Remember These?

[Ray P]

No problem Steve, I'm not blamng you

I wasn't even aware of the 13E1 before you started this project.

Will be interesting to see how it shapes up as you will no doubt perform some fettling over the coming days. I will watch with interest as I mull over the decision I need to make.

[Ray P]

I'll have a look at the regs you suggest.

Steve, if its of interest I can donate one of these to the project?

http://www.audio-talk.co.uk/phpBB3/view ... tatistical

[Ali Tait]

How does it compare to the mini beast Steve?

[Cressy Snr]

I'll have a look at the regs you suggest.

Steve, if its of interest I can donate one of these to the project?

http://www.audio-talk.co.uk/phpBB3/view ... tatistical

I've got four of those made up Ray.

[Cressy Snr]

Hi Ali,
I'm afraid the Mini Beast is well beaten.
I don't think it's any fault of the Mini Beast itself; I think it's the just that the valves in my amp are better. The basic circuit is almost the same as the Rozenblit amp, apart from the use of a CCS on the cathode as opposed to the choke loading and negative bias supply on the MB.


I was talking with Steve, when I bought 3 off, 13E1 from him a few weeks ago and he suggested that 13E1 would perform better than EL/PL509, simply because they are better made, use better materials, are tough as old boots, and British, from the last great era of valves, ie the mid '50s to the late '60s. As Steve knows his stuff about old Brit valves, I wasn't surprised when it turned out he was right.

I have two good pairs of 13E1 now, one from the '60s and one from the mid '50s, so hopefully they'll do their stuff for a long time to come.

[Cressy Snr]

or the CCS chip

You could add a series resistor to reduce the CCS dissipation.

Could have a play with that idea later on, after I've done the rest of the building work. It'd be interesting to push the 13E1s for another ten watts dissipation. OTLs are so bloody inefficient though, it may be questionable in terms of getting any more output power. Breakup might be pushed further out OTOH, though my ears give up before I can get it to clip.

I strongly suspect, that the excellent performance of this OTL in my system may be down to the flat impedance curve of the Fane 12-250-TC speaker driver. It is a very easy load.

[pre65]

I strongly suspect, that the excellent performance of this OTL in my system may be down to the flat impedance curve of the Fane 12-250-TC driver. It is a very easy load.

Is the 15" version (that Ant uses) as easy a load ?

[Cressy Snr]

I strongly suspect, that the excellent performance of this OTL in my system may be down to the flat impedance curve of the Fane 12-250-TC driver. It is a very easy load.

Is the 15" version (that Ant uses) as easy a load ?

Yep.

EDIT: One caveat, is that the Re of the 15 incher is 5.2R as opposed to 7.2 Ohm of Re for the 12 incher. Given that difference, I suspect that the 12 incher would perform better in an OTL situation than the 15. Doesn't look like much, but in OTL speaker drive capability terms, it could be quite significant.

[Wolfgang]

After listening for a while with the 6SN7/6C33 OTL I tried to find reasons for the different sound compared to TS amps.

The TS amps also use a cascaded grounded cathode input stage and still they all suffer from too much "brightness" in relation to a solid lower mids foundation. Or we could say that they don't deliver enough lower mids/upper bass for the otherwise wonderful openness in the upper mids/treble. For overdamped rooms/rather less sensitive speakers with x-overs this can be exactly the right amount of "boost" to make it sound right. But for single driver speakers and acoustically treated large rooms it is not so well balanced anymore.

I had started to experiment with adjusting the four 300Bs of the 300B SE OTL for the same Ip, long before I started building the 6C33, because I simply could feel that too much fluctuations cannot be good for good SQ. Rozenblit thinks it is good if all tubes operate differently because it makes a better soundmix (as he wrote in one of his rare posts referring to the discussion about missing autobias for the Pinnacles).
I could find that the SQ can be improved a lot by making each tube adjustable with a separate pot, giving each filament its own transformer, and each tube its own buffer cap. The sound changed in the direction of a single tube OTL like the 6C33 for instance. This is also true for the Pinnacle. The other dramatic change - interestingly enough also improving in the direction of the 6C33 OTL - came from lowering the NFB quite a bit (increasing the resistor) and rather adjust it to the speakers than getting it down to the lowest output impedance/ highest possible DF. I haven't tried this with the Pinnacles yet but I am sure it will have the same positive effect.

