Feel free to ask Myles

[Danzilla]

Myles -

 

What would the general changes in tone be for swapping the preamp tube (currently a 12AX7) in a Vox AC4 to either a 12AU7 or a 12AT7? I had read somewhere that the 12AU7 would tame some treble, but an ad for a Bitmo Mods kit for this amp included a 12 AT7.

 

As always, your wisdom is appreciated.

[myles_rose]

Myles -

 

What would the general changes in tone be for swapping the preamp tube (currently a 12AX7) in a Vox AC4 to either a 12AU7 or a 12AT7? I had read somewhere that the 12AU7 would tame some treble, but an ad for a Bitmo Mods kit for this amp included a 12 AT7.

 

As always, your wisdom is appreciated.

 

Less gain, less output, less life. An AU7 is a driver, not a tone generator. An AT7 is a terrible tone generator as well. If you want to drop the gain use a real 5751 (NOS) or a 12AY7.

[davidm]

Myles,

 

It's been quiet here for a while. The two Rivera forums I used to frequent are inactive these days. Strange...

 

I hope you're doing well!

[myles_rose]

All is fine with me. I think it is summer vacation and many folks are just away.

 

[Caevan O’Shite]

Hey again, again, Myles.

 

I'd like to know, all other things being equal/remaining the same, what little differences I might expect between using an 8 ohm/65 watt speaker and a 16 ohm/65 watt speaker connected to either the 8 ohm or 4 ohm outputs of my Fuchs Lucky 7 head.

 

In this case the speakers would be vintage Celestion-inspired Scumback 'Scumnico' 12" Alnico speakers with an additional Neodymium-magnet plate on the back.

 

Thanks again, again!

[mybrotherjames]

hey myles!

 

I'm wanting to retube my Rivera M-100. It still has the original preamp tubes and a set of Groove Tubes GTEL34M with a 7 rating in it. I've had the amp about 15 years but haven't used it much in the past 10 years.

 

A little backstory on how I do use it. My brother and I write songs together and record them for fun in our home studio. He usually uses a Les Paul Standard with seymour duncan 59/jb, his ibanez prestige s-series, or his new favorite, my epiphone genesis with dimarzio's(i forget which ones, they were there when i got it.update: brother says they're virtual paf dimarzios). He plays through an Ampeg VL1002 and Tubeworks 4x12 with eminence speakers(again the model eludes me). I play an Epiphone et-290 with Kent Armstrong P-90's, a stock 68 telecaster, or my dad's 68 epiphone olympic II. I play my rivera through a crate(please don't laugh... most my friends berate me about it daily) 4x12 loaded with a pair each of celestion v1280 and gt70 speakers. Neither of us use pedals. We play stuff that is very "90's sounding" as it has been described to me.

 

So, what tubes could recommend to me? The amp hasn't been serviced in over ten years, so I'll be taking it my dad's amp tech to get everything in spec.

 

Also, I just noticed the inside 2 tubes on the rivera seem to be running hotter than the outside pair. Maybe that's cus i run it triode instead of pentode? i usually play the amp at it's lowest power setting with a 4ohm load.

[myles_rose]

mybrotherjames,

 

Let me take this one step at a time....

 

The M100 is a great amp. One of the greatest monsters on the planet, past or present.

 

Preamp tubes don't really wear out for the most part in guitar amp use. They go bad for other reasons. If you have no problems and are happy with the tone then save your money and keep the original tubes. If the output tubes are not giving you problems and are #7's they should be fine. Check the bias. If you know what it was set to originally when the GT tubes were installed you can compare the past setting with the current setting to get an idea of wear and condition.

 

The back story is not really a part of the issue as tone is subjective. If you like it then all is fine and dandy.

 

As far as the inner pair running hotter - if you are on the low power setting you only have B+ on two tubes of the quad. What you are seeing is normal. Swap the inner and outer pairs every few months to keep them wearing about the same. You may find that the tubes are no longer a matched quad if the amp has a few hours on it in this config.

 

Hope this helped. Happy playing!

 

[mybrotherjames]

Thanks Myles!

