Groove Tubes 928-PR Substi-Tube

These 928-PR's are amazing at what they do. They can be a bit tricky to install as the guide pin on the adapter is a smaller profile than your 6L6 tubes will have. In this regard, i would like to see some type of orientation marking on the guide pins of these adapters. So, just be very careful and do not rush at inserting these into your amp. I'm allowing a score of 5 here 'cause of the lack of an orientation marking to make the install process more user friendly plus the added bonus of perhaps not installing them incorrectly and messing up your amp!

Okay ... now for the good stuff! These babys are tonal blessing! I prefer class A amps - or at least class A output power. I'm using a '65 Super Reverb reissue. I have wondered how a class A power section would render itself to a classic Fender preamp section. I'm happy to report it's a great marriage of the two. My Super with these little darlings becomes a Voxish hybrid that can make you wonder why you would ever want to spend a couple thousand upon a boutique amp. I have had three Matchless amps - my fave of them was the Chieftain head. I hear remnants of that tone from my Super now with the 928-PR's. I also think that having alnico magnet speakers are a must for the better class A tones you can achieve using these.
I noticed right away and suspected a big change to the midrange of the eq section. It's more musical and way more active than having the 6L6 tubes running.
I have no probs getting a great dynamic tone using either my Strat or PRS McCarty ... so, what i'm saying is single coil pups and
hum-b's work equally well for me. This is however due large in part to the preamp section of the Super Reverb with it's famous ability to render a great tone from either single coil or HB coil pups.
I also have the added bonus of the very pedal friendly environment the Super Reverb has in the preamp.
My 928-PR's came with grade 3 tubes and sound great. The overall volume is lowered and tube distortion occurs a lot sooner and a lot sweeter.
I recently just got a pair of grade 1 tubes and replaced the 3's. Same tonal response was found and tube distortion happened earlier than at using the 3's .... albeit , not that much sooner.
So, if you get a pair that are rated at 2 or 3 .... don't bother getting a pair of 1'zs.

Too early out to report any failures or gripes - so far so good!

No need to contact them at this point - bonus thus far!

I've been playing guitar a very long time now. I won't reveal just how long - just trust me on this ... i'm an old hand at this stuff. As a result , i know gear , taste , and tone. I know what works and what doesn't work (that comes only with experience)at sculpting tone.
I also am like any of you - i have my likes and dislikes. Well , i like the Groove Tubes 928-PR's in my Super Reverb and very gratefull these little blessings exist! Many players will swear that a Super Reverb is the one and only amp they could live with if it came down to only one. Using the 928-PR's in a Super Reverb adds more value to those claims. Again , i must point out that class A power reacts better tonally when using alnico speakers. That's not only my opinion - but my opinion with experience.
The overall tonal possibilities are greater now having a class A power section behind one of the classic Fender preamps of all time.
This coupled with knowing which pedals to use when sculpting a desired tone becomes almost infinite.
The one other variation i can also use to my disposal is speaker mixing being there are four to work with. As a combo , the Super Reverb lends itself to some of the same speaker chemistry that other players perform to their 4x12 cabs .... in this case it's 4x10.
My suggestion to any Super Reverb user is to get a pair of these. I see no need to go beyond a rating of 3 however for the tubes themselves if you truly want these babys to perform as they're advertised to do. I would suspect that getting into the 4 and higher ratings things will become more stiff by the tubes not yielding to break up as readily. I'm sure the same Voxy sweetness will be there but also increased volume levels to get to tube distortion. But, you may like that for your needs.
Bottom line is these are a great product for a Super Reverb with alnico speakers .... go get some. You may think that i'm posting a review of the Super Reverb more than that of the 928-PR's. You would be wrong to assume that. These converters are just that - tube replacements with the added bonus of class A properties. No matter which amp you are using , the amp itself will determine if you are going to like these things or not by how the preamp interacts with the now new class A power output. Don't forget - your speaker(s) play a huge role as well in the overall tone rendering. Here's where experience pays off at using a product like the 928-PR's .... when one knows the benefit of class A EL84 performance being married to a given characteristic preamp / speaker setup.....oh yeah! Thank you Groove Tubes for these little darlings!

pull the old tubes out and plug these in. you're done.

I am very impressed with these tube convertors. I put them in my main amp a Groove Tubes Soul-O-45.

In my opinion class A/B amps only give truely good tone with strat/tele style pickups. Class A amps sound too harsh with strat/tele pickups, but are a must for humbuckers. Like I said that's my OPINION.

