New SE With Triode Mode KT120/150

[Cressy Snr]

The Super Rocky development chassis for the proposed new amp, has had an output stage rebuild today.

The reason for doing this was that I wanted to get those KT120s out of the vicinity of the output transformers. So...the output stage circuit was dismantled. The heater wiring was moved to the front set of octal sockets, which had housed the original 6SN7s. This was then followed by a rebuild of the output stage circuit.

The KT120s now occupy each end of the front row, with the 6N1P between them:

OPTs now run nice and cool and I was able to raise the HT to its previous level.

MH4s are on their way from Steve’s and Ant has ordered the aluminium for the new build top plate.

[izzy wizzy]

Bit like musical chairs. Good to know the redesign will have the desired outcome.

[Cressy Snr]

Yes, it’s coming along quite nicely.

Testing the rebuild did show up a slight issue with the 6N1P front end. The two triode sections were poorly matched in the valve I was using.

When I first introduced the 6N1P, I’d just checked for 2V (or thereabouts) of cathode bias, without measuring the anode voltages (too tired and it was late) and had just accepted the fact that it was working. It turned out that it was reading +/-20V anode volts between sections, which was way outside the 10% I’d normally accept.

I plugged in another that had an OTK mark (the previous one didn’t) and it was +/-3V between sections, which was a helluva lot better.

[Cressy Snr]

So we have another little test concluded with most satisfactorily results.

I put the KT120s into ultra-linear mode this evening and the results were pretty good. I’ve only ever used it in triode and pentode mode, and like pentode mode, I wasn’t expecting ultralinear mode to be that viable unless feedback was employed, but it seems to work fine with my Fanes without it.

I thought I’d try SEUL after having a look at Michael Abdellah’s single-ended ultralinear KT88 amp, on the DIY Audio Projects website. His SEUL amp uses a 6N1P driver and he doesn’t use any feedback, so I thought, why not try it out? The connections were there on the Hammond 1627SE output transformers, so it wasn’t exactly rocket science to give it a go.

The best feature of the KT120s in UL mode is in the portrayal of voices. They appear in the room between the speakers, large as life. This was also a characteristic of my pentode amps, when I was into push-pull. Plenty of shimmer to cymbals too.

Working off the the loadline tools website, it looks as if the amp is now giving 17W per channel. Very useful.

So the new amp will be equipped with a “Triode/Ultralinear” switch.

[Cressy Snr]

So the new amp will be equipped with a “Triode/Ultralinear” switch.

Er...no it won’t.

It’s ultralinear all the way. Great sound and real world power levels. The Hammond 1627SE output transformers are also stonkingly good in ultralinear configuration, as are KT120s, though that last bit shouldn’t be all that surprising, as that is how they are designed to operate. Might as well get focussed on one thing and go with it. Waiting with anticipation for those MH4s.

[steve s]

Thought you would have them by now steve. But when I was in the post office the woman behind me was complaining how long small parcels where taking.

[Paul Barker]

It’s ultralinear all the way.

Thread title needs altering lol. I can’t talk my dyslexic thinking box moves wildly from stepping stone to stepping stone in my posts and visits many random asides along the way usually culminating in an entirely different direction.

[Cressy Snr]

Thought you would have them by now steve. But when I was in the post office the woman behind me was complaining how long small parcels where taking.

No, not got them yet Steve. Our Ant was also complaining about the length of time things were taking to arrive. Because everybody is shopping online the channels are full and staff is short.

[Cressy Snr]

It’s ultralinear all the way.

.... I can’t talk my dyslexic thinking box moves wildly from stepping stone to stepping stone in my posts and visits many random asides along the way usually culminating in an entirely different direction.

A bit like me with this project. It was on a whim, that I tried ultralinear and in this particular application, I can’t fault it.

No matter how much I try to talk/think my way out of it, ultralinear is just so much better in every respect, with this valve and these output transformers. It’s weighty, solid, powerful, and clean, which is just how I want it.

I suppose the moral is, that if you want the true sound of single ended triodes, then use real direct heated triodes. Otherwise, use your pentodes or beam tetrodes how they are designed to be used, and enjoy them, how they are meant to be enjoyed.

Ultralinear GK71 or 813 anyone?

[izzy wizzy]

I suppose the moral is, that if you want the true sound of single ended triodes, then use real direct heated triodes. Otherwise, use your pentodes or beam tetrodes how they are designed to be used, and enjoy them, how they are meant to be enjoyed.

Ultralinear GK71 or 813 anyone?

You've reminded me, should have stopped at that side street with the 813s. The OPT I have has ul taps but didn't use them. Too many scars from past failures I guess. Good result for you though.

[pre65]

Ultralinear GK71 or 813 anyone?

Unfortunately, my big Hammond OPT does not have UL taps.

[Paul Barker]

The ultimate would be the opt feedback winding and an ultralinear tap or two, one for each ultralinear percentage you would like to make sure is right for you.

There is a Llundahl which has the feedback winding like the Quad II opt design. Most Lundahls are so flexible you can play with options such as this.

I put a Quad feedback winding on my last Pp amp played at Owsten juts beside Mark’s 300b. I thought my PP amp worked, most attention was on the discussion about Mark’s bass qualities so I didn’t get any feedback, but I liked it. Yes the quad feedback is another thing you musnt neglect to incorporate in youre pre-build ideas.

[Cressy Snr]

The MH4 globe meshies, courtesy of Steve, have arrived this morning.
Handsome little divls they are too.

Need to start drawing up some diagrams and ordering some parts.

[IslandPink]

Yum ! - they did look nice when I went looking for data & pics a few days ago.

[Cressy Snr]

Picked up the 18 x 14in afrormosia chassis up today:

Two of my Eyuda 80uF oil filled motor run caps will once more, be gracing the top plate of an amp with their presence; once I’ve polished them up that is.

Now I have the unenviable task of taking the Super Rocky to bits, in order to to liberate the transformer set. I’ll be using the NVA clone until I get the amp built and running.

Because of the globe MH4s and the possibility of using KT150s, I’m naming this creation “The Globular Cluster”