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Thread: fender ,93 the twin ,red knob

  1. #1
    sid
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    fender ,93 the twin ,red knob

    Hi i am new to this forum,i am wondering if there is anyone out there who is familiar with the "fender twin red knob amp " ,I have recently got it to restore ,i am not an electronics expert but will have a go at simple repairs .The main problem on this amp is that the reverb send signal is none existant ,i have swapped valves and also fitted a new driver transformer but still nothing ,I can not make any sense out of the schematic and cannot find a layout diagram for it,could anyone suggest if it maybe a resistor or cap at fault ,any advice would be greatly appreciated, cheers .

  2. #2
    Senior Member patlaw's Avatar
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    Why did you replace the driver transformer what made you think it was defective it would be best to use an oscilloscope to trace the signal through the circuit to know where the problem is just shotgunning parts is expensive.

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    What test equipment have you got?
    Are you aware of safe working practice, eg Safety Tips For Working On Tube Amplifiers
    Is R56 the V8 reverb driver cathode resistor ok?

  4. #4
    g1
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    Also, you mentioned you have no "reverb send signal", but we should begin from scratch.
    How did you determine the send signal is non-existant?
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  5. #5
    Senior Member Pedro Vecino's Avatar
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    Is the reverb selector (clean-both-lead) set correctly? Any symptom that can be damaged?
    g1 likes this.

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    For the OP - I just want to mention you must be very careful with the PC boards in these amps - very easy to lift a pad or trace while soldering (much more than most).

  7. #7
    sid
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    Quote Originally Posted by sid View Post
    Hi i am new to this forum,i am wondering if there is anyone out there who is familiar with the "fender twin red knob amp " ,I have recently got it to restore ,i am not an electronics expert but will have a go at simple repairs .The main problem on this amp is that the reverb send signal is none existant ,i have swapped valves and also fitted a new driver transformer but still nothing ,I can not make any sense out of the schematic and cannot find a layout diagram for it,could anyone suggest if it maybe a resistor or cap at fault ,any advice would be greatly appreciated, cheers .
    Thanks for your interest and thoughts. As I said I'm not a tech, the reason I changed the driver cus it was recommended on a forum I found it was also easy for me to install, I tested it by wiring a speaker to it as suggested on that forum no sound coming through. I am aware of the dangers of valve amps and after seeing a friend of mine been shot across the room after accidentally touching a cap I am very cautious. I will probably take it to a tech soon just wondered if anything was obvious.

  8. #8
    sid
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    red knob

    Quote Originally Posted by pdf64 View Post
    What test equipment have you got?
    Are you aware of safe working practice, eg Safety Tips For Working On Tube Amplifiers
    Is R56 the V8 reverb driver cathode resistor ok?
    Hi i only have a digital multi meter ,as i said i am not a tech im actualy a mechanic ,i got this amp for 150 quid,with two new celestion speakers instaled,it was very beat up but it works except the reverb ,someone has taken the tank out and just instaled in out jack plugs on the back of the cab ,why i dont know ,so i want it put back to original spec .If i touch the return wire tip it makes a noise like an unplugged guitar sounds ,so i presume this is ok ,i read to simply test the feed just hook a speaker up to it and a signal should be heard when a guitar is played ,there is nothing no hiss or anything ,because it was easy to install and not expensive i fitted a new trans driver but no luck.The amp will need servicing anyhow just thourght i would have a go to see if i could fix it .Do you repair amps ?i also live in staffordshire sunny stoke on trent .cheers

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    Quote Originally Posted by sid View Post
    ...someone has taken the tank out and just instaled in out jack plugs on the back of the cab ,why i dont know ,so i want it put back to original spec .
    Putting it back to original is a good thing. When the person that removed the reverb modified the amp, he may have removed some parts in the amp that could cause your problem.

    If you have a camera, post a photograph of the reverb area of the pc board and perhaps we can see something that has been altered.

  10. #10
    g1
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    How about that switch Pedro asked about in post #5?
    That is what routes the signal to the driver tube.
    Certified Dotard

  11. #11
    sid
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    ok i will get a photo tomorow ,there are two wires that have been cut and cannot see where they went ,one goes from reverb 3 on the pcb (the centre one )the other comes from the mains transformer tag BR its a thin black wire,looking at photos on the web these two wires disapear under the front pcb where the knobs etc are ,but theres no photos of the underside .

