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Old 31st December 2010, 02:12 AM   #21
w5jag is offline w5jag  United States
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Default Chinese 6146 in the Simple SE

I am still running 6146B's in the amp, with no changes since my last post. It sounds pretty good right now.

I bought a pair of chinese 6146's to try out, as I have read varying comments about them, and wanted to try them for myself. The ones I received are trade dressed out as Shuguangs, and marked 6146B on the tube.

Physically, they somewhat resemble an RCA style tube, as the getter flash is in the base of the tube rather than on the side of the bottle, and the plate is a dark black material. Interestingly, the bottle is noticeably shorther than U.S. made 6146's, and this is apparent right out of the box, even without a U.S. tube to compare to. Other points of difference are that the base pins are squared off, rather than nicely tapered or rounded as on U.S. tubes, and the plate cap is somewhat smaller in diameter than U.S. tubes. It may be that the cap is correctly sized for current chinese manufactured parts, but I am using Millen ceramic caps and I had to adjust them a bit for a tight grip. In operation, there is a lot of visible filament/cathode glow with the Shuguangs, which is very much unlike U.S. tubes which have little visible emission from the filament/cathode.

I didn't do much in terms of testing them electrically. I checked both the tubes to make sure the external shield was internally connected properly (it was), and compared the transconductance (on my TV-7/D) to some NOS U.S. made 6146A and B and found them to be identical. I didn't set up to measure interelctrode capacitances since I didn't think it matttered much in audio service.

These chinese 6146B tubes work and sound very well. They have been in the amplifier since the day before Thanksgiving, and I have had no urge to swap them out with anything else. The amp runs very long hours as the PA in our home entertaiment system, particularly this time of year, and the tubes already have substantially more than 200 hours on them, with no sign of electrical or sonic degradation. If anyone is awake in the home, the amp is likely to be on. Often my wife forgets to turn it off, further increasing the run time and hour count.

They seem to have a larger power dissipation capability than the old U.S. made tubes. I haven't really defined what the limits are, but I know that the U.S. tubes will red plate well before the chinese tubes. I think the difference could be as much as 20% extra Pd in the Shuguangs. I cannot get them to flouresce, even at plate voltages approaching 450 volts (the U.S. 6146 won't flouresce either, unlike 2E26 that will turn so blue you can see it in ordinary room light).

In summary, I would not hestitate to use the Shuguang 6146B as a modulator tube, or in an audio application like the Simple SE. I think I would use them in preference to NOS tubes in an audio application. As for RF applications, can't say - yet.

I like the 6146B so much in this application, that I am seriously considering building an amp to better exploit the tube, and the other low screen voltage sweep tubes. So many worthwhile projects, so little time, unfortunately.

Happy and prosperous new year to all.

Win W5JAG
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Old 10th February 2011, 12:54 AM   #22
w5jag is offline w5jag  United States
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Snowed in and playing around last night with my digital camera.

Pictured are 2E26's. The one on the left is marked as Westinghouse. The one on the right is an RCA. The Shuguang 6146B are starting to show some color at about 750 hours or so, but it may be too faint to photograph.

These pictures are at ISO 80, max aperture, and 8 seconds exposure - the longest my digi cam will do.

Win W5JAG
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File Type: jpg 2E26 wide resize.jpg (106.9 KB, 772 views)
File Type: jpg 2E26 Close 2 resize.jpg (113.1 KB, 677 views)
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Old 3rd March 2011, 11:10 PM   #23
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I just discovered a couple of RCA 8552's in the basement which are 12 V equivalent of the 6146B. They look brand new.

I haven't built a Simple yet, but intend to, probably using EL34's as suggested. However, if I get curious enough, I may try these 8552's once I have a working system. Even though I don't really need any more power than the EL34's, I do wonder what the 6146B-types could do on output power. What do you think the capability would be, keeping a decent THD? Also, or course, I'd be primarily interested in sound quality compared to the more conservative approaches.
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Old 8th March 2011, 02:59 AM   #24
w5jag is offline w5jag  United States
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Quote:
Originally Posted by sprinter View Post

..... I do wonder what the 6146B-types could do on output power. What do you think the capability would be, keeping a decent THD? Also, or course, I'd be primarily interested in sound quality compared to the more conservative approaches.
10 watts, or so, in single ended pentode, I would think. I haven't tried to measure mine.

