| Author | Message | ||
     Trent |
Hi. I just recently bought a 212 Sixty-Five. It's the old kind with the 12ax7 in it. It has mismatched power tubes and when I play through it, it sounds very quiet for an amp this size and breaks up incredibly fast. I figure I'll put new caps and tubes in it, but I've never done work on an amp before, so this is a learning experience. I know the dangers and will act accordingly. Anyway, I've been reading the posts here and on Harmony Central and have learned quite a bit, but I'm not sure exactly what I need to replace in here. Here's a pic of the inside of my amp: 212-65 innards I can see the five big silver electrolytics. Do all of these need to be replaced? Do I need to worry about the smaller black caps I see? On the Harmony-Central review page for the 212-65 the latest review states that he replaced the big purple ones (Mallory) with Sprague Atoms as well as some of the other caps. Should I do this too? I plan on photo-documenting this process and making a tutorial as I go. Maybe this will be of use to someone? Thanks. | ||
| mike kaus |
You need only to replace the silver ones in your amp. Make sure that you replace the small silver round ones as well. THe ones on the bias board(far right upper corner) are very critcal as well. All the silver ones including the ones on the driver board(back center) are to be replaced. The black ones and the yellow ones, leave alone. That amp will have to be biased so pay attention to that as well. I don't really sugest you follow that old "1/2 volt at point Y" crap. That allows for two tubes to be radically out of match and still having a total cathode current of 50mA for two tubes. Get a bias adapter that allows reading the cathode current directly OR put a 1 ohm resistor from pin 8 to the 10 ohm resistor temporarily and read the VOLTAGE in mV. That will equate to a direct reading of cathode current. Mike. | ||
| Mark-NL |
Hey Trent Could you make that photo-thingie you are going to make available here? I think my 212-65 is in need of a recap too. Not planning on doing it myself though (i'm scared as hell of getting shocked), but i'd like to see how it's done! Mark | ||
| Trent |
Thanks Mike. So if I have this correct: Bias board: 2 150MF 500V Driver board: 1 150MF 500V Main board: 2 150MF 500V I see some smaller black w/ silver strip caps on the bias board (2 very small ones and 2 slightly bigger ones) and one on both tube sockets. On the main board I see one smaller silver cap and two very small black ones. I'm not sure of the size and I'm having trouble making out values/locations on the low-res schematics I downloaded. I'll probably post about biasing once I get new tubes. If I understand you, I can get by without an actual bias adapter ($$$) by using a 1 ohm resistor and a multimeter? Mark: Sure thing. I'll post a link here once I'm all done. And I hear you about the shock...better safe than sorry. | ||
| Mark-NL |
Trent, Maybe this can help you: its a fairly high res GIF of the 2275 chassis (which i think your 210 is) http://www.drtube.com/schematics/musicma n/gb2.gif | ||
| Mark-nl |
..212...same thing, only bigger  | ||
| Trent |
Thanks Mark, but mine is actually the 2475-65 chassis with two EL34s and the 12ax7 inverter. | ||
| Mark-NL |
According to the DR. Tube site, the pic above applies to the 2475 chassis aswell. | ||
| Trent |
Hmm, yea I saw that. Weird. It shows 4 6L6 tubes on there...mine has two EL34s and a 12ax7. Mine is also older than 1980. Maybe the rest of the changes are only minimal, though? | ||
| Mark-NL |
Don't ask me.. Can't tell a tube from a cap  (I can offcourse, but i'm not too technical , can't understand that diagram at all.. //offtopic: Where you from TRent? you seem to be online at NON-US times ;) | ||
| mike kaus |
You DO know about the filter caps on the underside underneath the cover don't you? Those are the most important. You didn't mention tem in your list so I assume you didn't see them. The ones on top are in the front end and bias section, the ones underneath the cover are the actuall filter caps. Mike. | ||
| Trent |
Wow, I kept reading about these ones and couldn't find them. Thanks. Here's what I found in there: 2 20MF 450V 1 100 MF 450V 1 50 MF 450V 2 100 MF ??V (black, marked with uF instead of MF) The 100MF one is a Mallory and is wrapped up in heatshrink with the two black 100MF ones (unsure of voltages) and a couple resistors. It appears that the Mallory 100MF is wired in parallel with the two black 100MFs in series. It smells like bandaids in there. My goal out of all of this is to have a nice list of cap values/ratings to order. BTW, are the other caps I mentioned in my last post (the small black ones and single silver one) also to be changed? Thanks. Mark, I'm on the west coast of the US...not too late :p. | ||
| mike kaus |
Your total under the hood should be 2-20's@450 and 2-100's @450. If it's black, it's been replaced. I don't know where that 50@450 came from unless it's been changed too. Send me a pictur if you can, maybe I can help. Mike. | ||
| Trent |
Sorry for the delay. Here's a picture: Filter caps Any ideas? Do you need more info? | ||
| Trent |
Ugh. Here is the real picture: Filter caps | ||
| Trent |
Anybody? | ||
| mike kaus |
Sorry-didn't see a post. This thing has been hogged on. My sugestion is get the schematic and put it back original. That soldered together mess should NOT be there. I assume he was trying to make do with what he had. the big silver one LOOK original but I can't see the values. The only four caps under the "hood" should be two 20mF@450v and two 100mf@450v. | ||
