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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 6th August 2019, 03:26 AM   #31
Tubelab_com is online now Tubelab_com  United States
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Before the attempt at flying model aircraft, I hung out at a local slot car track (if you can remember those). I rewound motors and even hacked up a couple of them and made one big one with a really long armature and 4 magnets. I won a lot of races and made a few bucks at that hobby, but that fad got too expensive for kids, and thus died off in the mid 60's. Before the track closed a Lafayette Radio Electronics store opened two stores down, which became my new hangout. They let me play the guitars and talk on the CB radio. When I finally got my ham license in the 70's a randomly assigned novice call was issued, KB4LRE. I liked it even though Lafayette was gone, so I still have it even though I'm now an extra.

Olson's was a step down from Radio Shack or Lafayette.....a pretty big step at that. They improved when they were bought out by Teledyne, at about the time Teledyne bought Acoustic Research, so we sold a lot of that stuff. Olson's house branded stuff was like the others built by the lowest Japanese bidder, most was junk, but there were some diamonds in the rough to be found. Their "Concord" branded cassette decks were made by Nakamichi and lived up to their standards. The potted OPT's were Tamuras, and all of the Olson branded guitar speakers were Utahs. Some of the house branded HiFi drivers were crap, but some were Eminence, and good ones at that.

Quote:
you're using the Hammond 1628SEA transformers, right?
Yes, that's what I have. Tonight I successfully squeezed 40 watts through them at just over 3% THD. I stuck in a pair of the biggest sweep tubes I have, the 36LW6's that I used last night. This time I decided to beat ohms law with current, not voltage. I had to bend or break every spec in the book, but I was going to see 40 watts of SE power flow out of this thing, with both channels running, or blow it up trying......

I connected my 8 ohm load to the 16 ohm tap. This puts a 2500 ohm load on the tube. Mr Ohm says I need to put 316 volts RMS (447 V peak) of audio across a losless OPT and it will draw 126 mA RMS (178mA peak) of current through the tube. This means that the idle current through the tube MUST be at least 178 mA to avoid touching cutoff. 178 mA of idle current will drop 30 volts of B+ in the OPT. The tube will see 70 to 100 volts across it on the current peaks of nearly twice 178 mA. This means I need about 550 - 575 volts of B+ to get 40 watts.

So I set the big power supply to 600 volts, set each tube to idle at 175 mA and cranked it up. I hit 43 watts at 5% THD, and 2.7% in one channel and 3.3% in the other at 40 watts.

there was about 500 volts across each tube at idle. The current was 175 mA that's 87.5 watts per tube, and you know what they were doing. The picture has had it's contrast and brightness enhanced. They were really not glowing that brightly, but one is obviously not even, and the other one is evenly glowing, is missing it's key, and has some permanent glue stain fingerprints, but most of the skin has burned off!

I reduced the voltage and current until there were no traces of glow in a dark room. That took 500 volts at 150 mA leaving about 60 - 65 watts burned in the tube and 32 watts of audio output. .

The Hammond OPT has a max current spec of 120 mA. I ran it at 175 mA so saturation was seen a lot. At 20 Hz I couldn't go past 4 watts, and at 40 Hz I could get 10. Even at the lower 150 mA current saturation was still a problem.

So if someone really wanted a 40 watt SE amp it would probably take a proper OPT, and TWO big sweep tubes per channel.

At my next opportunity I will revisit the 5K route with 30 watts as the target power level, and try the Edcor OPT.
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File Type: jpg P2920693_x.jpg (670.4 KB, 507 views)
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Old 7th August 2019, 02:46 PM   #32
Tubelab_com is online now Tubelab_com  United States
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Last night's experiments were somewhat a repeat of something I did about 13 years ago with different results. Big Hammond OPT VS big Edcor OPT.

Unfortunately, this time I don't have FFT capabilities yet (dead computer) and it is not a true A/B test since I simply swapped out one of the big Hammonds for an Edcor. This leaves an unwanted variable in the test, the fact that I'm using a different audio path for each OPT. I have already confirmed that the two channels are well matched in level, but the absolute distortion numbers for each channel are slightly different primarily due to different output tubes.

I would trust the power output and relative frequency response numbers to about 0.1dB, The absolute distortion numbers may be a bit off, but the relative changes across frequency are valid.

Previous testing showed a sizeable HF notch falling somewhere in the upper audio band on the Hammond. The depth and frequency of this notch was highly dependent on the tube and configuration being used. Much of my testing used a KT88 in triode or UL and showed a loss of 3 to 5 dB at 20 KHz. The big Edcor has the same notch, but is comes into play well above the audio range. The Hammond is considerably larger than the Edcor, and thus has more inductance and capcitance due to more wire and iron. All of this metal requires more energy to magnetize and demagnetize quickly, so it's losses will be higher, especially at higher frequencies.

