Best Tube 4 Solid State

[Jay]

Miguel,

I was wrong about ECC88. What I have are 7189 (like that in the other thread). I thought I was saying EL84.

Tony,

I think the 5842 is the military version, right? If you are going to upgrade your pre-amp to the Euridice, I will need to follow your progress

I don't know how to tweak tube amplifiers. If your circuit differs from the Euridice, it will be nice to have one. This is because the relative values for OPT and supply voltages (transformer) are what I don’t understand (or at least don’t remember) and thus what I’m afraid of. I don’t want to buy an OPT, reject the amplifier and cannot re-use the OPT for other projects.

It will be nice if you or anyone can give me a brief explanation about OPT choices for this purpose.

[apassgear]

My circuit differs from the Euridice only in the way that I have replaced the OPT whith a plate load resistor and added a coupling cap at the output, 2x 5.6uf Axon's. The bias is set at 18 mA with a 30 Ohm resistor at the cathode.

For this reason I'm running the stage with +B of 180V but will lower this to about 100V as soon as I add the OPT. Since I have a string of zeners as voltage reference on the regulators this will be a very easy task.

I will be rolling my own OPT and see if I can replace the plate and output cap with some advantage. In any case the output power will be greatly improved maybe by a factor of 10!!! Way over kill for the Aleph but is nice to have spare drive power and lower impedance in a line stage.

On comercial OPT I know of two offerings that will fill the bill, One is the Batolucci M2 or M3 size design for these type of tubes at around US$143 for the small size (enough in my opinion and would be my first pick) and the other is the Lundahl LL1660 gapped for 18 mA, cost aroud US$85. Yes they are not cheap. You could find others at lower cost but would not take the risk if I had to buy them.

The Bartolucci was used by Thorsten Loesch on his implementation of the Euridice circuit, see his web page.

And have read on other forums of using Lundahl OPT with good results. My opininon is that this OPT is just on the limit for the 417A which I now have it biased at 18+ mA so would have to cut down on the operating point to some 12 or 14 mA.

Still interested?

[apassgear]

Jay,

If you have available the long green you won't regret buiding the Euridice, this one is for keeps if well implemented.

During the years as DIY I have tested (and built) quite a number of line amps from SS , hybrids and tubes. Tubes from the 12ax7, 6SL7 families and 6DJ8 (6922) of course not all the possibilities with these but in any case quite a number of those including cathode followers (which sucks IMO).

The best experiances have been the 6922 and way better the 417A (5842) (in my audio system), both as common cathode.

I would have to add in justice to the 6922 that this L amp was not as well implemented as the later 417A, and think the 6922 is an excellent tube if not overloaded say for a tube amp application, but not to the task of a 10K load as an Aleph or Zen.

[apassgear]

Jay,

Have a look at the Frank's Ultimate Line Amp thread, here you will see a very interesting proposal from Frank, on development phase.

[Jay]

Tony, sure I’m still interested.

The OPT, I think I have a pair lying around, but don’t know if they are suitable (I think they will if Lundahl are really gapped for 18mH). They are from the 18W 7189 if I’m not mistaken. But instead of doing an internet purchase, I think I’ll prefer to have a professional winds the OPT for me.

But then if I found out it is true that this one is good, I would find the best components for the substitution. But I would still use solid state for the final amplifying section.

As long as I can remember, in the Euridice I saw 5V and 6.5V supplies. I noticed that 6.5V is common for the heating elements. But, why cannot we use 5V for both? Or 6V for both? In case such TR is difficult to get? Wait, we can use a separate TR, cannot we? So it’s not as difficult as I thought…

Well, searching information for 6922 and 5842 (as well as their substitutions) and doing a market survey for these tubes are first things I’m going to do.

[apassgear]

Jay,

The drive power available from the 5842 is way higher than that of the 6922 which is a double triode, also I would not recoment to use the later one in parallel sections even if it can be done such as shown on the World Audio Design web site that Maxwell suggested.

You may try the OPT you have, the 5842 will drive it (I think)though not optimally since what you have will be gapped for higher current. Wait a second, I guess what you have is for a push pull amp and those are not gapped in any case you may also test it and see if it doesen't get to hot, say above 60°C. You could try the plate connection from the center tap to one of the ends of the primary and see what happens at the secondary. You will beed a +B on the order of 100V

Do you have access to a scope?

The PSU trany you need will depend on the PSU you will decide upon. Both tubes would need a 6.3 V heater supply, I like to use DC for this so a LM317T in texbook implementation will be nice, two regs will be needed for the 5842 one each for a stereo Line Amp. so a at least 10V secondary is needed for this (I use 18VAC secondary) and this can be from a separate trany (is what I have).

If you plan to rectify the +B with a vacuum tube you will need most probably a 5VAC depending on diode tube selected. can also be from a different iron.

The other voltage needed from the trany will be for the +B but onece again the voltage will depend on the way you plan to rectify if vacuum or solid state and type of regulator (if any) you will be using.

Plan for some 180V +B if you will be loading the plate of the 5842 with a resistor or around 110V +B if using an OPT.

In my case was all SS with a somewhat elabotated implementation, but think it was wothwhile.

So if you go SS only two AC voltages are needed.

[apassgear]

An additional comment on using a non gapped trany for this application.

I have to change what I said about using an ungapped trany with unbalanced DC. If you try this you will find that you will be working at the iron saturation region so nothing good will you hear.

So for an apropriate testing you need to use a gapped OT to avoid saturation on the iron.

Got carried away, sorry.

[Jay]

I have done the market survey for the tube pre-amps. And the result is I cannot yet find a transformer coupled pre-amp (One supplier is being importing parts for such a pre-amp).

I decided to build a 3-gain line stage using 3 units of 12AT7 per channel (I'm now collecting the parts), and need now a good recommendation or confirmation on the tube types…

The Mullard CV4024 (military) price is about 3x the 12AT7. Is it really worth to buy the Mullard?

The PS is using 6Z4, 12B4A and 12AT7. For the 12AT7 I will buy the cheapest (US$10-). For the diodes (6Z4), I wonder if there is better replacement (if it really affects the sound)??