audio-talk

Posted: **Wed Nov 07, 2018 6:59 pm**

Now this might not go anywhere so don't get excited...but.....

Inspired by Ray and Wolfgang. I dug a pair of these 13E1 out from my box of remaining valves (those I didn't offload Steve's way):

A SEOTL running 150V at half an amp is within their capabilities.

Do we think it's a go-er?

I'm being serious as I know well how OTLs can be a right b'stard, so I'd appreciate all the help I can get.

Posted: **Wed Nov 07, 2018 7:03 pm**

Yes, I remember your 13E1 valves.

Time to try an OTL.

Posted: **Wed Nov 07, 2018 7:04 pm**

Yes.
After hearing what both the Rosenblit 300B OTL and the Minibeast are capable of in my system. I thought a 1W 13E1 SEOTL might make an interesting project as a diy build. Of course, there is Ali's Mini Beast which I would like to buy off him, but it'd be interesting to see how an OTL of my own design, would pan out too.

Posted: **Wed Nov 07, 2018 7:13 pm**

As with the 6C33C, stopping the bloody things running away will be half the battle. GM is 35mA/V

Posted: **Wed Nov 07, 2018 8:10 pm**

You little tinker !

Posted: **Wed Nov 07, 2018 8:15 pm**

Have you finished the building work yet Steve ?

Posted: **Wed Nov 07, 2018 8:37 pm**

Not yet. This amp project is something to do to stop me getting bored with the building work. The work is well on its way to being finished by December.

Posted: **Wed Nov 07, 2018 9:56 pm**

Interesting Steve. Wolfgang is the electronics brains of our little partnership and I'm sure he'll be interested and will drop by with some thoughts.

Should it be appropriate, and/or a road you're considering, I have some spare PCBs for the Aikido driver stage that Wolfgang and I are using for our 6C33C OTL amps.

Ray

Posted: **Wed Nov 07, 2018 10:31 pm**

Ray P wrote: ↑Wed Nov 07, 2018 9:56 pm Interesting Steve. Wolfgang is the electronics brains of our little partnership and I'm sure he'll be interested and will drop by with some thoughts.

Should it be appropriate, and/or a road you're considering, I have some spare PCBs for the Aikido driver stage that Wolfgang and I are using for our 6C33C OTL amps.

Ray

Hi Ray,
If I get going on this project I'd definitely be interested in the Aikido PCB to drive the thing.
The 13E1 in triode mode, has a mu of 4.5 as opposed to the 2.7 (I think) of the 6C33C. It also has the same 130R internal resistance as the Russian valve.
13E1 max plate diss is 95W, although I wouldn't want to be too near that. Morgan Jones had to pull the valve away from that kind of dissipation when he built the Crystal Palace amp. The twin heaters dissipate about 34W.

I wouldn't mind loading the cathodes with parallel 10 Ohm DCR, Triad C40X chokes and grid biasing them with a negative supply.

Posted: **Wed Nov 07, 2018 10:45 pm**

Just let me know if you want a pair of PCBs and I'll get them to you in a jiffy (bag). The boards include the driver stage but also hold the current sink and output caps that we have in the 6C33C schematic.

I've looked at the 13E1 and they're not quite giving them away!

As you know, heat dissipation will be one of the main issues to deal with. That's why I have the concentric cooling slots around the 6C33C sockets with the option of fans mounted in the bottom of the chassis - I'll post pictures as I progress my own build. Talking of sockets, a lot of the current manufacture septal sockets from China and Russia aren't great - good contacts are essential with the high currents we're talking about, which is why I splashed out on the old Johnson sockets I'm using. There's a guy on DIY Audio selling some sockets that look better than most (it's an old listing but I believe he still has some availabe);

https://www.diyaudio.com/forums/swap-me ... ocate.html

Ray

Posted: **Wed Nov 07, 2018 10:53 pm**

I have a pair of NOS English Electric Valve (EEV) military septar ceramic sockets, so I'll try those first. I'll let you know about the PCBs.
Thanks Ray.

I'm only using 13E1 because I have a pair from years ago. They are pretty expensive now.

Posted: **Thu Nov 08, 2018 1:30 pm**

Max. plate dissipation and current were the biggest limitations with the 6C33 for OTL operation. A 13E1 should be able to drive 8 ohm loads. Mu of the 6C33 is between 2,7 to 4 according to data sheet.
If I could get my hands on a pair of 13E1 I would use them of course in triode mode ( screen grid connected to the anode) and with CCS which has a lot of benefits for OTL operation. Could be a very nice project. I also would try to optimize the OTL (NFB) for the actual drivers/speakers (CDF) rather than adjusting them for highest DF. Not so much because of limitations of the tube like with the 6C33 but because it sounds much better. The 6SN7 driver stage should work fine as is. If the 13E1 needs more gain I would replace the 3 resistors at the second triode with a simple cathode resistor to ground bypassed by a cap. With the Neurochrome regulator for B+ (Ray's version) this hum cancelling feature is anyway not necessary. I use a simple CRC filter and there is zero hum.

Posted: **Thu Nov 08, 2018 2:24 pm**

Watching.

Posted: **Thu Nov 08, 2018 4:45 pm**

Wolfgang wrote: ↑Thu Nov 08, 2018 1:30 pm Max. plate dissipation and current were the biggest limitations with the 6C33 for OTL operation. A 13E1 should be able to drive 8 ohm loads. Mu of the 6C33 is between 2,7 to 4 according to data sheet.
If I could get my hands on a pair of 13E1 I would use them of course in triode mode ( screen grid connected to the anode) and with CCS which has a lot of benefits for OTL operation. Could be a very nice project. I also would try to optimize the OTL (NFB) for the actual drivers/speakers (CDF) rather than adjusting them for highest DF. Not so much because of limitations of the tube like with the 6C33 but because it sounds much better. The 6SN7 driver stage should work fine as is. If the 13E1 needs more gain I would replace the 3 resistors at the second triode with a simple cathode resistor to ground bypassed by a cap. With the Neurochrome regulator for B+ (Ray's version) this hum cancelling feature is anyway not necessary. I use a simple CRC filter and there is zero hum.

Thanks Wolfgang,
Looking at the dissipation figures, It looks as if Rozenblit gets 4W into 8R, out of about 120W of power tube dissipation per channel, so if I can get a good 75W plate dissipation without problems, which seems easily feasible, then I might be able to get around 2W per channel out of the 13E1 as a triode.
My Fane speakers are around 98dB efficient, so I should be fine with 2W.
Should be a great project.

Posted: **Thu Nov 08, 2018 5:05 pm**

Better get some PCBs in the post for you then Steve?

PM me whenever...

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