I'm not an audiophile, and the only other single ended pentode amp I have is an Elekit TU-879S, so my knowledge base is pretty limited. I just put the 6146's in the Simple SE for fun and to learn a little bit about using the tube in audio applications.

Comparing these two, the Elekit uses quite a bit of global negative feedback, wheareas my Simple SE has only a couple of local negative feedback loops - the cathode feedback around the OPT, and the plate to grid feedback on the 6146's. I think the Simple SE with the 6146's sounds as good as the Elekit, maybe a bit tubier. The amps are at different houses, so I can't directly compare them. I do have the same model speakers at each house so my memory is the only real variable.

I haven't run any of the regular audio tubes as pentodes in it - only 6146, 2E26, 6BQ6, 6DQ6, and (briefly) 6AR6/6384 and 6889. Right now I like the sound of the 6146's and haven't had much reason to use anything else.

Win W5JAG
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Old 13th March 2011, 05:26 AM   #25
w5jag is offline w5jag  United States
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A couple of scrapper transmitter carcasses followed me home from a hamfest today - a Heath SB-401 and an SB-400, both still had their power transformer on the chassis. The power supply in these transmitters is the same as the stand alone HP-23, IIRC.

A good way to make something into a scrapper is to burn out the power transformer, but they smelled OK, and I've never heard of these transformers being fragile. These were voltage doubler power supplys IIRC, with a high B+ around 800 vdc, a low B+ about 250 - 300 vdc, and a bias supply about - 130 vdc. If these transformers are any good, I'm going to use one to make another 6146 or 2E26 Simple SE.

There were a lot of tubes about; I got a half dozen NOS 6DQ6B's of various brands for a quarter each, a bunch of used micanol based 6SN7WGTA's and 6SL7WGTA's for a buck each, some NOS 6BQ5's for a buck each, and some others. There were tons of NOS 1625's about, and some other types I had not seen in quantity for awhile.

Win W5JAG
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Old 13th March 2011, 05:29 AM   #26
isaacc7 is offline isaacc7  United States
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I've got a bunch of 1625's, *dq6, and 2e26 tubes around. If I ever settle down, I'd like to make good use of them. Glad to know they can be useful for audio.
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Old 13th March 2011, 10:40 PM   #27
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Win,
When you get things settled out with the 6146B, do you think you could document what you did with diagrams and pics and share it here? I haven't yet built anything and I'm curious to know what you end up with and if you would do it again. Sounds like these could put out about twice the power of the 6L6's that I also have.

Thanks,

Ron (K7OEU)
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Old 20th March 2011, 01:28 AM   #28
w5jag is offline w5jag  United States
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Quote:
Originally Posted by sprinter View Post
When you get things settled out with the 6146B, do you think you could document what you did with diagrams and pics and share it here?
Ron,

I will do this, but it will be a while - it's a work in progress that is sharing time with some other diy projects, and since the current version of the amp is stable and sounds acceptable, rev II is not the highest priority.

Because I prefer to use parts that I can scrounge on the cheap, what I use may not be readily available to someone else, and the way I did my amp is certainly not the only way it can be done - it's just an example or suggestion.

Probably (in my view) the two most useful pieces of information in the entire thread so far are that:

1) the 6146 / 2E26 family of tubes can be made to function in the sockets on the Simple SE board without requiring any destructive modification to the pc board. Pin 3 on the power tube gets screen voltage - pin 4 must be left open because it is connected to the cathode internally. As pins 3 and 4 of the power tubes are brought out to individual pads on the edge of the Simple SE board, these rearranged connections are easily made. It is really just that simple (no pun intended);

2) the local plate to grid negative feedback (Schade) is an easily implemented, acceptable, solution to tame the single ended pentode shrillness, requiring only one resistor per channel.

