| Sjef |
Does anyone have any experience with the Sovtek 6C45pi-E tube.
I'm intending to use them in my transformer coupled preamp instead of the Raytheon 5842A and was wondering if anyone had a good advice about the bias operating point.
They wil be used with the existing power supply wich means that, depending on the current drawn, there wil be something btween 160 and 170V on the anode of the tube. The interstage transformer is a 4200/300 Ohm type rated at 30mA DC current. |
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| Sch3mat1c |
All I know (if I remember right) is that their data looks like either both halves of a 6080 in parallel (less dissipation), or a 6336's triode.
If you don't mind even more tubes than a 6AS7-based OTL, it's a good candidate.
Hmm, 4200 ohms sounds a bit high for it, and 300 ohms sounds a bit low.. I guess you're going for distortion or voltage, not power output, eh? :) (Unless that's the existing tranny and you just wanna reuse it, in which case the low Rp should swamp resonances and such very well. :cool: )
Tim |
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| fdegrove |
Hi,
Tim,I think you're confiding the 45 with the 41.
The 6C45PI is a driver tube while the 6C41 is a regulator.
For inspiration:
PAENG
Cheers,;) |
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| Colt45 |
yeah, youre thinking of 6S41S tim :-)
6S45P-E (some people like to muck up the translation from cyr. to latin, and use latin mixed with made up stuff like "pi" damn that irks me.)
its a little 9pin triode, Pa = ~8w IIRC.
its supposed to be pretty close to one of the old WE tubes.. (437A i think? memory is dead here, and im too lazy to look at data of the WE ones..)
http://www.mif.pg.gda.pl/homepages/...12/6/6S45PE.pdf |
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| fdegrove |
Hi,
| quote: | | (437A i think? memory is dead here, and im too lazy to look at data of the WE ones..) |
Your memory is O.K.
Cheers,;) |
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| fdegrove |
Hi,
And of course a pic of them both:
Ciao,;) |
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| Sch3mat1c |
Oh yea...thx Colt :cool:
BTW he's the one who keeps talking about buying some on ICQ ;) if it weren't for him I would've never posted and confused anyone :p
Tim |
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| EC8010 |
| 6C45P is a stunningly linear valve. It wants >10mA of anode current before it wakes up properly, but can operate with quite low anode voltages (100V). There does tend to be a bit of grid current, so you have to be careful if you take liberties with the (150k max.) grid leak resistor. Because Cag is so high, you can't really use it as a gain stage unless you drive it with a cathode follower (or a moving coil cartridge) unless you don't care/can't measure the HF response. It makes a superb cathode follower, but you need a >100MHz oscilloscope handy to find and tame the oscillation. |
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| fdegrove |
Hi,
If the datasheets I found are in any way reliable this is also a very low noise valve.
Req 100 Ohm??.
| quote: | | (or a moving coil cartridge) |
EC8010,you wouldn't be using a MC headamp with valves as I do?
If so I'd be very interested to share scheamtics etc.:cool:
Cheers,;) |
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| Colt45 |
| Here's a graph I just pulled out of a russian datasheet |
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| Gunderz |
why is the input resistance so low for this tube?
3,5 kohm@60MHz
And I see a slight problem with the anodevoltages you espect to have in your circuit, max anodevoltage for the 6C45 is 150V.
I have to admit that I'm planning to use them in one of my amplifiers, and I have bought a couple of them, but I havn't tried them out yet.
But what's it like to use 6C45 as the front end in an amplifier?
somebody said something about the need for a cathode follower to drive this tube because of the high input capacitance. |
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| fdegrove |
Hi,
| quote: | | somebody said something about the need for a cathode follower to drive this tube because of the high input capacitance. |
Either a cathode follower or an interstage transformer would do.
Cheer,;) |
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| EC8010 |
The 6C45 should be low noise because if its high gm (it only just meets the lower limit of its specification, though). I haven't used it in a low-noise amplifier. It should be ideal for medium output (0.5mV) moving coil cartridges.
All valves have low input resistance at HF because of frequency dependent losses in the micas, the glass, and various inductances and capacitances. We are not operating at 60MHz, so we can ignore this problem.
Cag is claimed to be 5pF, and mu actually is 52. A typical gain stage would be likely to have a gain of 45, so we could expect 240pF input capacitance. Most transformers or gain stages don't like that sort of load, hence my comments about usage. |
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| fdegrove |
Hi,
I know I can be a PITA but still....
| quote: | | EC8010,you wouldn't be using a MC headamp with valves as I do? |
You haven't tried anything along these lines,have you?