I felt a bit stuck with the class A/B Soul-O-45 amps because it works with pedals like nothing else and the preamp really sweetens my tone. I prefer the straight clean tone from my class A Gibson Goldtone GA-30rvs when using humbucker and p-90 guitars, but that amp does not take pedals well at all.

These worked exactly as I had hoped. Giving me the sparkle and clarity that was sometimes missing from my neck pickup. The stock speaker is a celestion clone so the tone has that vox matchless shimmer and clarity that I prefer.

I was worried that my amp would take on that class A buzz as well but it didn't.

These are nicely built. Someone on this page seems to believe you have to throw them out when the tubes go bad. No, no my friend just like the THD yellow jackets the tubes CAN be replaced. The bottom of the convertor is a tube socket.

Groove tubes has always been cool when I've emailed them.

great for power reduction, and getting class A tones from more common amps. Yeah, it's a THD yellow jacket rip off, but I think they did it better. I will probably get another set for my other soul-o-45.

They are tubes. You put them in the right place. My only beef with this was that I really had to struggle to get them all the way in. I put these in a Hot Rod Deluxe, and I am not a weak guy...but I literally had to FORCE these in.

Again, I have a 96 Hot Rod Deluxe...the 6l6 just sound plain horrible in conjunction with the POC speaker that comes with the amp. The evolution of my tone started 10 years ago when I bought the amp...all the way up through the purchase of these tubes. I run American Tele's through a pedalboard that incluces, Dunlop Wah, MXR comp, RAT 2, Fulltone OCD, Boss Chorus, Boss line selector, EH Small Stone, Line 6 DL4, Boss Eq...with an Ernie Ball volume and tuner tacked on the front.
The replacement of the 6l6s with these el84's is SPECTACULAR! Now, while I have to run my amp at about 7-9 it simply sounds amazing...and it brings my tone so much closer to what I am looking for. MUCH smoother...not the harshness of the 6l6s...and on the overdrive channel(which I only use at home)...talk about creamy overdrive. Yes, these do change your sound dramatically...but it is for the better.
Sure, I had to re-eq everything, but that doesn't matter. it was very worth it.

So far so good. no problems...Of course I still carry the 6l6's with me, cuz you just never know.
my only concern was that I had to FORCE them in...
still, I'm pretty confident.

don't know.

I play a mix of alternative/pop/rock...with some classic rock and blues mixed in. I play with a couple different bands in the area.
I've been playing since I was 11...so that's 14 years almost now...and I am very picky about my equipment. I've thought for a long time about getting rid of this amp, but frankly I can't afford to. So, I have had to look for ways to get what I want out of it. These tubes have done just that...they've stayed the exacution for a while.
Lost? I'd buy more. Stolen? I'd buy more.
I picked these over the THD yellow jackets because guitar center doesn't carry them.
That said, i am glad that I got these, cuz the reviews that I've read on the yellowjackets vs these have been more in favor of the groove tubes. That said, the groove tubes cost less...at first. but you have to keep buying the whole package over and over instead of just the tubes(as in the yellow jackets case).

The change to my sound is inspiring to me. that is invaluable.

These are cool aftermarket plugs that you put in your 6L6, EL34 sockets and convert your tube amp into a lower power class A amp. These substi-tubes accept the standard EL84 tubes new or NOS which is cool because they are inexpensive compared to the larger valves. Also, when you plug these in your amp you will not have to rebias it --- Way handy. And if you want to switch back to your original EL34/6L6's just slap em back in----no changes. I am using a pair of these in my Marshall JTM-45 reissue to knock the power down abit more for small gigs. One thing to keep in mind is that these will add some height to your orig tube height if you have a small cabinet. They worked in my reissue JTM-45 head fine.

These will change the tone of your original amp, Not in a bad way so much as, it just reacts in a different way with a vox*ish flare, if I may. I have owned EL84 amps before so I wasnt surprized about the tone change in a big way...I do not notice any added noise using these sockets-----nice,,,. I did contact Groove tubes about using these in my JTM w/ the rectifier tube and they said no problem. I can now push my JTM harder----power tube wise, I could only get my volumes up about 2-3 before using these. I loved the pushed sound of the JTM stock but it was way LOUD...28 watts i think stock. These adapters allow me to push my Marshall harder at stage friendly levels. I love em so far. Plus, the EL8's are cheap, even matched sets.

Ive had these in my amp for about a month of gigging........Knock on wood.........so far, so good. Emailed Groove Tubes about using these in my particular amp and they responded the next day ---plus sent me a great info site to check out tech stuff. Very helpful..

