1959 Fender 5F8-A Twin Exposed and Documented

Discussion in 'Amp Central Station' started by keithb7, May 6, 2016.

  1. peteb

    peteb Friend of Leo's

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    I have less experience not more, but the old filter caps I've measured have measured correct capacitance. I have not measured resistance of caps.

    The problem with measuring old caps is that they cannot be counted on to hold up at high, operating voltages.
     
  2. keithb7

    keithb7 Friend of Leo's

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    In comparison I measured the caps that I pulled from my 1973 Twin Reverb.
    Same cap values 20uF @ 500V.

    1973 Caps:
    24.66uF 0.40 ohms
    22.06uF 0.42 ohms
    25.54uF 0.47 ohms

    1959 Caps:
    23.1uF 1.99 ohms
    24.39uF 2.70 ohms
    16.21uF 5.2 ohms
    16.74uF 3.2 ohms

    Quite a difference in ESR ohm ratings. My understanding is as a cap ages the ESR ohm reading goes up.
     
  3. Alamo

    Alamo Doctor of Teleocity

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    What the heck is an ESR meter? :confused:
    since I had no clue, I searched and found this.
    I think I got some good information and can keep up with following the thread.

     
  4. old guitar player

    old guitar player Tele-Afflicted

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    That is one heck of an amp! Gosh, I thought Clapton and Keith Richards had already bought them all up...;)

    You're truly a lucky man!
     
  5. keithb7

    keithb7 Friend of Leo's

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    More thoughts on ESR meters and caps:

    Over the past few years, during my journey learning about amps, the topic about servicing these old relics is often unsettled. I'm not going try and settle the topic but share my experience. I'm a self educated tube amp hack so forgive my limited perception.

    If you talk to a Pro amp tech, all but a scant few in my travels say change all the electrolytics. If they are over 15 years replace them most say. There is electrolytic fluid inside them. I believe "electrolytic" basically means its a fluid that conducts electricity. As caps age, somehow this fluid dries up. This is especially true if amps are stored for long periods without any use. Amps that are used more often, essentially have healthier caps. Not all caps in your tube amp are electrolytic. Some are ceramic or mica, or other dry type capacitors. For example coupling caps, tremolo circuit caps are dry.

    Some amp fanatics, especially collectors say most old electrolytic caps are fine. Claiming those who change them just because they are old are foolish. I have heard them say "Send me all your old caps, I'll happily re-use them". I've read several emotional arguments from both sides. The general consensus seems to be if you want an old reliable amp that can be played and gigged, change the caps. Do what's needed. If you want to put it on the shelf and admire its original beauty, leave the originals in. Sounds simple right? I struggle with having an old amp and and rolling the dice whenever I power it up. Will an old cap fail? Could I ruin a transformer if a cap fails? There's 15 amps of power in the plug in your wall. The little 2 amp fuse keeps those 15 amps at bay. Thats all a healthy amp needs so the fuse is just fine. Say an old original bias cap is failing. Or a B+ power supply cap is failing. It starts to allow more amperage thru. The amplifier tries to pull more than 2 amps thru the fuse and the fuse melts. It does what its supposed to do. When your amp starts blowing fuses, something is up. Don't put a 5 or 10 amp fuse in it. If that cap fails with your new 10A fuse in there, now the flood gates are open. You're now pulling 10 amps of current through your amp. Something is going to melt or maybe catch on fire. Quite possibly your original power transformer windings will melt.

    This 1959 Twin had a 10 amp fuse it it when I bought it. It had a bias cap that was blown apart and spewed its guts inside the chassis. We can assume the electrolytic caps should have been changed by 1980 at least. I am keeping my fingers crossed when I get back into the amp, the PT is still working.

    Back to ESR meters. I am the curious type. I want to be able to analyze old caps. I had fully intended to change all electrolytic caps in this Twin anyway. An ESR meter allows me to check the health of a cap. But not dry caps as mentioned above. Next time I get engaged in a discussion around old caps I'll be better prepared. Lol.
     
