[regal]

Quote:

What does "mKA" mean for grid leak? 

 “MKA” – micro-ampermeter

 

[dsavitsk]

 
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Its only an issue I've seen with the 6c45,  its an unusual tube witch evidently leaks alot of current off the grid.  So you are forced to use a 10k pot feeding a 100k grid leak (following the 10x rule).   With most tubes you use a 50k pot and a 10x50k=500k grid leak.  But if you do this with the 6c45p considereable current will follow the pot shunt to ground.  That is if the datasheet is correct.   
Could be a non issue as I have yet to find a pair of 6c45p's that matched close enough to make a stereo amp so I don't speak from direct experience just what I saw on the datasheet.  I know there are lot of complaints with 6c45pi sounding hard due to oscillations but this could be part of the issue as well IMO.

 
This really is total nonsense.  Grid current is only an issue if you drive the grid close to positive. So don't.  Bias it enough that this isn't a problem. This is an issue with every tube, including the 5842.
 
The 150K limit is a 150K limit, not a 10K, limit.  The larger pot won't effect sound quality, or pot life. And, by the way, the 5842 has the same limit specified in the datasheet: http://www.mif.pg.gda.pl/homepages/frank/sheets/009/5/5842.pdf
 
The unmatchability of the 6C45's is also a myth. I've got piles of matched pairs.  Good lead dress and layout will quash the oscillations.  Again, it is an internet myth propagated by people who don't know how to use the tube. It is in my experience an extremely low distortion tube that sounds fantastic.
 
And I don't speak from what some guy posted on the internet.  I have used this tube extensively.  http://www.avguide.com/blog/can-jam-chicago-2010-international-head-fi-meet-part-2?page=1
 
@Adamus ---^  that is fine. The resistor is there just in case the pot loses contact for a moment.

 

[adamus]

cheers douglas, thats the only reason i do it.
 
My c3g build is coming on. Salas HV shunt tested. amp section wired up and tested at hv. The C3g's are needing a bit more bias than the datasheet suggests but hey ho. I have build it in such a way that trying single end tx will be easy. currently the salas shunt will be a bit overkill for the ccs loaded parafeed but every little helps i suppose!

 

[regal]

 
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Quote:

Its only an issue I've seen with the 6c45,  its an unusual tube witch evidently leaks alot of current off the grid.  So you are forced to use a 10k pot feeding a 100k grid leak (following the 10x rule).   With most tubes you use a 50k pot and a 10x50k=500k grid leak.  But if you do this with the 6c45p considereable current will follow the pot shunt to ground.  That is if the datasheet is correct.   
Could be a non issue as I have yet to find a pair of 6c45p's that matched close enough to make a stereo amp so I don't speak from direct experience just what I saw on the datasheet.  I know there are lot of complaints with 6c45pi sounding hard due to oscillations but this could be part of the issue as well IMO.

 
This really is total nonsense.  Grid current is only an issue if you drive the grid close to positive. So don't.  Bias it enough that this isn't a problem. This is an issue with every tube, including the 5842.
 

 
 
The whole point of this amp is simplicity and lack of capacitors in the signal path,  so the grid is going to be driven somewhat close to positive with a 2V LED bias.  But if you are saying its OK for the pot to take the brunt of grid leak duty I will have to try it and compare ,  like I said it could be a non-issue.  But IMO its worth exploring.

 

[Parafeed]

Quote:

The unmatchability of the 6C45's is also a myth. I've got piles of matched pairs.  Good lead dress and layout will quash the oscillations.  Again, it is an internet myth propagated by people who don't know how to use the tube. It is in my experience an extremely low distortion tube that sounds fantastic.

It's somewhat easier to end up with matched pairs when you've got "piles" of them to test and pair.
 
Regarding oscillations..... When I first started playing with the 6C45 (back in 2003) I had problems. The first batch of tubes I bought from a dealer in Lithuania were all prone to oscillate no matter how good the lead dress and layout. Stoppers and ferrite beads were required! Other examples I've purchased from different sources have not been prone to oscillate even without stoppers! So I'm not sure about this being an internet myth. I think there are batches of tubes more prone to oscillation than others.
 
Regarding the sound of the tube, it is a good sounding tube - sure. But (as with most frame grid tubes - 3rd harmonic) it has a certain sound, even when not oscillating. People who love the 6N6 (a really tubey sounding tube if ever there was one) and who would describe a ECC88 as being steely, thin, metallic, etc. etc. are not likely to be fans.

 

[FrankCooter]

Quote:

 
Regarding the sound of the tube, it is a good sounding tube - sure. But (as with most frame grid tubes - 3rd harmonic) it has a certain sound, even when not oscillating. People who love the 6N6 (a really tubey sounding tube if ever there was one) and who would describe a ECC88 as being steely, thin, metallic, etc. etc. are not likely to be fans.

Pretty much sums up my experience with this whole family of tubes. None of them sound like a good 6v6, much less a DHT. Feed them with a solid state power supply, load them with a CCS, and bias them with an LED, and you're getting pretty damn close to a solid state  amp. If that's what you want fine, but not a lot of tube character there. That said, I still like and use the D3A and the W.E. 418A.  I'm also interested in the 6HV5, both as a driver for the 845, and as a potential electrostatic "spud" amp.

 

[regal]

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Quote:

 
Regarding the sound of the tube, it is a good sounding tube - sure. But (as with most frame grid tubes - 3rd harmonic) it has a certain sound, even when not oscillating. People who love the 6N6 (a really tubey sounding tube if ever there was one) and who would describe a ECC88 as being steely, thin, metallic, etc. etc. are not likely to be fans.

