The BASH Amp's failed part was a Thermistor that I believe is used as a startup/inrush current limiter. I've seen several SVS 750W BASH Amps with similar failures in older PB13/PC13 Ultra subwoofers. Drivers checked OK with a meter and no apparent voice coil or other damage.
(BTW: I'm not referring to earlier/older BASH Amps SVS used in other subwoofers before the 750W PB13/PC13 ultras. I've seen some from as far back as 2002 era still working, as well as my two PB12/Ultra2's with BASH 1000W Amp. And the 750W BASH Amp's thermistor failures I've seen may be affected by usage (left on) or a specific manufacturer's lot/component used.)

PC13 Sledge 1200D Amp Fit Tip (not verified personally yet):
If you've determined the Sledge 1200D Amp has port tube interference in your PC13 Cylinder, try mounting the Sledge 1200D Amp upside down to avoid port tube contact. (I'm going to try that if my 1000D amp fails.) Since with the 1200D you use the (Bluetooth) SVS subwoofer control app (as there are no manual controls on the Sledge 1200D amp itself), having the Amp plate mounted upside down wouldn't bother me. (With the 1200D installed, I'd position the PC13 Cylinder so the Amp wasn't visible anyway.)

FYI: In late Oct. 2020, I asked Ed Mullen at SVS about the 1200D fit issue with PC13s, as IIRC there may have been a change in port tube location from the early builds of the PC13 (Cylinder) model. He said the 1200D Amp doesn't fit most of the original BASH Amp PC13's unless you make a spacer (he suggested 3/4" or 1" thick baltic birch). He also confirmed there was a PC13 Port Tube location change in later builds, to avoid contact with the Sledge 1000D Amps. (See update/notes below - some rare BASH Amp PC13s were built with the Port Tube change.) I had no fit issues with a 1000D Amp in my originally BASH Amp PC13, but it may have been a later production with the Port Tube change. Note my PC13 was made with a strip of foam tape on a Port Tube in an area where the Amp may make contact. (On Oct. 24, 2020 I removed the Sledge 1000D Amp from my PC13 (after 8+ years of use), and saw no evidence of contact on the foam tape, and felt no interference reinstalling it. I must have one of the rare BASH PC13s with the Port Tube change.)

More Info on 1200D Amp Fit Issues in (Bash Amp) PC13-Ultra
I saw a 2nd BASH PC13 owner report on the 1200D Amp upgrade, who after making a thick spacer, tried the 1200D Amp before installing the spacer. He said it fit OK. SVS's Ed Mullen replied with more info on the Port Tube orientation change (rare in an original BASH Amp PC13).

"The vast majority of PC13-Ultras with the BASH amps have major port interference with the 1200D. We did make a running change to the port orientation in anticipation of migrating to the Sledge STA-1000D. There weren't many PC13-Ultras made with the revised port orientation but still with the BASH Amp - you must have gotten one of those rare subs...
Regardless, all PC13-Ultra customers with BASH amps get the same advice - expect port interference unless a spacer is used - because that is the reality with nearly all of the BASH-equipped PC13-Ultras."

My 750W BASH Amp Component Heights above the Flange Gasket
(Right/Left is relative to viewing from front face of the BASH Amp)

750W BASH Amp Measurements
(Height from Amp Flange Gasket)
• Lower left side Heat Sink - 2.675"
• Lower right side Capacitors - 2.875"
• Circuit board at the top - 2.625"

The Sledge 1000D Amp fit OK in my original BASH Amp PC13 (and it's still working). But next time I remove it, I'll check the distance from the Amp mating surface to the Port Tubes in my PC13. (I may also have a rare original BASH Amp PC13 with the relocated Port Tubes.)

