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Thread: 6505 problem

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    Top Of The World WDFA5150's Avatar
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    Default 6505 problem

    I bought a 6505 head this time last year- it was retubed just before it arrived. After a while it started to crackle a bit after about 10 mins of playing then the bass would drop out leaving a trebly tone- no drop in volume- just no bass. I did all the usual things- contact cleaner on all the tube pins, in/out jack sockets etc and swapped preamp tubes incase one was bad. The problem would go away if I put it on standby and waited for the light to fade out then turn it on again.
    After all the messing around above it came good again for about 2 months then it started playing up again worse than ever.
    The only thing I didnt do was swap out the power tubes in case one was bad.
    Is it worth doing or does it sound like a different problem?
    I've heard that plate resistors (????) are an issue on this model- could that be the problem?
    Any help would be greatly appreciated-
    Sean
    I used to be 'sean112' but lost all my details!

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    Quote Originally Posted by WDFA5150 View Post
    I bought a 6505 head this time last year- it was retubed just before it arrived. After a while it started to crackle a bit after about 10 mins of playing then the bass would drop out leaving a trebly tone- no drop in volume- just no bass. I did all the usual things- contact cleaner on all the tube pins, in/out jack sockets etc and swapped preamp tubes incase one was bad. The problem would go away if I put it on standby and waited for the light to fade out then turn it on again.
    After all the messing around above it came good again for about 2 months then it started playing up again worse than ever.
    The only thing I didnt do was swap out the power tubes in case one was bad.
    Is it worth doing or does it sound like a different problem?
    I've heard that plate resistors (????) are an issue on this model- could that be the problem?
    Any help would be greatly appreciated-
    Sean
    I had a similar problem with a 5150 combo. Changed the preamp tubes and fuses then it did the same thing with the bass...

    wish I had advice for you better than what im gonna say..took it to the only amp guy in town and paid 300 to getit fixed just75 less than I bought it for
    Earn this...

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    Yeah...I had this happen a few times, and I thought it would be a tube too.
    Here's what I was told to do, and it usually works.
    Check the effects loop footswitch pedal input, as well as the input side of the loop. I know..sounds funny, but my old 5150 had a similar problem. click the footswitch a number of times with the amp powed up, but your volumes down.
    with the effects loop bypassed, bring your volumes up, and you should be good to go. If not, try plugging and unplugging your effects input numerous times, again with the amp powered up, but volumes down. It may not fix the problem, but it's the first simple thing I'd check. A tech told me about the problem years ago when I couldn't figure out what was wrong with mine.
    What I found (and others too) is the internal relay/switch gets sticky, or has dust that finds it's way into it. It's a small design flaw they've never seemed to eliminate.
    doing this seems to free it up.Good luck, and keep us posted!
    JJ

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    Top Of The World WDFA5150's Avatar
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    Thanks guys- as soon as I get a chance I'll give it a go.
    I wonder if Ed used the loop when he was using these heads? I've heard they were a pain from day one!
    I used to be 'sean112' but lost all my details!

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    Not sure when he'd have used it if at all...I know not live.
    The effects loops are ok. They just have that weird issue from time to time. It seems once it pops, it's good for a long time. It happened to me 3 or 4 times in total now that I think about it. Only that many times since 91 is really not a big deal.
    The plate resistors can be a problem from time to time, but most of those issues were fixed within the first year of production. Both me and my buddy had that issue early on. Mine went within two months, and his failed earlier than mine. Both got fixed free of charge.
    I'm pretty confident yours is the effects loop issue. One other thing you can try while you're at it is click the ohm selector through the ranges several times with the amp on standby. It's the same deal. dust can get in there, and you will lose your bass, and it'll go all trebly.
    I hope it's just something simple like this. Thought I'd give you these things to try before parting with your amp to get fixed and spending money on a diagnostic/repair for just a dusty contact.
    Other than that, they are real hefty amps durability wise.

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    Top Of The World WDFA5150's Avatar
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    Quote Originally Posted by we die young View Post
    Not sure when he'd have used it if at all...I know not live.
    The effects loops are ok. They just have that weird issue from time to time. It seems once it pops, it's good for a long time. It happened to me 3 or 4 times in total now that I think about it. Only that many times since 91 is really not a big deal.
    The plate resistors can be a problem from time to time, but most of those issues were fixed within the first year of production. Both me and my buddy had that issue early on. Mine went within two months, and his failed earlier than mine. Both got fixed free of charge.
    I'm pretty confident yours is the effects loop issue. One other thing you can try while you're at it is click the ohm selector through the ranges several times with the amp on standby. It's the same deal. dust can get in there, and you will lose your bass, and it'll go all trebly.
    I hope it's just something simple like this. Thought I'd give you these things to try before parting with your amp to get fixed and spending money on a diagnostic/repair for just a dusty contact.
    Other than that, they are real hefty amps durability wise.
    Thanks mate- VERY much appreciated!
    I used to be 'sean112' but lost all my details!

