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Thread: Filter caps for a Premier Twin 8?

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    Filter caps for a Premier Twin 8?

    I just got a '59 or '60 Premier Twin 8. As usual with an amp that old, it needs new filter caps. It has a 40x10x10x20mfd cap can; I think the 20mfd cap is the 6L6 cathode bypass cap, because I can find no other 20mfd caps on the schematic(s) I have. I want to replace it with another cap can; there's not much room on the chassis for anything else. If I replace it with a 40x20x20x20mfd can, will there be a noticeable difference in tone; if so, in what way? Also, would there be any reason not to use the last 20mfd, 450 or 500 volt cap as the cathode bypass cap for the 6L6?
    Thank you in advance for your opinions and advice.

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    When you recap a old amp you always get a difference in tone. It be tighter and louder. One man who get his Premier 50 back recapped said i destroyed his amp. It be too modern in sound. I had used standard values in caps and built a 40+10+10 with sprague atom electrolythic caps and and a 63 Volt 22mfd cathode bypass cap.
    I cut out the bypass cap and he liked it better.
    If you go up to 40+20+20+20 you will hear difference from how it is now. But no hearable difference from a 40+10+10+20.
    And you could use the left over 20 uf to a bypass cap without problems.

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    There are five versions of this amp. Does yours have a tube rectifier?

    OK, here's the deal:I've recapped several of these amps for customers with 40/20/20/20, with no sonic issues, and I restore A LOT of vintage amps. However, electrolytic caps DO lose capacitance with age, and these amps are pretty old by now. Therefore, you CAN get away with 20/10/10/10. No, the reduction in capacitance (which probably existed anyway) won't effect your low-end rolloff on the cathode bypass for the power tubes.

    If you have any hum issues with the 20/10/10/10 cap, you can always piggyback a 10uF or 22uF/500V cap onto the 20uF section internally to clean it up. But speaking from experience, I'd go with the 40/20/20/20. Shouldn't be an issue.

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    John R. Frondelli
    dBm Pro Audio Services, New York, NY

    "Mediocre is the new 'Good' "

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    Quote Originally Posted by jrfrond View Post
    There are five versions of this amp. Does yours have a tube rectifier?

    OK, here's the deal:I've recapped several of these amps for customers with 40/20/20/20, with no sonic issues, and I restore A LOT of vintage amps. However, electrolytic caps DO lose capacitance with age, and these amps are pretty old by now. Therefore, you CAN get away with 20/10/10/10. No, the reduction in capacitance (which probably existed anyway) won't effect your low-end rolloff on the cathode bypass for the power tubes.

    If you have any hum issues with the 20/10/10/10 cap, you can always piggyback a 10uF or 22uF/500V cap onto the 20uF section internally to clean it up. But speaking from experience, I'd go with the 40/20/20/20. Shouldn't be an issue.
    I really respect your knowledge and know you have worked in a lot more amps then i done. I'm a beginner - still learning.
    I always got tighter bass and better punch compared with how the amp sound before i swap caps. Rect tube or ss rect does not matter in that case.
    Do you mean i do something wrong?
    In that case i want to know what you do to keep the same worn out sound after you changed old worn out filter caps to new caps.
    Some folks like the old loose sound..

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    The reason I asked about the type of rectifier is that a tube rectifier will not tolerate overly-high capacitance, should you decide that you want really tight bass and increase the filtering.

    Looking at my schematics for the Twin 8, it looks like the amp in question here probably is the version with the 6X4 rectifier, which used a 40/20/10/10, with the 40uF being the first filter cap, and the 20uF for cathode bypass.

    As I said earlier, capacitance diminishes with the age of the electrolytic cap. Conversely, resistor value increases, so when repairing vintage amps, you have to choose between the ORIGINAL value, or the CURRENT value. If the part in question is shorted or open, you will have to guess, but it's safe to say that most old electrolytic caps have shrunk to between 40%-60% of their original value, while resistors will increase from about 10%-30%, plus you have to factor in the original component tolerances. It's all in the interest in modifying the sound as little as possible.

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    John R. Frondelli
    dBm Pro Audio Services, New York, NY

    "Mediocre is the new 'Good' "

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    Thank you

    Thank you guys for all your help and advice; after some careful measuring, I've decided to try and "shoehorn" some discreet capacitors in there. After reading jrfrond's explanation of how filter caps age, I decided to see how the amp sounded with the original values and go from there; I have no idea how the amp sounded after aging 50 or so years, because it came to me with no power cord, and when I installed one and brought the amp up slowly on the variac, it had that loud hum that's a characteristic of dried out filter caps.
    @jrfrond- you're right, it's the model with the 6x4 rectifier. When you replaced the filter caps on all those Twin 8's did you use a JJ 40x20x20x20mfd can or some other brand?
    @arnenym- when you removed the bypass capacitor on your friend's Twin 8, how did that change the sound?

