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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 15th April 2018, 08:17 PM   #201
colnago55 is offline colnago55  United States
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So here is my plan for the power supply for a mono blocks. I'll be using a 5AR4 for rectification, 6CG7's for drivers and KT88's for power tubes.

For the tubes Iím thinking of copying the power supply of the SSE and plan to use an Allied 6K7VG I have per the diagram below:

:http://www.diyaudio.com/forums/attac...1&d=1523821605

Would this work ? Are there values I need to change?

I'm assuming the 6.3V taps can go directly to H1 and H2. Correct?

For the mosfets Iím thinking:
http://www.diyaudio.com/forums/attac...1&d=1523823171

With PSUD I get 154 volts for the mosfets.

This is continues to be learning exercise for me.

Thanks for your patience, Jacques
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Old 15th April 2018, 10:15 PM   #202
Tubelab_com is offline Tubelab_com  United States
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OK, I'm a bit behind on this so I grabbed a hacked up SSE board and wired it's power supply section to the test amp breadboard. I used the same mos power supply that I have been using. I measured +142 volts and - 141 volts on the mos supply, 502 volts at idle on the main B+ and 445 while putting out 65 watts. The tubes in the amp are older Chinese KT88's and the SSE has a Sovtek 5AR4. My line voltage is usually in the 122 to 127 volt range but I didn't measure it today.

The Allied 6K140HF is Hammond's version of the Triad N-68X, either will work fine. I couldn't find a Triad.

I drew a schematic of what I have here, took a picture of it, and scanned it to PDF.

Note, I really did stick a 4D32 into an SSE......it didn't work well enough to add the second one. I keep this old board around for experiments that might end badly. It has been blown up and rebuilt more times than I can remember.
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Old 15th April 2018, 10:54 PM   #203
evanc is offline evanc  United States
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Tubelab Universal Driver Board, 2015 version
Great to see some more action. I have had both channels working on test speakers. I did have a couple of tubes play for a minute and then a crackle at the speaker a blue glow and I shut it down. When this happens the drive for the offending tube goes positive. Perhaps the warning about some of these tubes being gassy is proving to be pertinent.

I have some hardware coming and hopefully I can work out a measurement system so I can post empirical results. I also need to add some feedback. All in good time.

E
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Old 15th April 2018, 10:57 PM   #204
evanc is offline evanc  United States
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Tubelab Universal Driver Board, 2015 version
Another thing I am going to have to work out is how to preheat the heaters. My heaters and b+ come from the same transformers. The only reasonably priced relays that I see that can switch the b+ are solid state.
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Old 15th April 2018, 11:40 PM   #205
colnago55 is offline colnago55  United States
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Quote:
Originally Posted by Tubelab_com View Post
OK, I'm a bit behind on this so I grabbed a hacked up SSE board and wired it's power supply section to the test amp breadboard. I used the same mos power supply that I have been using. I measured +142 volts and - 141 volts on the mos supply, 502 volts at idle on the main B+ and 445 while putting out 65 watts. The tubes in the amp are older Chinese KT88's and the SSE has a Sovtek 5AR4. My line voltage is usually in the 122 to 127 volt range but I didn't measure it today.

The Allied 6K140HF is Hammond's version of the Triad N-68X, either will work fine. I couldn't find a Triad.

I drew a schematic of what I have here, took a picture of it, and scanned it to PDF.
Thanks George.

Some questions:

The results look good to me, were you happy with them?

How different is this schematic from the one you are developing for the new power supply board?

Were you able to listen to this setup?

I have a SSE board that is populated but not being used. Would it make sense to hack the board and use the power supply?

This seems like a cost effective path to monoblocks.


Thanks again, Jacques

Last edited by colnago55; 15th April 2018 at 11:44 PM.
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Old 16th April 2018, 12:51 AM   #206
evanc is offline evanc  United States
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Tubelab Universal Driver Board, 2015 version
Another thing I am going to have to work out is how to preheat the heaters. My heaters and b+ come from the same transformers. The only reasonably priced relays that I see that can switch the b+ are solid state.
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Old 16th April 2018, 01:16 AM   #207
Tubelab_com is offline Tubelab_com  United States
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Quote:
Great to see some more action.
I have been tinkering with this system off and on whenever I get some spare time. As you know this driver board design has been around for almost 10 years. The bare boards have been in a box since early 2015.

Several years ago back in Florida I had made a matching output board to test several theories. I had been experimenting with screen drive for years. With that I learned new and interesting ways to blow up tubes and other parts, and make some high powered amps. I kept looking for something more universal, exploring several ideas. One of them was something I called dual drive, feeding G1 and G2 at the same time. I made a test amp in post #29 and #30 of this thread.

