[PROJECT] Fender Twin

Discussion in 'The Squawk Box' started by Kuroyama, Jul 15, 2009.

  1. Kuroyama

    Kuroyama V.I.P. Member

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    [​IMG]
    Splattle and Cygnus... I went out today to Akihabara to find parts and tools. Ive got some insulated jumper clips, silver solder (apparently better for audio work) some flux to help keep the iron clean and improve my solder work by removing corrosion from parts and improving connections, as well as a solder removal tool to help minimize the solder present.

    But before we get into that, the video above shows how to drain filter caps. In it the guy talks about bridging the jumper cable with a "470ohm 1 Watt resistor". I was unable to find one. The resistor pictured above is a "475ohm 1 Watt resistor". Do you know if this will be as suitable for draining filter caps. The purpose of the resistor is to reduce reaction (arcing, sparking) when you make the connection from Cap positive end, to ground.

    But since MY resistor is 5 ohms higher than the suggested value, does that mean my filter cap drain time will increase? or that the "reduced reaction" (ie sparking or arcing) will be increased now because its 475ohms, not 470ohms... In short, how does the 5 ohm difference in the resistor affect my jumper for the amps filter caps when I go to drain them and thus maintain my heartbeat a few years longer?
     
  2. Cygnus X1

    Cygnus X1 Senior Member

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    No difference at all.
    The resistor value isn't critical, the wattage rating is.
    1 watt will work, I use a 5 or 10.

    Keep it clipped in while you are soldering.
    Sometimes those caps can recharge from the iron.
    Rare, but it can happen.

    Silver solder isn't really necessary either.
    60/40 works fine (unless it already has lead free solder joints. I doubt that though, given the year of the amp).
     
  3. Kuroyama

    Kuroyama V.I.P. Member

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    This will be the plan for the week. Wouldve started today but I was out at Akihabara getting the parts from above. Also, I need to get my multimeter from my office. Couldnt justify buying a 2nd one for home when Im gonna need that money for tubes.

    I did find a GREAT tube shop in Aki though!!! but WOW those are some high end tubes they keep in the front glass display!! $300??? $400??? Per TUBE??? Really? In restrospect I shoulda got pics. Ive heard and read lots about Chinese and Russian tubes, but these were all Japanese! I didnt even know Japan still made tubes!

    Also, whats the deal on "Matching tubes" I asked about matching tubes and the guy showed me some matched PAIRS of Chinese tubes... but they were only pairs. (?) Biasing seems to be an adjustment that you do once the tubes are installed, but this "matching" buiness... it seems they have to be BOUGHT that way ... or...???

    OH!! I just dug out the guys business card! They have a website
    ƒI[ƒfƒBƒIƒVƒ‡ƒbƒv@ƒAƒ€ƒgƒ‰ƒ“ƒXŠ”Ž®‰ïŽÐ
     
  4. Cygnus X1

    Cygnus X1 Senior Member

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  5. Kuroyama

    Kuroyama V.I.P. Member

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    Thx Cyg. Ill have to read up... question though. Do these guys ship to Japan? The Aki guy is only a 45 minute train ride away. Also, is there a tube forum you recommend? I know there are a lot of Amp forums out there, but this tube selection business is more complicated than I thought it would be. My Les Pauls are Made in Japan Epiphones (Gold top Standard, and a Junior) After LOTS of research I learned the level of quality I need, and the return on investment... I need to learn the same for tubes. I dont want rock bottom, but I wont pay hundreds per tube either. I need to find a nice "Junior" or "Studio" level of tube to target. I dont need any "signature model" or "custom" level tubes. No Slash model. No "Custom Shop" model for me thank you. Just basic quality. Ill grow from there.
     
  6. Kuroyama

    Kuroyama V.I.P. Member

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    Wow, only $70 for a matched set of FOUR? and they DO ship to Japan! Looks like I found my source. I havent decided what tubes Ill need yet, but they seem to have a very large selection. Bookmarked. Thanks Cyg.
     
