JAN-GE 5751 in MarkV Head

[bandit2013]

Definately need high gain in V2 and V3. The EH would be better served in v6. I found you can regain some bottom end with TS in the V7.

Here is what worked great for me: used this with the 7581, and when they went flat, installed Mesa STR420 and STR440's
V1 5751
V2 Ruby HG
V3 JJ HG
V4 TS
V5 TS
V6 EH
V7 TS

With the GrooveTubes GT6L6-R2 (#4) (SEDwngC) it sounded great, but then rolled again, returned all tubes with mesa to restore the benchmark tone. Rolled the tubes starting with V1. Before returning the chassis back to its shell, I left it out inverted on the 412 cab for a few days. If I liked the sound the next day the amp would be reassembled.


V1 5751
V2 RubyHG
V3 JJ HG
V4 EH
V5 EH
V6 EH
V7 SovT LPS

I did try other tubes in v4-v7. Mesa, Penta, and TS. My focus was to obtain tone that would complement my favorite guitars which are made out of walnut. Deep growling low end with bright top end, even the mid frequencies are rich. One nice thing I noticed, no hum, buzz, in any channels.


Get used to the 5751, experiment with all the channels for a few days, then change the tube back to a 12ax7. I had to go back and forth between 5751 and EH for V1. That took about a week to decide.

 

[mesa metal]

thanks bandit..ill try out the EH in v6 along with the tung sol in v7
im using the str440 at the moment,,,my guitar is all mahagony so i get good rich tone from it as well
i also didnt have buzz or hum in channel 1 it sounds really good...
ill definately keep the 5751 in there for awhile...one thing i did notice is the effects loop sounded crappy
so im not using it,,,,,im thinking now to get a delay pedal(strymon)for the front of the amp...
ill keep you posted..
http://www.grailtone.com/forum/viewtopic.php?f=33&t=63929
have you seen this post...i started to get this very same sound...mostly on ch3...

 

[bandit2013]

I have not experienced crappy loop yet. Lately I have been using the loop so I can play at volumes low enough not to disturb the neighbors when it gets late. I sort of wonder where the loop begins. V6 is the return stage, may be on the Reverb Return.

I did try the 5751 in the PI, did not like that at all. The brightness is from the STR440, Compared to SED's the STR440 are very bright, the SED's are too but not as chimey. If I compare tone, the 7581 (before they went flat) are very close to the SED's in full balance, but a bit brittle on the top end like the STR440's. If they still made the STR420's that would probably be my 2nd choice after the SED's. With the original STR440, everything was harsh and sounded terrible. The tube in V8 which is used in all power modes was the culprit, HF oscillation leading to redplate is a guess. So far have not redplated any tubes since I replaced the speakers. I suspect issue may have been a weak solder joint in the cab or dirty contact on the 8 ohm jack. Intermittent open circuit on the load could cause the OT voltage to spike, sure did not want to damage the MKV.

As for the hum, could well be the sour voltage at the wall. I can hear motor noise when the dishwasher is running. It may be on the same circuit. Also where I have my amp, there is a floor mounted outlet. I can pick up interference from that too.

 

[mesa metal]

I have not experienced crappy loop yet. Lately I have been using the loop so I can play at volumes low enough not to disturb the neighbors when it gets late. I sort of wonder where the loop begins. V6 is the return stage, may be on the Reverb Return.

I did try the 5751 in the PI, did not like that at all. The brightness is from the STR440, Compared to SED's the STR440 are very bright, the SED's are too but not as chimey. If I compare tone, the 7581 (before they went flat) are very close to the SED's in full balance, but a bit brittle on the top end like the STR440's. If they still made the STR420's that would probably be my 2nd choice after the SED's. With the original STR440, everything was harsh and sounded terrible. The tube in V8 which is used in all power modes was the culprit, HF oscillation leading to redplate is a guess. So far have not redplated any tubes since I replaced the speakers. I suspect issue may have been a weak solder joint in the cab or dirty contact on the 8 ohm jack. Intermittent open circuit on the load could cause the OT voltage to spike, sure did not want to damage the MKV.