See above. Very good.

These are a great idea if you want to calm your volume down and keep your tube feel. Yes, these will change your tone but its usable for me and if I want my amps original tone just pop my big tubes back in and go. Style of music is mostly blues rock. I got a good deal on a pair of these on ebay. They came w/ the orig groove tube El84's plus a extra matched set of tesla JJ El84's. I would get another set but I hope I never do because that would mean someone ripped off my Marshall head w/ these in it.

I am using it with a Diezel VH4S stereo head. The VH4S using 6L6 or EL34 is too bright and tight for my taste in studio or low band volumes. Using low power EL84s is perfect in my opinion. YellowJackets are OK, but the GrooveTube 928's are darker, rounder, fatter, a little spongier feeling, at about the same volume as YJ's.

There is an interesting comparison at http://www.groovetubes.com/assets/1778_GT928-PR_vs_THDYJSD_Test.pdf

This is a quartet of adapters for running EL84 tubes in a standard tube socket. Similar to a THD YellowJacket, but I A/B'd them and like the 928 better.

First set I ordered had one of the four adapters DOA, Groove Tubes asked me to send back all four, and the new set works fine so far.
Giving it a 7 because of the first DOA.

GrooveTubes sent a replacement in about a week. Could have been faster.

Playing 35 years, all styles, mainly rock, blues, r&b, jazz.
Would definitely buy again if they hold up.

They're easy to use. Just pop 'em into the exisiting tube sockets of your amp in place of your 6L6's or 6V6's. These were a breeze to install in my 70's Fender Deluxe Reverb. Unlike the THD Yellow Jackets, there is no ground wire to connect with the 928-PR's.

A word of caution: I first tried popping these into my 70's Fender MusicMaster Bass Amp, in place of the 6L6's. I turned on the amp. I heard "snap, crackle, pop!" I smelled a burning smell. My little MusicMaster Bass Amp was fried by these things. It's a mystery. They work great in the Deluxe. Come to think of it - it was a stupid move on my part to trust the 928-PR's with my Deluxe Reverb after they fried my other little amp. But I did, and they work fine.

One more word of caution: I emailed Torres Engineering about these things having fried the MusicMaster. I asked them to make an exception to their "no returns" policy, since they ruined a little amp of mine. They ignored my emails. It has been a week - still no response from Torres. "Boooooo" to Torres for chickening out. They could at least done me the courtesy of saying, "no - you're out of luck, we wont accept a return."

I give "ease of use" a 10, because when they work, they're a breeze to install.

These sound great with my 60's Fender Mustang's single coils. The sound is much like Groove Tubes States: chimey and vox-like. However, they wont turn your Fender into a Vox AC15 or a Matchless. However, what you do get is a nice morph between the Fender and Vox sound. I don't feel the attack and pick response are as lightening fast / in your face as with Vox or Matchless, but it makes my little Fender Deluxe Reverb less "squishy" and gives it more "presence" at lower volumes.

With my Les Paul Studio (with humbuckers), I actually prefer the sound of the old 6L6's in comparison with the 928-PR's. The humbuckers in consort with the 928's produce too harsh a "bark" for my tastes. My Les Paul's action needs work, so this will help, but nonetheless, I don't believe these tubes are an improvement with humbuckers. That said, I don't hate the sound either. Just not in love with it. EL84's just seems to match better with single coils.

I'm giving this one a six, because they fried the little MusicMaster Bass.

However, they do seem solidly built. They feel "real" as opposed to "toy."

Groove Tubes returned my emails promptly when I asked them questions.

Torres Engineering however, was great about emailing back when I asked "sales-related questions." They ignored my emails when I asked about a return.

Overall I like these things. Despite my debacle with the MusicMaster Bass, I'm glad I took the chance and popped them into my Deluxe Reverb. I can get a cool tone for recording, at lower volume. Not that these drastically lower the volume. They don't with a little amp like my 22 watt Deluxe. What they do though is to give this amp more "punch" and "bite" at a lower volume. There's more mid-range, less mush.

I found that these adaptors could not handle the current from a 1996 Fender Hotrod Deluxe or a 1982 Mark II Mesa Boogie(both class A/B with 6L6 power tubes) when the volume of these amps were turned above aprox 6.
There is a resistor inside that overheats and turns brown when done so. I suspect that tube life would be fairly short as well.
They are still usable at volumes below this however, and the resistor does not overheat, especially when using them with the covers removed and a fan blowing air on them.