Cheers,;) |
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| Gunderz |
Well, I'm just going to ask some rather odd questions.
But I Became a bit worried about the input capacitance when fdegrove said that this tube need a buffer-stage.
Actuall my plans was to use 6C45 as the first tube in an amplifier, the signal comes from a source through a pot and is den fed to the grid. But is this "impossible" because of the input capacitance?
I have attached a schematic of a circuit with a bufferstage, but the pot is placed between the buffer and the 6C45, but will this circuit still be an good alternative if the resistance of the pot is kept low?
In my circuit om going to use current feedback, and the gain will only be about 15-25. Will the current feedback provide some kind of compensation for the high input capacitance? |
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| EC8010 |
No, I haven't tried it as an MC input stage. Sorry, Frank.
If we assume a gain of 20, then the input capacitance will be of the order of 120pF, in which case the highest value volume control I would want to use would be 25k. |
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| Gunderz |
| I'm going to use an 10k pot |
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| EC8010 |
| quote: | Originally posted by Gunderz
I'm going to use an 10k pot |
Fine. No problem. Don't forget to use a 2k2 grid-stopper resistor, or it may oscillate. |
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| Gunderz |
Fine??
Is it Ok with a 10k pot if I use a bufferstage?
What if I dropped the bufferstage?
Will it still be fine? |
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| fdegrove |
Hi,
| quote: | | No, I haven't tried it as an MC input stage. Sorry, Frank. |
No problem,it's just that it looks a good candidate on paper,i.e. a current amp as opposed to a voltage amp.
I'll stick to my // E188CCs for a while longer.;)
| quote: | | Don't forget to use a 2k2 grid-stopper resistor, or it may oscillate. |
The best suited value should be determined on the O-scope,I think.
Cheers,;) |
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| fdegrove |
Hi,
| quote: | | What if I dropped the bufferstage? |
No,this tube needs to be current driven.;)
Ciao,:cool: |
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| Gunderz |
How can i determine the gridstopper on the scope?
What about small ferrites near the tubesocket?? |
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| fdegrove |
Hi,
You'll have to do some experimenting here,no hard rule for that.
| quote: | | What about small ferrites near the tubesocket?? |
That won't help the tube.
Cheers,;) |
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| Gunderz |
| I meant a ferrite in series with the signal, after the gridstopper or something, but as close to the tubesocket as possible |
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| EC8010 |
| quote: | Originally posted by Gunderz
Fine??
Is it Ok with a 10k pot if I use a bufferstage?
What if I dropped the bufferstage?
Will it still be fine? |
Where would the buffer stage be? I don't understand your question. |
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| Gunderz |
Have you seen the schematic I attached??
I think it's a bit odd because the buffer is located before the volumecontrol, so the buffer doesn't provide a signal directly to the 6C45 grid, but it provide a signal through a potmeter and then to the 6C45.
fdegrove said the buffer is needed, but do you think I can drop it?
Will a CD-player be avaiable to drive the high input capacitance? |
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| Sjef |
I don't understand the given value for the input capacitance of the 6C45. (I've read 120pf or even 240pF here) Can anyone explain ?
According to the datasheet this input C is about 12 pF, just a little bit higher than the 5842 (9pF) wich I'm jusing right now with a 100K potmeter. I'm not interested in rebuilding the preamp into a two driver stage.
maximum anode voltage rating of the tube is according to the datasheet indeed 150V but the tube seems to work properly with voltages up to 180 or even 200V |
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| 316a |
Hi folks ,
While we're on the subject of 6C45 , would this valve be suitable for use in a cascode ? I've often though about a differential cascode using the things
316a |
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| Gunderz |
Sjef you are right the Cga is about 11pF, but we have the Miller effect which increases the input capacitance according to the amplification. So actually the input capacitance is dependend on the amplification.
I don't know the exact Miller formula, but I this one will be an good approximation:
Cin=Cag(G+1)+Cgk
//eeehh, something is wrong with this formula, EC8010 calculated the input capacitance to be 120pF with 20* gain.
Maybe EC8010 will give you the right formula.
with a gain of 20 you will have a input capacitance of:
Cin=11pF*21=231pF
and the input capacitance would be even higher for higher amplification.
Sorry for my english, but I hope you understand anyway :) |
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| Gunderz |
If you use a tube in a cascode configuration the Millereffect will no longer exist and the actual input capacitance will be ~11pF.
