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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 3rd February 2018, 02:03 PM   #131
evanc is offline evanc  United States
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Tubelab Universal Driver Board, 2015 version
Continuing along and looking at parts on hand for 9 pin miniatures I have a bunch of 12au7 tubes. To my novice eye it looks like an OK fit.

It looks to me like the B+ for the driver board and the screen voltage called for in the 4d32 are the same 250 volts. Would it be OIK to power these off one supply. Linear or would a regulated supply be better? I have some high voltage regulator boards I could build up.
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Old 3rd February 2018, 09:07 PM   #132
Tubelab_com is offline Tubelab_com  United States
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The 12AU7 does not have a stellar reputation in the audio world. Much of that is noise, but some 12AU7's do indeed have a higher distortion than other similar tubes. In my testing I find that they are all over the place. One tube may work quite good, while an identical tube may exhibit high distortion. I have not tried any 12AU7's in this board. I did try some similar tubes (5963's) in the previous version of this board and they worked OK. My guess is that a 12AU7 may be OK for the first tube, but will not work too well in the second position due to the high voltages and signal levels involved.

The Driver board does not run on 250 volts in this application. I have not tested it below 350 volts, and that was when driving small tubes at low power (30 WPC and less). For the applications discussed so far in this thread I have run the driver board off of the main B+. It has been tested at 350 to just over 600 volts.

I will test the board at 650 volts next time I have a working setup. I have had it to 650 volts for short periods with no issues. The only things that might need changing is the dropping resistor for the first stage (500 volt cap after the resistor) and the plate load resistors on the second stage.

You will still need 250 volts or so for the screen grid. TV sweep tubes have a similar issue, except that they want 150 to 200 volts for the screen grid. I'm looking into a power supply that can generate all the voltages needed for these types of tubes.
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Old 4th February 2018, 01:46 AM   #133
Tubelab_com is offline Tubelab_com  United States
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I had some time today, but I found something more fun to do that fix a dead amp breadboard..........start building a new amp! Unfortunately my drill batteries died from use in zero degree F weather late last year. They were getting sick as I was using them, but I had hoped that they would recover. One wouldn't charge at all, and the other would drill one hole per charge. OK, they are 20 year old NiCd's.

I got the tube sockets and OPT's mounted. No wiring yet. This the divider that runs through the center of the chassis.
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Old 11th February 2018, 08:01 PM   #134
evanc is offline evanc  United States
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George had any time to play with your amp? I have had a couple very busy weeks at work but have managed to collect a few parts
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Old 12th February 2018, 02:36 AM   #135
Tubelab_com is offline Tubelab_com  United States
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Not much activity in the past week, except for some test fitting. The OPT's and power toroid were stolen from the breadboard for mocking up the chassis for the final amp build. It's my usual case of too much stuff for too small of a box.

It's tax time and this year medical expenses will be over half my income, so I need to find and document every freakin aspirin!

This computer has been acting stupid for a couple of months. Every week or two it will just red screen and start talking about a virus infection and my immediate need to call the extortion phone number in India. It also randomly tells me that it needs to be re-imaged (with a better virus, i'm sure) or that my McAfee subscription is expired. Oddly, these things happen right after I visit this site, or my email host.

Monday, it became totally useless. As soon as it was turned on, it went into full annoyance mode. Whatever was wrong with it, was not detected by Microsoft Security Essentials, Webroot, or McAfee. All gave it a clean bill of health.

I noticed the words "Ads by Counterflix" on some of the malicious pop-ups, so I went to a working computer and Googled it. Technically not a virus, so it escapes detection, Counterflix is a browser hijacker capable of delivering a virus into the target machine......There are several "cures" on the web, many are likely the kill, not the cure. I tried the free trial of MalwareBytes, which found 114 infections on this machine, and removed them. It seems to work OK now......Beware of Counterflix.

Now, back to my taxes.
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Old 12th February 2018, 10:05 PM   #136
evanc is offline evanc  United States
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Paperwork/taxes and the like just plain old suck for me. I can work physically hard all day (thatís my norm.) and be much less spent then if I sit all day pushing buttons.
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Old 13th February 2018, 02:03 AM   #137
Tubelab_com is offline Tubelab_com  United States
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Quote:
I can work physically hard all day (thatís my norm.) and be much less spent then if I sit all day pushing buttons.
Ditto.

