Re: Pentodes vs Triodes
thanks so much! 🙂 for your vote of confidence! LOL
So I have to get all tubes fired! I figured that.
I would have to change quite a few components to fit a ECC83 instead of a 6SL7 and I am not competent enough to know this. I was hoping to depend on a ready schematic like the one Wayne posted.
Retire me? Never!
corbato said:
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 safely replace the 6SL7 with 12AX7 till the time the former reach you. Sufficient to get you breadboarding.
I have tried all possible combinations and found triodes are best if loaded with a MOSFET a la kimmel style.
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
thanks so much! 🙂 for your vote of confidence! LOL
So I have to get all tubes fired! I figured that.
I would have to change quite a few components to fit a ECC83 instead of a 6SL7 and I am not competent enough to know this. I was hoping to depend on a ready schematic like the one Wayne posted.
Retire me? Never!
Tony said:
Barely. I'm 51.
@navin: Wayne's circuit is very much like my HF87 so I would have a hard time criticizing!
@navin
You have my full vote! Just the way Laloo Yadav has my fullest confidence 😉
Reg 6SL7 to 12ax7, the only thing that needs change is the valve base/ Octal in this case.
You have my full vote! Just the way Laloo Yadav has my fullest confidence 😉
Reg 6SL7 to 12ax7, the only thing that needs change is the valve base/ Octal in this case.
Hi all,
been off the grid for almost a week, but had the time to collect some of the parts I need. so who's building a version now?
navin, how's your amp going?
been off the grid for almost a week, but had the time to collect some of the parts I need. so who's building a version now?
navin, how's your amp going?
SY not to come down on you... 🙂 but what about those CD's that never hit 0dB FS (-6 to -5dB FS) and there are quite a few of them esp. those made back in the 80's? And the computer sound card output(s) esp. digital output, as mine is, as in playing mp3's where mp3gain was applied? Not to mention cassette decks (390mV-550mV), Reel to Reel decks (680mV, most Teac consumer decks, 775mV-1V standard level as in some AKAI's etc), VHS Hi-Fi (varies greatly), RIAA pre-amplifiers just to mention a few? Not everyone listens to 0dB-FS CD's.
And in my amplifier which has a 775mV input sensitivity and uses a 6U8A/6KD8/6F2 pentode/triode (pentode section as 1st stage) I can't hear any noise or hum unless I stick my ear IN the speaker, dead quiet
. So I don't think partition noise would be an issue unless you were using 98-100dB/1WM or greater spkrs. And I believe a lot of modern amplifiers were made with 775mV to 1V input sensitivity. IMO 2V is a little on the high side.Cheers Everyone
Wayne :=B
That's a pretty small minority of systems out there; for those who need it, sure, a 6dB gain in the preamp could be a good thing. I'm cringing at the idea of hooking up a VHS HiFi to my sound system... Fortunately, the DVD, DVR, computer sound card, CD player, and satellite box chez nous (nothing exotic) conform to modern output level standards.
There are indeed badly engineered RIAA stages that do not put out the same level as the vast majority of modern signal sources. The solution, in my mind, it to correct the mistakes or appropriately update at the source. Others may reasonably differ in their approach.
You have a point here and this is one where bad engineering cannot be corrected by the user. But even the worst CDs have a peak level better than -6dB. I can live with that in exchange for knowing that I will not be clipping my amp, but YMMV. This is a reasonable argument for having a few dB of gain in a line amp.
Back in the early days of CD mastering, level meters that showed 0dB were really showing -5db for fear of clipping, which is very nasty, unlike clipping in magnetic tape recording. I have dozens of CD's that never reach 0db, not taking into account average level. I have a very modern sound card which has a digital out. And to prevent clipping in an mp3 and/or to try and keep your collection of mp3 files consistent in (RMS or apparent) level you apply what's called mp3gain, which is a lossless process unlike normalizing. Most use the default level of -89db, 100db being full scale.
And now for VHS Hi-Fi 'cringe'. Using a very good player (not the ones you find at Wal-Mart) and using a tape that was mastered properly, even one that you may have recorded on a very good deck that was aligned properly, head switching noise will be almost absent or very low in level. This was and is the main drawback of VHS Hi-Fi. For those of you who have no idea what I'm talking about, it's a buzzing sound esp. during a quiet passage like during a soft solo, and very noticeable during applause. It does have the potential for good reproduction but for the head switching noise which as it seems they were never really able to hammer out. And to top it all off this is the same technology that was used to design DAT. A miniature VHS Hi-Fi mech. And in most early DAT recorders, 0db record level was really -5db FS.
In most commercial VHS Hi-Fi tapes the audio track was way over-modulated (FM) to begin with and mastered at something X real time as was/is the habit of the recording industry to produce as many copies as quickly and economicly as possible.
And as is this going off-topic and hi-jacking navin's thread somewhat, I apologize.
