Monoprice 50w Hybrid Amp
Comments
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An interesting read on using pentode tubes in a preamp:
https://www.ampbooks.com/mobile/tutorials/pentode-tutorial-1/
people do.
Northern New England tube guru Kevin Kennedy being one who is not averse to pentodes (and Kevin's amplifiers do sound good IME).
Some interesting discussion on the topic in the context of phono preamps at http://www.hifihaven.org/index.php?threads/truly-fantastic-tube-phono-kit-for-beginners.3471/
I may have mentioned this here before; if so, my apologies (I am too lazy to check).
Of course, the thing about the 6p15 is that it's a power tube -- that's what's weird about its inclusion in these little hybrid amps! On the surface, it looks like they designers of these amps picked a cadre of tubes to make them look like an all vacuum tube, single-ended stereo amplifier (which, of course, they are not).
Now, in fairness, it's perfectly possible to use a 6p15, or an EL84, or, heck, even a 300B as a driver stage for an RF modulator or, e.g., a high-power single ended triode amplifier -- but now we're talking components of a very different league.
(borrowed photo -- needless to day)
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@Zingo -- I have an actual question about these amps for you?
How do you manage to extricate the tubes from your amp?
My only success to date has been to partially dissect those stupid little cages until I can get some purchase on the tubes with my fingertips. I am tempted to just take them as off as possible, but I really don't feel like investing that much effort (they're kind of tedious to dissect)
I am in the process of sourcing some different (non-Chinese/generic) tubes to try in the 25 watt morph -- just to see if it makes any audible difference.
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I used my thumb and forefinger at the base of the tube in between the slats of those cages, and a thumb and forefinger on the top of the tube. It is an awkward operation, but was pretty easy once I figured it out.
When I take the bottom off the amp, I'm going to see if taking the tube cages off is easy. -
I used my thumb and forefinger at the base of the tube in between the slats of those cages, and a thumb and forefinger on the top of the tube. It is an awkward operation, but was pretty easy once I figured it out.
When I take the bottom off the amp, I'm going to see if taking the tube cages off is easy.
Thanks!
FWIW -- the tube cages can be disassembled from the top (at least somwhat) -- I couldn't resist taking a wrench to those little cap nuts*! There's a little decorative sleeve on each post, which is, in fact, an itty bitty piece of threaded rod. They come apart, section by section -- but I only took off the top section (three sleeves and posts) of one 'cage' to extract one small-signal dual triode. At that point, I decided it was too much work.
I am sure you'll get a look up her skirt (so to speak) before I ever manage to pop the case open and see what's in the 25 watter
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* You can pretty well imagine what kind of biologist I am. "Look at that cool critter! Let's cut it up, grind it up and see what makes it tick!" That's why I work in biotech I am what we call in the biz an old school, grind 'em and bind 'em kinda biochemist. -
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oooh, ooh! cheesecake pictures!
Seriously -- thanks. Gonna take a close(r) look.
The amp chips are tantalizingly not quite visible enough to identify (for me, that is -- I imagine there're folks who can look at your photo and know exactly what they are).
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I'll take a closer look tonight but what I can read is TDA2xxx; I'll pull the specs sheet on the chip amp when I confirm the model.
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You got further than I did with the ID.
That said, I am doing a little meta-analysis of the tube PCB, as that's within my capabilities, albeit barely
There are, of course, two tubes per channel: a small-signal dual triode (the 6n1) and a "beam power tube" (power pentode, the 6p15).
The 6n1 has the same configuration as many 9 pin miniature dual triodes (e.g., the 6922... which might even be a good sub for it!). That configuration is known as 9AJ.
http://www.tubebooks.org/tubedata/HB-3/Receiving-Type_Industrial_Tubes/6922.PDF
The 6p15 (EL86/6CW5) has base configuration of 9CV.
http://www.tubebooks.org/tubedata/HB-3/Receiving_Tubes_Part_1/6CW5.PDF
The convention of basing diagrams in tube manuals is to look at the tube from the bottom, so we can "easily" map the pins of the two tubes to @Zingo's fine photograph of the tube PCB (seen from below)
original photograph:
Here's what we're dealin' with, in terms of the four tubes plugged into that PCB:
I took @Zingo's photo and cropped and rotated to line up with the tube basing diagrams taken from the two PDFs above (which come from Pete Millett's wonderful on-line resources, via the equally wonderful http://tdsl.duncanamps.com/tubesearch.php ). I hope this isn't too confusing!
