needed, a cascode can give similar gain to a pentode, but without the partition noise.
SY,
How did you learn so much about tubes? I hear stories about your age... you have a 5 year old son... you can't be be more than 105 years old. Explain please... again if need be.
How did you learn so much about tubes? I hear stories about your age... you have a 5 year old son... you can't be be more than 105 years old. Explain please... again if need be.
SY said:
2V is ok for CD but what about stuff like the ipod. I assume this was 1V? Still a triode input is adequate right?
SY, I assume by your silence that you find Wayne's 6SL7-6SN7-EL34 schematic to be ok. I have a few questions to be answered while I await my 6SL7 and Wayne's answers. I am in NO hurry.
see post 262 for the schematic
http://www.diyaudio.com/forums/showthread.php?s=&threadid=69042&perpage=10&pagenumber=27
and post 284 for the questions.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=69042&perpage=10&pagenumber=29
Pentodes vs Triodes
Pentodes vs Triodes
Yes start with SB XO. Remember, tube amp building calls for special techniques. You can only learn as much by reading or being told. You need to get hands on experience to figure out all those tricks. I will be suspired if your first shot amp comes out smelling like a rose. No intention to discourage you, but I recon you need 2 years of hand on exposure to build something top-notch. So start gaining that experience NOW!
You can safely replace the 6SL7 with 12AX7 till the time the former reach you. Sufficient to get you breadboarding.
More of a personal choice actually. My main source is Vinyl and the extra gain doesn’t hurt. Plus Mr. Miller is not that daunting here 😉
Last couple of years I have been experimenting with Triodes and Pentodes. I have tried all possible combinations and found triodes are best if loaded with a MOSFET a la kimmel style. To me a Pentode input stage sounded more natural and airy compared to a, say SRPP stage. As I said it is IMHO and YMMV. Right now I am fiddling with triode strapped 6SJ7’s for my WIP 300B amp. That should take care of some of your anxieties such as partition noise and high sensitivity 🙂
Pentodes vs Triodes
You wouldn’t be getting correct readings unless all the bulbs are fired up.
Yes start with SB XO. Remember, tube amp building calls for special techniques. You can only learn as much by reading or being told. You need to get hands on experience to figure out all those tricks. I will be suspired if your first shot amp comes out smelling like a rose. No intention to discourage you, but I recon you need 2 years of hand on exposure to build something top-notch. So start gaining that experience NOW!
You can safely replace the 6SL7 with 12AX7 till the time the former reach you. Sufficient to get you breadboarding.
More of a personal choice actually. My main source is Vinyl and the extra gain doesn’t hurt. Plus Mr. Miller is not that daunting here 😉
Last couple of years I have been experimenting with Triodes and Pentodes. I have tried all possible combinations and found triodes are best if loaded with a MOSFET a la kimmel style. To me a Pentode input stage sounded more natural and airy compared to a, say SRPP stage. As I said it is IMHO and YMMV. Right now I am fiddling with triode strapped 6SJ7’s for my WIP 300B amp. That should take care of some of your anxieties such as partition noise and high sensitivity 🙂
If I had to cascode, I would use a Pentode as the top guy.
Considering your elaborate scheme this could turn out the understating of the year. You better hurry up. Unless you are thinking of this as a post retirement blues remedy
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