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Old 11th June 2010, 03:27 AM   #1
Yaho is offline Yaho  United States
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Default 6bg6 and 8k opt power amp project

Hi
I am a newbie who is getting brave to build a first tube power amp.
I've been reading some posts about 6bg6/ga tubes with much interest. And I decided to build a power amp with these tubes. And I just ordered a few of them. I do have a pair of opt that are around 8k. Would you point me to some schematics that I could use? I am not looking for a high power. I will be happy with 15-20w. I would like to try triode pp. However, I am very open to your suggestions. I rather have a good sounding amp than to insist on my ignorance. Finally, my speakers are 16ohm and 90+ efficient.

Thank you.
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Old 11th June 2010, 08:56 AM   #2
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look for 6l6 / 807 / 1625 circuits.

Ping Shoog and Miles for info on 807 circuits - they have done a fair bit with them.

In triode and according to the spec sheet you are stuck with a 350V B+ limit and hence not a lot of grunt, HOWEVER - with TV tubes, the datasheet screen (and in fact any) maximums can often be, ahem, conservatively disregarded.

See tubelab's posts for the bleeding edge of this black art.

Do your OPTs have a 16 ohm tap?
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Old 11th June 2010, 10:55 AM   #3
Yaho is offline Yaho  United States
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aardvarkash10

Thanks for the reply.

Yes, my Opts have 16 ohm tap. And I've done some researches in the past few weeks and found a couple that looked manageable to me.

First http://hollowstate.netfirms.com/DIY_files/777.gif I do have three questions though.
1. Would this circuit suitable for 6bg6?
2. How can I make it a fixed bias amp?
3. And what are those 2 6GX8 in the circuit? Do I need that?
I know these questions may sound pretty stupid. But that's where I am now as a newbie .

Second http://www.joeltunnah.com/images/6L6amp_schematic.JPG

It looks simple enough for me to follow. But he is using 3.k OPT and mine are 8ks. So, I don't know if the circuit will be suitable for me. May be there is a quick fix that I don't even know about.

I have emailed Shoog before for a different top. He is a great guy. I will definitely email him for this project.

Thanks again.
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Old 11th June 2010, 11:57 AM   #4
Arnulf is offline Arnulf  Europe
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Quote:
Originally Posted by Yaho View Post
2. How can I make it a fixed bias amp?
If you have to ask, you really don't want that

Quote:
3. And what are those 2 6GX8 in the circuit? Do I need that?
Magic eye tube (volume indicator in this particular circuit). No, you don't need it.
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Old 11th June 2010, 01:55 PM   #5
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You are talking about these specific tubes from this vendor, right?

6BG6 To 6L6 Vacuum Tube List

If you just ordered any old 6BG6GA, you should not assume they can be substituted for a 6L6/807.
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Old 11th June 2010, 04:33 PM   #6
Yaho is offline Yaho  United States
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Quote:
You are talking about these specific tubes from this vendor, right?
No, I bought mine from some place else. That's why I am wondering if I need to find a schematic just for the 6bg6s or to modified the schematics I've posted here.

Thanks
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Old 11th June 2010, 10:57 PM   #7
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Originally Posted by Yaho View Post
No, I bought mine from some place else. That's why I am wondering if I need to find a schematic just for the 6bg6s or to modified the schematics I've posted here.
You MIGHT have some tubes that have big internals stuffed in them, for example I bought a batch of 19BG6GA's a while back and some of them were the big plate versions that is typically called "Super 6BG6GA" on the forum. If I were you I would either find a way to verify this or probably play it safe and build a design for true 6BG6GA's, or something designed for 20W sweep tubes.
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Old 11th June 2010, 11:22 PM   #8
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Originally Posted by leadbelly View Post
If I were you I would either find a way to verify this or probably play it safe and build a design for true 6BG6GA's, or something designed for 20W sweep tubes.
Even the "Super" version doesn't like to be abused in triode, I found that out the hard way.

Jeff
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Old 12th June 2010, 12:14 AM   #9
Yaho is offline Yaho  United States
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Quote:
play it safe and build a design for true 6BG6GA's, or something designed for 20W sweep tubes.
Any suggestions? I am getting more confused!!!

Quote:
Even the "Super" version doesn't like to be abused in triode
Could you tell me what you mean by "abuse"? I am not following you at all.

And how about this one then?

http://www.pimmlabs.com/web/Tabor3s.gif

Thanks
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Old 12th June 2010, 01:15 AM   #10
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Originally Posted by vinylkid58 View Post
Even the "Super" version doesn't like to be abused in triode, I found that out the hard way.
Really? Do you know if was plate dissipation or screen voltage that did them in?
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