But I don't know if 6C45 is a good tube for cascode configuration.
In fact the author behind TubeCAD once said that the only tube good for cascode is the ECC88.
316a... wouldn't it be difficult to use a cascode configuration in a differential amplifier?
What about stability? |
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| EC8010 |
| quote: | Originally posted by Gunderz
fdegrove said the buffer is needed, but do you think I can drop it?
Will a CD-player be avaiable to drive the high input capacitance? |
I've gone back to your diagram. Any CD player should be perfectly capable of driving a 10k volume control, so I don't see why you shouldn't be able to drop the buffer. No doubt Frank will say why he felt you ought to keep it.| quote: | Originally posted by Gunderz
Cin=Cag(G+1)+Cgk
//eeehh, something is wrong with this formula, EC8010 calculated the input capacitance to be 120pF with 20* gain.
Maybe EC8010 will give you the right formula.
with a gain of 20 you will have a input capacitance of:
Cin=11pF*21=231pF
and the input capacitance would be even higher for higher amplification. |
The formula is correct, but where did the 11 come from? My data sheet says Cag = 5pF, hence 120pF (OK, strictly 125pF + 11pF = 136pF, but the gain was given as between 15 and 25).
6C45 ought to make an ideal cascode, but you would definitely need a good oscilloscope standing by to hunt down and kill any oscillation.
I am also surprised by the stated 150V Va(max.). I have heard rumours relating to accelerations experienced by fighter aircraft as "explanations" for this figure, but does anyone have any hard facts? Given that mu is proportional to the ratio of anode/grid to grid/cathode spacing, higher mu valves should be able to withstand a higher anode voltage. As a reverse example, the PD500 has Va(max.) = 25kV and mu = 1050. This is a log-winded way of saying that I think it should be safe to consider Va(max.) = 250V. |
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| 316a |
...well I had no problems running 6SN7 in differential cascode , apart from the fact I did not have enough gain and needed more HT . Allen Wright uses uses differential cascodes in his PP1C amp and various others . The ECC88 is the preferred cascode valve as it has high H-K ratings , also low Ra . With 6C45 the H-k ratings won't matter as separate triodes are used therefore a floating heater supply would be used for the top pair , Ra is also lower with 6C45 than with ECC88 . It might work , then again could end up as an oscillator . Thoughts anyone ?
316a |
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| fdegrove |
Hi,
| quote: | | No doubt Frank will say why he felt you ought to keep it. |
Unfortunately I was wrongly assuming that the figure you had given before was the actual Cag.
So after some quick calcs I obviously came to the conclusion that this valve was very hard to drive without a grunty (CF) stage preceding it.
Sorry to lead anyone astray with this and to make up for it here a link to some circuit theories:
PAENG
Hope this helps,;) |
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| fdegrove |
Hi,
| quote: | | It might work , then again could end up as an oscillator |
This is what I'm afraid of.
But give it a try if you have them,if it doesn't work you can still recycle them for some other project.
Cheers,;) |
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| Gunderz |
10k volume control without buffer??
I think it will be a bit problematic, the input resistance will then be about 10k, but many CD-players will have problems driving low impedances.
The instructions manual for my CD-player says that the loadresistance should be higher than 47k, so what is it like to drive my CD-player with a 10k pot?
Well, my CD-player isn't very expensive, it's a Sony CDP-XB920 or something like that, can't remember the exact number.
Ok, my formula was correct then, but I took the wrong numbers... Thanks anyway |
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| Gunderz |
| quote: | Originally posted by 316a
...well I had no problems running 6SN7 in differential cascode , apart from the fact I did not have enough gain and needed more HT . |
Okay, I have never tried differential cascode, have only tried the "normal" one with ECC88. |
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| fdegrove |
Hi,
| quote: | | 10k volume control without buffer?? |
What makes you think you have to stick with that value?
IMO a 100K pot would much better here.
Cheers,;) |
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| EC8010 |
| quote: | Originally posted by fdegrove
PAENG |
Wow! Thanks Frank. My printer is now busy...
| quote: | Originally posted by Gunderz
10k volume control without buffer??
I think it will be a bit problematic, the input resistance will then be about 10k, but many CD-players will have problems driving low impedances.
The instructions manual for my CD-player says that the loadresistance should be higher than 47k, so what is it like to drive my CD-player with a 10k pot?
