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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 1st August 2019, 11:04 PM   #11
Sodacose is offline Sodacose  United States
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What a tease! Subscribed.

Thoughts with you and your wife as she recovers.
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Old 1st August 2019, 11:28 PM   #12
erikovsky is offline erikovsky
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Old 2nd August 2019, 02:00 AM   #13
Tubelab_com is online now Tubelab_com  United States
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I got one more experiment in today.

The date on these Hammond OPT's is 5-11-06. Yes I have owned them for 13 years and never found a suitable way to get HiFi quality audio through them. They can be seen here with one of the first SSE prototypes powering up some Lowther based horns. They sounded terrible here since the 106dB efficient Lowthers were loud with half a watt. The final "first SSE" wound up using a pair of Transcendars like those I just pulled OUT of this amp. They sounded quite nice with the big horns.

The power at clipping had dropped to about 15 watts when I traded the 3000 ohm Transcendar OPT's for the big 5000 ohm Hammonds. How do I get more power......turn the knob to the right!

I cranked up the power supply to 520 volts. That's as far as I want to push the 500 volt filter caps that are in the board. This brought 22 watts at the edge of clipping (5% THD @ 1 KHz). THD at 20 watts was around 2%. I backed the power down to 10 watts and turned the frequency dial on the 204C. At 1 KHz the THD is 0.68%. At 20 Hz the output drops 0.40 dB and the THD rises to 0.88%. Going much below 20 Hz starts making my all original Fluke 407D angry. It's current meter is hovering around 260 mA.

Spinning the dial in the other direction reveals a drop of 1.01 dB at 20 KHz. This is where the famous Hammond notch of anywhere from 5 to 15 dB resided in the past. This board has "tamed the beast." Turning the knob past this point sends the current meter on the Fluke beyond the end of it's scale, so I didn't test there. The OPT's get very capacitive beyond that notch driving the tube current up, and into the red zone.

Running the output stages at 520 volts and 105 mA brings on some mild red glow, so I must point out another feature in the UNSET board, albeit one that I botched pretty bad in the layout.....the "Any Octal Matrix." The board can be configured for almost any octal output tube from the little 6V6 and 6AU5's to the fat boy 6LW6......so you know where I'm going next. That's right, bigger tubes and higher voltage caps.
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File Type: jpg P2920684_x.jpg (891.6 KB, 403 views)
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Old 2nd August 2019, 04:45 AM   #14
vinylkid58 is online now vinylkid58  Canada
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UNSET is coming?
Looking forward to further testing. Hope your wife's BP improves soon.

jeff
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Old 2nd August 2019, 05:51 PM   #15
w5jag is offline w5jag  United States
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Quote:
... I cranked up the power supply to 520 volts. That's as far as I want to push the 500 volt filter caps that are in the board. This brought 22 watts at the edge of clipping (5% THD @ 1 KHz). THD at 20 watts was around 2%. ...
How much power can be obtained from a big DHT in SE, like SV 572, 211 or 845?

This reads like it is putting out as much power, at 1/4 to 1/3 the plate volts, and less distortion, as the big DHT's, and you haven't even gotten to the big sweeps yet?

I guess the 6146 family would work here like any other pentode sweep tube.

Dumb question: will this topology lend itself to being wrapped around real DHT's to linearize / enhance them?

edit: will there be any provisions for compactrons, or will we need to make an adapter?
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Old 2nd August 2019, 05:59 PM   #16
Mr_Zenith is offline Mr_Zenith  United States
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UNSET is coming?
Hey Win - you just reminded me of a massive stash of NOS 8552s (a 6146-oid) I have somewhere down in the basement. I "inherited" them when a volunteer fireman friend was cleaning out his fire station's equipment room. They're not good for much else, so maybe they'd work here.

