Dual Simple SE's in Push Pull w Differential Input

[Anchan]

Decided to return the KT88's. I realize I am pushing the transformer, and I don't need that much power. I ordered a quad of 6V6-S's. Looks like they are good up to 500V.
JJ 6V6S

I also have some EL84's, so I'll try out both. I am a little concerned about the choke 200ma rating when used with the EL84s. I probably should have ordered a bigger choke, but I am out of real estate on my chassis.

[Anchan]

I hooked it all up a on temporary piece of plywood, just to work out all the details, take measurements etc. A friend with a mill is cutting some holes in a proper chassis for me meanwhile.

Anyway, it sounds AWESOME. Absolutely fantastic. Thanks George for a killer design of the SE, and it really works great in PP.

I was a little concerned that the OPT were a little too big for the power I would be running them at, but there is a lot about of detail coming through. And the bass really extends very deep and clear.

In fact, the EL34's are probably way more power than I need. But I will run them for a while to see how I like them. I'll pop in the 6V6-S's later.

I feel like I am in the minority here, but after listening for a few hours, I tend to prefer the sound of UL vs triode strapped. In triode, I find the treble kind of grating and irritating, and the bass does not extend down so far. It could be that my speakers which are horn loaded, so I don't need need the mids highlighted.

Anway, I am very pleased. Thanks again George.

[Ian444]

So good to see a great outcome. You are a much smarter cookie than I would have thought. Big learning curve and you managed to put it all together, even with unorthodox differential input. I say extremely well done!

[Anchan]

Thanks for the complements, but it turned out to be a lot easier than I thought at the outset. Mostly followed George's instructions, and learned a few things along the way.

One thing I learned is that although the El34's do sound good indeed, it is a whole lot of power. Although the amp can be very delicate at low levels, it can be downright pummeling. Also, since I am using a single GZ34 tube + C354 choke, I seem to have restricted myself to 200ma MAX. The choke is getting damn hot and I've heard that the GZ34 doesn't like much more than 200mA either. I currently have the 84's biased at ~53ma/23W.

I am going to try to select some not so pummeling tubes (to my ears and power supply).

I'm looking for some tubes that like the 420-450 range, and that bias in this situation in the less than 40mA range.

So far, some likely candidates are:

6V6-S
7591-A (I think)

Any other recommendations? New production only, and not impossible to find.- Thanks

[tubelab.com]

Also, since I am using a single GZ34 tube + C354 choke, I seem to have restricted myself to 200ma MAX. The choke is getting damn hot and I've heard that the GZ34 doesn't like much more than 200mA either.

You can use 2 5AR4's and 2 chokes if you want. Just wire the power transformer secondary to both boards, and then run each board off of its own rectifier and choke. That's how I had mine connected. Your transformer has a 4 amp 5 volt winding, so there is enough current to feed 2 rectifiers. The rectifiers are essentially in parallel since they share a common heater winding.

Any other recommendations? New production only, and not impossible to find.-

Most 6L6GC's should work. I use the cheap Chinese ones. You are still going to get loud, about 30 WPC worth of loud. I think that you will find that the EL34's sound better though.

[Anchan]

Originally Posted by tubelab.com

You can use 2 5AR4's and 2 chokes if you want. Just wire the power transformer secondary to both boards, and then run each board off of its own rectifier and choke. That's how I had mine connected. Your transformer has a 4 amp 5 volt winding, so there is enough current to feed 2 rectifiers. The rectifiers are essentially in parallel since they share a common heater winding.

Ok, so all you are saying is populate both power supply sections of both boards. Have the HV secondary as well as the 5V secondary connect to both boards. Connect the 2 chokes to their corresponding board and thats it.

Since the rectifier filament appears to be tied to the unfiltered B+, and if each rectifier tube's output is slightly off with to respect to the other, I would think that the higher unfiltered B+ would 'go into' the lower potential B+. I have paralleled 2 power supplies before (not tube rectified), in which case I would put a diode on the output of each one, and connect the cathodes together. But really, I don't quite understand how the heater winding works, especially in a tube rectifier, so I totally take your word for it. I just want to make sure my interpretation of what your saying is correct before I go making 400+V connections.

[tubelab.com]

I would put a diode on the output of each one, and connect the cathodes together.

Think about it this way. The HV primaries are going to both boards, so the plates of the rectifier tubes are wired together. The 5 volt heater windings are going to both boards so the cathodes of the rectifier tubes are wired together. So what you have are two rectifier tubes wired directly in parallel. Yes they will not share the current exactly equally, but two tubes in parallel will deliver more current than one alone. It would be wise to use identical rectifier tubes to help equalize the current sharing. If you haven't placed C1 on one of the boards leave it out. This will make life easier on the tubes on start up and won't affect the voltage much. You need ONE C1 but two may be too much for the weaker of the two tubes.

You could simply wire the two chokes in parallel and run both boards on the doubled up power supply, but there is some channel seperation improvements to be gained by seperating the two channels after the rectifiers. So one choke drives each board using the C2 on its particular board. The ckokes will run cooler since each only runs one channel. This provides most of the benefit of dual mono operation without the expense of two power transformers.

Make sure each transformer wire goes to the same terminal on each board.

[Anchan]

I got it.

I have some more parts on order and will report back once I wire it up.- Thanks

[Anchan]

So I did what you said. Jumped the HV secondary and the 5V secondary from board 1 to board 2. I was careful to keep the same polarity on each. On board 2 I left off C1. I have 2 chokes now- each wired to its corresponding place on each board. The chokes are not 100% identical. One I got at dynakit parts, and is unshielded and as usual fairly ugly. The other is the same spec, but I bought from Triode. Triode has the nicer looking shielded version, and since I am out of room under the chassis, I figured this one looks OK to put on top.

Anyway, it was odd that the choke on board 2 (Triode elec) was getting warm (but not hot), and the choke on board 1 was not (dynakitparts).

I measured B+ on both boards. B+ on board 1 was 422V and on board 2 it was 407V.

Upon closer inspection, I realized that the new rectifier tube, on board 2, was not the same as the first one. My original rectifier on board 1 was a sovtek 5AR4. I ordered the same part again, but for some reason they sent me a JJ GZ34. Anyway, maybe this explains the weirdness. I'll see if I can return this JJ for the actual part I ordered.

Could the use of 2 different tubes cause this much of a discrepancy? I also wonder why one choke was so much warmer than the other. I'll check my connections again, but I am pretty sure its all correct. I have R2 installed on both boards. Is this correct?

[Anchan]

I just realized that I had both red wires from the middle of the OPT's connected together, both tying to the 2nd board's B+. That is now corrected, and each red wire from each OPT goes to its corresponding B+ on the different boards.

Each board is getting about 415-420 V now. I still plan on returning the JJ for a Sovtek.

When I had one rectifier and one choke feeding both boards, B+ was around 425-430V.