  7. Cygnus X1

    Cygnus X1 Senior Member

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    Try Ampgarage.com
    Good folks there, and some professional amp techs at that site.

    They put up with NOOB questions very well as long as you listen to their advise.
     
  8. Drudeboy

    Drudeboy V.I.P. Member

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    Just seen this thread. What a buy! I dream of bumping into something like this for a rebuild project.
     
  9. Kuroyama

    Kuroyama V.I.P. Member

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    Its a bummer having a Twin in the house that doesnt work, likewise, reading up to and actually repairing a tube amp is a little like learning Kung Fu, or learning to shoot firearms. Its a whole lot of fun, but you learn about the dangers/downsides...and some of the "magic" goes away. Anybody whos learned martial arts or learned to shoot knows what Im talking about I think. With guns you think its gonna be all Die Hard and Lethal Weapon... but the truth is much more grounded than that. And once you learn the reality of firearms, the next time you go to watch an action film... you find yourself nitpicking.

    Now that Im learning the complexities of owning a tube amp... its kind of a pain.

    Having said all of that, if I had it to do over again...I would without hesitation!! So shop away. If you have questions ask em! MLP is NOTHING if not SUPPORTIVE!!! These guys rock. You listen to em, and soon you will too.
     
  10. Cygnus X1

    Cygnus X1 Senior Member

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    You'll get more comfortable with the safety aspect as time goes on.
    Don't get lazy about it though!

    The first time you fire a dead amp up and play it, or experience a mod that blows your head off-that is what makes it worthwhile.

    Even better, designing something a little different and building it.
     
  11. Kuroyama

    Kuroyama V.I.P. Member

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    Still here! Working for a living in Japan can be a little less fun than working in Purgatory. Its 315am and I just finished reports and con calls to the US. Im getting some sleep as I have a meeting at 9am... So, the Amp is moved to the side. Amp Work resumes in 24 hours... (Friday night)

    Good night all!
     
  12. LPSGME

    LPSGME Senior Member

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    Old Fenders usually develop cold solder joints at the solder rivets where the parts connect - whereby the slightest vibration can cause a run-away static noise sound. One way to tell is to tap the circuit board with a non conductive rod or stick of wood to see if it triggers the noise. Or you can just re-solder all the rivets with a solder gun - but only after draining the high voltage off the power supply, or you might get a shock if not careful, and shocks can be deadly. Have a tech do it. It only takes 5 minutes once the chasis is out of the cabinet.
     
  13. Kuroyama

    Kuroyama V.I.P. Member

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    Geez that would be such a sweet easy fix!! Thanks for that info. What you described sounds like what Im going through, but my amp was made in 1996? 13 years long enough to drop a solder joint? Not saying its not possible. Also not saying I wont check it. (Short of that bad tube I found I got nothing else at this point) Im just thinking that its not as likely since people cheerfully run 50 year old Fender amps.

    Still, chopsticks dont conduct. And Ive got more than a few around here...
     
  14. LPSGME

    LPSGME Senior Member

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    Oh, I thought it was an old Fender with the hand wired boards. On those the problem I described is common, perhaps the most common.

    However, I don't see why a bad solder connection on a printed circuit (if that is how that amp is made) wouldn't also cause a similar problem.

    On a cold solder joint, bigger parts (like caps) will tend to vibrate more and thereby manifest the problem. It could be a cracked resistor; could be a bad pre-amp tube. It could also be the speaker rubbing. If it only occurs when you make the amp louder that either means the loud sound is creating a vibration that is causing (for example a cold solder joint to react) or you may just be exceeding a signal or electrical limit at which point the condition either happens or just becomes more apparent to the ear. For example the bias could be off, or a resistor supplying a voltage to a tube is loose or defective, or a cap is bad and is not filtering sufficiently - so that when the signal level goes up a 'clipping' or AC mix occurs or becomes more apparent to the ear.

    I guess it could be some bizarre problem with a transformer, but that's not going to cost much to fix either.