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Old 2nd August 2019, 06:23 PM   #17
w5jag is offline w5jag  United States
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... a massive stash of NOS 8552s (a 6146-oid) ...
There is a thread in this sub forum on using these types in the SSE.
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Old 2nd August 2019, 08:12 PM   #18
Tubelab_com is online now Tubelab_com  United States
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Quote:
How much power can be obtained from a big DHT in SE, like SV 572, 211 or 845?
Never met an SV572, but I do have an amp that can run a 211 or 845. It uses a first gen TSE board with a 45 tube that feeds a big PowerDrive board that has no problem driving anything into A2. It was used to extract 200 watts of SE power from an 833A on 1500 volts. With 211's or 845's the power at the edge of clipping is just over 30 watts. The 211 has a higher Mu and is easier to drive, but gives a higher output impedance which doesn't work well with some speakers. I prefer the 845 due to its better bass with my speakers.

Coincidentally the power rating on the big Hammond OPT's is 30 watts, so that's the target power level, and I believe that I can get there with a big fat sweep tube, or maybe two smaller ones.

I planned to test that theory today, but Sherri vetoed those plans. She will be away for a couple of hours tonight, so I plan to audition those OPT's with the existing board at a high volume level

Quote:
will there be any provisions for compactrons, or will we need to make an adapter?
That brings me to another decision point, and one of the reasons for not just ripping out the power supply caps and turning the B+ voltage up beyond 600 volts. The CED circuit design uses a mosfet and a pentode combined with some other parts to create the "triode." The mosfet will need to dissipate 5 to 20% of the power seen by the pentode. This means that a 40 watt sweep tube that's turned up into the 50+ watt region may need to burn 10 watts or so in the mosfet. That's not wasted power, it does get turned into audio with efficiency about the same as the pentode.

Yesterday's excursion to the 520 volt zone resulted in 44 watts being dissipated in the tube at idle, and 9 watts being dissipated in the mosfet. This drops as the amp is driven and a lot of that energy gets turned into audio power, 22 watts at full crank. This means different size heat sinks for different power levels. Yesterday the tubes had a dull red glow at idle, but the heat sinks were too hot to touch. Going beyond 500 volts means bigger heat sinks as well as bigger caps. There isn't room for bigger heat sinks on the board, but provisions for top or board mounting are included.

My initial thoughts, and this test board, put everything on a board that's about the same size as a TSE-II. The idea was to design two, maybe 3 boards. One for octals, one for 12 pin compactrons, and maybe one for 9 pin Novars and Magnovals. The heat sinks that are used here are good for power levels up to 15 watts or so, and higher power levels could use the chassis for heat sinking.

Maybe its a better idea to go with the modular approach with separate smaller boards that can be wired together to build amplifiers of any size. The mosfet would be on the board with it's associated tube, but could be mounted on on top or bottom, possibly in one of two locations.

Any thoughts / preferences.

Quote:
will this topology lend itself to being wrapped around real DHT's to linearize / enhance them?
I'm not sure exactly how this would work since the screen grid is a driven element, and part of the triodization process. I'm sure that the concept could be applied to a true triode, but I haven't gone down that road yet. There were far too many pot holes and speed traps on this one.

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you just reminded me of a massive stash of NOS 8552s
I had about 50 6159's but gave them all to a ham that wanted to build a big linear amp. I probably still have a few 6146's in a box around here somewhere. I have dozens of tubes I want to stick in this thing ranging from 6V6's to big fat sweep tubes, but it will take a while to burn through and document them all. It appears that the triodization process requires some different parts resulting in different drive levels for each grid. This may need optimization on a tube number by number basis. I have had good luch with small and medium sized sweep tubes so far. Just sticking a KT88 in place of a sweep tube didn't work well, but is has a much less sensitive screen grid.....time and testing will tell.
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Old 2nd August 2019, 09:40 PM   #19
w5jag is offline w5jag  United States
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I kind of like the idea of a hole in the board, and pads to skywire a builders choice socket to the board.

edit: assuming the length of skywired leads would not cause stability problems.
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Old 3rd August 2019, 03:18 AM   #20
Tubelab_com is online now Tubelab_com  United States
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I cranked up the power supply to 550 volts (max output for my old Fluke 407D), pointed a small desk fan at the heat sinks, turned up the tube current to 120 mA (max spec for the Hammond 1628SEA).

