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Old 8th March 2013, 09:18 AM   #1
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Default 2E26 Options

Hi,

I'm new here, I've read a lot of good stuff on threads here before.
I've been doing glassware amplification for about three years now, and i've come to thepoint there i'm learning how to design proper output stages.
Up till now, I've been learning all I need from education+diy. preamps, power supplies and triode power ( SE/PP) are things i can design already. at least they work

So, I finally decided to make an account and actually ask a question.
I'ts about Pushpull Pentodes. I've already got a nice amplifier so now i'm working on an amp that doesn't only sound nice, but also looks nice- better than this: (i'm the engineer there, too)
Circuits Online - Forum - Show your projects! Part 26.


I was aiming for a mercury rectifier, a nice glowing regulatortube such as OA3 to 0D3. that's all settled and fine. For output tube i'd like a nice topcap tube, but not too expensive. the budget is limited

Ive been loking around and my eyes fell on 2E26 tubes. I really like the looks ( and the price tag) on them. the datasheet mosty supplies data for Eg >0 but I dont want to go there.

The aim is a 15W amplifier. with my calculations I can get nowhere near there. but it should be easily possible with htis tube! i heard someone calling "14W SE" but that must be a little on the high side.

So, what i'd like to know, what kind of values to expect. Ra~a, Vb+, Eg, Iadc.
There 'll be a big electro market soon and i'd like to go shopping

my guess is something like Pda +/- 7W, Va = 250 to 350V, but then I don't know what Ra~a i should choose.i've no experience with these tubes.


I'll gladly hear your thoughts on this! ( & please tell me whenI'm doing things wrong)
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Old 8th March 2013, 10:54 AM   #2
DF96 is offline DF96  England
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Anode topcaps should be avoided if there are children or mobile pets in the house, unless you put a grounded cover over the valves. My guess is that you are one of those people who likes to display your valves, so top caps are best avoided. Insulated connections are available, but they can be large and ugly and a child could easily pull them off.

Mercury rectifiers are also best avoided. They emit UV, and can be fragile. They also contain mercury.
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Old 8th March 2013, 11:10 AM   #3
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The 807 is the best top cap valve for your purposes. Cheap and readily available. Better than the 2E26.
There are Quads at unbelievably low prices from Russia.

Regulator valves add a nice touch of colour to the amp, I use the VR150.

Mercury rectifiers are best avoided for the reasons mentioned.

Put it up on a wall shelf and use ceramic top caps and all is well with the world.

Shoog

Last edited by Shoog; 8th March 2013 at 11:13 AM.
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Old 8th March 2013, 12:08 PM   #4
45 is offline 45  Italy
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Most valves with flash getters do have barium. Barium is one of the worst materials for human health. Also, all power valves get rather hot!
If safety is a concern one should use a closed chassis regardless of anode caps and mercury rectifiers.
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Old 8th March 2013, 03:32 PM   #5
tricomp is offline tricomp  Denmark
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In your search for 2E26 info swing by RCA-815.
AFAIK they share much the same spec's exept for heaters.
Other than that they're very similar but not identical.

rgds,

/tri-comp
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Old 8th March 2013, 06:35 PM   #6
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Well, I'm a little young to have kids. i'll be 19 soon.

DF96, spot on! I'm a big an of nice lights such as regulators, magic eyes, VFD stuff, nixies and all other shiny and awesome glassware. strangely I don't like that 815 martian tube. But i'll definitely look at the designs made for them, I see the similarities.
also- how siilar is it with a CV415, except for the Pda?

I thought that the glass absorbed the UV? well, if i was wrong, i think there are too many dangers now. it'll stay in the cabinet, but i might have a 80 rectifier lying around here. It can replace the 82. marcury recitifiers tend to contain mercury...

VR150- the 0D3, the purply blue one? the only one of the four from that series I don't own yet. And how do you know the tube contains barium?

Well, I've played around with 807. Not bad. but I have limited space also and the tube can't extend over the base like the coke bottles. And the Pda is 25 watts, isn;t that a massive overkill? besides, the 2e26 is about 40 minutes on by bike away and about 3 euros per NOS tube. and it fits in an octal, hich i have plenty. else i'll have to get UX-5 bases, which I don't have in stock, and get the tubes from russia. But when find some at the electro market, i'll probably buy them.

But, still, how about this: anode voltage 300V, Ra~a of 7K, and an anode current of 30mA. (Eg -20V). quite similar to the CV415.
With my calculations I also end up at about 15watts...right?

Last edited by The Engineer; 8th March 2013 at 06:41 PM.
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Old 8th March 2013, 06:42 PM   #7
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2E26 was used in a number of commercial and ham VHF transmitters -- it's smaller than a 6146 with about 1/2 the plate dissipation. A DIYr in Viet Namh built an audio amplifier with a pair, but i can no longer find the page.
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Old 10th March 2013, 07:42 PM   #8
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I have another question, why do the grid-to-ground resistors have to be so small? any risk of oscillation if I make them too large, like 100K? That way it'll be easier to drive them, I do not intend to drive the grids positive anyway. else i'll have to fool around with cathode followers and i'm not much of a fan of those. or opamps...brrr.
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Old 10th July 2013, 09:37 AM   #9
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Default Result

I tried and i did it! The 2e26 tube is a nice and inexpensive tube, and the new amp is a real improvement to my setup.

The final result has 2c51 drivers and a 2e26 output tube, with VU-eyes and a 0D3 regulator. I sweeped the amp and the gain is constant between 15Hz and 30KHz, and lower elsewhere. The tube produces the 5W the datasheet promises with only a little distortion. But I don't need the full 5W and the distortion is very low at normal levels.

https://www.dropbox.com/sh/sf6t8ruowr22343/jyvgdjlm4n
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Old 10th July 2013, 04:48 PM   #10
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the dropbox link doesn´t work for me.

Anyway, you could likely get more power if you use screen drive.

I have experimented whit screen drive, those PL508 make real nice output valves!
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