    Are you able to isolate the problem to one of the two channels??????
    That would tell you a lot and help you deduce the cause.
     
  15. Kuroyama

    Kuroyama V.I.P. Member

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    Frak.

    I was up working until 3am last night after working until 4am the day before... I work for a computer company, but my job sometimes requires I work with the US directly, which means after working late, logging back in from home for a few hours at night. Id play the blues, but its a tough job market out there. Its good to have a paycheck. Anyway, I was gonna start in on the amp today, but the wife wants the go shopping for a vacuum. Translation: "come help me carry this home on the train". So hopefully amp work resumes tomorrow.

    When looking at PC/Server/Disk/Tape storage problems, we often look at the environment. Heat is bad. Dirt is bad. Running your machine in a hot, dirty environment?? Expect trouble. (yeah that means readers with Golden Lab, Airedale, or Persian cat hair gumming up their PC fans can expect shorter than average lifespans for their (beloved?) PCs.

    This amps previous owner kept it someplace where the air was VERY humid and dust flowed freely. Im guessing maybe the back of a garage? We live not too terribly far from a famous wealthy beach community. Just the type of place where some knucklehead with more money than brains might buy an amp like mine, then leave it exposed to the elements, then blame Fender for their poor quality amps. But thats another thread. If you look closely at the pictures above I think you can get an idea of the dirt Im facing.

    Tonight, MAYBE I can get my chassis out of the cabinet so I can "see" whats doing. Ill get that jumper clipped onto the filter caps and drain accordingly. Also got my multimeter to make sure its all clear. Cygnus gave me a list of readings to get, so, after a visual inspection of the remainder of my tubes and internal parts, I'll start there.

    (Of course... more Twin porn to follow)
     
  16. Dave C

    Dave C Member

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    The white crusty stuff at the base of the one tube is most likely glue...it just got a bigger dollop than the others. It's the silver coating inside the top of the tube that turns white if the tube has an air leak...so I wouldn't condemn that tube just yet.

    This link has the owners manual and schematics which might prove useful:

    Amp Guide » Fender Twin Amp (The Evil Twin)
     
  17. Cygnus X1

    Cygnus X1 Senior Member

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    Good observation Dave.
    My mind went immediately to the potential bad news but glue is a distinct possibility.
     
  18. Kuroyama

    Kuroyama V.I.P. Member

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    Thanks Dave. In this case there is no such thing as too much information. Sovtek Tubes might not be top shelf, but lets save the money for where I NEED to spend it. Just so Im clear on what turns white... Would the metal parts inside the tube turn white (I'm thinking frosted flakes whitish) if indeed there was vacuum loss?

    Im thinking that tube shop in Akihabara might be a good place to get my tubes tested. Do people normally charge for such a service? Is the testing as simple as pass-fail? what feedback am I looking for (if any) other than pass-fail?

    I was pretty crashed out this weekend. So, all I did was slap some wood together to make a stand for the amp chassis when I pull it out of the cab. Just some slaps of wood glued together.

    [​IMG]

    Please dont judge my soldering by my sloppy glue work. I glued the wood together while eating dinner and watching TV with the wife.
     
  19. Kuroyama

    Kuroyama V.I.P. Member

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    OK So what follows will be shots taken from inside the chassis. Ive got two concerns... well, 3 actually.

    1) I hooked up the voltmeter and got NO reading on the filter caps. Granted the amp hasnt been plugged in since the store, AND I pulled the power tubes, but shouldnt the filter caps retain some residual charge - unless there is a short?

    2) I think I see a bulge on the top of one of the yellow barrel caps. No liquid from any caps, but the bulge (if it is one) warrants replacement. Also, theres some discoloration at its base.

    3) I was worried about oxidation from the OUTSIDE of the amp... The inside of this thing looks like it did two tours with McHales Navy. Anyone know if this kind of oxidation will hurt the circuit?? Its all over. Maybe the entire amp has to be rebuilt??

    [​IMG]

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  20. Kuroyama

    Kuroyama V.I.P. Member

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