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    If you remove the cathode bypass cap you get a smoother, sweeter tone. It take down the volume a little, but i like the "older sound" better.
    Its easy to test and it does not harm anything. I have some amps with switches and i know several people have the cathode bypass caps on a switch just for easy switch in and out..

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    Quote Originally Posted by bluzmn View Post
    Thank you guys for all your help and advice; after some careful measuring, I've decided to try and "shoehorn" some discreet capacitors in there. After reading jrfrond's explanation of how filter caps age, I decided to see how the amp sounded with the original values and go from there; I have no idea how the amp sounded after aging 50 or so years, because it came to me with no power cord, and when I installed one and brought the amp up slowly on the variac, it had that loud hum that's a characteristic of dried out filter caps.
    @jrfrond- you're right, it's the model with the 6x4 rectifier. When you replaced the filter caps on all those Twin 8's did you use a JJ 40x20x20x20mfd can or some other brand?
    I used the 40/20/20/20 with no issues.

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    John R. Frondelli
    dBm Pro Audio Services, New York, NY

    "Mediocre is the new 'Good' "

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    on filter caps i wont give any advice - jfrond already covered that - i have a twin 8 - ok it is a ss rec with 7591 output - but as far as noise - when i first got it it had a constant hum - found unbalanced filaments - added pot - or the 2 100 ohm resisters would probably have worked - took care of that hum - had a harp player once try it and he wanted to buy it - i had to keep it of course - did rework the front end - to more of a fender circuit - if i remember it had something in the front end that was more like a grid leak bias thing - i know someone will correct me if am wrong - anyways it sounded better for guitar after - for me anyways - oo3

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    What gives?

    I replaced the filter caps, the 6L6 cathode resistor and cap, and the power supply dropping resistors and brought the amp up slowly on the variac. The pilot light lit up, the tubes glowed, but I got no sound. No hum. no hiss , no music. I went back and double checked my work today; everything looked in order, but I still got no sound. What could it be, defective caps, bad tubes, or what? Where do I start?

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    Last edited by bluzmn; 08-05-2011 at 09:35 AM.

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    OK, I decided to try switching around tubes first. First I switched in a new in box NOS JAN GE 6x4 which produced an immediate hum so load that I switched off the amp immediately; it may or may not be defective in light of what happened next. I replaced the old 6x4, and then swapped in a new(ish) Sovtek 6l6; I got the same hum that I did before I did the filter cap replacement. It's odd; the hum is loudest at the highest and lowest settings, and almost bearable in between. So then I swapped in an old RCA 6l6; again, no sound. The same with different 12ax7s. So, I put back in the original tubes, and lo and behold, I got that same hum from before the cap job. For some reason I got the idea to jiggle the 6l6, and I got that loud, persistent hum like with the 6x4; I jiggled some more and it went back to the milder hum. So, I "chopsticked" around the 6l6 socket; jiggling the bypass cap seemed to have some effect on the hum, so I'll replace that and see if it solves the problem.

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    Quote Originally Posted by arnenym View Post
    When you recap a old amp you always get a difference in tone. It be tighter and louder. One man who get his Premier 50 back recapped said i destroyed his amp. It be too modern in sound. I had used standard values in caps and built a 40+10+10 with sprague atom electrolythic caps and and a 63 Volt 22mfd cathode bypass cap.
    This is one of the situations that drives me up the wall. I've learned that it's a big red flag if someone says, "I LOVE the way my amp sounds!" My standard response is that if you love the way your amp sounds, then, by definition, there's nothing wrong with it and it doesn't need to be fixed. I don't care if it's literally on fire.

    An analogy that works well for me is that of the bald car tire. Yes, a car may drive very well on smooth, bald tires--on a dry road. But you have to put new tires on eventually. And the car will drive differently on a brand new set of tires. People seem to understand this, even the most tech-illiterate musicians, who also seem to be the ones most prone to complain about an amp that now sounds more like it did when it was new.

    John is right, of course, in that you can reduce cap values to approximate capacitors that are drying up.

    My favorite example of this situation is a Rhodes Stage Piano I worked on years ago. Supposedly, it had already been to two techs who couldn't fix a hum in it. I found a bad solder joint to ground and fixed it. The player then complained that it didn't have the "bite" that it did (due to a flaky solder joint). I advised him to put a distortion pedal in his signal chain, which he did, and it got him back where he wanted to be.