Before buying a used SVS PB13/PC13 Ultra with BASH Amplifier, I'd do this test first:

SVS PC/PB-13 Ultra (750W) BASH Amp Thump Test
1. Ensure Subwoofer and Receiver are OFF, no active input to the Sub.
2. Set the Subwoofer's "Auto/On" Toggle Switch to the ON (not "Auto") position
3. Power the BASH SVS subwoofer On (A/C power switch)
4. IF any "Thump" is heard from the driver, the Amp may have a failing thermistor. (If you're not experienced with electronics repair, have someone that is do this for you. Disconnect power and heed warning labels on Amp.)
   The photos below show TH1 location. It may have cracks, discolored hot spots, etc.
   I've seen an Amp with cracked thermistor (1/3 missing - see photo below) still work, but with a slight thump on Power-Up. Eventually it will completely fail however, so if any 'thump' is heard at power-up (again with the Auto/On switch in ON position - the "Auto" setting can mask this problem), have the Amp checked for damage to TH1.
   (If the Amp has already failed/has no output/sound, no LED, etc - check the fuse, located in a removable part of AC input socket. If it's blown, likely a new fuse will blow again. If fuses repeatedly blow, other components (not just the thermistor) may have also failed.)

BTW: In general I'd suggest using "Auto" mode rather than "On". And I would not leave the BASH Amp on all the time. (Regardless of type, I turn off all my A/V electronics when not in use.)

Not sure if EU Amps are different, but I've seen this problem on 3 USA/120V SVS 750W BASH Amps used with their earlier PB13/PC13 Ultra subwoofers. All had what appeared to be the same OEM (Green Disc/unmarked) Thermistor failure. A replacement I've used in US SVS 750W BASH Amps is Ametherm Part Number SL15 4R008-03. (IIRC, a post by Ed M. of SVS also listed this as a replacement P/N.) I need one now, but no local electronic parts dealers here have them. At the time this was written (2015) they were appx $1 ea (depending on quantity) plus shipping, for instance at Newark.
  This isn't the only possible failure mode/component of course, just one I've seen several times and something to check before things get worse/before buying. (BTW: I've had several of these Amps that almost seemed glued in, see below for a tip to remove stuck plate Amps I've used.)

  In 2011 here, a PB13 Ultra BASH Amp failed shortly after being sold by the original owner (about 2.5 years old). With the "Auto/On" Switch set to ON, it would "thump" (a very deep/low frequency tone) so forcefully when switched on that it rattled items in a small room. (That issue reduced the asking price significantly.) Within a couple months it failed, blowing the AC input power fuse at turn on. And my working PC13 BASH Amp (unknown age, bought used with no S/N sticker on the Amp) developed a much lower level thump at power up (not noticed if Auto/On switch was in the Auto position). Inspection of that Amp's thermistor showed it had cracked and about 1/3 of it was missing. (See green disc in right side of image below. Some others I've seen were intact but had cracks from stress/overheating.)

Cracked Thermistor (TH1) Example (SVS 750W BASH Amp, still working)
(A photo below shows where the broken piece of TH1 landed.)

A wider view of TH1 area of the 750W BASH Amp

The missing piece of the thermistor from the BASH Amp above was found on top of the (downfiring) driver's magnet/motor - luckily it did not fall through the pole vent, which did not have a screen. That's something I wanted to add considering the cylinder's design: a down facing driver, vertical port tubes and open pole vent.

Photo shows a piece of the Thermistor on top of driver magnet
(Left Port Tube has gray foam tape, but no BASH amp contact noticed.)

Tip for a 'Stuck' Subwoofer Plate Amplifier:
I've had several cases where after removing the mounting screws, the plate Amp still would not budge. (2 older SVS 13-Ultra's and 2 SVS PB12/Ultra 2.) I've never tried a large suction cup but doubt it would work well on the surfaces I've seen with several 'stuck' subwoofer plate Amps for repairs/replacements. (These were older SVS bash Amps without a lot of flat open areas and a brushed surface.)
  What I found that worked on those Amps was using a slightly larger screw in one of the Amp's mounting holes and using a screwdriver, tighten it just enough to have a good 'bite' into the through hole. (See photo below.) I then use pliers on the screw head to pull it out/break the 'seal' on the Amp. All these subs were over 5 years old - one more than 10 years old and the original gasket/seal was so tight it almost felt bonded on. (An alternate method: If you have a small flat head nail (smaller head diameter than the Amplifier screw hole) - inserting the nail head into the hole and using the flat head shoulder as a lever may work, but I've personally not tried that.)
  YMMV but carefully done, I've seen no damage and the original mounting screw head is large enough to cover any minor scrapes. Here's a pix using this method on a PC13 Ultra BASH Amp:

750W BASH Amp on PC13 Ultra
(Using larger screw to remove a 'stuck' plate Amp.)