I use these with both humbucker and single coil pickups. When both amps are turned up past 7, the sound is quite good(ie. classic rock grind/blues punch that is very responsive to pick attack). I don't recommend this for the reason given above. With lower amp volume, the adaptors still allow somewhat of a change of tone with a lower ouput wattage level.

The adaptors look well built(except for the problem described above) and I like that the covers come off, so that they can be cooled with a fan. I would be careful about overpowering them in any jam situation and would tend to use them more at home, where I can watch that they don't overheat. For this reason, I don't find them to be gig relible.

Groove Tubes gladly offered to replace the first pair that I bought when I told him about the fried resistors. I have not contacted them about the fried resistors in the second pair as I will use them at lower amp settings and may replace the resitors with ones that have a higher wattage capacity.

I like the idea of tube adaptors(plug and play convenience with most any kind of class A/B amp), but in reality these adaptors may work better with some amps than with others. Maybe they would not overheat with an amp that had power tubes other than the 6L6.

Bought em new at Guitar center. The 928-PR's turn your class A/B amp into class A 20watts if you use a duet. Comes with two EL84-S #7 which are JJ tubes and are great.
I have a Marshall TSL122, good amp but I wanted to get that thick power tube saturation at lower level volumes and get the amp to really open up. I am able to achieve that now. I use the inner two sockets with the EL-84's and leave the other two empty, no adjustment to bias (as they are self biasing) or ohm settings. It runs really quiet too, i was really surprised.
(Note: I also have Groove tubes 12AX7-C's in V1, V2 and stock pre-amp tubes for V3 and V4 phaseinverter. I use the V.P.R on my amp and that cuts the amp even lower in wattage and thats how I am really able to crank it the amp to 10 without my ears bleeding. Plus I am able to crank it to 10, in my house with NO ear fatigue.)
Only problem was it took me 15min to put em in, cause of the clamps to hold the power tubes tightly in place. The converter is a little wider than a regular EL-34, so that was a pain, but they did fit and missed the speaker. Didnt come with a manual...wouldnt need one, unless your not savy with tube amps and how they work.

I use a Gibson Les Paul studio plus with stock pickups. Monster rock performer cables. Boss TU-2. Morley wah. then my Marshall TSL122.
I LOVE my guitar sound now...it sounds wicked. It's more fun to play now then it ever was before. I cant wait till my next gig.(I'de rather push the amp and rely on PA to amplify me than having a huge monster on stage that i cant push past 2.) It's not easy to describe how the amp sounds, cause i'm not good at that anyway, all I know is a am now a big fan of saturated class A amps. Good EL-84's also help the situation, JJ/Telsa are the best out there right now, they sound thick and full and when saturated theres tight bottom and crisp highs. Sounds like a great amp now.
Great thing about it is, it's not a permanent modification. you can take out the converters and put back your el34s for full power again with no adjustments...or have two el84 and two el34's a mix of class A and class A/B, havnt tried it myself though.

It seems reliable...seems better built than THD yellow jackets. THD yellow jackets produce more heat and the 928-PR's transfer excess signal into excess signal like a pushed amp does. The 928-PR's just work better for me overall. Groove tubes as a clean record with me and I dont expect it to faulter anytime soon.

Groove tubes is gold when it comes to service and tech support. I cant even stress enough how great they all are. It's the service and support that really make me buy their products not some fancy logo or saying that our products the best. If i get into a jam I know i'll get help. and thats what us guitarists need more of these days. THD, Groove tubes, there both great companies with good support.
Overall some of the BEST support I have ever experienced and will always refer my friends and people I meet to groove tubes.

I play punk rock/ classic rock. I play Led Zeppelin, AC/DC, The Ataris, All american rejects, Lifehouse, that kind of music. And their also my influences. Been playing for a little over 3 years. Theres not much I hate about the 928-PR's. I wish they wouldve came with a lower rated tube, not a #7 but maybe a #5 or #4...but thats about it.
I compared it to the THD Yellowjackets for atleast a month asking questions and so forth...in the end the 928-PR's were the better buy for me. It's things like this products that help me focus on making great music and getting inspired to write. Just another problem solved of always trying to get a good sound out of my amp, now i just plug and play pretty much.
I highly reccomend the 928-PR's...even if you dont want to lower your amps wattage or whatever...its a great investment, plus el84 tubes are cheap to replace...and with my tight budget, it will just brings a smile to my face when i have to replace the tubes.
Another winner groove tubes!!