Years ago when used to consume all the audio mags of the time I bought an ear phono preamp....yes that one that is so cloned right now.With the 3 EI ecc83 s in it what does a London boy do ....find the best Mullard Valves for it of course.So a phone call to Rod of Valve And Tube Supplies and I have a set of the "best" ecc83.But only if I come to the
event held at NEC Birmingham.
Now at this point of my audio life all I know is what comes out of an amplifier not what's it in to make the magic happen.....I didn't even know what a resistor was 🙄
Anyway I pay my entry fee and enter this huge arena .....and it is here I pause in astonishment for it is a site to behold.There is stall upon stall containing everything relating to radio and television.
I mean here I could see the Japanese dealers buying up every single vintage Tannoy ....all the garrard 301s ....
So I get my Mullards from Rod and off I go just looking and browsing without a clue just soaking up the atmosphere and enjoying the vibe.
And the there it was.... a stall selling a lot of Japanese components and literature including Mr Shishido's book.
I picked it up held it in my hands only to realise the thing is written in all Japanese ....
As I put it down the stall holder says "I'll take twenty for that" ....What!? I say incredulously.
"Okay,give me a Tenner and it's yours"
So I own my very first audio amplification book by a famous author and don't have a clue about audio electronics.Remember I don't even know what a resistor is .....of course at that time I didn't know he was famous and I have no Japanese in me to understand it either.Oh and still have no Japanese in me but now can understand circuits.I think!!?
I have built the ecc88 phono preamplifier in the book.....very nice indeed.Thank you Mr Shishido.
I even had planned to build the 805 amplfier in the book but balked at the total price of such a project!!! And of course the high voltages in this amp...over 800Vdc!!
I hope to build a version of he's 4d32 amplifier and 826 and 2A3 and 801A ....Yes we can dream can't we.
BTW ...because Mr Shishido uses a 6l6GC in one of his 808 amps....sometimes being biased is a good thing!!
6L6 gets my vote.
event held at NEC Birmingham.
Now at this point of my audio life all I know is what comes out of an amplifier not what's it in to make the magic happen.....I didn't even know what a resistor was 🙄
Anyway I pay my entry fee and enter this huge arena .....and it is here I pause in astonishment for it is a site to behold.There is stall upon stall containing everything relating to radio and television.
I mean here I could see the Japanese dealers buying up every single vintage Tannoy ....all the garrard 301s ....
So I get my Mullards from Rod and off I go just looking and browsing without a clue just soaking up the atmosphere and enjoying the vibe.
And the there it was.... a stall selling a lot of Japanese components and literature including Mr Shishido's book.
I picked it up held it in my hands only to realise the thing is written in all Japanese ....
As I put it down the stall holder says "I'll take twenty for that" ....What!? I say incredulously.
"Okay,give me a Tenner and it's yours"
So I own my very first audio amplification book by a famous author and don't have a clue about audio electronics.Remember I don't even know what a resistor is .....of course at that time I didn't know he was famous and I have no Japanese in me to understand it either.Oh and still have no Japanese in me but now can understand circuits.I think!!?
I have built the ecc88 phono preamplifier in the book.....very nice indeed.Thank you Mr Shishido.
I even had planned to build the 805 amplfier in the book but balked at the total price of such a project!!! And of course the high voltages in this amp...over 800Vdc!!
I hope to build a version of he's 4d32 amplifier and 826 and 2A3 and 801A ....Yes we can dream can't we.
BTW ...because Mr Shishido uses a 6l6GC in one of his 808 amps....sometimes being biased is a good thing!!
6L6 gets my vote.
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There is a conflict in your driver stage between maximum current and minimal internal resistance of the tube. Three stage design, you should have enough gain to throw on 2:1 IT and cathode feedback.
I would choose lowest Ri tube.
I would choose lowest Ri tube.
Ups, now I see you want a cathode follower, not my speciality.
I was drown by shishido schematic.
The question was which tube that looks best next to the 808, but a technical discussion is of course most welcome too.
A prototype will be built to test different driver tubes (and possibly mosfets), with and without interstage transformers and different feedback topologies.
I know from previous experiences that a decent-sized power tube can push the grid of an 808 without much effort.
As mentioned before, I've had the 808 on the bench several times but never gotten as far as listening to them so I don't know what to expect. I made an 811A SET almost twenty years ago and as far as I can remember it sounded quite good and I have no particular reason to think that 808 wouldn't be at least as good.
Plan A is to get away with a moderate amount of local feedback around the output tube, if that fails I can always use a high gm pentode as input stage and hammer everything flat with a healthy dose of "Schade" feedback 😎
A prototype will be built to test different driver tubes (and possibly mosfets), with and without interstage transformers and different feedback topologies.
I know from previous experiences that a decent-sized power tube can push the grid of an 808 without much effort.
As mentioned before, I've had the 808 on the bench several times but never gotten as far as listening to them so I don't know what to expect. I made an 811A SET almost twenty years ago and as far as I can remember it sounded quite good and I have no particular reason to think that 808 wouldn't be at least as good.
Plan A is to get away with a moderate amount of local feedback around the output tube, if that fails I can always use a high gm pentode as input stage and hammer everything flat with a healthy dose of "Schade" feedback 😎
Some "RCA Ham tips" from 1939 about the 808. Nothing about using them as audio outputs in class A of course but still a nice curiousity from 40 years before I was born: http://n4trb.com/AmateurRadio/RCA_Ham_Tips/issues/rcahamtips0203.pdf
As far as appearance then the larger rounder 807 bottle
appeals to the look cool factor.
far as performance wonder how the 6L6 bigger brother 6550 holds
up.
