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I have to say I can't fully agree with the dislike of 12AT7s.   I expect it depends on the circuit in which you use them, how you bias them, etc etc.  

 

They are just another valve in the series from 12AX7 to 12AU7, like 12AZ7, 12AD7, 12AY7, etc. and can do a great job.

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7 minutes ago, aussievintage said:

... it depends on the circuit in which you use them...

Eli Duttman points out in his El Cheapo that the non-linearities of teh ECC81/12AX7 are such that they largely cancel those of the EL84/6BQ5, so it becomes a solid combination. 

 

elCheapo-23jun06-map.gif

 

I can ceryainly say that our Class A triode variation is a stunning amplifier.

 

dave

Edited by planet10
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Can anyone tell me what would be a tube with equivalent gain to my E88CCs. For example has it similar gain to a 12AX7 or more like a 12AU7. These tubes I know the E??CC series I’m not familiar with. There appeared to be too much gain in my latest E88CC preamp “Continuum”.
 

I cut away Ck and now a lot better. And of course a lot quieter with less gain. Also I can run the pot in it’s more linear operating area now. Much better all round. Glorious sounding preamp, very relaxed. 

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20 minutes ago, mwhouston said:

Can anyone tell me what would be a tube with equivalent gain to my E88CCs. For example has it similar gain to a 12AX7 or more like a 12AU7. These tubes I know the E??CC series I’m not familiar with. There appeared to be too much gain in my latest E88CC preamp “Continuum”.
 

I cut away Ck and now a lot better. And of course a lot quieter with less gain. Also I can run the pot in it’s more linear operating area now. Much better all round. Glorious sounding preamp, very relaxed. 

 

A 12AT7 is about 55, 12AY7 about 40, ECC88/6DJ8 is about 33 and a 12AU7 is about 20

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32 minutes ago, mwhouston said:

Can anyone tell me what would be a tube with equivalent gain to my E88CCs. For example has it similar gain to a 12AX7 or more like a 12AU7. These tubes I know the E??CC s

The 6DJ8 is quite unique as it is a very high transconductance TWIN triode.  e80cc is probably the closest as a twin triode.  It's actually a very nice tube with a bigger envelope and more current power.  Many use it to drive output tubes.  Gold pins etc, Not cheap as a result.  From memory, gain is similiar to a 12AU7.

 

Lots of single triode similiar like 417, D3a e810f etc.

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3 minutes ago, Red MacKay said:

The 6DJ8 is quite unique as it is a very high transconductance TWIN triode.  e80cc is probably the closest as a twin triode.  It's actually a very nice tube with a bigger envelope and more current power.  Many use it to drive output tubes.  Gold pins etc, Not cheap as a result.  From memory, gain is similiar to a 12AU7.

 

Lots of single triode similiar like 417, D3a e810f etc.

 

There's lots when you start looking.  ECC85/6AQ8 with a gain more like the 12AT7 I think.

 

 

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7 minutes ago, aussievintage said:

L...some local negative feedback.

 

No thankyou!  A feedback free triode world is a beautiful thing. 😊

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2 minutes ago, aussievintage said:

There's lots when you start looking.  ECC85/6AQ8 with a gain more like the 12AT7 I think.

I've never seen those in audio.  Are they quite useable, as you can pick them up for peanuts.

(I like cheap these days...)

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3 minutes ago, Red MacKay said:

I've never seen those in audio.  Are they quite useable, as you can pick them up for peanuts.

(I like cheap these days...)

It's just another RF triode, and so,  I have heard, like the ECC88, the fear was that it can be a bit noisy, but in practice, people use ECC88 all the time for audio.

 

Our local https://www.evatco.com.au/6aq8-electro-harmonix  thinks they are good.

 

Do you guys know about this resource  http://tdsl.duncanamps.com/tubesearch.php     easy to look data on your possibly candidates.

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4 minutes ago, aussievintage said:

It's just another RF triode, and so,  I have heard, like the ECC88, the fear was that it can be a bit noisy, but in practice, people use ECC88 all the time for audio.

Yes, RF tubes can be noisey but man - do they have bandwidth!

 

Ypsilon use a ecc8010 as a driver in their SET 100 mono blocks to drive 16 transistors, zero noise there.

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After some comparing Amplification factors it appears the E88CC is closer to a 12AX7 than 12AU7.  As you may know the X7 is a high gain tube. I ‘tend go for lower gain tubes as the 12AU7 is. I cut away Ck to drop gain it also drops 2nd and to lesser extend 3rd order harmonics. Only about 3db off 2nd order. 
 

This give the preamp a slightly dryer sound, not as rich in harmonics. Suits me though making the preamp closer to true fidelity instead of enhancing or exaggerating harmonics. 

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3 minutes ago, mwhouston said:

After some comparing Amplification factors it appears the E88CC is closer to a 12AX7 than 12AU7.

Are you sure?  I looked at datasheets that give 100 for the 12AX7 and 33 for the E88CC.  Did you see my post, it's somewhere between a 12AT7 and a 12AU7 I think.