G1=G2/mu Scaled Drive Strawman Design

The output board I made basically had mosfets driving every element of a tube. I called it the Grand Unified Theory, or GUT board, and again blew lots of stuff up, and made some more high powered amps. One of those amps squeezed over 100 watts from a pair of small 13GB5 sweep tubes, and I designed an amp using those tubes. Before I could get boards made someone bought up nearly every 13GB5 in the US. The amp was tuned for the 13GB5 and didn't work well with other tubes. I had spent a lot of time and money on this, right about the same time that these driver boards came back from the board house. I was disenfranchised with the whole situation as another amp design I had was also orphaned when a Hong Kong buyer bought all of ESRC's 6HB6's in one purchase. That's why the driver boards sat for 3 years and I was near the point of pulling the plug on Tubelab.

During the recent tinkering with these boards, I discovered that some tubes could really benefit from some AB2 positive grid drive, and others didn't. I even managed to squeeze 30 to 35 watts out of a pair of 50C5 tubes (the output tube from a 50's vintage table radio) without melting them. There was some discussion about cheap power amps for guitar amps in this thread:

5E3 Blackface Single End Amp

As we know the power supply for a large power amp gets complicated. There are usually 3 different supplies B+, bias and screen in a pentode mode power amp, and 4 in this amp to reach AB2. A cheap power amp needs to operate from a single supply.

I dug the old GUT board out of the junk box since that was it's mission. It never worked right with some tubes, but really worked great with others, like the 13GB5. I wired the GUT board up to this driver board, and have been tinkering for a couple of weeks.

I found out that it is possible for things to go so far wrong that a perfectly good vacuum tube can shatter from electrical circuit malfunction. I have also solved the limitation that kept the original GUT board from properly working......in the simulator. It's now time to see if the circuits that live inside the mind of a PC will work in the real world.

After blowing up all of my mosfets a pair of tubes, several zener diodes, a tube socket, and about a dozen resistors, I took a week long break waiting on a reload from Digikey. Fridays build did something different it worked. I saw lots of power flowing from cheap tubes. I powered off, and was gone all day yesterday. This morning I turned it on, and yes, it still worked. 125 watts flowed from a 550 volt power supply at 1.5% distortion. Great......rip it up and build another one. This time with smaller tubes. Power up and it worked too. 60 watts from a pair of $1 tubes. I was building a new version with another cheap tube when I realized that I never posted the schematic for the KT88 power supply, so I pulled out my perf board output circuit and stuffed the KT88 board back in.

This idea if it works out will be something truly different and will require a different driver design if the single power supply idea is to be fully realized. Only time (and more blown parts) will tell.

Quote:
How different is this schematic from the one you are developing for the new power supply board?
This circuit is a pretty standard tube type power supply. I haven't decided whether to make a universal power supply, a simple power supply, or both.

for a power supply to be "one size fits all" it would need all the voltages seen here, B+, Mos+, Mos-, screen grid (for pentode amps), bias, and heater / filament. For a DHT amp like the TSE there needs to be one or more DC filament supplies, probably with voltage regulators. The screen supply needs a regulator, and so do the bias supplies for some amps. Putting all of this on one board can make for a rather large board, much of which would not be used for many amp builds.

What's different in this schematic, from what I would put on a universal power supply board other than some missing (not needed here) blocks? I would add the option of using silicon rectifiers, Like what was in the SSE, and the option for two more diodes for a full wave bridge. This allows the use of cheap Antek toroids for lower powered amps. I would also add terminals for adding a pair of chokes to the +/- Mos supplies instead of the resistors shown.

Quote:
Were you able to listen to this setup?
No, It only existed for about an hour, just long enough to verify that I didn't make any stupid mistakes in my drawing.....I have been doing too much of that lately. Many of last weeks exploding parts were due to a blatantly stupid arithmetic error....a 24 watt tube does not like being forced to eat 200 watts of dissipation! I seem to get diodes backwards a lot too, especially zeners. I built it, stuck in a pair of cheap Chinese KT88's fired it up and got the power and distortion numbers that I expected, then took it all apart, and started wiring up another experiment.

Quote:
I have a SSE board that is populated but not being used. Would it make sense to hack the board and use the power supply?
You would only be using the tube socket, two caps and some resistors. I would wire it all up on a piece of perf board, or point to point, but that's how I usually make things. I had the dead SSE board in my collection, so it looked like the quickest way to do a simple test.
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Old 16th April 2018, 02:46 PM   #208
gideon1990 is offline gideon1990  Netherlands
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Just caught up with the thread and besides the cool progress I hope you are feeling a bit better than you did a few weeks ago
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Old 16th April 2018, 03:06 PM   #209
colnago55 is offline colnago55  United States
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Thank you George for the schematic and the guidance.

I'm going to charge ahead with my KT88 monoblock build based on your power schematic.

I'll keep asking questions.

Still learning as I go.

Thanks again, Jacques
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Old 20th April 2018, 02:34 PM   #210
colnago55 is offline colnago55  United States
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Hi George,

Just to be sure and for others who may refer to this schematic in the future, I'm assuming the choke shown between the 47uf (500V) capacitor and the 120uf capacitor is a Triad C-14x or equivalent (6 H, 150 ohms, 200ma).

Is that correct?

Thanks, Jacques
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