 

I thought the back story part was relevant cus i prefer a single coil darker mid tone(gain in the mid-lowmid range) and my brother prefers humbuckers and a brighter mid tone(gain mid to highmid range). he calls his tone "tight" and mine "sloppy" but when we play together it fills out soooooooo nicely. maybe that's what i should have said? lol

 

I'm naturally a drummer so guitar specifics elude me.

 

thanks again

~Jason

[Caevan O’Shite]

Hey again, again, Myles.

 

I'd like to know, all other things being equal/remaining the same, what little differences I might expect between using an 8 ohm/65 watt speaker and a 16 ohm/65 watt speaker connected to either the 8 ohm or 4 ohm outputs of my Fuchs Lucky 7 head.

 

 

 

FWIW, in this case the speakers would be vintage Celestion-inspired Scumback 'Scumnico' 12" Alnico speakers with an additional Neodymium-magnet plate on the back.

 

Thanks again, again!

[myles_rose]

Using the entire output transformer winding (16 ohms in a 4-8-16) will generally give more fidelity than using a fraction of the output stack. Some folks swear by this. Others can't tell a difference. Try it and report what you found

 

[myles_rose]

Thanks Myles!

 

I thought the back story part was relevant cus i prefer a single coil darker mid tone(gain in the mid-lowmid range) and my brother prefers humbuckers and a brighter mid tone(gain mid to highmid range). he calls his tone "tight" and mine "sloppy" but when we play together it fills out soooooooo nicely. maybe that's what i should have said? lol

 

I'm naturally a drummer so guitar specifics elude me.

 

thanks again

~Jason

 

I believe the M100 has P-Comp so single coils, humbuckers, strong or weak pickups can be compensated. If not, it really does not matter much in the end. It is personal taste and preference.

 

[Caevan O’Shite]

Using the entire output transformer winding (16 ohms in a 4-8-16) will generally give more fidelity than using a fraction of the output stack. Some folks swear by this. Others can't tell a difference. Try it and report what you found

 

OK; so- my amp has only 8 and 4 ohm output-jacks; so,

 

an 8 ohm speaker connected to the 8 ohm jack will potentially give more fidelity than using the 4 ohm jack,

 

what might I expect from a 16 ohm speaker of the same type connected to the 8 ohm jack?

 

I'm just trying to decide between 8 and 16 ohm models of the otherwise same speaker, for use with two different tube amps- one with 4 and 8 ohm outs, the other switchable between 4, 8, and 16 ohms.

 

I use both amps in a "play the amp" dynamic way, cranked, adjusting the guitar's volume-knobs and my "touch" to range from clean to mean to scream.

 

As always- THANKS!

[myles_rose]

Using the entire output transformer winding (16 ohms in a 4-8-16) will generally give more fidelity than using a fraction of the output stack. Some folks swear by this. Others can't tell a difference. Try it and report what you found

 

OK; so- my amp has only 8 and 4 ohm output-jacks; so,

 

an 8 ohm speaker connected to the 8 ohm jack will potentially give more fidelity than using the 4 ohm jack,

 

what might I expect from a 16 ohm speaker of the same type connected to the 8 ohm jack?

 

I'm just trying to decide between 8 and 16 ohm models of the otherwise same speaker, for use with two different tube amps- one with 4 and 8 ohm outs, the other switchable between 4, 8, and 16 ohms.

 

I use both amps in a "play the amp" dynamic way, cranked, adjusting the guitar's volume-knobs and my "touch" to range from clean to mean to scream.

 

As always- THANKS!

 

Best results will be obtained by using the same impedance as the speaker on the tap with the largest number. 8 ohm tap with an 8 ohm speaker if you only have 4-8 taps.

 

[Caevan O’Shite]

Thanks!

[Alex73]

 

Hi Myles,

 

 

I recently purchased a Fender Princeton Reverb re-issue (the silverface one), and a few days after I took it home, on my first chance to crank up the volume (5 or 6), I started noticing a rattle / hiss on some low and medium frequencies. The noise kicks in only 5-10 min after I turn the power on and stops whenever I touch the stock GT 6v6-s output tube on the left, near the 5AR4 rectifier.