Well, my CD-player isn't very expensive, it's a Sony CDP-XB920 or something like that, can't remember the exact number.
Ok, my formula was correct then, but I took the wrong numbers... Thanks anyway |
Most CD players use an op-amp at their output. Although distortion rises for loads below 2k, most op-amps are quite happy with 10k loads. It may be that there is some passive circuitry that causes the 47k specification. Unfortunately, if you use a 47k volume control, the output resistance will form a low-pass filter in conjunction with the input capacitance of the 6C45. You could always put the volume control before the buffer, as a cathode follower has very low input capacitance, and you could even use a 1M volume control if you wished... |
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| Gunderz |
Eeehh, I'm a bit confused....
EC8010 said that he would use a 25k pot or less for my configuration(gain= 20). Then I said I'm planning to use a 10k pot if you used the schematic I attached.
Then EC8010 said it was okay, but then I hear that I don't need the buffer because of some misunderstanding.
So now is it a problem to use a 10k pot because of the driving capabilities of my CD-player(and many others). |
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| fdegrove |
Hi,
Instead of complicating the amp with this,wouldn't it be easier to build a proper line amp?
Just a suggestion, ;) |
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| Gunderz |
That may be an idea. But I don't think it's a very good one, my power amp will then be a bit depend of the line amp.
But...thanks for the help |
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| fdegrove |
Hi,
| quote: | | my power amp will then be a bit depend of the line amp. |
How so?
What you could too is put the volume controle in front of the CF and up its' value to say 50K.
Cheers,;) |
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| EC8010 |
| This thread seems to have evolved into a discussion of how to solve the problems posed by using a 6C45 as the input valve of a power amplifier. Is there a particular reason that you have chosen this valve rather than any other? Do you want to share the whole power amplifier diagram? |
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| Gunderz |
Well, I have heard a lot of good words about 6C45 and I wanted to try them, so I bought a couple.
But I haven't tried them yet.
Other tubes? I have 6922, ECC82, 6H30.
Sorry, but I haven't got the whole schematic in a proper format to publish here, just on paper.
And the current design is just preliminary, a lot of changes have to be done during the experimenting.
In fact I haven't tried none of my current drawings for this amplifier.
But the design I have now use 6C45 as the input tube, 12BH7 is used as a differentialpair phase splitter and KT88 is used as output tubes(ultra-linear). |
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| Sch3mat1c |
Heh.
If you're so concerned about input capacitance, grab a pentode and exchange the excess gain for NFB later.
Tim |
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| EC8010 |
| quote: | Originally posted by Gunderz
Well, I have heard a lot of good words about 6C45 and I wanted to try them, so I bought a couple.
But I haven't tried them yet.
Other tubes? I have 6922, ECC82, 6H30.
|
6C45 is indeed a very nice valve, but not ideal as the input valve of a power amplifier. 7N7 would be ideal.
Your 6C45's could be used in a cathode follower line stage (following a 100k volume control). |
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| Bas Horneman |
Hi, What does make the 7n7 an ideal tube as the input tube for a power amplifier?
Is it not a 6SN7 in a loctal Jacket?
Regards,
Bas |
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| EC8010 |
| quote: | Originally posted by Bas Horneman
Hi, What does make the 7n7 an ideal tube as the input tube for a power amplifier?
Is it not a 6SN7 in a loctal Jacket?
Regards,
Bas |
Bas,
indeed it is. But 6SN7s are becoming very expensive. 7N7 has good linearity, manageable Miller capacitance, and isn't too hungry on HT current. |
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| Bas Horneman |
| Mmm, I still have a couple of 7N7 that I bought from Fatbottle!! And some nice teflon loctal sockets...also priced very well...Looks like my Blue sky 813 is going to use the 7n7 after all...maybe something like 7n7 cap coupled to 6c45pi transformer coupled to 813. |
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| EC8010 |
| quote: | Originally posted by Bas Horneman
Looks like my Blue sky 813 is going to use the 7n7 after all...maybe something like 7n7 cap coupled to 6c45pi transformer coupled to 813. |
You might need a bit of a step-up (1:1.5?) to drive the 813. I think it will take a fair bit of juggling to marry 6C45 to 813. Alternatively, were you intending to use the 6C45 as a transformer coupled cathode follower? That might work rather nicely. |
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| 316a |
Hi Bas ,
Sorry to confuse the thread . A possibly good candidate for driving an 813 would be the 6EM7 or it's cheap series string equivalents , 10EM7 , 13EM7 and 15EM7 . This has a high mu (66) and low mu (5-6) 750r Ra beefy section all in one bottle . This may possibly make a very simple way of driving an 813 is the sections are cascaded . As for Fatbottle , well....rumour has it he's hanging around this forum now .