| Trent |
Thanks. The two 20mF@450v are untouched (on the left side of the pic). The fun begins with the two 100mF@450v in series. The large silver one in the back is a 100 and appears to be the top-most of the two 100s in the schematic when looking at the filter board. It has a red/white wire leaving one end and the other is connected to an orange wire leaving the board and also wired in series into the following: A 50mF@450v in parallel with two 100mF@350v in series. This effectively makes the lump a 100mF cap, as the schematic specifies. There is a 2Kohm resistor into one of the 100s in the series and a 2000Mohm resistor into the other 100 in the series. My only guess is this was an attempt to keep the voltage low enough to be within the 350v rating on the non-original caps. If my logic is correct, all I need to do is remove the lump and put a single 100mF@450 into its place with one end connected to the other 100mF@450 (orange wire leaving board) and the other with the green wire (I believe the ground). Sound right? Hopefully this makes sense. | ||
| mike kaus |
Yup-sounds like you've got a handle on it. Just make SURE you have the polarity right since you're replacing a batch. It's easy to get the pathways confused. | ||
| Trent |
Thanks for the help Mike. One last time, here's my shopping list: Bias board: 2 150mF@500 Driver board: 1 150mF@500 Main board: 2 150mF@500 Filter board: 2 20mF@450, 2 100mF@450 In total, I need 5 150mF@500, 2 100mF@450, and 2 20mF@450. Does this sound right? 9 caps in total? Also, any suggestions on brands/online shops to order from? Thanks again. | ||
| mike kaus |
You don't need to get the ones on the driver board that big. I think the size will be prohibitive. Look at them but I think the bias board caps are 150v and some of the others are even 25 and 50v. Check for sue but I'm pretty sue I'm right. No schematice in front of me and the amps are buttoned up but the ones on the main board are probably 25v which you will prob have to sub 50v. | ||
| Trent |
You were right! I had some extra zeros in there. Bias board: 2 150mF@50 Driver board: 1 150mF@50 Main board: 2 150mF@50 Filter board: 2 20mF@450, 2 100mF@450 5 150mF@50, 2 20mF@450, 2 100mF@450 I can't make out the values on the schematic I have...it's really fuzzy. Am I missing any caps? You mentioned small ones in an earlier post. Right now I see 9 caps that need replacing. Also, any suggestions on an online retailer? Brand of cap? Thanks for all the help! | ||
| Terry |
Hi You will allso need to replace the PVC caps on top of the power tubes with new ceramic disc 3000V/.001 Mouser # 539-HT102M or you can update to the 3000V/470PF Mouser # 539-HT471K You have one old and one new one now! All so replace the PVC caps on the drive board with new 600V/.047 Muoser #75-715P600V0.047 On the 450V/100 use Mouser #140-XAL450V100 The TVA are to big for hear. The 50V/150 Mouser # 75-TVA1311----450V/20 Mouser # 75-TVA1712---- now You can go to work and fix that AMP | ||
| Trent |
Awesome. Thanks for the part numbers. I have a couple quick questions. 1) The 20@450 replacements you mention are 75-TVA1712 which are 40@450. Would the 75-TVA1906 (20@500) be more similar to the originals? Maybe there's a reason for the increase to 40? 2) You mention updating to 470pF@3000...will this sound different compared to the .001@3000? What do you mean I have one old one and one new one now? Thanks. | ||
| Terry |
Trent, Sorry about that wrong # I gave you...it should be 75-TVA-1709 for the 450V-20. From looking at the picture of your amp on top of the power tubes, on the one on the left you have a brown PVC capacitor. And on the right, there is a reddish newer looking one. Is this not correct? Also I see the wired on your output transformer are long and hanging on top of the one board. This tells me that somebody has replaced the output transformer, and did not trim the wires. On the disk capacitors they suggested using the 470's. I have used both. And unless you have a super ear, you will nor hear much difference, but the power tubes are supposed to do better with the 470's. If you look at the other schrematics on the other amps, this is what they are using. And this is what I was told by Tom Walker, the man who helped design these amps. They are very easy to change, so if you don't like the 470's, you can put the .001's back in. When you are working on your amp, please use solder wick to take off the old solder. And do not use a solder gun, they are too hot for these boards. P.S. Use good tubes, I think Mike has suggested he likes the JJ's or the C's or if you are lucky enough to have some old US made tubes. | ||
| Trent |
Thanks Terry. Yes, the cap on the right power tube is orange as opposed to the dark brown/purple Mallory cap on the other tube. I'll go with your suggestion and update them. As for the transformer, I hadn't even paid attention to it. Upon closer inspection it is different. The wires are not cloth-covered like the majority of the wires and they are not trimmed short and routed like the others. I took some pics of the transformer. It has some brown on it that I hope isn't rust or a bad sign. I can make out a couple numbers on the top: 550 [can't see]...next line: 9 [maybe] 969 [more stuff i can't see]. pic1 pic2 pic3 So far this is the second previous repair that we've found in here. Hopefully it's no big deal and new tubes/caps solves my low volume/slight breakup on low notes problem. I think I'll go with JJ's since I'm in Oregon already. Biasing this is going to be an adventure as well. I've read through the archives but I'm sure I'll have some questions. I keep reading about not measuring both tubes at the same time, but rather individually. Complicated? I don't have access to a bias measuring tool besides a couple multimeters. One last thing. Is there an easy way to pull the board out so I can access the underside to desolder the old caps? Or is there an easier way? Thanks to everyone! This place is a godsend. | ||