Remember a dirt cheap easy to get big bottle with
top electrode was the 6146 and its fussy screens.
Endless surplus of those guys in the 90's
appeals to the look cool factor.
far as performance wonder how the 6L6 bigger brother 6550 holds
up.
Remember a dirt cheap easy to get big bottle with
top electrode was the 6146 and its fussy screens.
Endless surplus of those guys in the 90's
Here's a thought...use your pentode driver as pentode.Take its cathode tied to 808 grid for direct drive.The anode is tied directly to a tap on the output transformer for partial feedback.
A quick look at the 6au5 pdf and I think it will fit.A slightly higher Sg2 voltage somewhere over 150v for about 30v vk .
So the driver is well screened from power supply hash,has the brawn of goliath and the brain of einstein to control the 808 output.And of course great sound!!! 🙄 🙂
A quick look at the 6au5 pdf and I think it will fit.A slightly higher Sg2 voltage somewhere over 150v for about 30v vk .
So the driver is well screened from power supply hash,has the brawn of goliath and the brain of einstein to control the 808 output.And of course great sound!!! 🙄 🙂
I agree that the 807 is the best looking of the bunch, it just bothers me a bit that it is almost as tall as the power tube. Something with the same bulb shape but smaller would be ideal!
I don't have the data for all these tubes in my head but assuming they can handle the dissipation and ~100mA peak cathode current, then the one with the highest gm should be the best choice for a cathode follower. E130L would be ideal, but they seem quite rare and expensive.
This sounds very familiar to a circuit I tested around 2012 or so: An 807 wired as a follower direct coupled to the 808, but with the screen grid connected to a tap on the OPT primary winding for feedback. I seem to remember that it worked quite well but the G2 voltage worried me a bit, around 400V at idle and then 100-150V swing on top of that. Probably too much for an 807 in the long run but perhaps an audio tube (6L6GC, KT88, EL34 or something) could handle it safely.
6Y6 should work, I even think I have a few on the shelf. Unknown condition though.
It's not really breadboarding time for this project quite yet but I couldn't resist doing a quick experiment with the setup that is still on the bench after testing tubes and output transformers some time ago. I mentioned CFB from the 16 Ohms secondary tap earlier. As the 808s are DHTs, that would require floating 7,5V 4A filament supplies that can swing +-20V or so with low capacitance to ground, This could become a problem, especially if I get lazy and decide to use my pair of 7,5V 20A switch-mode power supplies that I use for the tests.
After scratching my head for a while I figured that I should be able to get the exact same results if I drive the (mosfet...) follower with an interstage transformer and inject the NFB signal from the 16R tap into the "cold" end of the secondary winding:
No DC through the speaker winding and no need for floating filament supplies, so far so good. It even seems to work and gives a whopping 4dBs of negative feedback. Worth mentioning is some nasty HF instability (which probably can be cured by cleaning up the rats nest of clip leads and replace the 150H choke from grid to ground with a resistor or CCS to a negative rail) plus the fact that 4dB NFB probably isn't enough and the IT will be in the way for any global NFB. Bummer.
It's not really breadboarding time for this project quite yet but I couldn't resist doing a quick experiment with the setup that is still on the bench after testing tubes and output transformers some time ago. I mentioned CFB from the 16 Ohms secondary tap earlier. As the 808s are DHTs, that would require floating 7,5V 4A filament supplies that can swing +-20V or so with low capacitance to ground, This could become a problem, especially if I get lazy and decide to use my pair of 7,5V 20A switch-mode power supplies that I use for the tests.
After scratching my head for a while I figured that I should be able to get the exact same results if I drive the (mosfet...) follower with an interstage transformer and inject the NFB signal from the 16R tap into the "cold" end of the secondary winding:
No DC through the speaker winding and no need for floating filament supplies, so far so good. It even seems to work and gives a whopping 4dBs of negative feedback. Worth mentioning is some nasty HF instability (which probably can be cured by cleaning up the rats nest of clip leads and replace the 150H choke from grid to ground with a resistor or CCS to a negative rail) plus the fact that 4dB NFB probably isn't enough and the IT will be in the way for any global NFB. Bummer.
Payday today, an event usually celebrated by buying something stupid that I don't really need. In this case, a bunch of cheap Soviet dual tetrodes with dual top caps and a funny looking glass bulb. With both sections in // they should be as good as any of the tubes in the first post as a cathode follower, and I imagine they can look good* with the socket mounted from below on standoffs so that only the top half of the tubes stick up through the chassis. If not, I can always build something else with them.
* Good as in "high Frankenstein factor", not good as in "rare expensive 1930's triode that would look genuine next to the 808".
* Good as in "high Frankenstein factor", not good as in "rare expensive 1930's triode that would look genuine next to the 808".
The G or the GA? Back to the beauty contest again. I got a bunch of the similar 6W6, but that GT isn’t as pretty for sure. If it had a top cap…..
Those old “110 volt AC/DC audio output” tubes do lend themselves to all sorts of off-label applications.
6Y6G would look great next to the 808, and it seems to have a decent gm too. Unfortunately they don't seem very common here in EU, and buying tubes one by one and pay shipping for each one would quickly get rather expensive.
The last thing I did before bedtime yesterday was to line up one each of 808, 6AV5GA and CV1135 (~2C22, 7193) in a row in front of one of the output transformers. They all have black bakelite sockets and look quite good together, will post a picture later.
The last thing I did before bedtime yesterday was to line up one each of 808, 6AV5GA and CV1135 (~2C22, 7193) in a row in front of one of the output transformers. They all have black bakelite sockets and look quite good together, will post a picture later.