316a |
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| Bas Horneman |
Fatbottle is that you? ;-)
The 6EM7 looks like a real good candidate..I believe Vinnie at the AA has posted something like that has he not?
O well it it still such a long time away... that 813..Who knows I might run into a couple of those tubes you mentioned.
I'll stop hi-jacking this guy's thread..I was just curious why the 7N7 was an ideal tube. You know how us amateurs are like when some tube is touted as ideal or good..price of the 7n7 has probably gone up $1 as we speak..
Cheers,
Bas |
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| 7N7 |
| quote: | Originally posted by 316a
Hi Bas ,
Sorry to confuse the thread . A possibly good candidate for driving an 813 would be the 6EM7 or it's cheap series string equivalents , 10EM7 , 13EM7 and 15EM7 . This has a high mu (66) and low mu (5-6) 750r Ra beefy section all in one bottle . This may possibly make a very simple way of driving an 813 is the sections are cascaded . As for Fatbottle , well....rumour has it he's hanging around this forum now .
316a |
If you are going to drive your 813s directly from a CD player, whilst the *EM7 series would work well, you might have too much gain.
316A is on to a good thing with these dissimilar triodes. I have tested certain types for distortion and early indications are that they look good.
You could look for example at 6EW7/10EW7/15EW7. These offer a gain of 20 from one section and 6 from the low ra section. You could easily drive an 813 very nicely from the anode of this beefy section. With simple resistance loading, the two stages would give you A of about 70, which would be just about perfect for driving 813s from a CD player, assuming that you are running the 813s at my favoured spot: 850V and 100mA = c. -75V bias.
7N7 |
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| 316a |
...they've heard of the 7N7 in Hong Kong . I sold 50 loctal sockets to a Chinese lady there who was using 7N7 in a commercial amplifier . I only asked her what she was using them for as for a split second I could nearly smell 3a/167m . Soon over there 7N7 will be as popular as special fried rice . Get them while you still can . 14N7's are the way to go though : $2 each on Ebay
ps You know those famous metal based Sylvania 6SN7WGT's ? Well the Sylvania tall-bottle 7N7 is identical in every way , apart from the basing and price of course !
316a |
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| fdegrove |
Hi,
Just for the record,I used a pair of 6EM7s to drive a PP 211 dome years ago.
Worked fine the 211 an should be fine for 813 too.
Not all of them are really cheap but if you don't stick to the 6.3V heaters then a whole host of cheap possiblities open up.
Guess they would find out about the 7N7 sooner or later...:bawling:
Cheers,;) |
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| 7N7 |
| quote: | Originally posted by fdegrove
Hi,
Guess they would find out about the 7N7 sooner or later...:bawling:
Cheers,;) |
Don't mention 7N7 on "Tubes Asylum".
The only valve they like is the 12AU7:devily:
7N7
;) |
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| fdegrove |
Hi,
| quote: | | The only valve they like is the 12AU7 |
Phewww....that's a valve for eunuchs.:dead:
Cheers,;) |
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| Kuei Yang Wang |
Hi,
| quote: | Does anyone have any experience with the Sovtek 6C45pi-E tube.
I'm intending to use them in my transformer coupled preamp instead of the Raytheon 5842A and was wondering if anyone had a good advice about the bias operating point.
They wil be used with the existing power supply wich means that, depending on the current drawn, there wil be something btween 160 and 170V on the anode of the tube. The interstage transformer is a 4200/300 Ohm type rated at 30mA DC current. |
Well, nobody really answered this. A friend runs the 6S45PE in the "Euridice" and he perfers as much current though the Valve as he can get. He also tends to prefer a sound charateristic that I personally find overly bright.
I personally must side with Ciro Marzio who preferred the WE417A with less current and more anode voltage sonically. Having played with WE417A, 437A, 6S45PE,c triode wired high Gm Pentodes and 6922 and derivates I consistently find that I prefer lower current, higher anode voltage operating condistions, they tend to give a more relaxed, composed and insightfull sound.
What is the upshot of this? Try both the JC Morrison/Dr. Arthur Loesch doctrine of "Hot and Low" and the Ciro Marzio/Kondo/Kuei Yang Wang doctrine of "cold and high", especially when combined with underheating the Valve at the tollerance limit.
