The Other 13E1 SE-OTL

[Ali Tait]

Looking good Ray.

[Ray P]

So I've had a good spurt of progress with the 13E1 project and have now completed assembly of one channel and had it playing music - worked first time too so maybe I'm getting the hang of this DIY audio buiding, that's four projects that have just worked!

Power supply for the 13E1s is CLCLC but I'm using a Maida regulated supply for the input/driver stages based on the 6H30pi. 13E1s are getting around 160V and the input/driver 150V. I'm using a K&K Two terminal Cathode Current Sink, set to 475mA at the moment. I've set the feedback resistor to 2K5 for now using some 20turn preset pots so I can experiment when I get the build progressed further.

The only scary moment was on first turn on when I was in danger of damaging or destroying the 13E1. The K&K current sink documentation says you can preset the current level and that's what I did but on turning it on it was much higher and so would be exceeding the max dissipation of the valve - I haven't worked out why that happened yet. Anyway, after quickly turning it off I did what I should have done all along and set a very low curent that I could then adjust upwards!

I can't give any definitive view on the sound quality as there more set up needed and I only listened through a cheap sacrificial loudspeaker that I keep for these purposes - it hasn't had to be sacrificed so far.







Also, I contacted the chap who supplied Ant with the Olive wood for his TT power supply and he's going to provide me with a piece large enough for a front panel for this project - nice (hopefully)!

[Cressy Snr]

You’re in for a treat once you’ve got it all up and running on your main speakers.

[Ray P]

I hope so Steve. Unfortunately I have to work for the rest of the week so it'll be the weekend before I get the other channel done - I don't want to try and rush it when I'm getting tired and make a cock up!

[IslandPink]

Scary stuff with OTL's, but good progress, watching with interest.

[Ray P]

I folowed up on the information Ant passed me and have just ordered a large Olive wood chopping board to repurpose as a front panel for this project. The ebay seller was accomodating and is going to select a board that is large enough. Should hopefully look nice - as long as my limited woodworking skills do't let me down!

[Ray P]

Second channel hooked-up, tested and producing music!



Now I need to pluck up the courage to plug in the Lowthers and give it a proper go - time for a break and a coffee!

[Ray P]

I also worked out why I got the high current sink measurement with the first channel - I set it up using a 20V supply, including using that as the power for the voltage reference section of the current sink - what I should have done is used the B+derived power (via a dropper resistor but still higher voltage) for the voltage reference section and the 20V just for the cathode input. That's what I did with the second channel and it worked perfectly with presetting the cathode current. Obvious when you think about it so a bit of a numpty error but I learned and no harm seems to have come from it.

I'll get that coffee now.

[Cressy Snr]

Get on with it man!

Seriously though. I was shaking when I powered mine up with a broom handle from six feet away, but it all worked in the end.

[Ray P]

The deed is done

Temporarily sitting on top of the Atacama rack with plenty of ventilation around it.



Source is my little Shanling portable headphone player via the Aunt Corey buffered passive.

It plays music! I'm having a listen now, first impressions are very positive.

[IslandPink]

Nice work , excellent !

[Cressy Snr]

Wahey!

[izzy wizzy]

Great milestone Ray. Well done!

[Ray P]

I like it!

It's quite different to the 300B OTLs and I think I can say that overall it is better - maybe not quite as sweet at the top but overall the presentation is much fuller and weightier; Instruments and voices have a richer timbre and the bass is nice and detailed but has much more presence. Detail and imaging is up there with the 300Bs. With the 300Bs (and the orignal Transcendent SE-OTL before that) I have always thought that my Lowther horns could sound a little 'lightweight' at times but this amp seems to address that such that I found myself wondering why I'm planning another speaker project. And this is all with the amp straight from the bench and I've not experimented with the cathode current (475mA) or feedback (pots set to 2.5K) and this is still with my portable headphone player (playing FLAC files, no MP3 involved) as the source. I'm excited about the prospect of plugging in my DSD decoder as the source as my next step and spending more time with it.

BTW, the Lowthers are 15ohm units so giving the amp an easier ride than typical speakers.

On the downside;

• There's a tiny amount of hum but only really audible if you're close to the speakers

• It's an effective room heater - nice on those cold, dark winter nights! At the moment it is emanating that 'newly warmed electronics' aroma.

[IslandPink]

I did hear there's a heatwave moving up from the South, later this week !