Post edited by mhardy6647 on -
so, pins 4 and 5 are the filament (umm, heater) supplies for the two tubes -- the PC traces for the filament voltage (which should be, typically 6.3 VAC) are very obvious at the top of the PCB as shown in this (rotated) photo
In terms of signal, the business end of any triode tube is the grid (input) and the plate (output). There are two plates and two grids in a dual triode tube like the 6n1.
Triode "unit" 1 has pin 7 connected to grid and pin 6 to plate; "unit 2" triode has pin 2 connected to grid and pin 1 to plate.
It appears that "unit 2" of the 6p1 is unconnected -- at least pins 7 and 8. Now, I am assuming that this is not a multilayer PCB (which may or may not be the case). That's fine, of course -- the other unit seems (?) to be wired up.
The "output" (plate) of the unit 2 triode is at Pin 1. I can't tell what's happening with that trace due to the ribbon cables
The 6p15 is interesting, I think. -
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easy stuff
The filament or heater is the source of electrons, the working capital of a tube (or a transistor). In tubes like these, the heater heats the cathode to boil off electrons.
There's a high voltage applied to the plate to attract and accelerate those electrons. Their migration from cathode to plate is modulated by a signal (music!) applied to the grid. This is the essence of the simplest vacuum tube amplifier, the triode. In the present case, the 6n1 has two triodes in one glass bottle.
That beam power tube (pentode), the 6p15, has a couple of other grids which are used to modify the properties of the electron flow from "grid number 1" to the "plate".
To paraphrase Linus' explanation of Christmas to Charlie BrownAnd that's what tubes are all about, Charlie Brown
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So -- grid one of the 6p15 (tube on the left in my flipped, annotated picture above) is connected to pin 2 according to RCA. It doesn't look like pin 2 is connected to anything on that PCB(?!) -- again, I am assuming it's a single layer board (which may not be true). Pin 3 (which is "grid 3", the suppressor grid, which is also tied to the tube's cathode, does look like it's hooked to something, though. It looks like it connects to pin 8, which is an "internal connection in the tube.
I am also perplexed by that ring on the PCB that seems to connect most of the pins (pins 1, 2, 6, 8 and 9) of that 6p15 together (?!?)
OK, my brain hurts, now, too.
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Aka magic glass things that make music sound nice.
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no magic, it's physics.
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Now -- transistors -- them things are evil. Black magic.
Something about N and P junctions, and holes and stuff like that...
the Devil's devices.
Heck, unscrupulous EEs even have to dope that lovely pure silicon with crud to make the substrate for transistors... them dang things is sullied, I tell you. Sullied. -
Sending mine back. There is so much distortion coming thru the speakers that it is crazy. Not acceptable.
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innerestin'... that's not an issue with the 25 watter here; it doesn't sound bad, truth be told.
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Might be something wrong with this one...
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Conradicles wrote: »Sending mine back. There is so much distortion coming thru the speakers that it is crazy. Not acceptable.
I am having the opposite experience. Even with the Chinese tubes, if I let the unit warm up for about an hour, I have a very nice listening experience with multiple sets of speakers. -
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^^^^^ Why is Wally Shawn dressed like a hippy?
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Don't get me wrong...this little booger has potential...but mine is faulty.
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Conradicles wrote: »Don't get me wrong...this little booger has potential...but mine is faulty.
Ya that seems to be a pattern I see online; some units seem to be good and some seem to be problematic on delivery. Maybe mine will become problematic? -
If mine wasn't so noisy, I would totally keep it and call it a win.
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Gonna RMA it for another one?Conradicles wrote: »If mine wasn't so noisy, I would totally keep it and call it a win.
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Gonna RMA it for another one?Conradicles wrote: »If mine wasn't so noisy, I would totally keep it and call it a win.
Yeah -- it only took "us", what, four tries?
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Gonna RMA it for another one?Conradicles wrote: »If mine wasn't so noisy, I would totally keep it and call it a win.
Na, probably go vintage... -
Conradicles wrote: »Gonna RMA it for another one?Conradicles wrote: »If mine wasn't so noisy, I would totally keep it and call it a win.
Na, probably go vintage...
vintage hybrid amp?
There were some, but generally speaking not in a good way
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I listened to a vinyl rekkid Childhood's Greatest Hits with our 2-1/2 year old granddaughter today on the 25 watt MP amp, and you know what? It sounded mighty darned fine. Loudspeakers used were Polk Audio Monitor 5 ("Series 2"? -- at any rate, a pair in black vinyl woodgrain finish, sporting the dreaded SL2500 tweeters).
https://store.cdbaby.com/cd/willwright2 (couldn't find an easy link to the LP version, but I am sure they're out there... it's a dandy, well recorded children's record)
https://www.youtube.com/watch?v=MrCPIrs90eg