Pretty much sums up my experience with this whole family of tubes. None of them sound like a good 6v6, much less a DHT. Feed them with a solid state power supply, load them with a CCS, and bias them with an LED, and you're getting pretty damn close to a solid state  amp. If that's what you want fine, but not a lot of tube character there. That said, I still like and use the D3A and the W.E. 418A.  I'm also interested in the 6HV5, both as a driver for the 845, and as a potential electrostatic "spud" amp.

I like the 6n6p even SS B+ and LED its still pretty tubey.  Had it on a DAC stage but it was not quite detailed enough in that position.

 

[Parafeed]

Quote:

Pretty much sums up my experience with this whole family of tubes. None of them sound like a good 6v6, much less a DHT. Feed them with a solid state power supply, load them with a CCS, and bias them with an LED, and you're getting pretty damn close to a solid state  amp. If that's what you want fine, but not a lot of tube character there.

Well, you can always add a little flavour to the recipe. Regal will probably have a heart attack at the mere mention of a cathode follower, but 6C45 (CCS loaded, red led bias) driving a 6N6 Broskie cathode follower sounds very good. The 6N6 takes the "edge" off the 6C45 and adds a little warmth back to the mids but not blunting the speed or detail of the 6C45. (The BCF doesn't have the "closed-in" sound of a typical cathode follower.)

 

[FrankCooter]

Another idea would be to use  a triode connected EL84 type. You can buy NOS Mullard EL822 on Ebay for $12.00 a pop. In triode mode, the EL822 has a mu of 23 and an rp of about 3k. Close enough to use with with your 5k:32 Electra-Print transformers and a pair of Grado's.   Real easy to drive as well. One of the things I've noticed over the years is that small power tubes can often sound very good when used as voltage amplifiers.  I've seen some European designs  (Thorsten's?) that use EL84's to drive 300B's. Few things sound better than a good triode connected EL84.

 

[adamus]

its you want a classic 'tube'  sound then agreed, the el84 triode connected is superb.
 

 

[dsavitsk]

 
Quote:

Feed them with a solid state power supply, load them with a CCS, and bias them with an LED, and you're getting pretty damn close to a solid state  amp. If that's what you want fine, but not a lot of tube character there.

I guess I am looking for an amp, not a filter. A well designed tube amp, IMO, should not impart "tubiness".  At any rate, I think tube character is actually more a function of electrolytic caps.  Get rid of them, and the grain and lush and lack of detail seem to disappear.

Quote:

 
Regarding the sound of the tube, it is a good sounding tube - sure. But (as with most frame grid tubes - 3rd harmonic) it has a certain sound, even when not oscillating. People who love the 6N6 (a really tubey sounding tube if ever there was one) and who would describe a ECC88 as being steely, thin, metallic, etc. etc. are not likely to be fans.

Here's a 6C45 driven hard into a parafeed OPT.
 

 
For reference, 2nd is at 0.1%, 3rd is at 0.004%. At normal listening levels, the 3rd drops into the noise, and the 2nd is below the hearing threshold. heck, much of the second in the measurement is from the OPT.


Quote:

The whole point of this amp is simplicity and lack of capacitors in the signal path,  so the grid is going to be driven somewhat close to positive with a 2V LED bias.  But if you are saying its OK for the pot to take the brunt of grid leak duty I will have to try it and compare ,  like I said it could be a non-issue.  But IMO its worth exploring.

I think it's a non-issue.  But, using a 10K pot is not a bad thing, so I am not trying to talk you out of anything. Just wanting to say my $0.02 about whether this tube is any good.
 
I also think that with your basic design goals, you are going to be closer to the sort of amp I might make, than some of the others mentioned.  But, it really is about experimenting and finding what you like. There is no right answer.
 
Quote:

I like the 6n6p even SS B+ and LED its still pretty tubey.  Had it on a DAC stage but it was not quite detailed enough in that position.

I definitely think the 6N6 works better as a differential tube. SE it is a little too mushy for me.

 
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Well, you can always add a little flavour to the recipe.

 
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Another idea would be to use

 
Guys, regal has a fine design -- lets let him build the basic topology before he adds additional stages. There is a lot to be learned from working to optimize a single tube.

 

[regal]

 """ " " Healthy discussion I think.  Here is the FFT of the 6SN7 hybrid amp from my sig (yes 2H -78 dB) with the volume level set a bit over normal use,  building the WE417 OPT amp is more of an experiement into if I can stomach an output transformer vs a SS buffer.   Next step would be #26/45 DHT headamp (long term dream.)   As far as filters go ,  all amps are filters and no one has the "Davinci code  " that correlates an FFT plot into our brains perception so I keep my mind open when it comes to topology and design philosophies.  Meaning I like to study Dsavisk, Cooter, Parafeed, and Alex's styles.
 
 

 

[00940]

@dsavitsk: those are rather impressive numbers for the 6C45. Out of curiosity, what's the power used for "normal listening levels" and "driven hard" ?

 

[Parafeed]

 
Quote:

Here's a 6C45 driven hard into a parafeed OPT.
 
For reference, 2nd is at 0.1%, 3rd is at 0.004%. At normal listening levels, the 3rd drops into the noise, and the 2nd is below the hearing threshold. heck, much of the second in the measurement is from the OPT.

Interesting. Definition of "driven hard"? Would you mind giving more info - load, op point.....

 

[dsavitsk]

Measurements were taken with the tube biased by a single 1.8V red LED.  Plate load is a 10M45 mosfet cascode CCS at 18mA.  OPT is 8K:32.  Input signal was just short of inducing grid current (around 3Vp-p, though I did not take a careful measurement)  which is ~300mW or so, maybe a little more. Note that this would be more than a watt, maybe 2, with much lower OPT primary. Normal listening levels I'd put in the 5 to 10mW range.