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Old 30th November 2010, 12:01 AM   #1
taj is offline taj
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Default What to do with 6DQ6B's?

I was recently given a nice big box of about 3-400 old used tubes, and despite a dearth of common audio output tubes, there is an abundance (12+) of 6DQ6B's (Octal sweep tubes) that look pretty darn healthy. Also, about 2 dozen 6SN7GTB's (wuhoo!)

So which circuit approach do the 6DQ6B's suggest to you seasoned veterans? I'm not ready to tackle screen drive, I'm still trying to wrap my head around the more pedestrian configurations -- I'm not an EE or pioneer. I realize they use low screen voltages, as most sweep tubes do, but otherwise I'm not sure what special considerations to watch out for. Would these tubes work well as triodes? No UL taps?

Are there any amp designs currently floating around that use similar sweep tubes that I can use as a base, then just adjust the operating parameters to suit? This is just a circuit design learning exercise for me, not a construction project per se.

..Todd

Last edited by taj; 30th November 2010 at 12:10 AM.
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Old 30th November 2010, 12:08 AM   #2
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Incidentally, if anyone needs any one-off tubes of the [mostly] TV pedigree, I probably have what you need. We can trade for something. Just let me know what you're looking for. (I will be keeping/using the standard fare tubes though.) I'm still going through the BIG box and haven't gotten to everything yet.

..Todd
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Old 30th November 2010, 12:24 AM   #3
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build a sodding huge AB1 amp! Start with the datasheet linked from this thread - it gives you the outline for the output end of a 30w to 80w amp - and the drive requirements become reasonably clear based on that.

Miles has built a tame (as in controlled, not lame) and well defined amp based on similar tubes - see the full write-up here.

With the sn7's in the right places and perhaps a bit of sand to assist as required, you could build a killer amp with the 6DQ6-B...
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Old 30th November 2010, 12:28 AM   #4
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Quote:
Originally Posted by aardvarkash10 View Post
build a sodding huge AB1 amp!
Ha ha. Well, I didn't mean I was going to use all of the tubes at once! Just a pair or whatever. Thanks for the info.

Now that I think about it though... nah... well.... nah...

..Todd

Last edited by taj; 30th November 2010 at 12:31 AM.
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Old 30th November 2010, 12:32 AM   #5
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coward!

Fortunately, you only need a pair in PP AB1 to get to 80W...
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Old 30th November 2010, 12:59 AM   #6
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Quote:
there is an abundance (12+) of 6DQ6B's (Octal sweep tubes) that look pretty darn healthy.
I learned how to blow up tubes, and make a few working amplifiers along the way, back in the 1960's. All of my tubes came from the trash dump where the price was right......FREE. I would pull the tubes and transformers out of discarded black and white TV sets. The 6DQ6 and its little brother the 6BQ6 were the most common and the ones that I learned on. I have recently revisited both tube types.

Quote:
Would these tubes work well as triodes?
It is possible, but they really don't like it. I have stuffed them into a Simple SE and made them work in triode mode, and another Simple SE builder has used them in his amp. The low screen grid voltage rating must be violated to make them work in triode. Every tube acts differently in this regard, so some will work and some will glow.

Quote:
Are there any amp designs currently floating around that use similar sweep tubes that I can use as a base
I have tried them and at least 20 other sweep tubes in Petes magical red board. The board is designed for 12 pin compactrons but I rigged some octal sockets in mine for testing. You will get about 35 watts with Petes recommended 340 volts of B+ and a 6600 ohm OPT, and over 50 watts with 450 volts.

Posted new P-P power amp design

Astute tube hackers may realize that the 6DQ6 and the 6BQ6 have the same pinout as the popular 6L6GC except for the plate cap. Connecting a wire from the plate cap to pin 3 makes the SOCKET compatible. This does NOT mean that every 6L6GC based amplifier can use a 6DQ6, but some amps can. The amp must have adjustable bias that goes to -50 volts or so, and you MUST reduce the screen voltage to 150 or so. A big resistor and a 5 watt zener diode works in guitar amps. I have seen an old Bandmaster crank out 70+ watts with a pair of 6DQ6's. Hifi amps might benefit from a better screen supply.

The 6BQ6 will make a Fender Champ SCREAM until the power transformer blows up. I learned this lesson when I was about 12 years old. Thats where it all started. I made several 6BQ6 based "Champs" back then out of old TV parts. I never understood why the little 6BQ6 worked so well in SE amps like the Champ but the 6DQ6 just glowed red and wasn't loud. That was long before I knew about things like impedance, bias, and load lines.
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Old 30th November 2010, 01:36 AM   #7
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Quote:
Originally Posted by taj View Post
Are there any amp designs currently floating around that use similar sweep tubes that I can use as a base, then just adjust the operating parameters to suit? This is just a circuit design learning exercise for me, not a construction project per se.
Check out W5jag's Simple SE amp on post #107 & 8:

Another Simple SE builder

jeff
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Old 30th November 2010, 03:10 AM   #8
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My first ham radio transmitter used the 6DQ6 -- keyed the cathode and made TV's go fuzzy all over the neighborhood.
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Old 30th November 2010, 04:20 AM   #9
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Quote:
Originally Posted by jackinnj View Post
My first ham radio transmitter used the 6DQ6 -- keyed the cathode and made TV's go fuzzy all over the neighborhood.
That's probably the result I'll get with an amplifier.

..Todd
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Old 30th November 2010, 07:42 PM   #10
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I just discovered/realized (discovized?) the 6DQ6B is virtually identical to the 6JN6, besides the obvious form factor mutations, and there are a bunch more designs floating around for the 6JN6 for me to look at.

I prefer the looks of Compactron over Octal, but I guess beggars can't be choosers.

Quote:
I have tried them and at least 20 other sweep tubes in Petes magical red board. The board is designed for 12 pin compactrons but I rigged some octal sockets
Hi Tubelab, Yeah, Pete's amp is a good reference for me. I think I also have a big pile of those pentodes (6CB6A) he uses for the differential. I'll check when I get home.

It looks like I have plenty of resources to play with.

..Todd
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