When I listened with the improved 300B SE DC I was very impressed and thought I had found my final amp. After listening to the 6C33 for the first time (adjusted for perfect sine and CDF for the DX4) I couldn't believe how much better my system could still sound and how much potential was still in there which I hadn't even touched for all these years. The message for me was clear: there is a lot of dormant potential in the TS OTLs but the best sounding OTL is one with a single output tube and with as little parts as possible. Pity that we won't have a direct comparison between the OTLs with a 6C33 and the 13E1 if Ray doesn't finish his 6C33 OTL.

[Cressy Snr]

The message for me was clear: ...the best sounding OTL is one with a single output tube and with as little parts as possible....

Well I have to agree there Wolfgang. Thank goodness the 6C33C is available and (though rare and expensive in comparison) the 13E1. The 13E1 is probably the ultimate for single tube OTL operation, unless there is another big series-pass regulator tube out there, that no-one has thought of using yet.

Reluctantly I have to put the breadboard away until the new year as I have a room remodel to finish off, but once that is done, I'll try optimizing the feedback. I think it is pretty close at 4K7 Rfb, maybe 4K2 will be the optimum value, but this afternoon I played the Claptone remix of the track "Liquid Spirit" by Gregory porter at a healthy volume and found that the poweful bass synthesizer underpinning the track was actually playing a tune and separated itself out from the pounding synth bass drum. It was easy to listen to the complex and subtle front to back and side to side layered effects and sampled audience noises. I have not heard this track as well reproduced on any other piece of equipment I've had in the system. Truly an eye-opener, have to say.

[Ant]

Heard it today, it does the otl thing at the top end with lovely silky treble, but doesnt let go at all at the bottom
With the fanes on the end of it.
It just doesnt seem to run out of poke. In some ways it reminds me of the f5. But better.

It requires a very nice box or boxes to put it in

[Ali Tait]

Hi Ali,
I'm afraid the Mini Beast is well beaten.
I don't think it's any fault of the Mini Beast itself; I think it's the just that the valves in my amp are better. The basic circuit is almost the same as the Rozenblit amp, apart from the use of a CCS on the cathode as opposed to the choke loading and negative bias supply on the MB.


I was talking with Steve, when I bought 3 off, 13E1 from him a few weeks ago and he suggested that 13E1 would perform better than EL/PL509, simply because they are better made, use better materials, are tough as old boots, and British, from the last great era of valves, ie the mid '50s to the late '60s. As Steve knows his stuff about old Brit valves, I wasn't surprised when it turned out he was right.

I have two good pairs of 13E1 now, one from the '60s and one from the mid '50s, so hopefully they'll do their stuff for a long time to come.

Cheers Steve, look forward to hearing it.

[Ray P]

I took the plunge and committed to buying a pair of 13E1 valves - decision was helped by selling on my Slagle autoformers.

[Cressy Snr]

I took the plunge and committed to buying a pair of 13E1 valves - decision was helped by selling on my Slagle autoformers.

I don't think you'll be disappointed with them.

We need to keep quiet. The buggers are expensive enough as it is!

Mind you, having said that, there are plenty of peeps around, who, without blinking, will pay a heck of a lot more for posh 300Bs

[Ray P]

Yes Steve, they're not commonly available but I still paid less than I would for even a a pair of EH 300B Golds. I will keep an eye open for another pair in due course, maybe even some NOS.

Fortunately the 6C33C and 13E1 amps share most of the parts so I have options to build both should I feel so inclined. The main thing I need for a 13E1 build is a transformer for the output stage B+ (more volts and amps than the one I have for the 6C33C can deliver) but I can probably make use of the toroids I offered to lend you a few posts back. 135VAC * 1.414 = 190VDC, minus 20V or so for the CLCLC filtering, gives a B+ of circa 170V; each secondary is rated for 1100mA so they'll be good for a B+ current of 500mA, which would mean 85W dissipation - maybe pushing things a little?