As for the hum, could well be the sour voltage at the wall. I can hear motor noise when the dishwasher is running. It may be on the same circuit. Also where I have my amp, there is a floor mounted outlet. I can pick up interference from that too.

i had a little chuckle just now..yesterday i could hear some kind of interference sound through the cab...
was going to put the 5751 in the PI spot you had mentioned before it didnt sound that good..
last night i was using the loop as well to keep the volume down a bit so maybe at the lower volumes it doesnt sound that good anyway
i probably wont get those rubys,,,i want to get a set of russian power tubes so i may opt for the tung sol 6L6str??
or a set of the sed from tubedepot....ill see if those will cut down on the brightness at all...

 

[bandit2013]

I have a set of svetlana's in my mkIV and they sound great. Still does not compare to the Mark V. So far the best sounding power tubes I have used are GT6L6-R2 (relabeled SED's) and the Mesa STR420 (which is out of production). Excluding the bottle shape, the STR420's look similar to the SED's but inverted. They were originals on the Mark IV. (the one's I have used NOS that I had in storage and bought them the same time I got the MKIV). After playing through the V with the Groove tubes I am beginning to love CH2 cruch mode even more. Talk about punch in the face kick (may have something to do with the EV.... I did update the bucket once again)

http://s1272.photobucket.com/user/b...rt=3&o=0&_suid=136662852284908614272734387215

What best describes the sound with the 5751 in the PI, the thread on ring modulator issue, sounds like crap.

If you still have your mesa 12ax7a, tube roll starting with a benchmark. V2 and V3 definately requires a HG tube. Placing a HG in V1 gives you brittle mud. You could try using all tung sols, that will give you flat and lifeless tone and then roll in tubes to change the character. Having a high gain tube in V6 will distort the loop. Since that is the final gain stage for ch3, the amplidue of the signal should be sufficient so a HG tube is not necessary. Yep, in case you ask I tried the 5751 there too, same result as the PI position. V1 was the only place it works the best.

 

[mesa metal]

bandit that is great info for sure....thanks...and actually the JJ i have in V6 is 115/115 and may be to much cause i did notice the loop is a little on the hot side through the gmajor..i just got in the mail today a few unbranded mesa chinese tubes from the 90s nos..i may try one of those in the v6...
i also did experience putting a high gain mullard in V1 and sounded as you described to the tee..not sure i have 7 tungsols to put in the V id like to try that..

im not sure the ring modulation describes what is going on with that guys amp...it sounds like a dual note thing going on....i thought the sound he was getting was like a sorta microphonic tube sound untill i listened to his clip...very wierd for sure...

i still have all the mesas that came with the amp so ill try your suggestion on the rolling......first im going to change out the v6 for something with less gain
i even have some pentas that are in the 105/105 range..

i was looking at the black label speakers you have in the 4x12....i would like to stick a pair of those in the 2x12 cab......are they expensive....
also do you think the 7581s were a fluke that you got a bad set.....im thinking of trying those out...ill get them from tubedepot...
i need a little more bottom end to my amp..without using the eq to compensate......did the svetlanas give a good bottom end?
whewww im talking tooo much :roll:

 

[bandit2013]

The svetlana are not as full bodied as the SED's. They were a compromise, acutally thought they were true Svetlana but made by New Sensor so not the same company... I have them as stated in the mark IV. For driving a C90 (picures show a EV installed but look close enough, the power tube is against the magnet so I returned the C90 and used the EV in the cab rebuild.) I was able to get two lightly used EV's on ebay which are mounted in the upper holes (the pair was a bargan for $300), the bottom are new which have EV stamped on the cone. The new EVM12LBL cost $279 each ($10 more than the classics). Total rebuild of the cab cost $858. That was better than $1,116.00. I already had one of the EVM12L sitting in a box. I had considered other brands such as Emminance, JBL, and a few other brands that do not come to mind (weber, and some others ?)

As for the 7581, I believe the grid resistor used to bias the amp may not be the correct value. As for the plate voltage, still unknown since I have no means to measure anything yet. Short life span is typically linked to the grid resistor bias. But the short life may be related to process of the barium oxides on the cathode (assuming they still use barium, could be some other reactive metal oxide). I think a set of 5881 would have been a better choice. I have had great sucess with those in the past in the Mark III. There is always the TAD winged C. Some like them, some do not.

As for the preamp tubes, the gain is nothing more than a measure of potential for amplification. At what plate current will this occur? The measurement is based on a single frequency at a specified amplitude at a standard bias setting. Now comes the important part, construction of the tube itself. Shape of the internals, grid structure, smoothness of the plates, type of cathode, bla bla bla. I have found a few web sites that rate tubes based on frequency, the Tung Sols were well balanced, JJ and mullards were similar but tone is quite different. Do not get 7 tung Sol, you will not be happy. Unfortunately I did, very dull sound, did I say rather lifeless, if there ever was such a thing of an amp having soul, 7 tung sol's is as dull as sitting in a PTA meeting with 7 old ladies all taking in monotone voices with no soul.