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    I doubt Ed ever used it. Most amp builders/designers I know DESPISE effects loops. They don't usually do much of anything positive for tone or gain, and are simply a buffer. Also, they are generally mounted far away from the natural signal path of the rest of the preamp, introducing many many more inches of cabling and 2 jacks that get easily corroded, provide an entry for extra noise inside the chassis, etc. Believe me, in a high gain amp, an extra inch of internal cable run can mean a LOT more noise/hum/etc.

    And that's WITHOUT even using some crappy low signal level in the loop!

    IMHO, the best kind of effects loops are ones that don't exist. The second best kind are ones that can be completely hard-bypassed from exactly where they are in the preamp signal chain by a relay, but then of course, you introduce more potential for issues with that relay....

    I get the practicality of the FX loop on amps, especially for playing live, but still... it's an annoying "feature" that anyone who doesn't absolutely need it has to now deal with.

    I believe I heard a story about the Soldano SLO100 that Mike never wanted to include an effects loop for tonal and performance reasons, but quite a few guitar players absolutely demanded it, so it was deemed necessary to "sell the product" or something like that. I know they made a handful of SLO100's with a "no fx-loop" option and only 4 preamp tubes.


    Another interesting note;

    I built a high gain amp that was sort-of a modded clone of a known design, and I originally included the FX loop like the original had. I absolutely never used it, and so I eliminated it completely, along with it's 12AX7 buffer circuit. The amp sounded tighter and more aggressive without those extra 2 tube halves in the circuit. In fact, it sounded so much more aggressive that it wasn't a good thing... it took a super tight amp and made it sound almost brittle and with no "give" at all. I ended up putting the FX loop circuit back into the amp, but instead of running it out to the FX loop jacks, I chopped the wires off and hard wired it in bypass mode permanently, and then out to the power amp section of the amp. So the buffer gives me the extra "give", but it doesn't suffer from the issues of long internal wire runs or faulty jacks. I've considered doing this exact mod to my 5150....
    Last edited by mrjstudios; 05.09.14 at 05:51 PM.

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    Quote Originally Posted by mrjstudios View Post
    I doubt Ed ever used it. Most amp builders/designers I know DESPISE effects loops. They don't usually do much of anything positive for tone or gain, and are simply a buffer. Also, they are generally mounted far away from the natural signal path of the rest of the preamp, introducing many many more inches of cabling and 2 jacks that get easily corroded, provide an entry for extra noise inside the chassis, etc. Believe me, in a high gain amp, an extra inch of internal cable run can mean a LOT more noise/hum/etc.

    And that's WITHOUT even using some crappy low signal level in the loop!

    IMHO, the best kind of effects loops are ones that don't exist. The second best kind are ones that can be completely hard-bypassed from exactly where they are in the preamp signal chain by a relay, but then of course, you introduce more potential for issues with that relay....

    I get the practicality of the FX loop on amps, especially for playing live, but still... it's an annoying "feature" that anyone who doesn't absolutely need it has to now deal with.

    I believe I heard a story about the Soldano SLO100 that Mike never wanted to include an effects loop for tonal and performance reasons, but quite a few guitar players absolutely demanded it, so it was deemed necessary to "sell the product" or something like that. I know they made a handful of SLO100's with a "no fx-loop" option and only 4 preamp tubes.


    Another interesting note;

    I built a high gain amp that was sort-of a modded clone of a known design, and I originally included the FX loop like the original had. I absolutely never used it, and so I eliminated it completely, along with it's 12AX7 buffer circuit. The amp sounded tighter and more aggressive without those extra 2 tube halves in the circuit. In fact, it sounded so much more aggressive that it wasn't a good thing... it took a super tight amp and made it sound almost brittle and with no "give" at all. I ended up putting the FX loop circuit back into the amp, but instead of running it out to the FX loop jacks, I chopped the wires off and hard wired it in bypass mode permanently, and then out to the power amp section of the amp. So the buffer gives me the extra "give", but it doesn't suffer from the issues of long internal wire runs or faulty jacks. I've considered doing this exact mod to my 5150....
    I'm of the same mind. I don't use effects loops as a rule on heads, or performing live, ( I mic my amp, and process that signal), but on a combo, or something for banging around the house, they can be handy to add a delay, reverb, chorus....a simple way to give a little polish to your post gain stage sound rather than just dry. I think I read somewhere now that I think about it, where ed did use the effects loop intentionally for a buffer occasionally around the RHRN era. I remember word of 50' of cable. Not sure why specifically, but he said something about softening the signal ...I seem to recall something to do with a specific factor in his live rig....

