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Old 22nd March 2011, 04:20 AM   #31
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Originally Posted by tubelab.com View Post

Please understand that the SSE was never designed or tested with 6146's or many other oddball tubes. Amp damage is a real possibility when trying something new.
So noted. You must have taken a law course or two in school, too!

Actually, my own motivation with the SSE is to experience this whole SET phenomenon for myself. I've never even heard one. I want to compare it with the other common amp types including a P-P tube amp, two or three SS amps that I have, and a Tripath amp. This design looks like a very good platform for experimentation with various class modes and feedback. Trying different tubes may be fun later on, especially if I figure I just need a couple dB more to be happy... I did build a little spud amp for my dorm room when I went off to school many long year ago, and that actually worked pretty well. Now, where did I put that???

Anyway, thanks for putting a better perspective on things. I haven't done any building for years and I have some re-learning to do about these "obsolete" devices.
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Old 22nd March 2011, 01:02 PM   #32
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So noted. You must have taken a law course or two in school, too!
Never took those. Too much memorization involved and I have CRS. All my formal education has been technical. RF, IC design, general EE, and CE classes, and as much programming as I could stand. Only the very minimum BS classes required to graduate.

I made those statements because I believe that too many people (myself included) get an idea or two ot three and then buy something as a starting point, like the SSE board, make several modifications in the initial build, and then it doesn't work. How do you figure out what went wrong. Was your initial build OK, was one of your ideas a little misthought, or was the combination of several good ideas not agreeing with each other. I have been working on a Grand Unified Theory breadboard project to combine many of my ideas into one design. I have now tossed the second board into the trash. I can't make them work.

After working at Motorola for 38 years and learning all about designing experiments it has been made rather clear to only mess with one variable at a time. That way you can figure out what works and what doesn't.

In my case I bought one of Pete Millett's big red boards. I fully intended to hack the $%@* out of it to extract obscene amounts of power out of it, and I stated that fact in his thread when I bought the board. I however built the board almost exactly as Pete intended, installed the tubes that Pete specified and fired the board up in "as designed" condition. After listening to it for a while and figuring out all its quirks, then I started making mods.

As I stated in my previous post, when going where the designer never intended some experimentation will be needed. Some experiments work, some don't, and some blow up! I experienced all three in my quest. I had parts violently explode twice, and I fried a few resistors and one tube. I now have a 250 watt tube amp in my living room. I have seen over 500 watts flow out of the board. (Pete specified 36 watts)

The point I'm trying to make is, build the board as close to the stock configuration as possible, listen to it, play with it, then tweak away. Only change one thing at a time, and listen to each mod for a day or two before moving on. Try not to make any changes that you can't undo. It sounds like the long way to get there, but it will save you time, parts, and frustration in the long run. I have a SSE board that has been hacked beyond recognition dozens of times. I use it for most of my "extreme" experiments. It is still alive and working although it isn't very pretty and has a few burnt spots.
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Old 22nd March 2011, 05:08 PM   #33
w5jag is offline w5jag  United States
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The KT88 should flat kick its butt as would most sweep tubes. I get 14 watts out of a KT88 in UL mode.
With numbers like these, it's hard to justify use of the odd ball tubes except for the fun of doing it and the learning experience.

I'm interested in seeing what that new KT-120 can do. I think I have adequate power supply iron on hand, but I would have to fork out for some bigger OPT's just to get started. I'd like to get a pair of the big honkin' Edcor's, but KT-120's + big honkin' Edcors = $250 bucks + or -, and the time involved. Not sure I need to know that bad.

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Some experiments work, and some don't.
For me, it's more like some do, most don't. I try to keep the expensive failures to a minimum.

I've pulled the better looking of the power transformers from a scrapper carcass, and no load testing seems to indicate it's good. To get a sufficiently high B+, it's going to take a doubler or even a tripler. I know that will work for a low duty cycle ssb rig, but for an audio amp, I have no idea. I hope this will be one of the experiments that work. The bias supply seemed to be wired in an odd way in both of the carcasses; more experimenting than I've planned on may be involved.

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Do you know how many of the big hitters from the main forum have told me that this just isn't true.
I haven't had a chance to try running it through the CCS yet, but I intend to do so. I may bump that ahead of working on a new power supply.

I need to be working on building some test equipment, so I can have some baseline numbers to work from.

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Old 22nd March 2011, 06:06 PM   #34
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Originally Posted by tubelab.com View Post
I have been working on a Grand Unified Theory breadboard project to combine many of my ideas into one design. I have now tossed the second board into the trash. I can't make them work.
So now you know how Einstein and Richard Feynman and Steven Hawking, et. al., have felt when they all had to trash their GUT boards.! Don't feel bad, you're in pretty good company...
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Old 27th March 2011, 12:25 AM   #35
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I did a little more playing around with the SB-400 power transformer this afternoon. The HV secondary is 283 volts AC; I breadboarded a solid state half wave voltage doubler and got 780 volts DC out of it, about what I expected.