I found using the Mesa tubes which were selected for certian operating characteristics to be the bench mark since this is the tube the preamp circuits are built around. Preamp tubes with different construction and materials will have different characteristics even if they are identical to the mesa 12ax7A. Opps getting late need to go to work.

 

[bandit2013]

Here is a link on preamp tubes that may or may not be useful.

http://www.amplifiedparts.com/tech_corner/12ax7_comparison_of_current_made_tubes

Most of the data sheets, information, etc for audio amplification is geared for clean distortion free operation.
How well the tube sounds when it is driven into clip (full saturation, and turn off) is one of the goals for a guitar amp. Also the frequency response is important for tone character. What makes it sound good is the upper harmonics of the signal are lost due to the transfer characteristic and frequency response of the tube. When it comes to distortion, solid state amplifiers do not roll off the upper harmonics which results in square wave generation. There is a term for the amplified sound will all harmonics present, called "shot noise". For an example, take a large metal bowl and from a distance drop several hundred small sized BB's or "shot" into the bowl. In other words, if you change the "o" to an "i" in the word shot you will get a better idea of the sound without doing the experiment.

Tung Sol's are flat (meaning no exagerated frequency band is created). They are best served as driver tubes since it will not accentuate highs over the mids or low freq. Some may say they are dark, consider that the lower frequency from the guitar signal is higher in voltage compared to the higher frequencies you will get more base. Tubes are essentially voltage controlled current sources. More voltage applied to the grid, more change in current will occur in the plate.

I found this interesting, a step back to the good ol days when I studied amplifiers in detail.

http://sound.westhost.com/amp-basics1.htm

As for the 5751, when placed in the PI (V7 for the MKV) the response was identical to the ring modulator issue on another thread. It had similar effect when placed in V3 (did not bother to try it in V2). I found this tube useful if the overall tone of the power tubes was brittle or super bright. I do not seem to have that issue with the SED's, I can tolerate the high frequencies even with a standard 12ax7 in V1. If you seek full distortion with no clarity on what note you are playing, do not bother with a 5751. I do not run my amp clean in CH2 or CH3. When driven hard, it is amazing what a chord sounds like with definition than mud. I have not noticed a performance issue with the 5751 (the one I have anyway). Unfortunately, the new builds of the 5751 are not so good. If you can find NOS JAN's it may be worth your while (assuming your amp runs hotter in the high frequencies and there is no other way to tune it out).

 

[mesa metal]

so far bandit i like the 5751 in the amp..the clarity is amazing on channel 3..i still have the heavy tone i like..i actually turned back on the gain control to about 1 oclock....had it at about 3 30 before..sounds great....ill try a tung sol in V7 to see what that sounds like.....as for the power tubes i may try a set of the tung sol 6L6 or just spend the money and get the sed winged c..some great info .... thanks bandit ...
not sure how you feel about the mullard 12ax7 but thay didnt sound too bad when i had them in V4 and 5.
when i took out the stock mesa (JJs)i made sure i marked wich spot they were in......the factory had markings on the V1 tube...
im thinking on getting a couple more of the 5751 to have on hand.....tubedepot has the jan phillips....would like to get a jan ge...
thanks for those links some really good info,,,,,,,love the technical stuff..

 

[bandit2013]

It may be difficult to get the Philips version. Not sure when they went out of production.

I have never tried a mullard. There is also bugle boy, and some other NOS brands too. I was willing to give something a try to roll off some of the high frequencies. The lower gain JAN-5751 was an option that did not cost too much for an NOS tube. The stock 6L6GC STR 440's and the 7581 had similar tone characteristics. More than just bell tone, more like "shut that damn kid up" issue. There is not much of a drop in gain, nominal is 75 compared to 100. I believe that the HF pain I was suffering was caused by the Power tubes. Not quite shot noise in distortion, I had the same feeling about channel 1 as well. The EVM's did not change the overall character of the tone, the sound very close to the V30 but better (just my opinion, not expecting anyone to take sides). The GT6L6-R2 was the final fix. With an EH12ax7 in V1, things are bright but not " use duct tape if you have too!" (I am still refering to a child's high pitch screech that they tend to do while you are out to dinner tying to enjoy a quiet meal just as emphasis that most can relate). I like the 5751 as a primary stage tube so it will remain in V1.