 

4 minutes ago, mwhouston said:

I cut away Ck to drop gain it also drops 2nd and to lesser extend 3rd order harmonics. Only about 3db off 2nd order. 
 

This give the preamp a slightly dryer sound, not as rich in harmonics. Suits me though making the preamp closer to true fidelity instead of enhancing or exaggerating harmonics. 

 

So that little bit of LFB is making it more linear?    I used 6SN7s without cathode bypass in my 6B4G/2A3 SET.  Figured there'd be enough funny stuff coming from the output stage anyway :) 

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8 minutes ago, aussievintage said:

Are you sure?  I looked at datasheets that give 100 for the 12AX7 and 33 for the E88CC.  Did you see my post, it's somewhere between a 12AT7 and a 12AU7 I think.

I'm with OZ vintage here Mark.  I'm not sure what spec sheets you were looking at.

 

But no twin triode  will have the transconductance of the 6DJ8, and that is why it is sounds good. (not that it is a personal favourite of mine at all, it's a love/ hate thing)

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7 minutes ago, planet10 said:

That is correct i believe.

 

dave

 

 

Looking at 250V HT it appeared closer to a X7 than a U7 with half  the gain. I also noted the gain varies with HT so I did compare apples with apples. 

Edited by mwhouston
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From the data I looked at, too me, I thought the E88CC a high gain tube. Bruce of oddwatt agreed the E88CC a higher gain tube than the one he designed the preamp for. I compared the tubes at the same HT. The gain varied with HT. 

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1 hour ago, Red MacKay said:

The 6DJ8 is quite unique as it is a very high transconductance TWIN triode.  e80cc is probably the closest as a twin triode.  It's actually a very nice tube with a bigger envelope and more current power.  Many use it to drive output tubes.  Gold pins etc, Not cheap as a result.  From memory, gain is similiar to a 12AU7.

 

Hey Red,

 

I found the Tungsram e80cc sounded better than the Euro version. It's also much cheaper! Yep, can replace a 12au7.

 

Also ran across a single triode that looks very interesting and is similar the the 6c45, called 6s4p. A "DR" version is available and is a 10,000 hour rated tube and it has gold grid wire. Can be had for about $6 a tube which is a heap cheaper than 6c45's these days.

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16 minutes ago, mwhouston said:

From the data I looked at, too me, I thought the E88CC a high gain tube. Bruce of oddwatt agreed the E88CC a higher gain tube than the one he designed the preamp for. I compared the tubes at the same HT. The gain varied with HT. 

Nearly every sheet I have seen so far quotes 33 at  100 volts.  What is the voltage across them in your circuit?

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2 minutes ago, mwhouston said:

You might be right. I’ll check the suggested HT. 

You've got me doubting myself now too :)   I assumed the figures in the datasheets were anode voltages.

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I'm building an AKSA 'Paris' (JFET-based) head amp for @MattyW.

 

This is a very interesting build because Matt wanted it to be able to cope with 3 situations:

  1. accept 2 inputs - as he has 2 arms on his TT - and select one or the other to go through to the head amp PCB.
  2. but be able to bypass the head amp PCB, for when he mounts a 'normal' HO MM/MI on one of his arms.
  3. and have all switches - plus input RCA sockets for load plugs - on the front panel.

 

Matt has a large collection of carts which span:

  • normal HO MMs/MIs
  • rare LO MMs/MIs - such as a Pickering XLS-4500S (0.33mV), Stanton 785LZE (0.6mV) and Grado 'Statement' series (0.5mV)
  • and LO MCs.

 

He has been using various SUTs with his LOMCs but SUTs are no use with his LO MMs/MIs as they deliver a completely wrong loading to the cart.  The Pickering and the Stanton like to see 100K, whilst the Grado (if it's anything like a 'normal' (HO) Grado) will probably like 33-35K.

 

With the default load resistor on the head amp set to 100K, the load which the cart sees can be adjusted by using load plugs (which work in parallel with the default 100K on the PCB).  This arrangement works equally well for his LO MMs/MIs ... and his LO MCs.  :)

 

Here are some pics:

 

The actually head amp PCB (small!!  64mm x 58mm).

 

 

789884722_ParisPCB.thumb.jpg.2aeff9e35fe191e8d9beb89dce217f42.jpg

 

The front panel:

 

 

1916855231_Paris-DualFP.thumb.JPG.a7c657d626bf4383daa632d69362909b.JPG

 

The back panel:

 

 

658847917_Paris-DualBP.thumb.JPG.acc4dfd62170edd3de7f6a80b94c5d62.JPG

 

Andy

 

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Bruce’s suggestion is 215 on the plate of the active load. I’m about 230. Easy enough drop with a 5W limiting resistor. There is a 4uf PIO final HT cap in the preamp. A further resistor before the cap will add further filtering not that it is needed.  The HT is choked filtered with 400uf in a double (soon to be a triple) Pi. There is DC on the heaters. 

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22 minutes ago, mwhouston said:

Bruce’s suggestion is 215 on the plate of the active load. I’m about 230. Easy enough drop with a 5W limiting resistor. There is a 4uf PIO final HT cap in the preamp. A further resistor before the cap will add further filtering not that it is needed.  The HT is choked filtered with 400uf in a double (soon to be a triple) Pi. There is DC on the heaters. 