I took the chassis out of the cabinet and, although considerably diminished, the noise was still there.

I believe that this problem is worsening every day, as now, with the chassis back in, I can hear it even at low volumes (2-3).

I guess I am fairly right into thinking that there is a microphonics issue with that power tube.

 

Yesterday, I wrote an email to the vendor (who has not replied yet), asking whether tube replacement in case of defects is covered by the amp's warranty.

I expect the answer to be yes...but...

I live in France, and if they have to ship the amp back to a Fender tech center it might be weeks before I get it back.

Also, I heard/read so much negative stuff on Fender's customer service, I guess I'd have to cross fingers hoping that they acknowledge the problem and don't send the amp back without fixing anything.

 

I could buy a new tube, but GT 6v6-s r4 tubes (yes, mine are rated 4) are currently available around here only in bulks of 4, which I cannot afford right now, nor can I afford having a pair of them shipped from the US (for some reason, the r4 seem to run low on the market these days, and I cannot find any US vendor who would ship a single tube to Europe for a decent price).

 

So...I have 3 questions.

 

My first question is: can I swap the pair of power tubes in the Princeton with any pair of matched "medium rated" GT 6v6-s without having to re-bias, or do I specifically need to get hold of the r4 if I want to avoid re-biasing?

 

Also, I remember reading a post from you where you said that you could name same-quality, same-specs tubes for half the price of what GT tubes sell....

So, here's my second question: is there a brand/model of tubes that I could easily find for a moderate price and that would allow me to replace the pair of GT 6v6-s r4 while sparing me the cost of bringing the amp to a tech to get it re-biased?

For instance, since GT 6v6-s seem to be, in fact, re-branded JJs, could I get away with ANY pair of JJ 6v6-s, without caring about the rating, and just swap the tubes with no need to re-bias?

I understand that "good-working" tubes are actually only those that fall in the GT medium rating, so would a pair of properly tested JJ 6v6-s naturally fit that rating?

 

My third question: could the problem come from a wrong biasing, which would have led the tube to wear off this soon?

If the answer is yes, I guess I would need to have the amp checked anyway, and, for lack of funds, I would have to trust Fender's job (if they do anything at all) until better times come into sight, financially speaking.

That would also mean that I'd have to say good-bye to my new amp for some time, just in the middle of our honeymoon!

So i really hope that your answer to my third question will be "no check of bias needed, just a tube problem", which in any case doesn't really make me believe in the wonders of GT testing methods.

 

But that's another topic, and, as you pointed out many times in the past, that problem pre-dates by far the GT Fender-era!

 

 

~Alex

[myles_rose]

Alex,

 

1- have the amp sent for warranty service. Fender probably has somebody in France.

 

2 - get rid of the GT tubes as they are not matched. Get good tubes and rebias.

 

in Europe go to www.watfordvalves.com for tubes

 

 

If tube bias was that far off the tubes would have either blown in minutes or the amp would have had no level at all.

 

Once the amp is working properly we can address other issues.

[Alex73]

Myles,

 

 

Many thanks for your quick answer.

 

After kissing it good-bye and shedding a tear on it, I'll ship the amp to Fender (got an answer from the vendor, since they are closed for summer holidays I'll have to ship it myself...and, too bad, I live in a tiny French apartment, so I had to get rid of the original box!!).

 

I'll buy new power tubes (your advice? JJ 6v6-s? Other?) and re-bias ASAP, but with my current low funds I might have to stick to the GTs for a while...I just hope that Fender is going to replace the stock 6v6s with a pair of matched tubes, before sending the amp back (IYO what are the chances they will do so?)

 

Wow, 20 years ago I would have been so lost...high praises to the power of the web, and higher praises to you for easing guitarists' lives up all over this planet...please, don't tell me you do this for OTHER planets as well!!!

 

 

Cheers,

 

Alex

[myles_rose]

Alex,

 

If you get power tubes that meet spec your bias adjustment may be close enough. Don't go for any of that early or late distortion nonsense.

 

The JJs are sturdy, more than any other new production tube but they sound more like 6L6 than 6V6. Princetons are not hard on output tubes. I'd opt for a nice NOS pair if you can afford them. Mike at www.kcanostubes.com has some great deals at times. If you talk to him say hello from me. He can also supply great advice as well.

