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Post subject: Tube related question(s)
Posted: Mon Jun 16, 2014 4:03 pm
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Aspiring Musician
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Hey guys, I am in need of assistance :)

I only bought my first tube amp, the supersonic 60, half a year ago so I have no experience regarding different tubes and whatnot.
The other day I noticed there was quite a bit of hiss on the burn channel (it seemed to be a bit more noticeable than when I first got the amp, but granted, I did start running it quite hot with the gain) and a sort of a "twang" sound coming from the amp when playing open low E string on the clean channel, Bassman mode. It didn't seem to do it when I fretted the string or played any other string, but I don't think it's guitar-related. Didn't sound like it.

Anyway, I figured I could at least test whether the tubes are loose and check which tubes are in it.

I found out that I have JJ ECC 81 tubes instead of 12at7 tubes (in every position that previously had the 12at7's) and JJ ECC 83S tubes instead of 12ax7wc tubes (again, every position) in the amp.

So my questions are whether you think the hiss and the twang could be tube related and whether they are the "correct" tubes to have in the amp? The previous owner said he put better tubes in it, are they better? What are their pros? What are their cons? Should I look for alternatives when I have to retube the amp? If so, which ones would you suggest?

Thanks :)

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Post subject: Re: Tube related question(s)
Posted: Mon Jun 16, 2014 4:40 pm
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Aspiring Musician
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Wish I could help,but the Supersonic 60 is an amp I am not familiar with,except by name/model only. Arjay,...can you help here? I'd like to help,but I sure don't want to lead this guy down the wrong path. Let me go to the amp page and check the specs,...that might help us out here as to what tubes should really be in there and what the amp actually calls for.

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Post subject: Re: Tube related question(s)
Posted: Mon Jun 16, 2014 4:55 pm
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Aspiring Musician
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Okay,...just came from the amp page and looked up the specs for Supersonic 60. The tube complement should be as follows. In your preamp section you should have six 12AX7 tubes and two 12AT7 tubes. Power tubes should be 6L6,...two of them,...matched pair of course,and bias adjusted correctly,...seek help of an amp technician if you are not sure how to do that! Without looking at a tube chart or schematic diagram,I can't tell you what positions the preamp tubes should be in. 6L6 tubes are obvious as the have the larger base. Is your amp pretty new or is it an older model? Retroverbial(Arjay) and 63supro are your amp gurus here,along with Shimmilou,and a few others. Hopefully they will come on and fill in the gaps. ECC83 are your European equivalent of the 12AX7 I believe,..I'll have to look that up. I'm learning about tube amps,too,...so you are not alone! Not sure of the 12AT7's European equivalent,...help us out here,guys!

73
Dewey
KC9SYJ

"73" is amateur radio operator jargon for "Best Regards"

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If it aint' broke,...don't fix it! I like to keep my amps and guitars factory original,...no mods necessary,...don't want them,...don't need them!

My gear as of now;
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Hot Rod Deluxe III amp
Champion 20 amp
'59 Bassman LTD Reissue


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Post subject: Re: Tube related question(s)
Posted: Mon Jun 16, 2014 5:35 pm
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Aspiring Musician
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Thanks mate :) I don't know how to read the schematics myself, but I found someone dumbed them down enough into a layout diagram that the likes of me can understand :P
It's here:
Image

I checked the tubes in my amp based on this layout and they seem to be in correct positions, they're just different ones.
The 6L6s in the amp are Sovtek's (and from what I read, Sovtek tubes are supposedly fine tubes) and yeah, they're the only ones I am absolutely sure are in a correct position, even if the layout above is a false one :lol: A question - when biasing the tubes, do you have to bias only the pre-amp tubes (so the 6L6 pair), or do the other tubes also have to be biased? Just so I know in case of a failure of a tube on a gig or somewhere, if I could swap out any tube without biasing (provided I had the same type of tube, of course).

Unfortunately I can't check the amp's model as I don't have it with me, I have it at home. Due to some weird reason me and Fender TSL haven't been able to figure out, I can't access Fender site or forums from home :( Anyway, I am guessing it's around '08-'10 model.

Again, thanks for the help :D
Best regards :) (and thanks for letting me know what that 73 means, at first I had no idea and at least now I know the meaning and thus my reaction if I ever hear it IRL :lol: )

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Post subject: Re: Tube related question(s)
Posted: Mon Jun 16, 2014 6:11 pm
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The ECC81 designation is the European nomenclature for a 12AT7, just as the ECC83 translates to a 12AX7. Thus, your amp's tube array is correct insofar as having the right bottles in the right sockets.