TAD wing'd C may be an option. They look similar in design to Mesa STR420 without the bulbous bottle. So far I am happy with the GT's.

Now if there was a web site that provided bode plots ( frequency response curves) for each preamp and power tube that would be perfect.

 

[bandit2013]

I was at it again, rolling tubes. I do like the tone of the 5751 but wanted to see what else would make a difference.
There is some character change but suttle when opting for V4 and V5. I have tried many different tubes there. For my application either EH or Mesa works best. Same applies for V6. The Sovtek LPS was a keeper for V7. Since I had Doug's tone kit for a 7 preamp setup, I had to find alternates for the Penta Lab tubes, I had one that went microphonic, the other two still okay. Since I had changed the Power tubes I have not revisited the original mix for the tone kit, in other words, pop in a tung sol in V1. I am beginning to see why many use it in V1. Very nice response in all channels and it does not spoil the party. Not as bright as the 5751 either. Considering the cost of the Tung Sol tube vrs the NOS JAN-GE or JAN-Phillips I would recommend the Tung Sol. When I had the 7581 on board, the amp was too bright, even with Doug's tube kit. I bought the Jan 5751 in hopes to tone things down and it worked. I was actually able to adjust the gain, treble, and presence and not hate the result. GT6L6GC-R2, aka SED winged =C= made a huge difference, and they are finally waking up and I want to take advantage while they are still good. I have also notice that the 5751 has become brighter over time, also the pins have gone to a silver color to black ( must be silver plated). I guess that could be an issue with NOS tubes (depending on vintage).

 

[mesa metal]

I was at it again, rolling tubes. I do like the tone of the 5751 but wanted to see what else would make a difference.
There is some character change but suttle when opting for V4 and V5. I have tried many different tubes there. For my application either EH or Mesa works best. Same applies for V6. The Sovtek LPS was a keeper for V7. Since I had Doug's tone kit for a 7 preamp setup, I had to find alternates for the Penta Lab tubes, I had one that went microphonic, the other two still okay. Since I had changed the Power tubes I have not revisited the original mix for the tone kit, in other words, pop in a tung sol in V1. I am beginning to see why many use it in V1. Very nice response in all channels and it does not spoil the party. Not as bright as the 5751 either. Considering the cost of the Tung Sol tube vrs the NOS JAN-GE or JAN-Phillips I would recommend the Tung Sol. When I had the 7581 on board, the amp was too bright, even with Doug's tube kit. I bought the Jan 5751 in hopes to tone things down and it worked. I was actually able to adjust the gain, treble, and presence and not hate the result. GT6L6GC-R2, aka SED winged =C= made a huge difference, and they are finally waking up and I want to take advantage while they are still good. I have also notice that the 5751 has become brighter over time, also the pins have gone to a silver color to black ( must be silver plated). I guess that could be an issue with NOS tubes (depending on vintage).

i knew you would like the tunsol in V1 8) i have tung sols in V4 and 5 at the moment but going to try a chinese mesa or the eh....i just scored some nos mesa tubes and two of them are unbranded in mesa boxes and one 12AT7,,,and one 12ax7(not mesa) made in west germany but i have know idea what make it is because the name is worn off...i did like the tung sol inV1 but im still liking the tone of the 5751....by the way when i got it from tube depot the pins were black so i very lightly went over them with 2000gt sandpaper.....i also need to try a different tube in V6 i have a jj high gain and i think its overdriving the effects loop..tube rolling is time consuming but a lot of fun...try out a mullard some time but dont get one with too high gain...it is basically a sovtek lps but they sound very different......a bit smoother overall
so far for all the tubes i changed the LPS still stays in V7...

 

[bandit2013]

I had considered the other flavors of the lower gain preamp tubes, but settled on the 5751. I had TS in V1 when I retubed the V the first time. I did not like the tone with 7581 power tubes on board, it was brighter than I expected, for some reason I was focused on preamp tubes than power tubes. 12AT7 would have been my next option if the 5751 did not fix the hyper brightness of the amp (which was related to the power tubes). The final tone fix did not trim the high frequency response (different speakers).

