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Old 11th January 2012, 04:04 PM   #1
wicked1 is offline wicked1  United States
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Default Tubelab SE and 3.5k tx advice

ARG, I meant the title to be "Simple SE and 3.5k TX Advice" (if a mod see's this and is bored, you could change it )

Hello,
I built the tubelab SE several years ago w/ some Bud Purvine (o-netics) 3.5k 300b output tx's.

I've sense then changed them to some Hashimoto 5k tx's. 300b's still sound great w/ them, and I often use some 307a tubes in the amp which like the 5k tx.
So, anyway, I've got the 3.5k tx's as spares now, and would like to use them.

I'm leaning towards building a simple se, mostly because it's different than what I've got now. I'd also like to get as much power out of it as possible. (it's for a friend who doesn't have good speakers yet).

So... Am I doing the wrong thing by using the 3.5k tx's in a simple se? (would using them in a 300b se amp be a better idea?)
And, if the simple se is not a bad idea, can you recommend some tube's that may work well w/ the 3.5k? I don't have a power tx yet, so can get whatever I need there.


Thanks for any advice to help me get started!
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Old 11th January 2012, 06:03 PM   #2
jrenkin is offline jrenkin  United States
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Any interest in selling them?
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Old 12th January 2012, 03:59 PM   #3
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Quote:
Originally Posted by wicked1 View Post
So, anyway, I've got the 3.5k tx's as spares now, and would like to use them.

I'd also like to get as much power out of it as possible. (it's for a friend who doesn't have good speakers yet).

And, if the simple se is not a bad idea, can you recommend some tube's that may work well w/ the 3.5k? I don't have a power tx yet, so can get whatever I need there.

Thanks for any advice to help me get started!
KT88's.........

Do the transformers have UL taps?

Here is a link to Tubelab's "tubes and transformers" page for the simple single ended:

Tubes & Transformers

Note that the tables are for triode wired finals, I think you can get 10-12W or so out of UL wired KT88's with a healthy B+ and idle current.
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Old 12th January 2012, 04:20 PM   #4
wicked1 is offline wicked1  United States
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I don't want to sell them

No UL taps.

I did read the tubes and transformers page, and it looks like the lower 3k outputs are less than ideal in most cases.. so was just specifically wondering if it's even worth using them for something other than 300b's.

Has anyone set up pentode mode on the SSE? Looks like some power supply mods would be needed.. I'd probably build a regulator for the screens.

Last edited by wicked1; 12th January 2012 at 04:22 PM.
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Old 12th January 2012, 05:43 PM   #5
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Quote:
Originally Posted by wicked1 View Post

No UL taps.

I did read the tubes and transformers page, and it looks like the lower 3k outputs are less than ideal in most cases.. so was just specifically wondering if it's even worth using them for something other than 300b's.

Has anyone set up pentode mode on the SSE? Looks like some power supply mods would be needed.. I'd probably build a regulator for the screens.
3.5K should be fine for KT88's.....looks like you can get 6-7W in triode mode.....

What speakers are you planning on using?
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Old 12th January 2012, 06:07 PM   #6
wicked1 is offline wicked1  United States
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well,
This is for a friend, so i'm not sure yet.. Personally, and while testing, they're some relatively high efficiency fostex horns.

I think the kt88's built to George's specs are the way to go..
I've been thinking about it, and my output TX's are "20 watt", built for 300b's, so I probably don't really want to push more than 10 watts through them.

So on that note, if I'm going to run only kt88's, should I look into a bigger power tx? the hammond 278x or something to be sure I get 500v b+? I have a box of 5u4g rectifiers (so I'll use one here) which drop the voltage an extra 20v or so from the 5ar4. I fear the 274bx w/ that rectifier and the kt88's will drop down to close to 400v. I'll also definitely use some cl-90's.. When I added 2 of them to my 300bSE (one to mains, one to center tap of the b+) it dropped my b+ by 50v!

--And, I'm still open to the advice of skipping the simple, and just building the regular SE w/ 300b's. I'm really only going this simple se route because it's different than what I've already built. I don't expect the simple is really that much less expensive.. the SE only has a few more caps and chips.

Last edited by wicked1; 12th January 2012 at 06:15 PM.
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Old 12th January 2012, 06:18 PM   #7
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Originally Posted by wicked1 View Post
well,
This is for a friend, so i'm not sure yet.. Personally, and while testing, they're some relatively high efficiency fostex horns.

I think the kt88's built to George's specs are the way to go..
I've been thinking about it, and my output TX's are "20 watt", built for 300b's, so I probably don't really want to push more than 10 watts through them.

So on that note, if I'm going to run only kt88's, should I look into a bigger power tx? the hammond 278x or something to be sure I get 500v b+? I have a box of 5u4g rectifiers (so I'll use one here) which drop the voltage an extra 20v or so from the 5ar4. I fear the 274bx w/ that rectifier and the kt88's will drop down to close to 400v.

--And, I'm still open to the advice of skipping the simple, and just building the regular SE w/ 300b's. I'm really only going this simple se route because it's different than what I've already built. I don't expect the simple is really that much less expensive.. the SE only has a few more caps and chips.

KT88's are a lot less $$ than 300B's......

The 5U4 drops a lot of volts, probably not the way to go for a high B+, since electrolytic caps rated for greater than 500V are difficult/impossible to find. You could consider SS rectification, that's an easy way to get a higher B+ for a given power TX. I know there were a few issues with popping the SS rectifiers in the Simple Single Ended, but with proper diode selection and power TX selection it may not be a problem. A SS rectifier will also yield a lower output impedance power supply.
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