Of course the screw doesn't have to be as long as this one. It was just one I had on hand.
TIP: A little silicone lube on the gasket area may make future removals easier.
(To the right in picture is an upside-down PB12/Ultra 2 after a driver reinstall.)

  After seeing several SVS 750W BASH Amp failures like the above over the years, I'd want to inspect the Amp before buying any older used PC/PB13 Ultra. IMO, a used Sledge Amp Ultra is a better choice even if it costs a bit more. If it originally shipped with the Sledge Amp, I'd also be more confident that the driver hasn't been abused as the Sledge Amp has much better driver protection (limiter/compressor) than the BASH Amp. I liked that the old Amp's knobs and switches made it easy to see all settings at a glance (vs the small LCD screen with scrolling menu on the later Amps), but I'd pick an Ultra with Sledge Amp over the BASH every time.

  The later "13-Ultra" series 1KW (RMS) "Sledge" 1000D DSP Amp is a much better design than the BASH, and likely more reliable (lower parts count, DSP vs Analog design). But with the Sledge's different gain structure and lower input sensitivity, its Amp "Volume" (Gain) setting will be much closer to max than the BASH Amp for the same output levels. (Gain adjustment on 1000D Sledge Amps is labeled "Volume".) And although many probably never use all its features, a combination of Room size Compensation (adjustable frequency and slope), variable port tunes (16Hz, 20Hz or Sealed) and Parametric Equalizer (adjustable frequency, cut/boost, and Q) allow a VERY wide range of signal shaping. See SVS's Guide to Sledge DSP Amplifiers. SVS Sledge Amp PDF user manuals are available for download at their website.

Ported vs Sealed Subwoofers
I've seen posts from (sealed) SB13 owners saying they switched because the Ported 13-Ultra (or later PB-4000 model) was less "musical". To quote SVS' Ed Mullen, the PB13 in Sealed Mode is a 'textbook sealed sub' (plus benefit of larger enclosure), but I can't recall seeing any notes from those that said they switched to a sealed only model mention trying the PB/PC Ultra's sealed mode and/or any of the Amp's PEQ (and other) options. Using the room size compensation, you can set the same rolloff as a sealed sub and still retain the deep bass lower distortion and higher headroom of a ported sub. Remember a sealed woofer must quadruple its excursion to maintain the same SPL when frequency is halved. Read down the page of Audioholic's SVS PB-4000 review tests for more details, and also their Subwoofer Myths item 1 & item 8 on Sealed vs Ported. Here's a quote from item 8:

"If a ported subwoofer sounds boomy it's either a poor design with a non-flat response or is poorly set up (which is not something inherent in ported designs). Well designed ported subs are just as tight and articulate as sealed subs. In many cases, the increased tightness some perceive from sealed subs is simply the fact that there is less bass coming from the bottom octaves in a sealed design".

  Of course the room, Subwoofer location and listening position are major factors in how any subwoofer sounds/performs. And don't assume the best location will be the same for every model. (Ideally test data from Room EQ Wizard (REW) (or similar utility) is key to finding the best location for your specific room and setup. Most won't do that but at least experiment with placement. My PC13 is in a front corner.)

My Comments as a SVS PC13 Owner
  For a single sub, unless smaller size is a must, I prefer a (quality) ported model that offers adjustable modes. Both PB13 & PC13 have Sealed/16Hz/20Hz modes, PEQ, room size compensation, etc. The PB13 has a bit more SPL at the lowest frequencies than the PC13 due to cabinet volume, but that's not a factor for me. (My small room has significant room gain in deep bass.) I chose the PC13 over the Box model since it has a small footprint (appx 16.6" diameter, 47" tall), and is light enough (appx 92 lbs) to be moved without help (unlike the PB13's 155 lbs). And being down firing, I position it with the Amp facing out for easy access. Positioning and phase alignment with other speakers are major factors in Subwoofer in-room performance. (And don't forget the old saying "It's always the Room". After fixing a major null due to phase cancellation, the performance improvement was dramatic.) I've not had to use it, but SVS support can assist customers with Subwoofer setup, optimizing, integration with your speakers, and troubleshooting.