Any Simple SE that has been tested and found to be working nominally is a candidate for this conversion, provided that a suitable screen voltage can be provided the power tubes. I built a crude screen supply from a separate screen winding on my power transformer that is working well. If you search "6159" in the main tube forum, you'll find a schematic for a 6146/6159 amplifier that uses a dropping resistor and zener diode to generate a screen voltage off the main B+. A separate transformer or a couple of small filament transformers back to back, as suggested above, would also make a good screen supply (better than a dropping resistor and zener, imo). There may be other ways.

I'm surprised, actually, that with this thread having been up for several months, that we're not seeing pictures of other 6146 / 2E26 Simple SE's. 6146 may not be the best tube for hi fi use, but it does seem to be a tube family that consistently generates interest in the diy community, with a few threads about it in the main forum, requests for schematics, etc. If a thread talks about non mainstream audio tubes, the 6146 always seems to come up.

Win W5JAG
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Old 20th March 2011, 07:28 AM   #29
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Win,
Thanks a bunch. I'm a bit of a scrounger too and I already have a couple of 12V versions of the 6146B, so it would be fun to see how they do. Like you, though, it's kind of on a back burner for now and of course, I'll do it first with the 6L6's that I also already have and get it going before modding. I think that 6L6's should just work without changes, although with a bit less power than EL34's. Is that your impression?

Thanks for the tips. If I do it first, I'll post results here.

Ron
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Old 22nd March 2011, 02:20 AM   #30
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Quote:
Even though I don't really need any more power than the EL34's, I do wonder what the 6146B-types could do on output power. What do you think the capability would be, keeping a decent THD?.......10 watts, or so, in single ended pentode, I would think. I haven't tried to measure mine........Sounds like these could put out about twice the power of the 6L6's that I also have.
Keep in mind that W5JAG is running the 6146's in pentode mode. The power output is almost always higher in pentode compared to UL or triode. A 6L6GC can do 9 or 10 watts in pentode.

The power output in pentode mode is most influenced by the B+ voltage and OPT load impedance, provided the tube you are using can adequately drive that impedance. In other words given a tube and a B+ voltage, the power output will go up as the load impedance is dropped, until the tube can no longer handle the load and then the distortion goes up. I haven't tried a 6146 in the SSE yet, but I am going to guess based on what I have seen in P-P experiments that it can beat the 6L6GC, and maybe the EL34. The KT88 should flat kick its butt as would most sweep tubes. I get 14 watts out of a KT88 in UL mode.

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. I don't mind blowing up a board or two or three, but then I like fireworks and I have a lot of boards! I had a capacitor explode when playing with 6DQ6's in one of my SSE's. Any time you go where no one has gone before, you must be prepared to experiment. Some experiments work, and some don't.

Quote:
2) the local plate to grid negative feedback (Schade) is an easily implemented, acceptable, solution to tame the single ended pentode shrillness,
Do you know how many of the big hitters from the main forum have told me that this just isn't true. Schade doesn't work with a triode driver tube, and won't work with a CCS load. Also more than one person says that the 12AT7 just sounds horrible in a SE amp. I won't tell if you don't!

Quote:
A couple of scrapper transmitter carcasses followed me home from a hamfest today
I went to a small hamfest Saturday morning and for the first time in years I came home with ZERO tubes. There weren't any worth buying.

Quote:
I'm surprised, actually, that with this thread having been up for several months, that we're not seeing pictures of other 6146 / 2E26 Simple SE's.
The SSE doesn't get used for experiments by many users. Most people just build and listen. I have hacked up a few. I even have one made into a 50 watt P-P guitar amp. Sooner or later I will find the time to document what I did. The SSE board is connected to a driver / preamp board that contains three 12AX7's. That is a perf board / flying wire furball that I made / tweaked over two years. I have no idea what is on the board any more.

I know I posted a picture of an SPP board cranking out 60 watts or so with 6BQ6's stuffed into it. I can't find the picture but the board is still on my bench.
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