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#1351234 - 03/12/02 12:21 AM Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES
This is one place you can post amp questions and I will try to help.


I am putting this post up here, so if you have a question or have a comment, just post a comment here and when I see the email notification I will answer back here as quickly as I am able. If I don't get to it in a day or two, please forgive me.

I generally try to get to this in the early morning or later evening, but while we are testing and destroying tubes (which takes time while they "bake"),I try to get onto this.

Ashley Danielle is the gal in my avatar and the head of Guitar Amplifier Blueprinting Artist Relations. Ashley is also the girl biasing the Fender Deluxe Reverb in my avatar. Ashley was recently in the Slash and Billy Idol videos.


Regards,

Myles


Edited by myles111 (03/29/07 05:18 PM)

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#1351235 - 03/12/02 12:57 AM Re: Feel free to ask Myles
Wickerman_dup1 Offline
Platinum Member

Registered: 01/05/02
Posts: 1201
Loc: Michigan, USA
First off, thank you so much. You're a great help and I really apreciate you sharing your knowledge with us. Thank you.

Now, I use a Carvin Nomad. 50 watt, 1x12, 5 12AX7s, 4 EL84s. I love the overdrive channel, it's real crunchy and can go from a good, transparent, slight overdrive to full on metal crunch. I really enjoy the dirty channel but the clean breaks up real fast. Even on practice volume (loud, but not painful) it tends to get a little distortion. I was wondering if there were any tubes (I'm not sure if I need better preamp or power amp tubes) that stay a little cleaner but can still get some good crunch.

Stock 12AX7s - Groove Tubes GT12AX7R
Stock EL84s - Sovtek EL84/6BQ5
_________________________
WickerMan

Rushing forth your memory lost
In your mind you know the cost
Guitarist cranked - organ too
With you on bass you'll shake the pews

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#1351236 - 03/12/02 01:48 AM Re: Feel free to ask Myles
Dak Lander Offline
MP Hall of Fame Member

Registered: 01/10/02
Posts: 7729
Loc: Temecula, LoCal, USA
Hello Myles,
Jeez, this brought all kinds of things to mind...

I'll be polite.

I'm happy to have you put up a specific post to make it easier to get to your info about amps & such.

Now, can you help me play better to sound better through any amp???? \:D \:D \:D

_________________________

Our Joint

"When you come slam bang up against trouble, it never looks half as bad if you face up to it." The Duke...

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#1351237 - 03/12/02 12:21 PM Re: Feel free to ask Myles
Boggs Offline
MP Hall of Fame Member

Registered: 03/07/02
Posts: 2841
Loc: Rochester,NY,UNITED STATES
Wickerman, I have heard of really good results, similar to what you describe you are looking for, by using JJs. A friend of mine on Carvin's and Keith Miller's board uses a BelAir and he loved the difference they made in it. He's primarily a blues player. Terry Hartley. If you want, I'll get you a link to him. You should hear his sound clips... He's got great tone and plays some good stuff! Boggs
_________________________
Check out my Rock Beach Guitars page showing guitars I have built and repaired... http://www.rockbeachguitars.com

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#1351238 - 03/12/02 02:02 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by Wickerman:
First off, thank you so much. You're a great help and I really apreciate you sharing your knowledge with us. Thank you.

Now, I use a Carvin Nomad. 50 watt, 1x12, 5 12AX7s, 4 EL84s. I love the overdrive channel, it's real crunchy and can go from a good, transparent, slight overdrive to full on metal crunch. I really enjoy the dirty channel but the clean breaks up real fast. Even on practice volume (loud, but not painful) it tends to get a little distortion. I was wondering if there were any tubes (I'm not sure if I need better preamp or power amp tubes) that stay a little cleaner but can still get some good crunch.

Stock 12AX7s - Groove Tubes GT12AX7R
Stock EL84s - Sovtek EL84/6BQ5
Wickerman;

Those amps are pretty versitile, but have a gain structure that was designed for the most part for the distortion and compression you hear.

There are a few things you can try though.

The first and easiest, would be to replace the 12AX7 in the preamp position that is closest to the input jack. This is V1. The Russian (Sovtek 12AX7WA as stock - Groove Tubes), is a pretty high output 12AX7. Try a 12AX7C (a Chinese 12AX7), as it has a little less gain.

If you want it cleaner, then in that same position try a 5751, a tube that is much the same as the 12AX7 but with about 30% less gain.

The final thing you can try, in in the last preamp position (the preamp tube the most close to the power tubes), probably V5, replace that 12AX7 with a 12AT7. This has less gain but more current drive capability and will give you more clean headroom and less output stage distortion.

If you need more ideas after those simpler ones, drop me another note here and I'll try to help further. Unfortunately, that particular amp is a pretty strong amp and when you get into that area, its a bit harder to tone them down.