The Hammond has always demonstrated monster bass, but subdued highs in listening tests, and the Edcor always made more power output in the same amp.

Almost all OPT's have this resonant notch, but it usually falls above the audio range. It is a resonant pole formed by the stray winding capacitance and the leakage inductance. Driving the OPT with a low impedance source is effectively like putting an equal valued resistor in parallel with this resonant pole. It lowers the circuit "Q" widening the notch and lessening it's sharpness.

I have preferred the Edcors in 300B TSE's and KT88 SSE amps which is why the Hammonds have been in their boxes for 13 years. My Edcors spent several years in a TSE that ran triode wired 307A's. I stole the power transformer and choke out of that amp several years ago, and eventually dismantled it before moving out of Florida, freeing up my early vintage Edcors which were painted bright metallic blue before Edcor switched to the more subdued color that used today.

I have decided that this little test board is going to get stuck into an amplifier ASAP. I want it to see some continuous use and have a lot of listening time with it since it is a rather radical departure form the norm. The original TSE went through a lot of changes in the two years before Tubelab was born. It was my first SE amp design, so maybe this one won't take so long to prove itself. So which OPT's will I use? Bench testing is fine, but it doesn't tell me which one I will like, so I will probably make a slab of wood amp like the first SSE, or drill the top plate for three different OPT's if I make a chassis.

Test Data......Test #1 both channels driven from the same audio generator. B+ is 550 volts, idle current is 120 mA, tubes were 36LW6's, OPT's wired for a 5K ohm load and no clipping was observed on either channel. Edcor on one side, Hammond on the other. I set the output power to an even number on the Hammond side, and measured the power on the Edcor side. The same HP8903 was used to measure power by moving the test lead. The Edcor consistently made about 12% more power than the Hammond. This matched the data from 2006.

...Hammond.......... Edcor
...1 watt...............1.125 watts
...5 watts..............5.611 watts
...10 watts............11.26 watts
...15 watts............16.83 watts
...20 watts............22.48 watts

Test #2 Frequency response. Note that most testers use a low power (often 1 watt, even on big amps) for this test to make better numbers. I ran each channel at 10 watts output measured at 1KHz, then varied the frequency recording relative power output and THD. Mild saturation was seen on the Edcor at 20 Hz and is the reason for the increased THD.

..............Hammond............................. Edcor
20 Hz.....-0.37dB 3.56%................-0.44dB 5.03%
30Hz......-0.17dB 2.12%................-0.22dB 2.77%
50Hz......-0.08dB 1.55%............... -0.09dB 1.81%
100Hz....-0.02dB 1.44%................-0.03dB 1.47%
1KHz...........0dB 1.20%.....................0dB 1.36%
5KHz......-0.11dB 1.01%...............-0.07dB 1.24%
10KHz....-0.25dB 0.94%..............-0.20dB 1.39%
15KHz....-0.49dB 1.24%...............-0.34dB 1.95%
20KHz....-0.79dB 1.89%...............-0.58dB 3.05%

This data is a radical departure from what I saw years ago. The "Hammond notch" is still there, but is moved safely out of the audio band. Tube current starts rising at the frequency extremes, which is normal.

OPT saturation and insufficient primary winding inductance causes increased current at low frequencies, and indeed the Edcor channel current starts rising below 30 HZ while the Hammond can run at 20 watts at 20 Hz.

Winding capacitance causes tube current to rise at the high frequency extremes. Tube current started increasing in the 15KHz range on both channels with the Hammond going up much faster. Neither channel had any problems cranking out 10 watts at 20 KHz which is probably more than will ever be seen in real music, and into the smoking tweeter range for many speakers.
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Last edited by Tubelab_com; 7th August 2019 at 03:41 PM.
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Old 28th August 2019, 05:35 PM   #33
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Hallo George, any progress ? been silent a long time in this thread, thought first you blown up, but see you live and answering other threads / topics ! =)

Will this project be of a near future with possible pcb:s ?


I would like to order from you but i still wait on the solution for the TSE-II About R5
Or it will work fine with replacement Ohmite 42J270E ?
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Old 29th August 2019, 05:04 PM   #34
Tubelab_com is online now Tubelab_com  United States
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Quote:
been silent a long time in this thread
An unfortunate series of events (wife in hospital, grandkid in hospital, and myself with a broken tooth / crown / root canal) have kept the Tubelab workbench dark for several weeks.

