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Discussion in 'Amplifiers' started by RedGuitars, Jan 23, 2018.
This one is from Exp. Those of you waiting for the "big" version....just grab one of these.
Just got a call from my Sweetwater rep and he said the MT15 got pushed out again to late July.
My SW rep got promoted and my new guy never calls......Your post was not what I was hoping to read.
Yeah my dealer (In Europe) told me the expected date was pushed to early August (when it used to be June).
I don’t understand the messages saying they arrived at PRS – or will it take a month to check them?
Anyway, I can wait. Just excited to get it.
That was a great video
Phil needs to start looking after himself a bit more though
So how about a lunchbox size MT50 with the bigger transformer and then a full size MT100 with a quad of 6L6’s. Then Mark can ditch his Mesa amps live and run the big boy MT amp...
I would imagine "the initial shipment" has made its was to the PRS Maryland facility, and not all existing orders will be fulfilled immediately. So your dealer may have to wait for wave 2 or 3.
Pretty much what I was told - the first shipment would likely be spread out, kind of like the Silver Sky was.
The parts issue was handled about as well as you can handle it, but with a solution that does take time. It stinks for PRS and for everyone whose buying one. Since I’m buying one, it stinks for me. But I REALLY feel bad for you guys who are waiting on one and don’t have an ARCHON to keep you busy while you wait. That is pain on a different level.
Heat dissipation would be a major engineering challenge. Plus, there is not a huge jump in volume going from 17 to 50 watts because the human ear perceives sound on a logarithmic scale. To double the volume of a 17W amp, we need an 8-fold increase in power (136W). What going from 17 to 50 or 100 watts does is increase the clean headroom of the power section. That is fine if all the guitarist is seeking is preamp distortion, but that pretty much does away with a lot of the the magic of tubes. The change in power amp operation is why a tube amp sounds different as it is turned up. A Marshall 50W amp operates in class AB when run at low volume. However, when cranked up and driven hard, a Marshall 50W switches over to class B operation and produces significantly more than 50W. The tone of the amp also changes. A Vox AC30 only operates in class A when used at low volumes. When cranked and pushed, it switches to class AB because the tubes pull more current through the cathode resistor resulting in an increase in bias voltage.
As an aside, the plate voltage on the MT15 has to be under 300VDC. That is a very conservative way to use a 6L6. Most 6L6 amps have a plate voltage of at least 400VDC.
I will give you a really good example of why the power stage is critical to tone and feel in a tube amp. Anyone who has played any of the amps that derive from the original EL84-based Caliber series of Mesa amps has noticed how lively these amps are when it comes to playing. There is an explosive peak followed by compression. This power stage just sings. The reason behind it is explained in the Dyna-Watt patent: https://patents.google.com/patent/US4713624A/en.
Here is the page from the Studio .22+ schematic that includes the power supplies and the power stage. The power stage power supply (high voltage supply) is in the upper left-hand corner
This type of power supply circuit is known as a Pi filter because it resembles the Greek letter Pi. The "A" power supply node (390VDC) is the power tube plate voltage, and the "B" power supply node (295VDC) is the power tube screen voltage. In many power supplies, the 5.6K resistor is an inductor known as a "choke." The combination of the 5.6K resistor and 30uF capacitor is the secret to Dyna-Watt. It establishes what is known as a long RC time constant. In this case, R=5,600 ohms and C=0.00003 farads; therefore, RC = 5,600 * 0.00003 = 0.168 or 168 milliseconds, roughly 1/6th of second. That is the time that is takes for the capacitor to charge to ~63% of capacity and discharge to ~37% of capacity. When the capacitor discharges, the screen voltage sags, resulting in a period of compression until the capacitor recharges. After the capacitor is fully charged, a guitarist can get another explosive peak, which is not only great for playing the blues, but makes all kinds of playing very touch sensitive. I am absolutely certain that Dyna-Watt was a happy accident. The Calibers were Mesa's first attempt at building a budget amp. A resistor was used in place of a choke between the "A" and "B" nodes to reduce cost. There is little doubt in my mind that 3x30uf was used in the high voltage power supply to cut cost and reduce the number of different parts that needed to be stocked. The large resistance value was necessary to get the screen voltage down to 295 VDC, which is pretty much straight from the RCA handbook for the 7189. The 7189 is a beefed up version of the EL84/6BQ5. A true EL84/6BQ5 can only reliably handle 300VDC on its plate, more specifically, a 300VDC potential difference between its plate and its cathode. A 7189 can handle a 400VDC plate-to-cathode potential difference. In fact, the operating parameters for the power section of this amp are basically straight out of the RCA handbook, including the -15VDC fixed-bias control grid voltage.
