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Old 27th December 2011, 02:25 AM   #1
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Default 829B 3E29 Pentode PPP?

A while back an electronics shop (mostly Ham stuff) was going out for retirement. I picked up some really cool tubes, but especially loaded up on a bunch of 3E29/829B's. So this post got me thinking. Likewise this one. Tube tinkering has just about dropped off a cliff for me. Priority is a Heathkit SB-301 and SB-401 that I want to get up and working.

But I've got components. I've gots transformers. And Pete's new Mono PP board has me thinking...

Plenty enough examples of folks putting both sections into parallel triode, but... Quad 3E29's in a pentode parallel push pull arrangement?
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Old 27th December 2011, 03:46 AM   #2
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Quote:
Quad 3E29's in a pentode parallel push pull arrangement?
I don't see why not. I have a bunch of these guys too, but they are all crusty looking and well used. I lit several of them up a few years ago to see if they worked, and most of them did. A few were unbalanced enough (section to section) to have one side glowing bright while the other side showed no color. I also have some 815's and some bigger Amperex RF dual tetrodes with gold pins (don't remember the #). They will all see some test time.

If Pete's board is ready before I get my latest driver board done, I will get 1 or 2 of his. Otherwise, I have just completed layout on yet another universal driver board. There are 3 new ones. Haven't built any yet since I am 1200 miles from my lab.

Good luck with the old Heathkit stuff. My first rig was a Heathkit (again don't remember the #). I am slowly designing and building a ham rig of my own design. It does not use any tubes though. In the mean time I have a little Yeasu.
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Old 27th December 2011, 07:17 PM   #3
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Check out the Chineese FU-29 amplifier. It's an amazing sounding amp and quite original piece of gear, the iron in it is excellent and parts quality is decent with Nichion and Wima caps. I caught the thread "My FU-29 has Fried" and thought it to be an interesting amp. A little more research turned up schematics on one of the other Audio forums. Beware of the original model fitted with some sort of time delay relay... that model has issues. The later model with chrome chassis and black cover over the transformers is much more reliable. When mine arrived I went straight to a pair of RCA JAN 829B's and Russian 6N1's and 6N3's for added reliability. Good 829's are uber cheap on Ebay! That has paid off quite well and it is sonically the finest amplifier I've ever owned... out of 160+ amplifiers over the years. It has also been completely reliable attributed to the decent RCA tubes. A quad of Russian GU-29's that arrived were all gassy... At $320.00 USD this amplifier is an absolute bargain!!

Mark
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Old 30th December 2011, 08:57 PM   #4
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For my birthday I got some amp time. Priceless. One of my first amp build attempts (and failures) was a 41hz amp4. I found I can get about the same thing assembled for $40 without any postal service fried semiconductors.

Here's the interesting part. Instead of using standoffs, nuts and bolts I used the "Velet Crochet". Yeah. That's Velcro to the rest of ya'll. The neat part was that I could add and remove parts and rearrange them with out any problem. The real-deal Velcro really grips!

I'm just thinking, aside from heat issues, perhaps my next tube amp will employ the use of velcro to hold down the big pieces.

I do have access to a club ham shack. Really nice antenna, ICOM 746Pro. Without CW I can't do much down the spectrum other than 10m. I've not had time to play though.

Mr Tube Lab. I'm certainly game when those universal driver boards materialize.
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Old 30th December 2011, 11:22 PM   #5
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829B's were used in PPP mode in SPARK/CAYIN 500 series amplifiers. I repaired lots of these amp's and reliability was the main issue. Even with independant bias adjustment for each section of the tubes about 50% of them were so unbalanced from the start that correct bias was impossible, with one section plate glowing red. Long term bias stability was very poor and careful selection of the tubes allways needed, as well as regular re-biasing. Due to the common (single) cathode structure of the 829B you'll need two separate A-meters to simultaneously measure plate currents, which is both unconvenient and dangerous. My conclusion is that the 829B (a small transmitting tube) is not the best choice for class A or AB audio applications unless you're prepared for constant re-biasing ,high tube reject rate and poor reliability. PLease note my experience is only based on RCA and CETRON branded tubes, there might be other brands which are more stable and consistent, but I'm not aware of.
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Old 31st December 2011, 12:28 AM   #6
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The need for constant manual biasing seems to be a common problem in many amps. I was just thinking of how I could employ a voltage sensor, and a way to control resistance using something like a raspberrypi.org board and an I/O board with a few sensors and controllers. Then just have it sample the bias current every few milliseconds and adjust if out of range. Could even have means to detect a fault and thus flip a SPDT relay to shut things down.
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Old 31st December 2011, 01:05 AM   #7
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Those 829,832 and all their equivalents are a royal pain in the a** when used in a linear amplifier. You need to have a really, I mean REALLY large batch to measure each one for balanced current. It doesn't matter whether these are american 829, russian GU** or european QQE**/** they all were designed fpr Class-C switching operation. Furthermore, selecting them for equal current is just half the work. You also need dynamic balance. The transconductance also differs heavily. Here is a PDF with some QQE Data. Just look at the Ia and ΔIa and rethink your project.
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Old 1st January 2012, 05:09 PM   #8
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I think all of you will find that anything that produces really good results is a pain in the a**. Indeed careful matching of sections is a requirement in any properly constructed tube amp and should really be done to all tubes in use. I have stuck with JAN CV829's in my amp and have had no trouble at all. No doubt you'll find the JAN tubes to have much tighter match between sections to begin with as I have. If used carefully and kept properly biased the 829 is an amazing sounding tube. An autobias arrangement would be nice if it doesn't contribute negatively to the sound. Otherwise it's not that big of deal to me to set bias every 20 to 30 operating hours.
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Old 21st December 2012, 09:30 PM   #9
wicked1 is offline wicked1  United States
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Quote:
Originally Posted by whitelabrat View Post
But I've got components. I've gots transformers. And Pete's new Mono PP board has me thinking...

Plenty enough examples of folks putting both sections into parallel triode, but... Quad 3E29's in a pentode parallel push pull arrangement?
Did you ever build this? I was starting down this same path last year, and somehow missed this thread. I'm about to jump in and finish it... But am wondering if you had any success.

And those saying the two halves are badly mismatched, how does it compare to two 807's, or other tubes? Are you simply saying there's no magic, and it's no better than two tubes, even though they are in the same envelope? Or is there something particularly bad about these?
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Old 22nd December 2012, 07:22 AM   #10
tricomp is offline tricomp  Denmark
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Originally Posted by the_manta View Post
Furthermore, selecting them for equal current is just half the work. You also need dynamic balance. The transconductance also differs heavily. Here is a PDF with some QQE Data. Just look at the Ia and ΔIa and rethink your project.
Can someone please re-post this referenced paper on QQE-Symmetry?
The link is dead and not captured on Wayback-Machine.
Thanks

/tri-comp
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