Both doctrines give very different sonics from the same valve - decide which you like.
Sayonara |
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| fdegrove |
Hi,
| quote: | | Both doctrines give very different sonics from the same valve - decide which you like. |
Well I'm quite aware of what you can do with a valve to change it's sonic footprint,I find striving for a romantic, lush sound is very much a matter of taste.
I do agree however that a predominantly even order harmonic distortion picture is more pleasing to the ear,it is still just that...distortion.
If one were to strive for an as neutral and faithful to the source as possible equipment I suppose some people may still object?
Cheers,;) |
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| Sjef |
| Thanks, that's the answer I needed. Think I'n going to use a potmeter at the cathode for a while to see wich bias point I really like. I don't care about a little distortion or coloration as long as it sounds good to me and as long as I enjoy music with it , it's o.k. with me. |
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| Kuei Yang Wang |
Hi,
| quote: |
If one were to strive for an as neutral and faithful to the source as possible equipment I suppose some people may still object?
|
Uhhh, so EVIL even order distortion. Uh so EVIL Distortion. So very EVIL, even more EVIL than Kuei Yang Wang
DISTORTION is DISTORTION is DISTORTION is DISTORTION.
Evil distortion. All DISTORTION IS EVIL. ALL EVIL IS DISTORTION
The ear produces in it's mechanical system around 32% 2nd Harmonics DISTORTION at 94db SPL.
Evil Ear. EVIL DISTORTION EAR. Ear should not listen Music.
Must cut of ear for faithfull reproduction....
Why feel I suddenly compelled sunflowers to paint and strawhats to wear?
The absence of measurable simple distortion does not guarante subjectively neutral "sound" just as the presence of measurable distortion does not automatically lead to "colorations".
The world is one of many dimensions, experiences and nuances.
There is no "Black" or "White" is the real world. And light is the left hand of darkness.
End of sermon/brainfart.
Sayonara |
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| fdegrove |
Hi,
LOL.
| quote: | | There is no "Black" or "White" is the real world. And light is the left hand of darkness. |
What if I happen to be left handed?
Cheers,;) |
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| EC8010 |
Well, Frank. That's obvious. You are beaten at school and deserve to be repeatedly horse-whipped in later life. Why else do we have the word "sinister" as opposed to "dextrous" (dexter)?
I believe Leonardo da Vinci was left-handed. |
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| fdegrove |
Hi,
| quote: | | I believe Leonardo da Vince was left-handed. |
No need to remind you that Albert Einstein was a Pisces just like me....
Please don't clone me yet.... I'm ambidextrous too.:)
Sigh....;) |
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| 7N7 |
To paraphrase Gertrude Stein: distortion is distortion is distortion.
It is perfectly true that if we want low distortion - rreally low distortion, then we ahve a transistor amplifier, perhaps with loads of feedback. Ugh! Sounds cold.
On the other hand to mangle a metaphor, I do not want to listen to my music through rose-coloured spectacles.
This is what I have heard listening to 300Bs single-ended driving Lowthers etc. All very cosy but not what I want.
Must be my ears I suppose;)
7N7 |
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| Sch3mat1c |
| quote: | Originally posted by Kuei Yang Wang
The ear produces in it's mechanical system around 32% 2nd Harmonics DISTORTION at 94db SPL. |
I wonder how they measure this. And I wonder how they figure the brain, or any other component of the ear, don't counter the effect.
Tim |
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| fdegrove |
Hi,
| quote: | | This is what I have heard listening to 300Bs single-ended driving Lowthers etc. |
Sounds like adding insult to injury to me....:dead:
Cheers,;) |
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| pedroskova |
Bringing this back up top...any comments on substituting the 6C45pi for the 6dj8 in Steve Bench's 12ay7/6dj8 cascode phono pre(other than slight changes in network values)? Would it be more prone to oscillation, etc.,...?
http://members.aol.com/sbench101/Preamps/RIAA5.gif |
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| siu sin man tho |
hi,
I use the 417a, 5842 to drive my 45 tube SE amp.
I use 91ohm in the cathode resister.
I try from 150ohm to 47ohm.
91 ohm I feel the best.
the 6c45 driver 300B use 1:1 interstage I still testing.
Its is not easy to find a very high quality 1:1 interstage.
Good bankwidth, not more than 30ma. If more than 50ma the sound was quite rough.