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  6. keithb7

    keithb7 Friend of Leo's

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    Ok, I'm back and ready to make some progress on the Twin. Thinking about documenting a few steps with video just for fun. No editing. Just record and upload.
    He we go. Progress as time allows.

     
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  7. t-luxe

    t-luxe Tele-Afflicted

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    Awesome. Thanks for sharing.
     
  8. Mayas caster

    Mayas caster Tele-Holic

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    I didn't read your other post. You didn't find this jewel in Canada??? Make it live again and enjoy it.
     
  9. keithb7

    keithb7 Friend of Leo's

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    I replaced the two failed bias caps, and plugged amp into light bulb limiter to see what voltages I get.
    No sound from amp so I started probing around.

    As I have limited formal electronics training I am hoping I can post a few questions and those in the know can help me along.
    Schematic and layout here for reference:

    [​IMG]

    [​IMG]



    Here is what I have found so far in my Twin:

    Red wires into rectifier, pins 4 & 6 measure 416V AC. Yellow wires going into rectifier tube 5 volts AC.
    DC voltage coming out of rectifier tube, pin 8, that goes to stand-by switch reads 197.5 VDC. Measured at the connection on the standby switch. Found a bad standby switch. I don't have a spare, so I wired removed the switch temporarily and soldered wires directly together, eliminating switch.

    Powered up amp. DC voltage on first two B+ caps climbs as high as a meagre 10V DC, then starts dropping and stabilizes at about 7 VDC. These are the original B+ caps still in there for now. Unsure if these are a problem yet at this point. I did record original cap readings, read with an ESR a couple of posts above here.

    Next item in the power supply, I turned to the choke. I Took an resistance reading between the two black wires going in and out of it. I get 99 ohms. According to a Classictone replacement choke, the resistance is about 105 ohms. So I think my choke should be ok.

    I am a unsure why the rectifier tube is putting out 197.5 VDC. I have a new Sovtek 5AR4 that I also put in there. Same results measured as vintage tube. Any ideas on the power supply?
    Before I go ahead and replace the original power supply caps.? I agree they are old and should be changed anyway, before I do, I am wondering if they may be part of the symptoms I am seeing so far. Thanks.
     
    Last edited: Jun 3, 2016
  10. Wally

    Wally Telefied Ad Free Member

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    400VAC....across from 4 to 6 or from each leg to Ground? if the measurement was across those two pins, that is obviously low. If it was from each leg to ground, it is high. If it was across the two pins, pull the rectifier and take that measurement again. If the voltage remains at 400VAC across the two pins 4/6, then one might think that the PT is incorrect for this amp or that winding has been compromised by abuse. The heater filament voltage at 5VAC is obviously correct.
    If removing the rectifier causes that voltage to rise to a 'proper voltage', then one has to conclude that there are problems downstream. Pull all other tubes, reinstall the rectifier and check things out. If the B+ is still low, one might think that those old filter caps are of no use regardless of what a meter says. If the voltage comes up with the tubes out, reinstall the tubes....power tubes first and working your way back to the preamp input stages. Where does the voltage fail to maintain proper levels? Fwiw, I am guessing that the last two sentences in this paragraph is not going to be of any use and that the problem exists either in the PT or the filter cap section. I could be incorrect...again.
     
  11. keithb7

    keithb7 Friend of Leo's

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    Thanks Wally. With rectifier tube out I measure 468V AC across both red pins. About 230V AC off each one individually to ground.
    The amp did have a 10A fuse in it, and a blown bias cap. The transformer in it does not appear stock to me.
    I think we have enough clues here to start shopping for a PT.
     
  12. Wally

    Wally Telefied Ad Free Member

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    Decisions, decisions...... I would be looking for a 'voltage adjusted' transformer that will yield vintage B+ with modern wall voltages. Mercury for sure offers one. Classic Tone may, also. Others????
    I also suggest replacing all electrolytics. Ime, there is reason to even question replacing them. Ymmv.
    I would measure every resistor in the circuit. Coupling and tone caps...Hey....try your ESr meter on those Astrons. I have never replaced any of those as long as they were working. Tweeds from 1955 and earlier use tone and coupling caps that are not as durable, but since you will be working on a player amp you can forget about keeping everything 'vintage', IMHO. No expensive caps are needed...just correct values, IMHO. There is a loooooong thread on that question.....just the most recent one, right?
    The thing is to make it correct, ime.
     