So then, subtract the cathode voltage and is it about 100V ?

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I'm very much looking forward to the Paris head amp.  I'll finally be able to try my low output moving iron carts and see what all the fuss is about. In theory it should better moving coil. :)

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4 minutes ago, MattyW said:

I'm very much looking forward to the Paris head amp.  I'll finally be able to try my low output moving iron carts and see what all the fuss is about. In theory it should better moving coil. :)

I'd be interested in how well it works too.

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20 hours ago, Red MacKay said:

 

What are the 12AT7s doing in your circuit?  What gain is required from them?  Can you give up a little gain?

 

 They are the output valves in this circuit, the Broskie Unbalancer.

 

John put me on to a guy who had built several of these using the TP DAC and he was a wealth of information, and seem to do lots and lots of tests and comparisions so for the moment I'm following what he recommended, he seemed like the eternal tinkerer where I'm more a set and forget guy.

 

I tried cleaning the pins but dont think it made much/any difference.

 

If I'm going to measure Vk for the output valve I'm wondering where I should measure, at the top of R13 & 14?

 

Johon say "In the Unbalancer circuit, the differential input stage sees a constant-currentsource at its coupled cathodes, which allows the circuit to even better ignore common-mode signals and automatically sets the desired cathode-bias voltage for input triodes."

 

With that  in mind where should I mearuse Vk on the input valves?

 

I had a bit more of a listen last night and all in all I'm thinking the preamp sounds pretty good except for the underlying noise. Part of my problem is, Im always listening to my main syatem in the dead of night and where I am is very quite so any noise is easy to hear. One side has more crackle that the other so I'll do some valve swapping to findout which valve is causing the issue.

 

 

Broskie Unbalancer.JPG

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Definitely spoiled for choice at the mo. The one in play, in my main rig, is “Continuum” with the E88CC tubes. Just dropped HT down from 230V to 215 and added another cap to the heater DC. Sound very good. Slowly getting some hours up in the new tubes and parts. 

2D7EF0FC-1618-40D8-90F4-68BBF9D0A6DA.jpeg

BDC11DC3-C645-47FC-9DE2-407E682CF8CC.jpeg

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Another project I'm doing during 'lockdown' is a 40w Class A amp designed by Hugh Dean and described on DIYAudio, here:

https://www.diyaudio.com/forums/solid-state/344540-alpha-nirvana-39w-8ohm-class-amp.html

 

It's 40w into 8 ohms ... with +/-27v DC rails; I'm building a pair of the 4 ohm version, as I intend to use 2 stereo amps with my Maggie mid panels & ribbons (mids, 3.2 ohms and ribbons 2 ohms).  So I guess they will output 25w or so, into 8 ohms - which will be plenty for the 2 ohm ribbons, anyway!  :)

 

 

291426050_ANBuild-BeforeWiring.thumb.jpg.32082441e5a3c595acfaf877d4148057.jpg

 

 

At the front is a power supply for each channel (each has a 300VA toroid).  These PSs are designed to be able to deliver 5amps continuously, with low ripple; see here:

https://www.diyaudio.com/forums/group-buys/336479-slb-smooth-butter-active-rect-crc-cap-mx-class-power-supply-gb.html

 

The cool thing about their design - and that of the amp boards (mounted on the rear panel) - is the devices that need heatsinking (2x transistors in the case of the PS, 2x MOSFETs in the case of the amp) can be remotely sited, connected using Molex 4-pin connectors.  The PS transistors actually don't need that much heatsinking (I over-subscribed!!  :) ) while the amp's MOSFETs are clamped between the Dell finned CPU coolers and the 5m aluminium L-brackets they are mounted on.  Noctua 14mm thick, 92mm fans are mounted on the case bottom ... with 92m holes cut directly underneath the fins.  So this should keep the MOSFETs acceptably cool!  :)

 

Each pair of MOSFETs is mounted on a 'Snubber PCB' - which contains some SMD components, as well as the MOSFETs.  A closeup of the way they are mounted is shown here:

 

 

371572554_CPUCooler-AssembledSide.thumb.jpg.30ebdd93f45eecc9f461568f8b390bb4.jpg

 

 

The amp PCBs themselves are mounted on the rear panel; underneath them are speaker protection PCBs - see here:

https://www.diyaudio.com/forums/group-buys/340694-ready-run-rtr-ssr-dc-speaker-protection-delay-gb.html

 

Now I have to wire up this first amp ... then do it all again for the second amp!  :(  At least all the PCBs for this, are done.

 

Andy

 

 

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Damn, that looks awesome Andy. I've never seen CPU heatsinks used in Audio gear before.  Your build is causing me to salivate!

 

Combines my old hobby with audio.  I'd love to do with old Thermalright heatsinks as I could never afford them back in the day. ;)

 

Due to the far higher efficiency of those heatsinks I daresay you won't even need fans?

 

How much does such a build cost. Purely out of curiosity.... Not that my curiosity doesn't often lead to purchases. :(

Edited by MattyW
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