Too low is very easy to core saturate & lack of bass.
thanks
Thomas :idea: |
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| Sjef |
| The 6C45P is very prone to escillation indeed. But if handled with proper care it won't be a problem. Be sure to use grid AND kathode stoppers as close to the tube as possible. Keep all the leads very short. This will solve all the oscillation problems. If this doesn't help enough then shield half of the tube with copper foil and connect it to earth. Do not shield the whole tube, it has to dissipate heat, shielding half the tube was good enough for me. |
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| siu sin man tho |
hi sjef,
would U care to tell me that U use which material to half shielding.
thanks
Thomas |
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| fdegrove |
Hoi Sjef,
| quote: | | AND kathode stoppers as close to the tube as possible |
What do you mean by cathode stoppers?
Cheers,;) |
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| Sjef |
I have used some very thin copper foil (0.01mm) and wrapped it around the tube. This is held in place by a piece of silverwire wrapped around it ande twisted on the ends. This wire was connected to earth.
By Cathode stoppers I mean that the 6C45P has four legs on the tube wich are all connected to the cathode. Use all four of them and solder a small resistor of 10 to 22 Ohms directly on them, as close as possible. These four resistor come together at the other end.
Don't worry about the effect of negative feedback that you create with this unbypassed cathode resistor. They are all in parallel, so four times 22 ohms is only 5.5 Ohms. That won't do much with feedback.
All of this sounds if the 6C45 is a horrible tube. It isn't, it just takes a few precautions and then it's as quiet as a good tube can be. I've had more problems to get an ECC88 in SRRP silent. |
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| fdegrove |
Hi,
| quote: | | By Cathode stoppers I mean that the 6C45P has four legs on the tube wich are all connected to the cathode. Use all four of them and solder a small resistor of 10 to 22 Ohms directly on them, as close as possible. These four resistor come together at the other end. |
All these pins are already internally connected from what I see on the basing diagram.
Again, sorry, but I fail to see how these resistors are going to change anything.
Pin #4 and #5 are the most remote from the cathode proper, wouldn't it then make more sense to divide the calculated value for the cathode R in two and use these two resistors there?
I must say I'm not familiar with that particular tube so forgive me if I have the wrong of the stick here.
Cheers,;) |
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| EC8010 |
I've experimented with 6C45, and found that it will oscillate.
If you use it as a cathode follower, it needs good local decoupling of the HT, plus grid-stoppers. A 200R cathode-stopper was also needed when I applied 2n capacitive load. (Same principle as adding a series resistor at the output of op-amp cable drivers.) I've never seen the point of connected to all grid, or cathode, pins. They are there to allow good RF layout in any design.
As the upper valve of a mu-follower, it gave far less trouble. |
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| James D. |
Hi Frank,
I have found the same as Sjef with this little beastie. You must connect small cathode stoppers to all the cathode lugs or cut then off right against the base. They act as small LC stubs and set off the parasitic oscillations of the tube... This thing is a little rocket but can be tamed by standard good rf practice so I use grid stoppers and anode stoppers. I haven't needed ferrite beads yet or to shield the tube itself...but I stand ready too! Once that is done it is a great little tube and (to my taste) goes really well driving a 2A3 etc.
ciao
James |
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| Sjef |
By using all the grid and cathode connections you wil decrease the inductance lead to the grid/cathode. This inductance while very small makes an oscillation circuit with the parasitic capacitance of the tube, so keep it resistive instead of inductive. Remember that the tube tends to oscillate at MHz frequencies, not at audio frequencies. I don't if the inductance plays a big role here, but when you don't use all the gride/cathode pins they will make brilliant antennas with these frequencies.
You can see the cathode of the tube as it's second input. If you use a cathode resistor bypassed with a capacitor you create an almost zero Ohm lead to the Cathode via this capacitor. That's why adding an unbypassed small value resistor helps here. It doesn't degrade the sound, it doesn't cost anything (well some resistors), it's very easy to apply and it did help for me, so I don't see the problem here. |
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| fdegrove |
Hi,
James,
Thanks.
Sjef,
Don't worry, the only problem was me not realising how sensitive this ****** is.:(
Anyway, thanks for the explanation.
Cheers,;)
P.S. Why not use a screening can? |
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| pedroskova |
| Thanks for all the info. I think I'll stick with Mr. Bench's original design. I'm already in over my head. :nod: |
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| Sjef |
A sreening can might do the job as well, I don't know, I didn't have one. I'm only afraid that the tube might get too hot in a can.