 

[Alex73]

Thank you Myles!

[myles_rose]

You are quite welcome

[haywired2]

Good morning Myles,

I'm always looking for what's for sale and I ran across this on ebay. They claim that you blueprinted this particular Classic 30 and if that's the case, what would that amount to? I have two of them and was just wondering.

 

http://www.ebay.com/itm/Peavey-Classic-30-1X12-Tweed-Tube-Amp-/181395118704?pt=LH_DefaultDomain_0&hash=item2a3bfdda70

 

Thanks

Scott

[myles_rose]

Good morning Myles,

I'm always looking for what's for sale and I ran across this on ebay. They claim that you blueprinted this particular Classic 30 and if that's the case, what would that amount to? I have two of them and was just wondering.

 

http://www.ebay.com/itm/Peavey-Classic-30-1X12-Tweed-Tube-Amp-/181395118704?pt=LH_DefaultDomain_0&hash=item2a3bfdda70

 

Thanks

Scott

 

A lot of folks make the claim I have blueprinted the amp. Ask where they are located. If not in So Cal it is probably not true as the amps can only be blueprinted with the owner/player present for the entire process. I have had folks drive amps out from Chicago, Nashville, Texas and Alaska but don't recall any of those non-local ones being a Classic 30.

 

Find out the original owner's name. Amp serial number too. I keep files on every amp I ever touched. Get the date of blueprinting if possible or a copy (photo) of the paperwork that is supplied with every blueprinting job. The reasons for the paperwork are to have a record of how things were, how they changed and to show that the amp was indeed blueprinted. The seller should take a photo of the paperwork and post it in the listing.

 

[haywired2]

Good morning Myles,

I'm always looking for what's for sale and I ran across this on ebay. They claim that you blueprinted this particular Classic 30 and if that's the case, what would that amount to? I have two of them and was just wondering.

 

http://www.ebay.com/itm/Peavey-Classic-30-1X12-Tweed-Tube-Amp-/181395118704?pt=LH_DefaultDomain_0&hash=item2a3bfdda70

 

Thanks

Scott

 

A lot of folks make the claim I have blueprinted the amp. Ask where they are located. If not in So Cal it is probably not true as the amps can only be blueprinted with the owner/player present for the entire process. I have had folks drive amps out from Chicago, Nashville, Texas and Alaska but don't recall any of those non-local ones being a Classic 30.

 

Find out the original owner's name. Amp serial number too. I keep files on every amp I ever touched. Get the date of blueprinting if possible or a copy (photo) of the paperwork that is supplied with every blueprinting job. The reasons for the paperwork are to have a record of how things were, how they changed and to show that the amp was indeed blueprinted. The seller should take a photo of the paperwork and post it in the listing.

 

It's someone in Garden Grove, but I don't need another one. I was just wondering what you can do to a C30. It already sounds pretty good. I installed a set of JJ's and a Weber Blue Dog, but you know how we are, always looking for more.

 

Thanks

Scott

[myles_rose]

Scott,

 

If in Garden Grove it may very well be true. Like I said, I always supply paperwork.

 

There are many things you can do to a Peavey Classic 30. They are .... well .... classics

 

[southboundsuarez]

Hey Myles,

How good of an idea is it to run a pair of Sovtek 6L6GC's in a Fender reissue '65 Deluxe, designed to run 6v6?

Do you think that it would be reliable enough to gig weekly, or is it a disaster waiting to happen at the most inappropriate time?

In my application the plates of the 6L6 are recieving about 380V and the cathode current is 44mA , for approx static dissipation of 17 watts?

The stack has minor mods mainly tone and coupling caps to reduce the brite and slope the treble. No power supply mods, the stock filter caps appear in good condition. I am running the stock OEM tube recto, whatever Fender uses... I also increased the coupling cap to the PI, and I am running a very nicely balanced NOS 12ax7, replacing the stock 12at7 PI

My first concern is overstressing the power supply. So far it seems to run fine. I cant help but wonder if that slight but sweet sounding amount of sag is detrimental? My second concern is for the mismatch on the output tranny with the 6L6 and the stock 8 ohm emminence speaker? Is it safe?