Staring at the voltmeter, reality began to set in a bit - the output transformers will need to take 1.5 KV without breaking down. Are there any known to be reliable at that voltage? They won't have to take much current - 40 ma would probably be enough.

As noted in the KT-120 thread, setting a new OPT on fire is not the best diy experience, and I suppose if it failed in service the speaker could be toast as well.

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Old 14th April 2011, 02:32 AM   #36
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I'm interested in seeing what that new KT-120 can do. I think I have adequate power supply iron on hand, but I would have to fork out for some bigger OPT's just to get started. I'd like to get a pair of the big honkin' Edcor's, but KT-120's + big honkin' Edcors = $250 bucks + or -, and the time involved. Not sure I need to know that bad.
I can say that the big Edcors were money well spent. I have not heard enough good things about the KT120 to cause me to part with my money. I did however decide to try a little experiment of my own.

All this talk about stuffing transmitting tubes into the SSE made me think about trying it. But, why would I stick in a tube that is smaller than the KT88's that I have been using? Well, I have 813's, 828's, 845's and 211's, but they won't work in the SSE. People keep telling me to try a certain tube that is used in Collins transmitters, but I don't have any.

Ebay must have grown tired of me dropping minimum bids on lots of stuff, but never buying anything, so they sent me a 10% off coupon. Still, I didn't win any bids, so on the coupon expiration day I sprung for some 4D32's. OK, now I have got something that could kick the KT120's butt!

Do they work in the SSE? Lower the grid resistor to 100K, put in 100 volt cathode caps, and 10 watt resistors, wire in some BIG sockets and crank them up. Yes the screen grid rating is 350 volts, yes thay work fine in triode at 500 volts. I get 10 watts. When I have time, I will get the big Edcors and try UL mode.

I have been using an external power supply for testing. A big Antek with SS rectifiers would be the cheap ticket here. B+ caps will need to be rated for more than 500 volts.

I took a picture with a 6146 stuck in the rectifier socket for size comparison.....Don't try this under power!
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Old 14th April 2011, 03:01 AM   #37
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But, why would I stick in a tube that is smaller than the KT88's that I have been using? ...so on the coupon expiration day I sprung for some 4D32.
Since I'm guessing most of us aren't familiar with the 4D32, I thought maybe I'd share a link: 4D32

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In Class C a single valve can produce up to 100W at up to 60MHz with 600V anode and 1.25W grid drive. In AB2 a push-pull pair can deliver 125W.
Keep in mind the heaters of these tubes draw nearly FOUR AMPS each. Not exactly a "plug & play" replacement for KT88 in your Simple Single Ended. Even still, a very nice science project. Now I want one too.
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Old 14th April 2011, 05:03 AM   #38
w5jag is offline w5jag  United States
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Does 4D32 use a thoriated tungsten Filament?

I seem to recall reading on the Collins reflector that many of those late production Raytheon 4D32's were gassy, so keeping a meter on them might be prudent.

I wonder if choke loading the transmitting type tubes might be a worthwhile approach to take advantage of their high voltage capability, and keep the high voltage out of the OPT.

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Old 14th April 2011, 02:20 PM   #39
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Keep in mind the heaters of these tubes draw nearly FOUR AMPS each.
They make my Fluke power supply groan when I plug the board into the power supply. An Antek 4T400 should be adequate.

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Does 4D32 use a thoriated tungsten Filament?
It is a conventional indirect heater inside an oxide coated cathode.

Quote:
I seem to recall reading on the Collins reflector that many of those late production Raytheon 4D32's were gassy,
I bought 6 tubes, all NIB. Two of them were bad. The seller is sending replacements. One has completely gone to air. The second one glows purple and sucks lots of current. The seller does not want them returned, so after the replacements arrive there will be pictures of a purple 4D32 glow!

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I wonder if choke loading the transmitting type tubes might be a worthwhile approach
Maybe. The maximum plate voltage spec for the 4D32 is 600 volts. I assume that my Edcors are safe at that level.

I plan to stuff these tubes into a certain red board to see if they can beat the big sweep tubes. Other P-P experiments are also planned.
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Old 14th April 2011, 04:10 PM   #40
w5jag is offline w5jag  United States
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The second one glows purple and sucks lots of current. The seller does not want them returned, so after the replacements arrive there will be pictures of a purple 4D32 glow!
Awesome. I have not seen a 4D32 up close, but it looks like a septar socket.

If so, what about 829B's? Paralleling everything in the bottle should get 60 watts plate dissipation. 5894's would get 80 watts plate dissipation with everything in parallel. Both are 600 volt tubes. 5894B can go 750 volts.

I don't know what the current market price of these tubes are, but I have a bunch of each type - they might also be a KT-120 butt kicker.

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