Regards,

Myles

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#1351239 - 03/12/02 02:06 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by daklander:
Hello Myles,
Jeez, this brought all kinds of things to mind...

I'll be polite.

I'm happy to have you put up a specific post to make it easier to get to your info about amps & such.

Now, can you help me play better to sound better through any amp???? \:D \:D \:D

daklander;

Well, I'm not the most proficient player around for sure, but I see you are also in So Cal. Maybe we can get together ... you show me a few things, I'll show you what little I know, and maybe we'll both play a little better \:\)

I can show you a few little things to play on any amp that will show the strengths and weaknesses of a particular amp. That might help?

Regards,

Myles

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#1351240 - 03/12/02 04:44 PM Re: Feel free to ask Myles
Wickerman_dup1 Offline
Platinum Member

Registered: 01/05/02
Posts: 1201
Loc: Michigan, USA
Thank you very much Myles. You're the best!
_________________________
WickerMan

Rushing forth your memory lost
In your mind you know the cost
Guitarist cranked - organ too
With you on bass you'll shake the pews

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#1351241 - 03/12/02 08:04 PM Re: Feel free to ask Myles
rickystratcat Offline
Member

Registered: 03/03/02
Posts: 7
Loc: Fayetteville,NC,UNITED STATES
Hi Myles,one of the posts that got missed was mine.What I had asked was for your thoughts on substitutions for the 12AX7 other than 12AT7's or
12AU7's.I've been playing with some interesting substitutions with the 12BZ7 and 12AZ7 but I DO NOT
know enough yet to be comfortable.Can you help me understand more about tube substitution(particularly
the dangers to life and equipment)?Thanks,Ricky

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#1351242 - 03/12/02 10:12 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by rickystratcat:
Hi Myles,one of the posts that got missed was mine.What I had asked was for your thoughts on substitutions for the 12AX7 other than 12AT7's or
12AU7's.I've been playing with some interesting substitutions with the 12BZ7 and 12AZ7 but I DO NOT
know enough yet to be comfortable.Can you help me understand more about tube substitution(particularly
the dangers to life and equipment)?Thanks,Ricky
rickystratcat ...

Sorry I missed your post. I have written a bit on this before, so you may want to look at some of my other posts, maybe the one on the 12AX7LP.

Basically, as long as your amp is not opened up to the innards of the chassis, there is not too much exposed high voltage.

You can swap preamp tubes all around with no danger to the equipment or yourself. There is no adjustment necessary either.

A 12AT7 will give less gain than a AX7 .... and in the phase inverter postion, will yield more clean headroom before the onset of distortion.

a 12AU7 will do the same thing, but to even a greater change than the AT7.

Some folks prefer (the late SRV) 5751 tube in the first gain stage.

If you have other questions, just drop a post here, but first look around on my webpage as this is covered in a few spots.

Regards

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#1351243 - 03/12/02 11:20 PM Re: Feel free to ask Myles
rickystratcat Offline
Member

Registered: 03/03/02
Posts: 7
Loc: Fayetteville,NC,UNITED STATES
Hi Myles,I appreciate your response.I went to your website and looked around again(I had been there before but I went back in case I missed what I was looking for).Checked out your son's site too. \:\) I think it's great.Anyway,I guess I need to re-state my
question better.I'm interested in tube substitutions
OTHER THAN the 12AT7's and 12AU7's.Specifically the 12BZ7 and the 12AZ7.I've had great results playing with those tubes in the different slots and I don't know anything about them I've searched the net high and low and I can't seem to find the information I'm looking for.Have you experimented with these tubes or can you point me in the right direction?Thanks,Ricky

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#1351244 - 03/13/02 04:40 AM Re: Feel free to ask Myles
Dan South Offline
10k Club

Registered: 01/04/02
Posts: 13114
Loc: Metuchen,NJ,UNITED STATES
Are you related to Floyd?

Sorry, couldn't think of a good question. \:D
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The Black Knight always triumphs!

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#1351245 - 03/13/02 03:16 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by rickystratcat:
Hi Myles,I appreciate your response.I went to your website and looked around again(I had been there before but I went back in case I missed what I was looking for).Checked out your son's site too. \:\) I think it's great.Anyway,I guess I need to re-state my
question better.I'm interested in tube substitutions
OTHER THAN the 12AT7's and 12AU7's.Specifically the 12BZ7 and the 12AZ7.I've had great results playing with those tubes in the different slots and I don't know anything about them I've searched the net high and low and I can't seem to find the information I'm looking for.Have you experimented with these tubes or can you point me in the right direction?Thanks,Ricky
rickystratcat...

Sorry, I misunderstood your question it seems.

I focus on the 12AX7, AT, AU, 12BY7A, and some of the older 6L and 6S series. They are the most common tubes in guitar and bass amps.