  13. keithb7

    keithb7 Friend of Leo's

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    I pulled the light bulb limiter out of the test. Plugged straight in to the wall.
    15 amps on tap. Oh boy here we go.

    Read 575V off both red wires at rectifier.
    Got up to 128V DC on the first B+ caps and some crackling.
    I plugged in a guitar and we have a signal. That's exciting. It's a weak signal but it's there.
    Old caps coming out, F&T's going in then another update.
     
  14. Wally

    Wally Telefied Ad Free Member

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    Okay, Keith.....the current limiter makes all voltage readings a waste of time, IMHO. The limiter is there to indicate shorts and perhaps to keep an old cap from failing due to full voltage....
    After firing it up on a limiter, one goes to full voltage to see what goes on. I still would have pulled the tubes because of that low B+....????128VDC?????.
    Fwiw, a Variac is a really useful tool for an old amp,that has not seen voltage in a long time. It takes the day to bring the voltage up in steps, but it is a safer way to bring an amp like this online, IMHO.
    I started to note a few minutes ago that I had accidentally gone back to page two and caught the pic of those filter caps.....3 bulges and one with an open relief hole. No reason to wonder if one should replace them....ESR readings are meaningless in this situation, ime. As peteb noted above....full voltage is different than a meter's testing stresses. It is sort of like e tube tester.....maybe a 'good' tube will work....but there is a good chance that it won't sound good even if it tests good, right? I don't question old e-caps.....I know what they sound like, and I know what fresh caps do for the sonics,...even with the same tubes in place.
     
  15. keithb7

    keithb7 Friend of Leo's

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    Its all coming together slowly. I like learning by doing and trying things like this. I'd be lying if I did not admit that the value of a '59 Twin with original caps in it, had some effect on my efforts to try running the amp without replacing the caps. It's crazy. People with more money than brains who'll pay a premium for an all original amp, even if not working. Fresh caps going in...
     
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  16. JGOCTO

    JGOCTO TDPRI Member

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    Yea, this is a great thread!
     
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  17. Wally

    Wally Telefied Ad Free Member

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    IF a vintage amp is dead mint, I will leave it as is. I will also not play that amp much except to exhibit that it functions....processes signal. The amp will be described as all-original, mint condition. It will command top dollar, and the new owner can do as they please with the amp. I have had exactly one old Fender that fit that description...a 1964 1X15 Vibroverb...the SRV amp. The fellow who bought it looked at the from 6 feet away while listening for about 10 seconds, asked how much, and went to get the Benjamin's. It looked brand new, it processed signal, and it broguht top dollar. Fwiw, years before I had that amp I owned a Nov, 1963 Vibroverb. I had to replace the PT. I recapped it. The speaker had to be reckoned. A famous player passed on it at a show because it had the work done. I later learned that he would not buy/play a vintage amp that had been recapped...muchless if it had a replaced transformer. That explains why his sonics in a live show at a small club here were the dullest, flattest sounds I have ever heard a big time player create....fabulous talent, lousy sonics = sad performance with exactly zero musical intensity, IMHO.
    When an amp has issues..cosmetic, originality questions, and doesn't function; IMHO that amp needs to be made to play the way that it should. This Twin is worth more making good sound than it is in its unplayable condition, right? It will never be a top dollar amp. It will be a very valuable amp nonetheless if it is putting out good sonics even with compromised but original tweed, original speakers, replaced e-caps and possibly a non-original PT. An original OT is a big plus, IMHO. It would also big great if that tweed did not exhibit the water stains. All if that is wishful thinking. This amp is in that player status, ime....albeit a rare player that will still command big money....just not as much as a good condition, all-original 5F8A would command. All of this said, we are all envious....not many of us get to own or work or play or even see one of these amps in person no matter what condition the amp is in.
     