| Terry |
You may not have Musicman transformer, it should be a 3-65 or a 5-75. Then 606-926 tells who and when made. This may be why the power caps are in such a mess. No easy way to get at the main board, set the head on its front side and prop it up so the knobs are down. | ||
| Trent |
I guess I'll replace the tubes and change out the caps and see where I'm at. Hopefully the transformer replacement is cool. The trace amount of rust on it will probably be a future project. Bob at Eurotubes says he tests the tubes to within 1mA on his matched sets. Would it be okay to just use the "Y" method with a matched pair from him? | ||
| mike kaus |
I've been replacing those caps on the main circuit board for years without taking the board up. Clip the leads close to the old cap and "tie" the ends iin with the new caps. Then solder quickly to keep from heating up backside too much. This is a quality fix and I have done it like this for 30 yrs. I don't like lifting boards with 30 yr old traces that can lift or crack. The Y crap is ok-I just prefer to check each tube seperately. I just put a 1 ohm resistor from pin 8 to the connection at the ballast resistor of each tube and read each VOLTAGE in mV. This is tha same reading you would get with a bias test device but you can probe each tube seperately. This is What the big boys do when they install test points in a new amp-same thing. If you can put them in sturdy enough, you can leave them IN for the next time too. Won't hurt a damned thing. Mike. | ||
| Trent |
Okay, it's been a while but the parts all came in and I finally got around to doing the cap and tube job today. Everything went great! I'll be making a small photo tutorial for future inquiries. In an attempt to not jumble the forums with multiple posts on the same project, I have a few remaining questions: 1) Reverb does not sound when I strum the guitar, but if I knock it or move it around it makes the expected spring reverb noises. Is this likely a problem with the reverb unit or something more involved? 2) I biased using the Y method just because it was so straight forward. I simply measured DC voltage across the 10ohm on the left tube. If I want to rig up the 1ohms to read individual currents, where do I wire them. I read pin 8 to the ballast resistor. Where/what is the ballast resistor? 3) I adjusted the bias until I read .5v across the 10ohm, and now the tubes put out some heat (I burnt a nice spot on my hand being clumsy while plugging the reverb unit back in with the amp on). I let it run for 15 minutes with master/channels all the way down, then adjusted bias. After playing my guitar through it for an hour or so, I checked the bias and it had gone back down to ~.4v or so, so I upped it. Is this normal? 4) The amp will now go significantly louder than it used to, but it's an odd kind of loud. I turned the master and volume to 10 just to see what it would do and the amp nearly knocked me over. It's not a harsh sound at all, just a kick-you-in-the-face-and-leave-you-for-d ead kind of sound. HUGE! I guess what I'm trying to say is it doesn't get loud and harsh; it just gets loud. I'm assuming this is the expected sound. 5) I replaced all of the electorlytics, the single ceramic on each tube socket, and the four ceramics on the preamp board. Do any of the other caps need to be swapped out? I notice a faint hiss at all volumes...it doesn't bother me and it's not that noticicable, but thought I'd ask if these amps were ever silent. Big thanks again Mike and Terry. | ||
| Trent |
I know I ask a lot of questions and I am more verbose than probably necessary, but bump anyway  | ||
| mike kaus |
A little hiss is normal. If you turned it all the way up, you have more stones than I do-those things are loud. It is common for the cathode current to drift a little after fire up and burn in-especially with new caps. You did replace the bias supply caps didn't you-the ones on the little board up by the front? those are very inportant too. No other caps need to be replaced unless they are bad-nothing maintenance wise though. Mike. | ||
| Trent |
Thanks for the info. I did replace the two caps on the bias board. Every electrolytic was replaced, and the four caps on the preamp board as well. It sounds great...can't wait to get home from work and play around some more. Any thoughts on the reverb problem? Oh, and where/what is the ballast resistor? | ||
| mike kaus |
The fact that the reverb rings when you hit it means that it's working-the reverb return is functioning. I'd look at the input to the reverb-the send cable and mostly the transformer inside the tank. It's probably got a bad tank. For some reason or other, tha MM tanks seem to be a little fragile. The ballast resistor is the big brown 10 ohm resistor coming off of pin 8 that both pin 8's are tied to. | ||
| Cameron Kinsey (gibson175) Username: gibson175 Registered: 09-2007 |
I had the same problem with the reverb exactly. Take out the tank, and look inside. The wires in there are extremely fine, and prone to breakage because they move with the spring. Check them all - bet you will find a broken one... |
