Marshall MXL V77 tube mic tube change...need help

Greetings,
I'm trying to replace the stock 12AX7 tube in my mxl v77 mic with a 12AT7 tube, but it looks like the tube is soldered in place. What is the best/safest soldering method to remove the stock 12AX7 tube? Thanks in advance .

-dejacky

are you sure that's not a socket? looks like a socket to me

Yes, it looks like a socket with the ends soldered..but i cannot pull the tube out!..so it seems that the solder must have melted to some of the ends of the pins? or if i'm completely wrong, can someone please tell me how to pull this out? ..having the tube glass break is not something i welcome :?

Eureeka, i got it out...it was in there SOOO tight :shock: . If any1 does this, I recommend getting small needle nose pliers and opening them inbetween the tube pins and the white socket body to efficiently pull the tube away from the socket...the provides provide efficient leverage.

I just noticed as I removed the old tube, I accidently separated one of the socket pins from this yellow wire. There is part of the old wire soldered to the pin along with a small glump of solder. Should I try to "desolder" this before re-attaching the wire, or would it be okay if I just re-soldered the wire back to the end of the pin (that has a small old wire piece & solder glump as part of the socket pin)? Lastly, is there a specific guage of solder I should use? your help is much appreciated!

i am curious why the tube change? i have one of those laying around. let me know if the change is for the better, i'd like to try it also. decent mics already though.

I just wanted to try it because it felt like the mic was sizzling when the spl's weren't pushed that much..so I wanted to try a lower gain tube. I'll be happy to let you all know how it turns out AFTER someone helps me out with the tube change...so I can actually change it properly

[quote author="dejacky"]

I just noticed as I removed the old tube, I accidently separated one of the socket pins from this yellow wire. There is part of the old wire soldered to the pin along with a small glump of solder. Should I try to "desolder" this before re-attaching the wire, or would it be okay if I just re-soldered the wire back to the end of the pin (that has a small old wire piece & solder glump as part of the socket pin)? Lastly, is there a specific guage of solder I should use? your help is much appreciated![/quote]

You could do it either way, as all you need is to establish good connection. If I was doing it though, I'd desolder it first--it just looks more professional.
Also, it is hard to see from the pic what is this "yellow wire", but if it is from capsule to grid, I'd make it as short as it is possible.

It's from the base of the mic, not the capsule. I have desolder wire, but I've never "desoldered" before...only soldered . Can anyone recommend a good online desoldering tutorial? Is there a certain type/guage of solder I should be using? I think I'll just solder it back on :grin: since the glump is tiny. Which solder should I use? Is there a particular brand/type/guage you'd recommend?


This is the solder I possess currently.

just go for it man, it's really not difficult at all even if you've never soldered before. that solder you have will work just fine - any solder will work just fine. silver solder is usually only used in plumbing because it's more expensive than regular lead solder, but i'm sure it'll work for this one thing.

i'd like to hear how it sounds! i've got a v77 on the way myself.

EDIT: Are you sure that the original tube is a 12AX7? I found a copy of the V77s datasheet from some time ago, and it says:
"The V77S features a 3-micron diaphragm, transformer balanced output, and a 6072 vacuum tube, which is known for its low inherent noise and broad dynamic range. "
The 6072 has even less gain than a 12AT7, so you might be taking a backwards step!
Maybe they changed which tube they used somewhere along the line? Seems strange to go from a very low-gain to very high-gain tube.

I'd use the smaller solder, simply because it takes less heat... and for desoldering, get a solder sucker... they are invaluable and radio shack has a little one that works fine.

[quote author="dejacky"] Is there a particular brand/type/guage you'd recommend?



[/quote]
Solders (Sn-Pb alloys) can have regulated melting point by some
other metall, which is compuunded.
Bismuth (Bi) usually shifts melting point low,
Silver (Ag) usually shifts melting point up.

For power tube socket, silver solder can be improvement,
For small tube, it is not significant. You can use normal eutectic
solder (63 percent Sn, Pb).
For semiconductor soldering, Bismuth solder is good.

Note for you: When solder tube socket, do it with some
old tube plugged

xvlk

Thank you for the information Dasbin, this is probably my mistake in thinking the V77 had a 12Ax7 tube...because I was too zealous to mod :razz: . But, the 12AT7 is in and the soldering is done!




Here are some published gain factors:

12AU7 - 19
12AY7 - 45
12AT7 - 60
12AX7 - 100

If the 6072 tube has less gain then the 12At7, how much does it have? Perhpas I should try a 12AY7 tube instead. Either way, now that I've loosened the socket, changing tubes will be easier now .

Looking at the specs sheets, the 6072 and the 12AY7 are very close - Duncan's lists them as equivalent, but they have somewhat different ratings. In any event, there's much more to tubes than just mu. Changing the tube might not be such a good idea...

Peace,
Al.

Thanks for the info Al . This was my first real DIY audio endeavor, so it was a nice opportunity to get my "feet wet" as they say. My next project is the "Scott Dorsey" mod to my Oktava MK012's. If I don't like the AT7 sound, I can always put the 6072 back in. Plus, it's a good opportunity for me to hear how different tubes will affect the sound of the mic. I'll make some audio samples so you all can hear as well...most likely guitar and opera-type vox. cheers and happy holidays!

V77 assembled with 12At7 tube:


HOLY COW! I just recorded small small test vocals and it seems to sound BETTER with the 12AT7. There is noticeably less sizzle on vocals and the overall sound seems cleaner and almost a little "thicker" sounding. :grin: . Going to try some guitar next Once I decided on vocal and guitar parts, I'll do a A/B comparison between the two tubes.

The china 6072 seems to be a china 12at7 maybe lower gain, look at the insides and compaire it to a china 12at7.

Which brand of 12AT7 did you use?


I'd definitely be interested in hearing those A/B recordings.

I used a standard Groove Tubes 12At7. After listening more closely, it feels like the stock tube has more of this "fake richness" quality of sound that gives it more body as a whole. But, even though the sounds seems to sound less 3D with this GT 12At7, there is less "buzz" to the sound and it seems like the mic retains a more steady recording tone. The tube insides of the 6072 and 12At7 look identical when I looked at them briefly. The stock tube just has more silver stuff in the top of the tube than the Groove Tubes (GT) 12At7. hope that helps..

I have a feeling you might be better served to leave the tube as a 6072, but a good brand, either a GT or (even better) some good NOS.

I don't have this mic yet so I'm not sure on the design, but if it's anything like most Chinese tube mics out there, it probably is running the tube on very low current so that their cheap Chinese weird-ratio output transformers can be used - which BTW is probably the main problem sound-wise.

If this is true then these are the things I would look at changing:

- 6072 to a good well-known brand
- Upgrade any cheap caps in the circuit
- Change cathode resister to smaller one, allowing more current
- this might require PSU upgrades
- Find a good output trafo to match

Yeah, that's a lot, and I don't know if I personally would put the effort into it, but I can't wait open up my V77 and see what we can see.

dasbin

You can't just change a cathode resistor without knowing the circuit.  I think the microphone is a transformerless model.  If it is like a v69 there is no transformer.  The tube in the 69 is used as a charge amp with about a gain of -1.  I own two 69s and have modded then.

 Most of the china microphone I have seen use a china made version of a 12at7.

EDIT looks like it is a transformer out circuit (blue dual bobbin)