  12. #12
    Old Timer Tom Phillips's Avatar
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    Attached is a gut shot of a stock 1990 "The Twin" which will be useful for you to see how they were originally wired. The resolution is good enough that you can zoom in to trace some of the wiring.
    1990-twin-gut-shot.jpg

    My tip is that you be VERY careful if you ever try to get to the far side of any of the PC boards. This is because the flying lead wires are not properly strain relieved and Fender used brittle 7 strand wire. The strands break easily (Birdcaging) when flexed to flip the board over and it doesn't take long before the wires break completely free.

    Very strange that someone would have moved the reverb send & recover connectors to the rear panel of the chassis.

    Cheers,
    Tom

  13. #13
    sid
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    Quote Originally Posted by Tom Phillips View Post
    Attached is a gut shot of a stock 1990 "The Twin" which will be useful for you to see how they were originally wired. The resolution is good enough that you can zoom in to trace some of the wiring.
    Click image for larger version. 

Name:	1990 The Twin Gut Shot.JPG 
Views:	2076 
Size:	617.5 KB 
ID:	33184

    My tip is that you be VERY careful if you ever try to get to the far side of any of the PC boards. This is because the flying lead wires are not properly strain relieved and Fender used brittle 7 strand wire. The strands break easily (Birdcaging) when flexed to flip the board over and it doesn't take long before the wires break completely free.

    Very strange that someone would have moved the reverb send & recover connectors to the rear panel of the chassis.

    Cheers,
    Tom
    Hey Tom cheers for the photo ,i know all about those crappy fly leads every time i have the pannel away a lead breaks,would have expected better from fender.any how i now have the pannel away ive noticed that the wire that has been cut must come from channel one on the pcb (reverb control end) as it is marked on the pcb with nothing to it ,it then goes to ch 1 on centre pcb ,another wire comes from the same ch 1centre pcb and goes to ch 1 on the other end of the front pcb ,the white wire goes to channel 2 centre pcb to front pcb.the mystery black wire from the PT marked BR SEEMS TO GO TO AN EARTH ON THE FRONT PCB.Bloody soldering iron has just packed up so ill get a new one tomorow and give it a go ill let you know how it goes cheers

  14. #14
    Old Timer Tom Phillips's Avatar
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    Fly lead strain relief

    Regarding the crappy fly leads in "The Twin." It is interesting to note that the earlier versions of the amp had strain relief holes in both the front panel and the main PCBs which the flying leads could be looped through to provide strain relief. However, in the examples I have seen, Fender did not loop the wire through those holes and the earlier amps had the same birdcaging wire issue. The assembly procedure fix should have been to route the wires through the strain relief holes but Fender revised the PCBs and the holes were eliminated on the new rev.

  15. #15
    Old Timer olddawg's Avatar
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    I haven't seen one of these evil twins in a while. Do the have an fx loop? If not, it may have been half ass modded for an fx loop. Try taking that send on the back as it exists and running it into another amp. If there is a signal there to amplify, then stick a pedal or rack effect between the existing in and out as is. If it works, you might be better of just putting a cheap stomp box reverb (or multiple effects whatever) there and be done with it.

  16. #16
    Senior Member Pedro Vecino's Avatar
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    Last edited by Pedro Vecino; 03-12-2015 at 12:29 PM. Reason: img to url

  17. #17
    sid
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    twin

    thanks a million for the pics ,i can now see where its all going wrong ,thats a nice clean amp,wish mine was like that .

  18. #18
    sid
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    Well good news today thanks to you guys. I have found where the cut wires go soldered them in and I now

  19. #19
    g1
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    The suspense is killing me.
    now...?????????????????
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  20. #20
    Supporting Member The Dude's Avatar
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    Maybe he got electrocuted in mid sentence?
    nsubulysses likes this.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  21. #21
    sid
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    I have a signal to the temp speaker and a signal from the out put side looking good
    sgelectric, g1 and eschertron like this.