But what all of this boils down to is what the builder has for input sources that will determine the needed input sensitivity. 😉
Wayne
And now for VHS Hi-Fi 'cringe'. Using a very good player (not the ones you find at Wal-Mart) and using a tape that was mastered properly, even one that you may have recorded on a very good deck that was aligned properly, head switching noise will be almost absent or very low in level. This was and is the main drawback of VHS Hi-Fi. For those of you who have no idea what I'm talking about, it's a buzzing sound esp. during a quiet passage like during a soft solo, and very noticeable during applause. It does have the potential for good reproduction but for the head switching noise which as it seems they were never really able to hammer out.
And to top it all off this is the same technology that was used to design DAT. A miniature VHS Hi-Fi mech. And in most early DAT recorders, 0db record level was really -5db FS.In most commercial VHS Hi-Fi tapes the audio track was way over-modulated (FM) to begin with and mastered at something X real time as was/is the habit of the recording industry to produce as many copies as quickly and economicly as possible.
And as is this going off-topic and hi-jacking navin's thread somewhat, I apologize.
But what all of this boils down to is what the builder has for input sources that will determine the needed input sensitivity. 😉
Wayne
corbato said:
very funny.
for those who dont live in India Laloo Yadav is a self appointed muscle-man cow-herd of the state Corbato lives in. He was the Chief Minister (similar to a Govener in the US) and when found to be corrupt appointed his wife to be the CM while he cooled his heel in jail. He is a media favourite because of his rustis sound bytes.
JojoD818 said:
Still Collecting parts! and wondering about stuff like CCS, Rectification etc...
cogsncogs said:
I used to use a PCM encoder/decoder with a VHS player for parties. Mix 4 hours of music on a VHS tape via PCM and enjoy. Today I use my ipod.
Tony said:
No I dont have the PSU yet. I am looking for a schematic I can use but I prefer SS. It is a space I am familiar with.
navin said:
Same here, I just completed my tubes including a quad of Svet EL34. The tranny I have has a secondary of 360-0-360 @500mA with taps at 340 and 350. It was originally intended for an ST70 clone project but got scrubbed to give way for another project. However this time I would like to take it slow and collect as much ideas as I can before I start building the amp.
I plan to use ss rectifiers as shown in my psu schematic. Since my first amp already uses tube rectification, I might as well make this one ss rectified. 😀
My only concern now with using ss rectifiers is how to soft-start the B+, I'm researching how to use an scr to control and ramp the B+ as the tubes are warming up.
Any ideas are very much welcome.
Regarding soft-start, I recall seeing the use of a thermistor some time ago, either on this site or in some article or other. Just off-the-cuff I cannot see a problem with that, and it is quite simple (the correct type, of course, following directly after the rectifier).
Anybody with experience of that?
Anybody with experience of that?
soft start thermistors are used on pc power supplies, you can string maybe 3 or 4 of them in series since they are low resistance.
i worry more about time delay on the B+ when using ss rects on power amps, they are a must imho.
i worry more about time delay on the B+ when using ss rects on power amps, they are a must imho.
Johan Potgieter said:
I use them, they work fine, but normally I put them on the primary side. For an EL34-type amp, a value of 100 ohms cold is a good choice- when hot, the resistance drops below 5 ohms.
Thanks SY.
I am encouraged by your comments. I have mentioned that I have completed a 2 x 100W job where I delay h.t. on by 18 S to give tubes time to get conducting , to avoid a 900+V surge. But then large pulses occur by the feedback ciruit sorting itself out with turn-on of the h.t., and I don't like (further delayed) relays in series with loudspeakers. (Some short output tube G1s momentarily).
Thermistor in series with the primary: That would also delay the warming up of the tubes, but will have the benefit of eliminating "heater-shock" - I will think about that.
Sorry to be somewhat off-thread.
I am encouraged by your comments. I have mentioned that I have completed a 2 x 100W job where I delay h.t. on by 18 S to give tubes time to get conducting , to avoid a 900+V surge. But then large pulses occur by the feedback ciruit sorting itself out with turn-on of the h.t., and I don't like (further delayed) relays in series with loudspeakers. (Some short output tube G1s momentarily).
Thermistor in series with the primary: That would also delay the warming up of the tubes, but will have the benefit of eliminating "heater-shock" - I will think about that.
Sorry to be somewhat off-thread.
Another solution for slow turn-on?
Found some circuits in the net which uses a high resistance, say 15K-20K inserted after the ss diodes and then shorted out after 10-15 seconds by relay contacts.
With this setup, the resistor would slowly charge the caps before being shorted by the relay contacts, the question is - would this still cause sparks/arcing and eventually pit my relay contacts?
I can parallel a small cap across the relay contacts for further protection against sparks.
Found some circuits in the net which uses a high resistance, say 15K-20K inserted after the ss diodes and then shorted out after 10-15 seconds by relay contacts.
With this setup, the resistor would slowly charge the caps before being shorted by the relay contacts, the question is - would this still cause sparks/arcing and eventually pit my relay contacts?
I can parallel a small cap across the relay contacts for further protection against sparks.
JojoD818 said:
wont you need a 6.3V from the power tranny too? do you have a shcemtaic of your existing PS?
Johan Potgieter said:
how do you achieve this delay? do you use a timer?
JojoD818 said:
maybe a MOV can help too.
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