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    Well, I was right about the cathode bypass cap causing the continued hum. I replaced it, and there remained only a very slight hum with the volume at zero which went away as you increased the volume. I got the original replacement cap at Rat Shack, but it was a Nichicon, so I thought it was OK; it must have been in that drawer for a long time. I replaced the filter caps with a CE Manufacturing (AES) 10x10mfd "tubular" electrolytic, which was the perfect size for the small space I had, and for the 47mfd and 22mfd I used AES's generic electrrolytics, because I read on another forum that they are Xicons. They're not; the only markings I could find on them (other than mfd, voltage and temp ratings) was a lower case "u" in a circle (it looks just like a lower case "n" upside down) - does anybody know who makes those?
    So, while the chassis was out, I decided to "chopsick" around; all my connections were solid, but it seemed like almost every solder connection from a component to an input jack or a pot made a "crunch" noise when I touched it. I figured I'd have to re-solder everything and replace the out-of-spec resistors (and some capacitors, too). Since I'd spent 2 all-nighters on it, I decided to put it back together, because I wanted to hear how it sounded, despite the crunch. Surprise; there was little perceptible hum, no crunch in any inputs, and the best sounding input was the one with the resistor farthest out of spec (interestingly, all the resistors, even a little out of spec, had gone down in value!). The amp sounded pretty good , and I'm a great believer in "If it ain't broke,don't fix it"!

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    Quote Originally Posted by Rhodesplyr View Post
    This is one of the situations that drives me up the wall. I've learned that it's a big red flag if someone says, "I LOVE the way my amp sounds!" My standard response is that if you love the way your amp sounds, then, by definition, there's nothing wrong with it and it doesn't need to be fixed. I don't care if it's literally on fire.

    An analogy that works well for me is that of the bald car tire. Yes, a car may drive very well on smooth, bald tires--on a dry road. But you have to put new tires on eventually. And the car will drive differently on a brand new set of tires. People seem to understand this, even the most tech-illiterate musicians, who also seem to be the ones most prone to complain about an amp that now sounds more like it did when it was new.

    John is right, of course, in that you can reduce cap values to approximate capacitors that are drying up.

    My favorite example of this situation is a Rhodes Stage Piano I worked on years ago. Supposedly, it had already been to two techs who couldn't fix a hum in it. I found a bad solder joint to ground and fixed it. The player then complained that it didn't have the "bite" that it did (due to a flaky solder joint). I advised him to put a distortion pedal in his signal chain, which he did, and it got him back where he wanted to be.

    My favorite shoes were the most comfortable just before they broke.....

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    I called up AES to ask what brand their generic electrolytics were; the salesman said he didn't know. When I told him I had read on a forum that they were Xicons, he said they might bave been at one time, but that they were basically whatever was available at the time. I asked if there was any quality control, and he said no. I didn't like the sound of that, so I went to a local repair guy and he sold me a 47mfd 500v Illinois cap and a 25mfd 25v Sprague and I installed them. I think the amp sounds a lot better now; more like a Premier should sound, smooth and fat. It sounds very similar to a Multivox Model 45 I have, but fatter. There are still some problems, though. There's a hum that starts at about 3 o'clock on the volume knob and continues to the end; what could be causing that? When I plugged a lap steel into it, every note I played was accompanied by that crunching sound I got when I was "chopsticking" all the solder joints in the input and preamp. Should I just resolder the whole input and preamp? And when I plugged in a guitar. it just sounded fuzzy and weak, and the bass notes just seemed to fade away; this is no big problem, because I'm going to be using this primarily (exclusively?) as a harp amp, but I want to make sure that this isn' t being caused by something that could come back and bite me in the ass later.
    Any help or advice you can offer will be greatly appreciated, because I've been wanting one of these amps for a long time, so thanks in advance.

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    Quote Originally Posted by Rhodesplyr View Post
    My favorite example of this situation is a Rhodes Stage Piano I used as piano for beginners years ago. Supposedly, it had already been to two techs who couldn't fix a hum in it. I found a bad solder joint to ground and fixed it. The player then complained that it didn't have the "bite" that it did (due to a flaky solder joint). I advised him to put a distortion pedal in his signal chain, which he did, and it got him back where he wanted to be.
    I had a Rhodes Stage Piano too which had the same prob.. I tried this process and it worked!

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    Last edited by gavin_rossdale; 09-18-2011 at 08:33 AM.

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    I have some of those i Phones. Guys, If you love downloading MP3 musics, the good source is from YouTube videos as it has the complete list from any online streaming. The instruction is as easy as 1,2,3, and the great thing is, its free. Just paste your YouTube URL and for a couple of minutes, it will be converted into MP3.

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    [URL="http://www.flockee.com/static/youtube-to-mp3/?title=youtube-to-mp3-converter&category=on-line-tools"]YouTube To MP3 Converter[/URL]

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