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  18. keithb7

    keithb7 Friend of Leo's

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    Thanks for the insight Wally. Its a crazy market, vintage amps. Especially when I'm dealing with a 1959 Twin. So many thoughts, scenarios, decisions...Head games really.

    All tubes out, original caps, power supply readings:

    Red wires on rectifier tube: 281.9 VAC, each wire.
    Yellow wires 5.836 VAC

    Plugged in rectifier tube only, all other tubes out. Measured DC voltage on B+ cap 1. Watched voltage steadily, somewhat slowly climb up to 200V DC. Turned off amp and replaced B+ caps with new F&T caps.

    With new B+ caps installed. All tubes out except rectifier. I measured B+ voltage on cap 1. Similar results, somewhat slowly watched b+ rise to about 320 VDC. It does appear something in the circuit is letting B+ power go to ground. I am getting an amplified guitar signal through the amp. Very distorted as I roll up the volume. Either channel. Not much volume. Gotta get that B+ up.

    More testing parts and update to come. The choke is a thought at this point. Not sure how to test it. An internal short to ground would certainly kill the B+.

    [​IMG]

    I'll glue or silicone the new caps in place soon. The later introduction of a mini circuit board under the dog house certainly brings more confidence.
     
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  19. Wally

    Wally Telefied Ad Free Member

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    What do you get if you lift the B+ feed wire from pin 8 on that rectifier and measure that rectifier output in that manner? I am so simple I have to know such things just to eliminate any 'wonderment'.
    And....you say that with the old caps in place, the voltage only reached 200VDC, correct? With the fresh caps in that doghouse, the voltage rose to 320VDC, correct? IMho, that is an improvement....but I have to ask....this is with wall voltage and not running off of the current limiter, right? What about the 8mfd/450VDC filter cap for the preamp that sits on the eyelet board? That needs to go as well, imho. I always take care of all electrolytics and general service before I fire an amp up. I remove caps, do some cleaning tightening, etc while the voltage is GONE, replace the power cable if that is called for----in short, I complete the 'overhaul' or at least all of the basic overhaul--- before I fire the amp up. Then I don't question certain aspects because those things have been taken care of...in the safest manner possible because there is no voltage present in the new caps. With certain amps of a certain age with certain tone and coupling caps, I replace those as well. After proper voltages are re-established, then one can ascertain what is really going on in the circuit and thereby get the amp working the way it should.
    Now....I know someone somewhere would say that it would be ill-advised to go about things this way with a 5F8A....but this procedure works for me. The amp gets going as quickly as possible and sounds good when I am through. that is the endgame, ime.
    IF I am going to sit and worry about what should or should not be done with regard to the market, I will simply sell the amp before I start and let someone else wonder about it. (;^)
    With this amp, I would HAVE to hear it; therefore I would have to get it going.
    I had a fellow in Cali question why everything on the board was replaced in some tweeds that I sold him....and he knew the situation before I sold them to him. I explained why I had had that done...before my tech days began by an excellent tech. HE still was wondering. I told him that that was why there was a bag full of worn out components with each amp and that if he wanted them back in they could be put back. Then I asked him what he thought about how the amps sounded..."FANTASTIC", he replied. I told him that I hoped he would enjoy them, and he had paid fair money....much less than excellent, original prices. These were 3 tweeds that were like this one of yours...each one was compromised as far as vintage value was concerned long before I got them. Since they were no longer by an stretch of the imagination in excellent original condition, I wanted them to function as players....and that is what they undoubtedly did and still do, I am sure.
     
  20. Cjl77

    Cjl77 Tele-Meister

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    I have a low power tweed twin that my grandfather gave me a couple yrs before he died. He bought it new. It had never been recapped when I got it. It sounded less than good. First thing I did was recap it. She came to life. When I first got her she went on the road for a while until I realized she deserves better than life in a van. I take her out to the occasional gig and she records great. I have 3 other vintage amps of equal value he gave me and 6-7 of my own. If I can't play them I don't want them! A couple weeks ago the twins plate resistors became noisy. They had drifted way out of acceptable spec. Had to go.
    I only replace parts the affect function. But over time and use things have to be replaced.
     
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