These amps require the EL84M to run reliably, which is a Soviet 6P14P-EV. The 6P14P-EV is a MIL-SPEC version of the 6P14P. The 6P14P is the Soviet equivalent of the EL84/6BQ5. The 6P14P-EV is the Soviet equivalent of the 7189.
Randall has done several interesting things with power supply stages. I was quite fond of my Mesa TA15 because on top of 5 voices, the three different types of power stage gave 3 completely different sets of feel and tone to each of the 5 voices. I think that amp was very close to true greatness, for a small versatile package. Mids control and a loop would have made it a lifer for me probably. I’d say chances are above average that I’ll own one again some day anyway. I can’t imagine not loving the MT15 though, so we’ll see if I still want one after that.
Interesting analysis of the Dyna-Watt.
Thanks for uploading this. I still have a studio 22 that I purchased in 1994. It’s such versatile wee amp, that I love the voicings of.
Recently, thanks to information gathered from this forum, I’ve been getting some of the best sounds I have ever had from it.
Long live the “Petaluma brat” !!
I have an MT15 and matching cab on order at my local PMT in Birmingham. I popped in yesterday to enquire how long they reckon the delay is currently. The salesperson got on to the phone to PRS UK and apparently they’ve pushed everything back to November now!
The DG30 also uses the 6P14P-EV (EL84M, 7189).
Someone told me that certain of the old Magnatones used them as well, but I have no personal info on this, it’s purely hearsay.
I use 1980s vintage Soviet tubes in my DG30. They’re supposedly rugged enough to last 50,000 hours, which is quite long for an EL84 type tube. The ones in my DG30 still sound great after over 3 years.
Best get some in stock as you and I plan on living into our bi-centennial!
The thing is that the 6BQ5s (American designation for the EL84) that were being sold at the end of American tube production were basically 7189s. The 6BQ5s coming out of the Sylvania plant were relabeled 7189s. There is a super 7189 called a 7189A that can handle a 440VDC plate-to-cathode differential, but it has a slightly different pin-out; therefore, it is not a drop-in replacement in many circuits. Several Magnatone amps were originally designed to use 7189As.
Another neat noval (9-pin) power tube is the 6973. It is not a drop-in replacement for a 6BQ5 or a 7189, but it is a cool sounding tube that was used in mid-range Supro amps. It is the sound heard on the early Zeppelin albums. The tone is instantly recognizable. Andy from ProGuitarShop demos a recreation of the Supro 1695T in this video:
I run the amp no more than 3 hours per week; 156 hours per year. If the tubes Live up to their spec of 50,000 hours of use, I should have 320 years and six months per set. And I have a spare set of NOS.
So, deducting the three years of use I’ve already gotten, I figure I have 638 years to go on my power tubes for that amp. I suppose a wise and well-prepared person would acquire several more backup sets in case immortality sets in, factoring in the likelihood that after 1000 years or so, modeling technology may finally catch up to sounding like tube amps.
Of course, I’m justifiably worried about the 12AX7s, and the EL34s and 6L6s for the other amps, not to mention rectifier tubes for the Lone Star. I do snap up a few NOS preamp tubes whenever I can find good prices, as well as NOS EL34s (I’ve got three spare sets of Siemens), so I’ve got a little stash going, but it won’t last more than 10-20 years.
I’d better get busy!
“Les, the rest of the components on the amps won’t go all that long, you know.”
“Hmmm. It’s very possible I don’t want to be immortal, then. Hey, anyone know whether keeping the amps under vacuum seal when they’re not in use will keep the components from deteriorating through oxidation?”
I have a copy of the Detroit Times (now a defunct newspaper, went out of business in the 70s) with the headline, “Kennedy Shot” that I wrapped in Saran Wrap in 1963 when I was a little kid. It hasn’t yellowed, and shows no signs of age. For real. Maybe I could wrap my amps and guitars in Saran Wrap and save them from the ravages of time?
“Les, you are truly out of your mind.”
“And that’s, like, a new discovery for you?”
Les, you better get busy playing!!!
Well when you and I start our “Transatlantic Thrash Jazz” duo - Ruthenium Cloud, those tubes are gonna get more than 3 hours exercise, so get busy!