With different power tubes on board, I have discovered a love/hate relationship with the 5751. Sounds great in CH1 and Ch3, but a bit weak on CH2. On the other hand, I have experimented with EH, Penta, Mesa, JJ, even tried the LPS in V1. I did settle on EH for v4-v6. EH in V1 put some punch on V2, but it was similar to the 5751 in the high frequency response. After discovering what happens with you use TS in all positions, give the TS another chance in V1 only. What would be an awsome option, have a global switch that would alter gain settings for V1A and V1B for that fine detail response of a lower gain tube, and a switch to return to a more high gain setting for adding a bit of mud to the overall sound. Either that, or make use of the unused triode V2B for an additional gain stage for channel 2.

As for the sulfidated silver pins, I had a bad idea, dip the tube into mercury and amalgamate the silver. I do not want to add heat to the pins as that may cause a breach in the vacuum envelope (I had considered using lead free solder to tin the leads). The silver oxides will add resistance but not high enough to pose any issues for the applicaiton (it may alter frequency response, the pins on the tube I got were clean and shiney out of the box, apply heat and other outgassing contaminants such as ink on the glass, VOC's released from the vinyl covering and wire insulation etc., the silver will turn black. I will have to experiment with some of my wife's silver cleaners with an old mesa tube. I do not think she will mind that I use it. I have not yet completed all of the tasks that she wanted me to do. I have decied to hand down all of her jewelry to her younger brother's daughters. It all depends on what happes with the estate. Sorry for the tangent there, she has been on my mind more than before since her birthday is just a few days away.

 

[bandit2013]

Update on silver cleaner, not effective. I could try tarn-x with aluminum catalyst. sand paper is an option but I do not want to remove any of the plating on the pins.

I have a fix for my preamp tube issue, Since I like both the 5751 and tung sol (or eh) in V1, I could always get another half stack and mark V head. I have been looking into other options, Road king, MKV combo, etc.... When is the Mark VI due to come out? Two amps are plenty for now (IV and V). There are other things I need to focus on first, but the option will be lingering in my mind for a while.

 

[mesa metal]

you could also try barkeepers friend and make a paste,,wipe a small amount on the pins and let it set for a minute or two and buff off,,,just another suggestion so as to not damage or take of too much surface from the pins,,,,the tarn-x may put a coating of some kind on the pins??
as for the 5751,,i need to try different power tubes to get the tone im really looking for...still a slight tad on the bright side...
here is what i have in there now v1-jan phillips 5751,,,,v2-JJ high gain117/118,,,v3-JJ115/116,,,v4and 5 tung sol,,,v6--JJ,,,v7-sovtek LPS
would be nice to have two amps with different tubes to play around with for sure

 

[mesa metal]

for the last 2 hrs or so i been doing research on the west german 12ax7 i got last week,,
so i been looking at a lot of NOS tubes and came across this website,,,has a lot of info and cool tubes,,,check out their ebay section and tube info section
http://www.highendtubes.com/
very cool website........i also stumbled on this site for more tube info
http://www.guitaramplifierblueprinting.com/12ax7.html
i think the tube i have may be a tungsram or rft..........ill get a picture and post in the tubes section
also some chinese tubes are peeking my intrest too
the quest continues!!

 

[bandit2013]

Having two identical amps would help.
I experimented with the 5751, tung sol, EH, mesa, etc with the Mark IV.
Setup: v2-v5 was mesa 12AX7A ( original tubes from mark V). Final stage: Svetlana 6L6GC
Rolling V1 results:
5751: very nice chime and overall channel 1 clean. Very smooth and glassy. Channel 2: well I never liked channel 2 of the mkIV since it always sounds like something is missing. Lead Channel: Bright, with typical gain (7) and drive (5), not much to say in terms of "wow never new the amp could sound like this" to mention. If you like the clean channel and do not use high gain for the other channels, this preamp tube fits the blues and jazz arena well, but is lacking for classic to modern rock.

Tung Sol: Same effect on channel 1 as the 5751 but with deeper bottom end. Channel 1 sounded awsome! Channel 2 was more difficult to control since there was more bass to filter out. Since CH1 and CH2 share the same parametric eq (mid + bass) it was not possible to get a good tone in CH1 and have the same effect in CH2. Lead channel, approaching the Mark V quality of sound. A bit dark at higher output settings. When I started the tube roll, I first experimented with Tung Sol. First setup was V1-V5 TS. Channel 1 was perfect in all respects. Nice deep tones with bell tone shimmer (it was pleasing not brittle). Ch2 and Lead was too muddy to enjoy through the single C90 speaker. Quite the opposite effect on this amp compared to the MKV (using all TS created a dull tone). I should have tried the full TS option through the 412 cab but I did not at this time. It only takes a few minutes to swap tubes in the MKIV.