There are larger more powerful subs available, but I'm very happy with the PC13 Ultra. (At the used price I paid, it was a steal.) Currently in a very small room (10x12x8) which is ideal for a sealed sub, but I want the ported option in case it's ever used in a larger room. In this small room I'm using the 16Hz mode (now called "Extended" mode) with room gain compensation, which can tame high room gain in deep bass, while still having the headroom of ported mode. I've used SVS Ed M.'s 2 PEQ tweaks for a bit more mid-bass punch (plus a mid-bass EQ boost in my Onkyo RZ830 AVR), and later fixed a big mid-bass null by adjusting the Subwoofer distance in the AVR. (While playing a mid-bass audio loop, I increased the Subwoofer distance to time align the Speakers & Subwoofer, using a SPL meter to check maximum output in that range.) Fixing that null made a HUGE improvement. (There are better methods for aligning speakers & subwoofer phase at the crossover point like REW, but I didn't have access to them.)

In this small room with suspended floor, the PC13 easily delivers room shaking bass.
(My wife complains it feels like an earthquake 2 rooms away during deep bass movies.)
Info on my speakers are in the Introduction at Onkyo RZ receivers Tips & Tricks page.

SVS 13-Ultra Subwoofers are well engineered products (see Josh Ricci's PB13 review Design Overview), with a very beefy 13.5" driver (appx 55 lbs, and a cone that's stitched to the surround), full featured amplifiers with excellent driver protection, from a company with a history of good Customer Support and warranty - even if you're not the original owner. (They replaced a failed 750W BASH Amp from a second owner PB13 Ultra that only had a few months of the original warranty left with a new ($599 list at that time) 1KW Sledge 1000D Amp. The only cost was shipping the failed Amp back.) They now have a 5 year warranty, free shipping in CONUS, a 45 day in-home trial (with free return shipping), and more - see their customer bill-of-rights for details.

SVS 4000 Series: The SVS PB-4000, PC-4000, and SB-4000 replaces the PB/PC/SB 13 Ultra models. The PC13 Ultra was replaced by the PC-4000 model with improved Sledge 1200D Amp, a Remote Control + (free) Bluetooth iOS/Android App for adjustments (3 PEQs, Phase, Polarity, Room Gain Compensation, and more) that supports saving your customized settings as Presets (Movie, Music, etc.) that you can change on the fly, and retains the variable tuning. Their Isolation feet replaces the PC13's baseplate (that I liked), but I'm glad they kept a Cylinder model in the lineup. Just before the Oct. 4, 2021 price increase, I was able to play with a PC-4000 ($1799 before Oct. 4th increase). A very polished product - great design/engineering, with improvements over my PC13 Ultra. The remote and iOS SVS app were very nice to have, more so than I initially thought as I rarely changed settings on my PC13. As a cylinder subwoofer fan, this would be my first choice. A beautiful (IMHO) design that delivers 95% of the much larger/heavier box model performance in a form factor that fits in my limited space and more easily moved than a PB-4000. (The PC-4000 is 92.4 lbs, the PB-4000 is 153 lbs.)

SVS has probably the best reputation for customer support of any Speaker/Subwoofer company I know. (I wish Apple had anywhere near that level of warranty and support.) There are other great Internet Direct subwoofer options like the JTR Captivator models, Rythmik, and Power Sound Audio; although they don't offer all the perks of SVS. (Power Sound Audio's policy is close - great customer service from 'Tom V.', one of the original SVS founders.) Good options if you don't DIY.
(Monoprice's 13" THX Ultra & 16" THX Ultra have amazing performance per $, but seen a lot of forum posts on amplifier problems, and some saying entire sub swaps offered rather than just a replacement amp. I hope they eventually have replacement sub amps in stock for affected owners. I think the Monoprice 16" would be called an 18" by some other companies.)

BTW: As of fall 2021, many Subwoofer companies have raised prices, in some cases significantly. Component costs have increased, as well as huge increases in shipping container costs. (IIRC some said a 10X increase from 2019 to 2021.) From what I've seen in Oct. 2021, SVS prices went up $100 to $400. (SVS prices include shipping, and even return shipping during the 45 day trial period.) Power Sound Audio & JTR prices also increased. (As of April 2022, the Captivator 4000ULF was $4,999 + shipping. IIRC in 2020 it was $3799 + shipping. If I had a large theater room and could afford it, I'd have dual Captivator 4000s & JTR front 3 speakers.)