Definately dont need a failure of this setup in the middle of a performance! But it does sound so very sweet!!! It doesnt appear to be too hot to the touch and is so far so good on the bench and in the living room.

Should I be nervous? Or do you think that with regular maintainence I can let this rig hit the road?

Thanks Brian

[myles_rose]

The amp, and it's output transformer, are not a match for 6L6s. You can do it, and sound will come out, but it will not be right.

 

If you want more wattage and headroom in an AB763 circuit buy a reissue Super Reverb, Vibroverb, Twin reverb etc.

 

If it were my amp I would not do it. 6L6s also don't have the same tone as 6V6s.

 

The again, if you use JJ 6V6s and bias to 75% you will get closer to what you are doing now. They are very stout tubes and trace and act more like a 6L6 than a 6V6.

 

[southboundsuarez]

Well, that answer certainly doesnt increase my confidence running the 6L6 ! Kinda tells me what I think I already know or should know better of.... You convinced me to order some JJ's for this amp. Had I had any 6v6's on hand I would have installed right from the very get go. However once I installed those 6L6's and heard this thing,, I was like WoW! I suppose I will have to build my own take on a 6L6 AB763 with some serious iron aboard it.

Normally, I prefer a good NOS 6v6 usually like the RCA blackplates. Seemed NOS 6v6 were plentiful and reasonable, but these days with smaller amps the demand has now exceeded the supply and the price and availibilty are starting to really reflect that. I have been hearing many good things about the JJ's for a couple of years now. I have had bad results with their preamp tubes being very microphonic. I think I will give them another try with these 6v6's though. They sound as if they are quite robust from what I have read. If they have similiar 6l6 sound then for the price its a win win.... otherwise maybe I will hunt down some NOS Brimar Coke Bottle 6v6's and can perhaps roll some recto tubes to get some sag..

 

[myles_rose]

If you like the tone of the 6L6's you can run them. Just bias them properly. Transformer mismatch is not unsafe for the most part. Folks do it often. Look at all the amp makers that say you can use a 6L6 or EL34 in the same amp. Not optimum but life rarely is optimum

 

The 6V6 is sweet and chimey. It has many of the characteristics of an EL84. Actually, the output transformer for an EL84 and 6V6 are the same unlike 6V6 / 6L6.

 

So ... in the end, what you are doing is person taste and there is no right or wrong. The reliability factor if the tubes are biased properly will be slightly lower due to the cheap parts Fender uses in the RI amps. But .... take that amp and upgrade the iron with some Mercury Magnetics stuff and you will be blown away by the change. It is the biggest change you can make and the iron is the heart and soul of the amp, the most expensive parts in the amp and the easiest place for Fender to cut price and corners.

[southboundsuarez]

Yes, indeed I agree about the iron! That's the route I was envisioning when I mentioned building my own Blackface . A beefier P.S. and a correct OP tranny & choke all ala M.M.! A pair of 6L6GC's throw in a tag board with some orange drops and silver mica caps.

Man, there must be a gutted basketcase reissue out there somewhere for cheap!? What ever happened to all the bargain silverfaces ya used to find so plentiful? Well I am going to build something along these lines someday,,, of course probably after everything is said done without compromise and toned how I ultimately would prefer for my own rig.... I likely will end with 6v6's anyways,,,,,, L.o.L. Sure love the loose jangle of some of those Mercury Magnetic output trannys. INDUCTIVE REACTIVE Circuit theory is simply magical mojo to me! How the hell do you simply predict or know that so many hundreds of windings around something spaced so far apart is going to equal that and that is going to be harmonically musical????! Amazing to me and I dont care about all the theory and mathematical formula the experts can show me, all those graphs and phase angles ect.... it isnt science.... it's magic and wizzardry is what I say! Pure witchcraft!

I got a tip on some decent RCA grey bottle 6v6 blackplates!!!! Cheap too! And its a girl that has em! Gotta go now!!!!

[myles_rose]

Happy Playing!