EH12ax7, Mesa 12ax7A : both sounded the same in the MKIV. Originally I had all EH preamp tubes on board. However, I transferred three of them to the MKV. Perhaps others have had good results tube rolling the MkIV. Best performance with all the same tubes either Mesa 12ax7a or EH12ax7.

 

[bandit2013]

for the last 2 hrs or so i been doing research on the west german 12ax7 i got last week,,
so i been looking at a lot of NOS tubes and came across this website,,,has a lot of info and cool tubes,,,check out their ebay section and tube info section
http://www.highendtubes.com/
very cool website........i also stumbled on this site for more tube info
http://www.guitaramplifierblueprinting.com/12ax7.html
i think the tube i have may be a tungsram or rft..........ill get a picture and post in the tubes section
also some chinese tubes are peeking my intrest too
the quest continues!!

Great links! I got lost in the last one. Great resource there.

As for barkeepers friend, not sure I want to use acid on anything electrical. It is difficult to remove the salts left behind. It works great on stainless steel though. I use that stuff to clean cookwear (only stuff that seems to work well on ALLCLAD. Acidic salts (residue left behind from acidic cleaners) and silver do not mix in the electronics world. There is a big issue with silver and dendrite formation. With silver and DC currents combined with acidic compounds you can wind up with silver hairs or wiskers that will eventually short out opposite oplarity. However, with a tube amp and 250V potential, the wisker would not last very long. Fine sand paper worked the best for cleaning the pins.

 

[mesa metal]

yes youre right about the acidic salts ..i didnt think of that.. ....works well on my copper pans though :wink: fine sandpaper is the way to go...
those are great links for sure...i may contact the guy who runs the guitarampblueprinting and see if he heard anything about the sed 6L6s
his blog site has a lot of info as well...i was reading about the genelex gold lion tube and doesnt seem to be that great a tube for the money...
any opinions on the JJ power tubes...i have an octet in the 2:90 and that sounds great..but being the MKV is so much different i wonder how they would sound in there...
if you havent seen this link yet this is a good one as well
http://www.tubefreak.com/tubefreak.html

 

[bandit2013]

yes youre right about the acidic salts ..i didnt think of that.. ....works well on my copper pans though :wink: fine sandpaper is the way to go...
those are great links for sure...i may contact the guy who runs the guitarampblueprinting and see if he heard anything about the sed 6L6s
his blog site has a lot of info as well...i was reading about the genelex gold lion tube and doesnt seem to be that great a tube for the money...
any opinions on the JJ power tubes...i have an octet in the 2:90 and that sounds great..but being the MKV is so much different i wonder how they would sound in there...
if you havent seen this link yet this is a good one as well
http://www.tubefreak.com/tubefreak.html

If you have good sucess with the tubes with another Mesa amp, no reason not to use them in another, especially if the amp uses the simulclass power circuit with fixed bias. From what I have read so far, many who like the SEDs rate the JJ's as their next favorite.

I experimented with several household chemicals to see what would work to clean the pins. Since the tubes were spent, I did not care if they got damaged. Bathroom type cleaners with acidic compounts: 2 hours soak, no change. Barkeepers Friend (works great on food particles, cleans stainless perfectly) 2 hours soak, no change. White wine vinegar: 2 hours soak, no change. Silver jewlry cleaner: 2 hours soak, no change. Gold and diamond cleaner: just as useless as the silver cleaner.
I did some searching for methods to clean tube pins, one suggested " magic eraser". That did not work either (had tube pins pushed into the spong after it was activated with water. The color change to the pins is probably an itermetallic migration than caused by thermal energy. Abrasive would clean the pin but weak chemicals will not. If the chemicals were strong enough the pin would probably disolve especially if the base metal is more reactive than the plating.

An odd observance: I expected the tubes to sink, assuming that the mass of the materials would be heavier than water. The tubes floated. That would indicate some inert gas may be present in the tube (probaly nitrogen). There is the effect of outgassing cause by heating the metals (trapped gasses will be released from heat). Since the tube did not sink, it is not a true vacuum. If the tubes had leaked, the flash would not be silver in color.