  22. #22
    sid
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    Top tip of the day folks ,when fitting a REVERB tank remember to remove the foam packing from the springs as it dont work too good with it on !! Anyways the good news is the red knob reverb is now working ,yes it took me a bit of time but i did it ,big thinks to all for the advice and coments cheers ,,

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    Quote Originally Posted by Tom Phillips View Post
    Attached is a gut shot of a stock 1990 "The Twin" which will be useful for you to see how they were originally wired. The resolution is good enough that you can zoom in to trace some of the wiring.
    Click image for larger version. 

Name:	1990 The Twin Gut Shot.JPG 
Views:	2076 
Size:	617.5 KB 
ID:	33184

    My tip is that you be VERY careful if you ever try to get to the far side of any of the PC boards. This is because the flying lead wires are not properly strain relieved and Fender used brittle 7 strand wire. The strands break easily (Birdcaging) when flexed to flip the board over and it doesn't take long before the wires break completely free.

    Very strange that someone would have moved the reverb send & recover connectors to the rear panel of the chassis.

    Cheers,
    Tom
    Hi Tom,

    I know this thread is a couple of years old. I thought those fly wires used on the Fender Red Knob Twin that travel from the 12ax7 preamp tubes and 6L6 power tubes to the pcb were 22 gauge core wire 300v rating. I noticed a few of them had part of the plastic shielding melted by PO. I will like to keep it as stock as posible and in the event i dont find the brittle 7 strand wire if the one i have is safe to use.

  24. #24
    Old Timer Tom Phillips's Avatar
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    Quote Originally Posted by jalexquijano View Post
    Hi Tom,

    I know this thread is a couple of years old. I thought those fly wires used on the Fender Red Knob Twin that travel from the 12ax7 preamp tubes and 6L6 power tubes to the pcb were 22 gauge core wire 300v rating. I noticed a few of them had part of the plastic shielding melted by PO. I will like to keep it as stock as posible and in the event i dont find the brittle 7 strand wire if the one i have is safe to use.
    I'm not totally sure what you are thinking about but...When I get one of these amps that have badly damaged flying wires from past service and the customer wants to keep the amp and make sure it is reliable and serviceable, I replace the flying wires with good quality 600V, 22 AWG, 19 strand wire. If the amp is one of the older models that has the PCB with the strain relief holes then I route the new wires through those holes thus correcting Fender's original assembly screw up. My feeling is that there is no logical reason to seek out 7 strand hookup wire to keep the amp "stock." The wire replacement may seem like a lot of work but, when compared to one or more wires braking off every time the PCB needs the back side accessed, it was well worth it to me and my customer to just replace them all.

    Cheers,
    Tom

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    Quote Originally Posted by Tom Phillips View Post
    I'm not totally sure what you are thinking about but...When I get one of these amps that have badly damaged flying wires from past service and the customer wants to keep the amp and make sure it is reliable and serviceable, I replace the flying wires with good quality 600V, 22 AWG, 19 strand wire. If the amp is one of the older models that has the PCB with the strain relief holes then I route the new wires through those holes thus correcting Fender's original assembly screw up. My feeling is that there is no logical reason to seek out 7 strand hookup wire to keep the amp "stock." The wire replacement may seem like a lot of work but, when compared to one or more wires braking off every time the PCB needs the back side accessed, it was well worth it to me and my customer to just replace them all.

    Cheers,
    Tom
    In conclusión the most closest to stock fly wire from the PCB to tube sockets on the Red Knob Twin is 22AWG 600V rated Stranded wire???

    https://www.amazon.com/BLACK-22AWG-S.../dp/B007VF7KQO

  26. #26
    Old Timer Tom Phillips's Avatar
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    Quote Originally Posted by jalexquijano View Post
    In conclusión the most closest to stock fly wire from the PCB to tube sockets on the Red Knob Twin is 22AWG 600V rated Stranded wire??? https://www.amazon.com/BLACK-22AWG-Stranded-Teflon%C2%AE-Insulated/dp/B007VF7KQO
    I am dis-trustful of that seller.
    The seller's bullet points say:

    • Stranded, Teflon Insulated 600 Volt Hook-Up Wire
    • Single Conductor Stranded, Silver Plated Copper Wire

    Reads like conflicting information to me and the price is no great deal.
    There is no reason to seek out "...closest to stock fly wire..."
    Please carefully re-read my posts #12, #14 & #24. The main points I made are to utilize the strain relief holes that Fender did not route the wire through AND to upgrade from 7 strand to 19 strand wire. This is for mechanical reasons not tone reasons. But...Fender eliminated those holes in the later versions of the amp. If your amp is one of those later models then you won't be able to take advantage of the existing strain relief holes. There are always other creative options but I have not needed to go there yet. The obvious option is to just be careful when flipping the PCB to work on the under side.
    #22AWG wire would be fine but not a firm requirement. But, for instance, if I only had #20AWG on hand then I would use it without worry. Again - The wire gauge will not affect the sound.