After two days of spreadsheets and a day of fighting the PC virus, I was glad to wake up this morning and find a bit over two inches of snow on the ground. I left the blower in the garage and shoveled out over 200 feet of two car driveway (mine, and my 82 year old neighbor's). The Fitbit shows 18,000 steps and 4400 calories burned.......beats sitting at the computer all day.

I have probably one more day's worth of tax BS, but it may take two if it's nice enough to get outside tomorrow.
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Old 13th February 2018, 09:10 PM   #138
angrypat is offline angrypat  United States
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Default pc trouble

Sorry you're having computer problems, it can be a real time suck and stress inducing p.i.a. When you said red screen I thought you were using linux, but then you mentioned microsoft security essentials, so not linux. Microsoft Security Essentials is barely better than nothing, Mcafee has improved alot but still would not be on my short list, Webroot scores well in reviews, I have used it, but it canned it after a short period, I don't remember why. Give Malwarebytes a shot, it's not a full time app, it's an on demand tool, also Avast is pretty solid, I haven't fired it after 2 years. All of these are free by the way.
Also many antivirus vendors offer a free one time heavy duty disinfect tool, be careful with those, they work, but can be heavy handed.
A free tool that is also helpful is SlimCleaner. Good luck.
This thread has me riveted, I have been collecting parts for 2 1/2 projects, but now I'm getting much more interested in tooobs because of your work and great writing! Keep it going.
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Old 14th February 2018, 12:37 AM   #139
Tubelab_com is offline Tubelab_com  United States
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so not linux.
I still use Windows 7 pro on this machine. Most of my other PC's are W7 home premium. I have a W10 laptop but it doesn't work right (bad hardware from ASUS that they wouldn't fix). I have an older open SUSE computer and an Ubuntu PC, but neither get much use.

Quote:
Give Malwarebytes a shot, it's not a full time app, it's an on demand tool
Malwarebytes now has a full time watch dog type app, but it is no longer free. It comes as a full featured download which will revert to the on demand only app after the 14 day free trial expires. I downloaded it and turned it loose on the machine. It found and fixed the previously mentioned 114 infections. The machine had worked flawlessly since then, so I may spent the $40 to keep the full time protection working.

Quote:
Webroot scores well in reviews, I have used it, but it canned it after a short period, I don't remember why.
That's what I was using when this started. Their scan found nothing, so I filled out a support ticket. This required a all night "profile" of my machine which I ran and emailed to them. They still found no infections in the PC. The next step was a phone call while they assumed control of the machine and remotely diagnosed it. During the call the machine displayed the red screen with the synthesized voice telling me to "call Microsoft support" at an 800 number that is forwarded to scammers in India. This locked Webroot out of the PC forcing me to turn the PC off and restart. Again no infections found.

That's when I tried MS security essentials and an old McAfee disk (2016?) that I had.
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Old 19th February 2018, 07:09 PM   #140
colnago55 is offline colnago55  United States
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Default Transformers

Hi George,

Are you far enough along in your testing that one could order transformers?

Given Edcorís 8-week lead-time, Iím thinking about ordering my transformers now.

Questions:

Is your current design for a KT88 amp now predicated on the 3300 ohm opts or could 5000 ohm ones be used?

Edcor offers several 5K push-pull opts. They have a 25, 30, 50 and 100-watt sizes. Iím put off by the 9.75 lbs. weight of the CXPP100-5K, and wonder if the 50-watt at 6.75 lbs. would be sufficient. They also make a 3400ohm 50-watt transformer. Whatís the trade off in going with the 50 watt opts versus 100 watt ones? Iím looking for 35 watts per channel.

Based on what youíve written about the power requirements I am thinking that the Edcor XPWR 222 or the XPWR 214 might be the closest match:

XPWR222 - 750V(375-0-375)@350mA, 6.3V@6A & 5V@6A
XPWR214 -720V(360-0-70-360)@400mA, 6.3V@4A & 6.3V@4A

Am I correct in thinking that a 5V tap is not needed in this design?

Another option would be to get a group buy together to order the ďexpensiveĒ Toroid transformer you are using. Per their website there is a big price drop as the quantity goes up:

1 = $280.16
5-24 = $218.11
25 plus = $157.47

I would be interested in that as an option.

Another question: How do the power requirements change for a mono-block amp?

Please let me know if I am jumping the gun and should wait for you to finishing your testing?

Thanks
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