Arjay

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Post subject: Re: Tube related question(s)
Posted: Mon Jun 16, 2014 6:18 pm
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Aspiring Musician
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Retroverbial wrote:
The ECC81 designation is the European nomenclature for a 12AT7, just as the ECC83 translates to a 12AX7. Thus, your amp's tube array is correct insofar as having the right bottles in the right sockets.

Arjay


Thanks for helping us out there,Arjay. In response to the biasing question,...only the power tubes are biased,...Arjay will probably correct me on this,...but the preamp tubes are self biasing(if there is such a thing),therefore you need not worry about biasing those,...only the power tubes! Again,if you are not sure how to do that,...by all means,have a good reputable amp tech take care of it,especially if you are new to tube amps! There's a LOT of dangerous voltages lurking around in that amp,...even if it has been turned off,unplugged,and has sat a while. Filter capacitors act like storage batteries and contain deadly voltages that can injure you,...or worse,kill you! Turn off and unplug that amp BEFORE pulling tubes,...and let those tubes cool down before touching them.

73
Dewey
KC9SYJ

P.S. Arjay,...not sure if this is correct or not,...but don't you have to discharge those filter caps before changing tubes as a safety precaution? I have never done it before and that is why I am asking. I don't want to go poking around in an area of ANY amp unless I know what the heck I am doing.

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If it aint' broke,...don't fix it! I like to keep my amps and guitars factory original,...no mods necessary,...don't want them,...don't need them!

My gear as of now;
Standard Strat
Hot Rod Deluxe III amp
Champion 20 amp
'59 Bassman LTD Reissue


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Post subject: Re: Tube related question(s)
Posted: Tue Jun 17, 2014 4:59 am
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Aspiring Musician
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Thanks Arjay :) So it all boils down to just having a different manufacturer, correct?

Thank Dewey, yes I meant the power tubes, 6L6s, don't know why I wrote pre-amp. Good to know I can change the pre-amp ones without any biasing, I am sure it's childishly easy for those who know how to do it and are a bit more handy when it comes to dealing with electricity and electrical components, but sadly I am not one of these people lol.
When I took the amp to a tech he, fortunately, warned me and told me the amp should be unplugged for a while before trying to open it up or anything like that. He didn't say how long I'd have to wait before changing the tubes, though, I didn't know that was as dangerous! Logic told me I should leave it unplugged for a bit, I didn't know I should discharge it though. I heard an efficient way of discharging the amp (I don't know if that tech told me this, or if I read it somewhere on these forums) is by trying to turn it on when you don't have it plugged in the electricity, that way the capacitors are supposed to transmit the electrons that were stored there after unplugging it, or something like that. Is that correct or is it still dangerous to swap the pre-amp tubes without some sort of discharger?

Best regards

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Post subject: Re: Tube related question(s)
Posted: Tue Jun 17, 2014 7:43 am
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You only need to discharge the caps if you are going to open up the amp to work on it. If you are only changing tubes, no need to discharge the caps.

What you might have heard about easily discharging the caps, is after playing, turn the amp off without first using the standby switch. This will allow the caps to discharge through the hot tubes.

Still, avoid touching the tubes' pins whenever swapping tubes, and be careful with aligning the pins' gap to the tube socket to insure no bent pins.

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Post subject: Re: Tube related question(s)
Posted: Tue Jun 17, 2014 7:55 am
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Aspiring Musician
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What you say makes sense,Shimmilou,and thank you for chiming in to help us out. I wasn't sure if you had to discharge the caps or not if only changing tubes. Well,...now we know.
I concur about avoiding touching the tube pins as those can bend,...or worse yet,if I may add,...break off! In the words of legendary bass fisherman Bill Dance "That would be a fine howdy do!" if that were to happen.

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If it aint' broke,...don't fix it! I like to keep my amps and guitars factory original,...no mods necessary,...don't want them,...don't need them!

My gear as of now;
Standard Strat
Hot Rod Deluxe III amp
Champion 20 amp
'59 Bassman LTD Reissue


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Post subject: Re: Tube related question(s)
Posted: Tue Jun 17, 2014 8:29 am
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KC9SYJ wrote:
Thanks for helping us out there,Arjay. In response to the biasing question,...only the power tubes are biased...Arjay will probably correct me on this...but the preamp tubes are self biasing(if there is such a thing),therefore you need not worry about biasing those,...only the power tubes!