Power output at edge of clipping (5% THD) rose to 25 watts.

Power consumption breaks down as follows:

The B+ voltage is 550 volts. The current meter on the power supply reads 270 mA for a total DC input of 148.5 watts. 2.6 watts are lost in the OPT's DCR. The mosfet eats 10.6 watts, and the tube burns 52.8 (yes it's rated for 15 watts. I promise I didn't melt them....... This is a total power input of 183.5 watts, but some power will be wasted turning line voltage into 550 volts DC, and some will be lost in the SMPS for the 26 volt heaters if used. I'm assuming that total power draw will be in the 200 to 250 watt range. The amp is class A, so the power consumption doesn't change much from idle to max power.

Scale that up to 30 watts output (maybe 600 volts B+). The heater consumption doesn't change, neither will the B+ current due to the OPT max rating, so the B+ power consumption goes to 600 volts * 270 mA = 162 watts, and the total goes to 197 watts. This looks like 225 to 275 watts drawn from the line.

In contrast that to my 845 SE amp. It ran 80 to 110 mA per output tube at about 1050 volts DC. We will call it 100 watts per output tube. This was derived from a backwards wired 480 volt industrial control transformer feeding a voltage doubler made with 5AR4's (10 watts per heater). Total power from the wall was over 300 watts but I don't remember the exact number. Their heaters draw 3.25 amps from 10 volts EACH and they need DC to be quiet. That's another 80 or so watts.

The driver was a complete 45 based TSE with a 450 volt power supply to feed the CCS load on the 45 (no OPT, just a powerdrive board). I don't remember the exact numbers but the complete amp drew well over 500 watts from the wall, and really heated up my room, so it didn't get much use in Florida.

So after turning up the power, I connected up some speakers and let it play for about 3 hours......ME LIKE!

After a couple hours I began to smell something toasty I was thinking the 500 volt cap eating 550 volts, but it turned out to be my old Fluke 407D. It didn't like running at max power for 3 hours, so I shut off the fun. I will be gone most of tomorrow and Sunday.


I sat there staring at the board and sketching out stupid ideas on scratch paper while I cranked out the tunes from the amp tonight.....here are my latest ideas, but I may change my mind by tomorrow. I'm really thing about a short path to building myself one of these with some chassis and stuff that I already have. I have the Hammond OPT's and some big Antek power toroids.....

Quote:
I kind of like the idea of a hole in the board, and pads to skywire a builders choice socket to the board.
That still leaves the issue of multiple different heat sink sizes. I'm now thinking of one board similar to this one with all 5 tube sockets and heat sinks like what's on the board now. It could work at power levels up to 10 watts and use any of the common older generation sweep tubes. Sort of like a cross between a TSE and a SSE.

Then for us experimenters and power hungry amp builders a second smaller board, ditch the rectifier tube since a 5AR4 will not support the power levels needed for a 30 WPC SE amp, so silicon (on board) or damper tubes (off board) must be used. There would not be any output tubes on the board either, just terminals for the 5 electrodes being used. I got visions of those 4D32's wired into this thing. The heater wiring could go to the board, or directly to the transformer or SMPS, with one terminal for the variable heater DC float voltage. The mosfets would be mounted on (or to) the board's rear edge to allow multiple mounting schemes.

I have a little push pull version where I did stuff everything on one board. It works really good, but gets too hot and was a nightmare to build. The heat sinks are on the bottom. It used a conventional pentode LTP for the PI / driver since the CED does not lend itself to being wired as a PI. The output stage is CED with a tiny 6GF5 sweep tube with a 9 watt plate rating. 50 WPC flows easily without and redness from an Antek power toroid, and 70 WPC can be had with the Fluke feeding a regulated 500 volts.
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