Quote:
Will this project be of a near future
I do plan for this to be a future Tubelab PCB, or more likely several PCB's, but it will not be near future. My wife was in the hospital for several days in bad shape. I spent a lot of that time in her hospital room with my laptop. I converted one of my simulations into a PC board, since I didn't have much else to do. That is the board seen in this thread. I had about one week of serious time to play with it, but it's hasn't seen power since.

Before it can become a Tubelab product it needs to undergo some serious testing and probably several board revisions. This board uncovered several layout mistakes (mostly part fitment issues) but did result in some serious surprises since I didn't expect it to work without major changes, much less work so well.

I now believe that a single board amp like the one presented here will be good to 15 or maybe 20 watts. Anything bigger needs more heat sinking on all of the silicon, so it will probably be divided up into multiple smaller boards. There could be a single board version somewhat similar to this one, and a set of modular boards for bigger SE amps and other useful things like a monster push pull version. Right now it's too soon to tell.

Before I go down this path I need to wrap up the TSE-II issues (like R5) and create some good build documentation, and update the web site. That is also true for the UD board.

Today I am in the process of clearing the workbench and setting up a space for shooting pictures and maybe video of board and amp builds and amp setup / testing. I have already put the UNSET in it's tote box on the shelf for now.

We had planned a two week vacation trip to Florida for mid September, but Sherri's health and hurricane Dorian may kill those plans. If we do go, I will take the laptop for some more board layout time.
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Old 29th August 2019, 05:25 PM   #35
leadbelly is online now leadbelly  Canada
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Sorry to hear that George. Hope that all is well with your family. Best wishes.
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Old 29th August 2019, 06:27 PM   #36
smoking-amp is offline smoking-amp  United States
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Hope everyone is progressing on to a good recovery soon.

I've been on various meds for the last few years for high BP, with only modest improvement and annoying side effects. Then I discovered Olive leaf extract, which worked as good as the prescription stuff, so the meds got dropped. Then more recently I found out about mushrooms containing Ergothioneine, a new vitamin - soon. We have DNA and a blood transporter protein that specifically supports ergothioneine. Has been found to be DNA conserved across all mammals even (better than most human vitamins are) and is highly retained in the body by the kidneys, over a week half life compared to 30 minutes for most things consumed.

Mushrooms cause blood thinning (may not be related to Ergothioneine, don't know yet). The research article I saw on them recently suggested a half cup of mushrooms twice a week, I think. (found to clear up memory fog) Since I rarely consumed mushrooms in the past, I then went and over-did that with 2/3 cup of mushrooms every day, and developed bad nose bleeds for a couple of weeks. Cutting back to just 1 x 2 inch mushroom per day (using WalMart Baby Bella salad mushrooms), I've been clear of any nose bleeds, and my BP has dropped back to ideal territory. No more meds or olive leaf needed. Worth a try, check with doctor. Do not take mushrooms before any surgery (for weeks).

Some other common items can cause or aggravate nose bleeds too. Turmeric/curcumin, aspirin, Omega 3 oils, various allergies, so steer clear of those while steadily on mushrooms. Some mushroom types need cooking, or may cause allergies too. (especially more exotic types)

Last edited by smoking-amp; 29th August 2019 at 06:34 PM.
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Old 22nd September 2019, 05:59 PM   #37
smoking-amp is offline smoking-amp  United States
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One caution
for consuming a mushroom every day (and no more than 1 !!! or maybe nose bleeds or too thin blood). Ergothioneine in mushrooms is good at removing Zinc from the blood, and could produce a Zinc deficiency over extended time. Best to take 1 or 2 RDA of Zinc a day with a steady diet of mushrooms, ie multi-vitamin/mineral (and no more than 3 x RDA, Zinc has a narrow tolerance window). Just to be safe.
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Old 7th October 2019, 02:20 AM   #38
Murdoc is offline Murdoc  Germany
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This sounds really interesting, smoking amp! My father will be interested in this for sure. Why I'm polluting this wonderful thread is the following:
Most mushrooms have a so called adaptogen function: The immune system will use it as some sort of universal fuel and use what it thinks is the most urgent to do. Every mushroom is different. You will find lots of scientific information in englisch and other languages, as mushrooms have been used for thousands of years, and just recently get discovered by the "modern" western medicine.

I don't know if every mushroom thinnes the blood. There are hospitals using mushrooms in the US for different purposes.
selfhacked is a good starting point for 4 different mushrooms, as they have listed all the cited papers.
Sorry again for the off topic!
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