Again,if you are not sure how to do that,...by all means,have a good reputable amp tech take care of it,especially if you are new to tube amps! There's a LOT of dangerous voltages lurking around in that amp,...even if it has been turned off,unplugged,and has sat a while. Filter capacitors act like storage batteries and contain deadly voltages that can injure you,...or worse,kill you! Turn off and unplug that amp BEFORE pulling tubes,...and let those tubes cool down before touching them.

73
Dewey
KC9SYJ




Dewey, tubes in 99% of guitar amps have an idle bias. Output tubes, like 6L6GC or 6V6GT. And smaller 9-pin pre-amp, gain stage, EFX, phase inverter stage tubes (12AX7, 12AY7 or 12AT7 --- AKA signal tubes).

The two main topologies used are FIXED and CATHODE biased. Fender's Class AB1 amps have FIXED biased output tubes. And CATHODE biased signal tubes.

FIXED bias puts a set, or fixed, negative voltage onto the signal grid. This voltage is often adjustable via a bias pot.

CATHODE bias puts an idle bias onto the signal grid via a cathode-to-ground resistor. Many times a bypass capacitor parallels this C2G resistor. In this style of setting, an idle bias is not easily adjustable. But, this is not a worry. Since tube current draw and the C2G resistor can work in a range of plate voltages and attached component values. Kind of a self-leveling effect to an extent.

This is why most CATHODE biased tubes do not need bias adjustment. And replacing the OEM tube with a wide range of similar pinout and spec'ed tubes is fine. Like putting a 12AY7 into a position which normally uses a 12AX7.

The only caveat is if the socket's parameters are far from the nominal operating mode of the tube. Such as the reverb driver tube, in many Fender amps. A healthy amp (reverb tranny and tank) can demand a lot of current swing to work. Between 10-20mA. The 12AX7 nominal operating conditions should not exceed 3mA. Substituting a 12AX7 into the reverb driver position = short & most possibly noisy 12AX7 life.

HTH! :D


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Post subject: Re: Tube related question(s)
Posted: Tue Jun 17, 2014 1:21 pm
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Thanks shimmilou, so the pop that happens if you turn the amp that way is basically just the byproduct of capacitors being discharged and not anything harmful to the amp itself? :)

About the pins - I was being very careful, needless to say I'd be pissed if I broke one accidentally :lol:

Thanks BMW, so if I understand correctly, the power tubes are 'fixed bias' and thus need to be biased, whereas the pre-amp tubes are 'cathode biased' and thus don't need to be biased and can easily be swapped? What would happen if a power tube wasn't biased? Would it just affect the tone and the tube's life-length, or would it in any way harm the amp?
I had a problem with a noisy reverb, but one of the wires in the spring broke, so the tubes supposedly didn't contribute to the noise (the amp tech fixed it for me). The amp is still a bit noisy, though, on the burn channel (the noise is, as usual, only afflicted by the gain and volume knobs). Would you recommend changing a tube? If yes, the tube from which position and what kind of tube should I get?

I really appreciate all the help :)

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Post subject: Re: Tube related question(s)
Posted: Tue Jun 17, 2014 4:05 pm
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Neimenljivi wrote:
The amp is still a bit noisy, though, on the burn channel (the noise is, as usual, only afflicted by the gain and volume knobs). Would you recommend changing a tube? If yes, the tube from which position and what kind of tube should I get?


Signal processing through the burn channel is notoriously noisy on these amps. I doubt that a tube swap will accomplish much in that regard -- only put some $$$ into the pocket of some unscrupulous tube vendor who will tell you different.

Arjay

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Post subject: Re: Tube related question(s)
Posted: Tue Jun 17, 2014 7:38 pm
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" Thanks BMW, so if I understand correctly, the power tubes are 'fixed bias' and thus need to be biased, whereas the pre-amp tubes are 'cathode biased' and thus don't need to be biased and can easily be swapped? What would happen if a power tube wasn't biased? Would it just affect the tone and the tube's life-length, or would it in any way harm the amp? "

Yes, FIXED bias tubes needs adjusting whenever the tubes are exchanged. Now, output tubes can be CATHODE biased. Like the single-ended Champ and Vibro-Champ. And many tweed era amps. These CATHODE biased amps are not as sensitive to the specific tube's current draw.

Idle bias does effect final tone and amp response.


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Post subject: Re: Tube related question(s)
Posted: Wed Jun 18, 2014 4:46 am
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Thanks Arjay, do you reckon a noise suppressor in FX loop could help?

Thanks for an explanation BMW, I get it now :D

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Post subject: Re: Tube related question(s)
Posted: Wed Jun 18, 2014 6:30 am
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OT: Neimenljivi, just a little shout-out for one of your countrymen. An AMAZING run this year. Anže is centering the face-off.

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