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    I use the loop in the 6505 for a sonic maximiser and a noise gate but not keen at all on running fx in it.
    I had a custom built 'super lead' at one point that I drove the front with using an ADA MP1 that I modded to the 'mod 3' sound- supose to emulate a 5150 (good for the rythme channel but not enough drive to sound like the lead).
    I was going to have a loop installed on it to run the preamp into the return but never got around to it. Since the 6505 has been playing up I've started using the 2120 as a preamp instead of just for detune and delay. I get the impression that if I ran it through a tube power amp it would sound massive. The preamp sounds on it are very impressive. The only gripe I'd have is that the noise gate on it is too much- even adjusted it chops the sound harshly.
    It's actually been cool fiddling with it- I only got it for detune but there's all sorts of cool sounds in it. This must have been the inspiration for the axe fx I think?
    I used to be 'sean112' but lost all my details!

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    Default 6505 problem

    I run my Maximizer, Delay, and MXR Micro Amp (to boost solos) through my 5150s effects loop. It's good for that IMO. I've run them up front with my other effects and they don't sound as good.
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    Hey WDFA5150...Just wondering if you got around to checking your FX loop switch input/jacks, and the ohm selector? I'm curious and hopeful to see if helps and gets the amp roaring again.
    JJ

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    Quote Originally Posted by we die young View Post
    Hey WDFA5150...Just wondering if you got around to checking your FX loop switch input/jacks, and the ohm selector? I'm curious and hopeful to see if helps and gets the amp roaring again.
    JJ
    Hey- just tried it.
    There is a definate improvment but I cant work out where to focus.
    I did what you suggested and got a small result so I gave all the jacks and switches a workout and it got better. Then I gave all the knobs a turn.
    After all that I've got the bass back but still a staticy/ fuzzy sound but its not as loud as before (the static).
    So all up- definately better but cant quiet nail down which knob/ jack/ switch made the difference.
    I'll give the whole thing another try tommorow and see if the problem dissapears- might pull the tubes and contact clean the pins and sockets too.
    Thanks mate- it's working better thanks to your advise and suggests I'm looking in the right area- a real good cleanup!
    I used to be 'sean112' but lost all my details!

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    Quote Originally Posted by WDFA5150 View Post
    Hey- just tried it.
    There is a definate improvment but I cant work out where to focus.
    I did what you suggested and got a small result so I gave all the jacks and switches a workout and it got better. Then I gave all the knobs a turn.
    After all that I've got the bass back but still a staticy/ fuzzy sound but its not as loud as before (the static).
    So all up- definately better but cant quiet nail down which knob/ jack/ switch made the difference.
    I'll give the whole thing another try tommorow and see if the problem dissapears- might pull the tubes and contact clean the pins and sockets too.
    Thanks mate- it's working better thanks to your advise and suggests I'm looking in the right area- a real good cleanup!
    Cool. I'd still focus on the FX loop switch a bit more. The thing is when you switch the amp on and off, you always hear the internal relays/switches clicking open or closed. sometimes with dust, or carbon tracking, they can hang, especially if you don't use the FX loop often, or at least click it over from time to time.
    Plug in and unplug the switch jack numerous times while clicking the effects on/off button on your footswitch, again, with your volumes down. and also focus on the ohm selector switch. slide that back and forth a bit vigorously.
    My Marshall SL with the old style prong connector was worn out, and the contacts were sketchy, so sometimes the bass would drop out completely, or I'd get wicked static. In that case, I fabbed up a new connector.
    If you can, I'd also recommend a can of that liquid air stuff. You know, for blowing dust off electronics that you can get at an office supply store. I've used that on my 5150 too, and it made all the difference. doesn't hurt to shoot some into your standby switch as well.
    I never had trouble with the control knobs. For as light as they feel (very low friction) , they are surprisingly resistant to dust getting in them. I don't recall hearing static on any of them in all the time I had the amp. Just seems to be the relays/switches that are the weak link. It can't hurt of course to clean your tube sockets too like you said.
    Just be careful in the preamp tube compartment. That board always freaked me out how much it flexes pulling and installing tubes. Some Engl amps felt that way too. I know they've stood up well, but I just don't like the way it feels, and I really don't like those little squeaks and clicks I used to hear when changing tubes. a little cringeworthy! I was always a little nervous that the board would crack, or at least break the circuit somewhere, although it never did happen.
    Last edited by we die young; 05.15.14 at 06:18 AM.

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    So- I decided to run the Digitech 2120 into the fx loop return to get an idea if the prob is preamp or poweramp one.
    The 2120 sounds fat! There's a patch called 'Death metal scoop' (I think) that sounds like a mk4 mesa boogie through the power amp section of the 6505. Check out 28 days 'rip it up' riff- the sound is almost identical after a/b ing it.
    There is no volume control from the amp though- it's done with the 2120- Im not sure about valve amps- if I run it like this does it put more pressure on the power valves or shorten their life?
    BTW- the crackling sound on the 6505 is preamp based- the 2120 sounds clean as through the power section.
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