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Old 13th February 2002, 12:57 AM   #1
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Default 829B tubes for audio?

Hi out there.

Recently i was offered some NOS RCA 829B tubes. It is a dual beam pover tube. Data comparable to kt88. I searched the net for some posible audio use and found that Cayin uses the tube in som rather nice looking amps. http://www.cayin.com/ (check the cayin 800MK) Has anny of you used this tube? I was thinking of building an pp triode amp inspired of the PP-1 amp http://www.vacuumstate.com/images/PP-1C_a.gif Anny coments on that. Anny advice is welcome.

Thanks Peter Jensen
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Old 13th February 2002, 05:01 AM   #2
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Default Re: 829B tubes for audio?

Quote:
Originally posted by webercarbmann
Recently i was offered some NOS RCA 829B tubes.
National Valve Museum 829B

It is possible, but tricky to get these transmitter tubes to work as audio (or at least i have been told many times), I just sold off at least a half-dozen of these, but have kept some 815s (same config as the 829s, but cuter looking -- short R2D2 looking tubes with top caps angled off at an angle so they look like antenna :^)

Transmitters often get used in A2 amps (which at this point in my learning curve i sorta understand).

Dennis in Perth, OZ has built a 2E26 PP amp. He knows a lot about these kind of tubes.

There is also a Japanese publication on building SE amps with transmitter tubes which is often quoted as a reference when the subject comes up. SE Amps by Transmitting Tubes by Kouichi Shishido. Available from EIFL.

I to am planning some amps based on Allen Wright's Forced Symmetry concept (EL34, EL84, EL95). And i'm sure Bernhard will chime in, he has heard one of Allen's mules and was quite impressed...

dave
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Old 15th February 2002, 08:37 AM   #3
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Hi again

Thanks for your reply dave. What is the tricky part in using transmitter tudes for audio? I know that some transmitter tubes work with high voltages but that is not the case with the 829B
Data http://frank.nostalgiaair.org/sheets/049/8/829B.pdf Is there a way to simulate how the tube vill behave in triode mode based on the current data.
You mention Allen Wright's Forced Symmetry concept, do you have a link with some more information on that?

Thanks Peter Jensen
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Old 15th February 2002, 07:08 PM   #4
HDTVman is offline HDTVman  United States
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The problem you can run into with transmitter tubes is that they can ocsillate at RF frequencies . Using the most direct / shortest wiring possible while keeping the input and output of the tube well seperated will help. A very low power supply impedance at RF will help also (good power supply bypass caps as close to the tube as possible). I'd try it.
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Old 16th February 2002, 08:10 PM   #5
dice45 is offline dice45  Germany
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Quote:
Originally posted by webercarbmann

... You mention Allen Wright's Forced Symmetry concept, do you have a link with some more information on that? ...


Please get in contact with Allen Wright himself and discuss your intentions with him. Just to be sure you get current, updated info concerning "forced symmetry" from him. As i know him, he'll be very informative and helpful concerning his power amp topology.

He is subscribed to this forum and should be accessible via the email button, otherwise search his website www.vacuumstate.com for an email link.
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Old 16th February 2002, 08:33 PM   #6
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Hi Group,

I have manually graphed many, many tubes - seeking a large linear triode for SE use. (I cannot reconcile the asking price for 300Bs)

Although I have not looked at the 829, I am most impressed with the European equivalent, the QQV06-40. My initial interest was triggered by old Philips figures quoting 3% distortion figures in classB modulator use! I would anticipate the 829 may well be equally linear.

When paralleled as a triode the QQV06-40 exhibits a plate resistance around 1000ohm and a mu of 8. When supplied with 425v. a load of 3k5, and biased at -40v, the tube outputs nearly 11 watts at an H2 distortion figure of 5%. That's nice, and there's more with 500v. (The g2 limiting value of 250v doesn't appear nasty at all and the run-away characteristic when breathing hard as displayed by the KT88/TT21 family just doesn't arise)

Two EL34s paralleled as a single triode are similar - more current, a little more output, a little less drive, and more distortion.

I have no qualms using tubes for other than their designated task. If you are looking for a nice super-linear, grunty driver for your output I have found nothing comes near the 6KV8. This is a TV tube with a frame-grid output tetrode and a very nice linear driver triode (gm of 60) Connect the tetrode as a triode. Distortion way under 1.5% is typical over a huge output voltage swing.

regards,

Graeme
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Old 16th February 2002, 10:34 PM   #7
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Quote:
Originally posted by webercarbmann
You mention Allen Wright's Forced Symmetry concept, do you have a link with some more information on that?
Forced Symmetry Seminar Pics

dave
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