    More about wire.
    If I needed to buy wire I'd go with a main stream source such as Mouser in favor of an amazon seller.
    If I was looking for some vintage wire, special deal or surplus wire then I'd be browsing at someplace such as Apex Jr.Home Page .

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    300v or 600v?

  28. #28
    Old Timer J M Fahey's Avatar
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    600V
    Juan Manuel Fahey

  29. #29
    Old Timer Tom Phillips's Avatar
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    Going in circles here.
    Read the information already posted in the discussion.

  30. #30
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    I only have 22 awg 300volts radio shack brand.

  31. #31
    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by jalexquijano View Post
    I only have 22 awg 300volts radio shack brand.
    So?
    Juan Manuel Fahey

  32. #32
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    The forums states a minimum of 600 volts

  33. #33
    Old Timer J M Fahey's Avatar
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    Premise A:
    Quote Originally Posted by jalexquijano View Post
    I only have 22 awg 300volts radio shack brand.
    Premise B:
    The forums states a minimum of 600 volts
    Conclusion:IF A: xxxxxxxxxxx AND B: yyyyyyyyyyy THEN: zzzzzzzzzzzzzzzzzzzzzzzzzzzzz

    Turn your brain on and fill in the blanks yourself.

    ----------------------------------------------------------------------------------------------

    Are you trying to solve a real problem or just trying us to post different opinions and have us fight each other while you munch on popcorn?

    You won´t draw us into that in this Forum.

    By the way, you also failed when you tried same in other, way more argumentative Forums such as the Marshall or My Les Paul ones, what makes you think you will succeed here?

    Advantages on Installing CTS pots and Bumblebee capacitors on a Les Paul Standard
    #1 User is offline jalexquijano
    Posted 13 May 2009 - 10:50 AM
    I own a Gibson Les Paul standard 50s neck with Burstbucker pro 1 and 2 pickups and which holds the stock gibson pots and the two 0.22 stock ceramic capacitors. Is it possible to obtain a more Led Zeppelin 1972-1973 (TSRTS) tone installing CTS pots and bumblebee capacitors? Is it recommendable or should i like the guitar stock?

    I have seen many upgrades in Mojo musical and RS, however im afraid that replacing the stock parts may worsen the gibson les paul sound.


    Quote jalexquijano
    Is it recommendable or should i like the guitar stock?
    .........
    Asking this is like asking other people to think for you.
    Do you like how the guitar sounds? Yes or no?
    Do you want to change how your guitar sounds? Yes or no?
    If you want to change how the guitar sounds than yes, change the pots and caps.
    You will get a different sound if you do this. If you don't like how the guitar sounds you can always go back to the stock electronics.
    Sadly this requires thinking and deciding on something by yourself.
    Scary, huh?

    Gibson Burstbucker Pro 1(neck) and Burstbucker Pro 2 (Bridge)
    #1 User is offline jalexquijano
    Posted 20 May 2009 - 06:08 AM
    Has anyone tried the Gibson Bustbucker Pro 1 and 2? I like the sound however I feel The bridge pickup is too bright or harsh? I believe my guitar came with stock Gibson 300k and 500k pots. Should I change them to all 500k Cts pots?
    ........................
    FennRx
    check his other posts...this is at least the 3rd time he's asked the exact same question
    ....................
    Tim Plains
    Posted 20 May 2009 - 09:36 AM
    jalexquijano, how many threads are you going to have about changing your pots and caps?
    Fukcing change them already.
    Juan Manuel Fahey

  34. #34
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    Well ill use the 22 awg 300v radio shack solid core hook up wire. Its difficult to get 600v

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