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Old 24th October 2014, 08:49 AM   #1
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Default 13E1 Stereo Single Ended Amp

Already provoked by people on this forum I have bought some of these beautiful tubes. I intend to build a stereo single ended amp as the kitchen hifi; it will be a long way from the sink!

Patrick Turner knows a lot about 13E1s and has suggested an operating point of about 400V anode to cathode, with 13% CFB. Screen grid to cathode will be 200-250V using a shunt regulator on that grid, and with about 30V on the cathode and 180mA bias the control grid will bias to around ground. I've ordered the OPTs from Silk so that plan is set in stone.

I'd be grateful for suggestions for the driver stages? Currently my basic game plan is to stick with Patrick's design of a 6CG7 CCS loaded triode gain stage into a choke loaded EL84...
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Old 8th December 2014, 05:56 PM   #2
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Default Once upon a time I purchased 6 NOS 13E1's

A long time later I got round to testing them...see attached picture.

Five measured bang on the money - Va=400V, Ia=180mA, Vg1=-45V, Ig1=10uA, Vg2=250V and Ig2=8mA gives total dissipation of 75W. This is the operating point I intend to use.

One poor guy had the getter blown to a white halo except maybe 5% still showing; I think he gets experimented on, although he still measured perfect.

One looked so very pretty with an enormous getter, but other than 50% above heater current spec (so 1.9A vs 1.3A @ 26V) he passed no current at all. I got frustrated and cranked up the anode to 600V with no grid bias hoping for some reaction and not a microamp passed. Dead as dead gets.

So four maybe five out of six good - how does that rate for expensive NOS?
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Old 9th December 2014, 01:30 AM   #3
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"50% above heater current spec (so 1.9A vs 1.3A @ 26V) he passed no current at all"

Probably air in the bulb causing the heater to loose heat and no cathode current conduction.

"expensive NOS?"

How much do these things go for? I see a couple that sold on Ebay for $34 and $50. They look like jumbo TV sweep tubes. In fact, with two sections inside, and de-rating it to Max Design at 67.5 Watts, they look just like two 6LW6 or 6LX6 sections in parallel. Let me guess, plate is 48 mm long and the cathodes are 7 mm wide.

I guess for the driver, it depends on how much 2nd harmonic cancellation you want. Can get more linear than the EL84, or is that just a follower.
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Old 9th December 2014, 03:12 AM   #4
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How about an triode-strapped E180F (6J9P-E) driving a triode-strapped 6W6GT (12W6GT). I didn't give it too much thought, but both are pretty linear. You would have plenty of drive.
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Old 9th December 2014, 06:57 AM   #5
45 is offline 45  Italy
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Originally Posted by smoking-amp View Post

How much do these things go for?
If you buy them from reputable sellers that give you some guarantee they are quite expensive. Regular price from Billington is 180 GBP each! They were intended for DC applications. See MJ book for some PP applications.
It seems to me they are appealing because of their high gm and power rating but in truth they are not the last word in linearity, especially triode-strapped.
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Old 9th December 2014, 06:25 PM   #6
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Default Now I have some output transformers!

"expensive NOS?" .. How much do these things go for?"

About GBP 120 for NOS in the UK. It seems they have been popularised by the MJ book and I guess there has been some hording. Between thinking about building an amp with these two years ago and buying the tubes that I have price has gone up 50%!

"in truth they are not the last word in linearity, especially triode-strapped"

I now also have the rather beautifully finished Silk (Thailand) output transformers (1900R + 13% CFB) - see picture. Great deal and great service from Silk. These commit me to tetrode output stage. Patrick Turner has built some amps where he says these linearise well with CFB and fixed G2. I know 13E1 is not a 300B but it sure looks pretty..

"If you buy them from reputable sellers that give you some guarantee " .. I hope so! Unfortunately I waited six months before testing them .. the only lessons I ever learn are expensive ones.

Drivers - the SE35 2011 Version per Patrick's website is my default plan; a paralleled 6CG7 with CCS into a triode EL84 with choke loading.

I have a hankering to build 'Shunt Cascode' that's been written about elsewhere on this forum - maybe this would allow me a single stage driver (shunt cascode to source follower). I have 6E5p's and want to try these out, maybe in the Patrick Turner circuit and / or the shunt cascade.

Thanks for the suggestions for a driver.. I also have 6J9P-E and 6W6GT (I bought the latter 5 each for a box of ten, and all of them work!) so I will definitely try that.

First stop is build the output stage, determine the drive requirements and go from there. I've just noticed the Silk OPT also has a 40% ultralinear tap, that + 13% CFB would generate a giant drive requirement but might be worth trying.

I have to rant about OPT vendors... why does nobody (I could find] want to build a design to specification? .. 'We have a special winding technique involving hemp leaves and phases of the moon etc' .. why is there so much BS around this? I got asked for the intended circuit by one vendor and got told I should not build a SE amp with GNFB!
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Old 9th December 2014, 10:51 PM   #7
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Originally Posted by Xpersephone2 View Post

I now also have the rather beautifully finished Silk (Thailand) output transformers (1900R + 13% CFB) - see picture. Great deal and great service from Silk. These commit me to tetrode output stage. Patrick Turner has built some amps where he says these linearise well with CFB and fixed G2. I know 13E1 is not a 300B but it sure looks pretty..
Yes you can get a good result of course. I just wanted to point out that other choices might be more convenient for someone who has to buy those tubes now. I think you are right about the MJ book effect...
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Old 9th December 2014, 11:50 PM   #8
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120 GBP, 180 GBP.....

Whew! I think I'll pass on those. I guess appearance is what really costs. The CFB approach should make for a fine amplifier in any case.

A little known driver tube that can do plenty of drive voltage is the 6GF5. 9 Watt and 700 V rated. Same design as the 6GE5 (& 6JN6 and a bunch of other re-pinned or capped types) which is reasonably linear. (and were well liked in Pete Millet's DCPP amplifier)

I was just diddling on a napkin here to see what could perform equivalently to the 13E1 and I came up with these parallel combos for us cheapskates:

2x 36LW6 or

4x 12GE5

These sum up to the same design max Watts, gm and rp (when re-scaled for shared currents), and even the same total equivalent heater current. Only difference is they would prefer 200V or 150V on g2 respectively. 36LW6 is available at $11 and 12GE5 was available on sale a couple of years ago at $1 each, maybe $5 now. I think I found my design approach. Maybe a 12HL7 single stage driver for grounded cathodes output, or a 6GF5 driver for high % CFB outputs.
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Last edited by smoking-amp; 9th December 2014 at 11:59 PM.
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Old 10th December 2014, 09:58 AM   #9
Zoran is offline Zoran  Serbia
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I have some ITT England (Blue logo) new and unused.
In original big cardboard labeled boxes with some sponge around tubes inside.
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Old 11th December 2014, 03:53 AM   #10
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Smile Partial resurrection!

...
"50% above heater current spec (so 1.9A vs 1.3A @ 26V) he passed no current at all"

'... Probably air in the bulb causing the heater to loose heat and no cathode current conduction.'

I decided to give this guy one last run round the block, as I noticed after his first outing that the next day about a third of the getter had vanished. Still no plate current but now 150V on the screen grid gave a blue corona discharge. So clearly gas, I guess I activated the getter by heating the tube, and that's got the pressure down low enough to permit the corona discharge (my distant memories of university tell me this means the pressure is probably down around low 10s% atmospheric) . I assume this guy will never recover (too much gas) , but the behaviour is interesting.
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