I also really like this tube, it's one of the most dynamic sounding tubes I've used so far. |
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| siu sin man tho |
hi,
can the 6c45 use a very thin filter like stainess steel plate to make cover corn for it. is it enough to shielding it.
sorry my english is not good. I don;t know how to explain, I hope U will understand.
thanks
Thomas |
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| Sjef |
| Yes, that will do as wel. As long as the tube is not totally in the open field it's okay. The main problem I have had without the shield was that there started a hum every time I came close with my hand (to turn the volume) This only stopped by touching the tube for and quickly move my hand away. Very strange effect. With the shielding this problem was solved. I did not need a complete shield, only a short circuit ring was enough. |
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| siu sin man tho |
hi sjef,
I also prepare use the mesh plate to make a cover for the 6c45.
Is it really a large dofferent???
thanks
Thomas |
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| siu sin man tho |
hi all gentleman,
I had a large problem, can anybody told me that the cathode resister for 6C45 use, whicg ohm in your test is better.
thanks
Thomas:bigeyes: :goodbad: :dodgy: :devilr: :dead: :clown: :idea: |
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| fdegrove |
Hi,
Thomas,
You could try 90R for the cathode R.
Cheers,;) |
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| siu sin man tho |
hi frank,
U so great. I was testing the 91ohm 1watt resister & feel very good. but i am think & hope to get more information that 91ohm is right or not,
Do U agree the cathode cap is 100uf.
I also testing.
thanks
thomas:bigeyes: :rolleyes: :bigeyes: :rolleyes: |
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| fdegrove |
Hi,
| quote: | | Do U agree the cathode cap is 100uf. |
I use at least 470uF.
Cheers,;)
P.S. This tube tends to oscillate easily, so you better watch it on a oscilloscope.:att'n: |
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| siu sin man tho |
hi frank,
I s 470uf will to large, I will test your advise tomorrow.
thanks
thomas |
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| EC8010 |
| quote: | Originally posted by Sjef
The main problem I have had without the shield was that there started a hum every time I came close with my hand (to turn the volume) This only stopped by touching the tube for and quickly move my hand away. Very strange effect. With the shielding this problem was solved. I did not need a complete shield, only a short circuit ring was enough. |
That is a sure-fire indication that the valve was oscillating. 6C45P oscillates very easily, and you really need a good oscilloscope handy. |
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| NG |
Hi Sjef:
Thanks for the good advices on how to stop oscillation.
I am a just a diy beginner. Can you explain to me a bit more about :
- use as grid stopper 1 k or should I use lower values, because my grid bias resistor for 6c45p is only 1 k !
- you mentioned for the cathode stoppers :"connect 4 x 20ohm resistors to 4 pins of cathode and then OTHER END comes together". Do you mean, just soldering the other ends together and leave it there OR should the other ends be soldered together and then go to the ground ?
Thanks for your help !
DoeiDoei
NG |
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| Sjef |
Hi NG,
1K for gridstopper should be sufficient in most cases.
The 4 cathode resistors are just some extra resistors soldered as close as possible to the tube pins. The 6C45 has four pin connection for the cathode so in this way you will use all four of them.
Thet are in fact in parralell with each other, yes soldered to each other at the end wich isn't on the tube pins. They do not go to ground but to the cahthode bias resistor. Just see the point where the four resistors come together as your new cathode connection of the tube, that's it.
good luck |
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| ashok |
What is the need to use all four pins if they are all at the same potential by virtue of being directly connected together inside the tube ? If one is used the others automatically get tied to the same voltage. If not , why ?
Don't understand this at all. |
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| Sjef |
| yes they are connected at the inside of the tube but only after a short lead wich is long enough to act like an antenna. Sovtek recomments using all four connection with eventually four stoppers for thei 6C45's because they are prone to oscillation at very high frequencies, yes in the hundreds of Mhz area. That's an area with very short wavelenghts and even a few mm is enoughto pick it up. This is also the reason why the tube has four cathode connections instead of one, this way you make the path a fourth of the inductance hence a fourth chance to pick up rfi. |
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| NG |
Hi Sjef:
Thanks for the explanation. I finally understand what the cathode stopper is all about .
For the grid stopper, do I need to put :
- 1 kOhm on pin 2 and another 1 kOhm on pin 8
- OR should I simply cut one of the grid pin short ?
Again, thanks for helping me out.
Best regards,
NG |
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