I think the best folks to talk to would be ...

Bob Pletka at http://www.eurotubes.com

the folks at KCA and those at Tubeworld.

Hope that helped somewhat.

Regards,

Myles

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#1351246 - 03/13/02 03:50 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by Dan South:
Are you related to Floyd?

Sorry, couldn't think of a good question. \:D
Dan South ...

Sorry ... not related. I am also not related to Pete the baseball player of the past. Come to think of it, I don't think I am related to anybody that the general pubic would know.

Myles

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#1351247 - 03/13/02 03:58 PM Re: Feel free to ask Myles
peel_dup1 Offline
Senior Member

Registered: 03/05/02
Posts: 60
Loc: Toronto,,CANADA
Hi myles
First of all thanks for your time and advice. this forum is amazing. its great to see knowledgable players help others. Polite bunch here too.

I reposted my early thread here to save you time. Here it is:

Im sure the little marshall jubilee posse would love to get your take on this amp - I tracked down the schematic for the 50w version and I wonder if you could take a look at it and advise on:

tube recommendations
getting good tube distortion (preferably high gain saturated)
whether a SS dist pedals or tube based dist pedals are better matched to this amp

..anything that you feel worth passing along.

thx in advance, peel
heres the link to the schematic:
http://home.att.net/~amptech/2550.gif

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#1351248 - 03/13/02 05:05 PM Re: Feel free to ask Myles
machinex_dup1 Offline
Member

Registered: 03/09/02
Posts: 22
Loc: Delaware, USA
Myles,

Im kinda new but have read alot of your posts, very informative, thanks in advance for taking the time to answer all these questions.

My question would be: what are the conditions in which to set the impedance of your amp and cabs?
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#1351249 - 03/13/02 06:40 PM Re: Feel free to ask Myles
peel_dup1 Offline
Senior Member

Registered: 03/05/02
Posts: 60
Loc: Toronto,,CANADA
Quote:
Originally posted by machinex:
Myles,

Im kinda new but have read alot of your posts, very informative, thanks in advance for taking the time to answer all these questions.

My question would be: what are the conditions in which to set the impedance of your amp and cabs?
BTW Machinex sorry about the switching problem on your jubilee. Im sure its not major. Get it fixed an crank that puppy!

Peel

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#1351250 - 03/13/02 07:51 PM Re: Feel free to ask Myles
machinex_dup1 Offline
Member

Registered: 03/09/02
Posts: 22
Loc: Delaware, USA
Thanks bro, its cool though I just got ahold of one of the better amp repair guys in our area so Im taking it to him tonight or tomorrow and hopefully he'll be able to take care of it ASAP, man I hope it doesnt bankrupt me, lol.
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#1351251 - 03/13/02 09:15 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by peel:
Hi myles
First of all thanks for your time and advice. this forum is amazing. its great to see knowledgable players help others. Polite bunch here too.

I reposted my early thread here to save you time. Here it is:

Im sure the little marshall jubilee posse would love to get your take on this amp - I tracked down the schematic for the 50w version and I wonder if you could take a look at it and advise on:

tube recommendations
getting good tube distortion (preferably high gain saturated)
whether a SS dist pedals or tube based dist pedals are better matched to this amp

..anything that you feel worth passing along.

thx in advance, peel
heres the link to the schematic:
http://home.att.net/~amptech/2550.gif
Peel;

All Marshall's have their own distinctive sound, partly because of their tone stack in the front end, but also partly because they keep a certain amount of crossover notch distortion in the output stage when they are properly adjusted.

The input is of high enough resistance that most pedals work quite well with these amps. I would play some with your bias, set it via the scope and crossover notch method rather than the current draw method on that particular amp, as you need to have the "Marshall notch" in there, but not too much ... not too little. A good Marshall guy can do this pretty easily.

Let he or she know at what settings you expect the play most often so it can be set for that particular area to be optimum, unlike the current draw method that is set at idle. Most amps like the current draw method just fine and dandy, Marshall's prefer a little different treatment to sound their best.

Keep the ECC83's in there if you want the Marshall sound, but try to find a very good one for V1 ... a NOS if you can spring for it. That is your tonal signature right there.

For V3, try to get a balanced (side A and side B of that tube should be less than .15 mA apart at 250 volts with a -2v bias). If you can get one at .1 mA or less, that is even better. Then make sure your output tubes are matched pretty closely.

If you want more clean headroom, I can help you with that, but then your Marshall won't sound as much as a Marshall.

Regards,

Myles

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#1351252 - 03/13/02 09:18 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by machinex:
Myles,

Im kinda new but have read alot of your posts, very informative, thanks in advance for taking the time to answer all these questions.

My question would be: what are the conditions in which to set the impedance of your amp and cabs?
machinex ....

Unless I don't understand the question, its pretty simple ... make them match! If you have an 8 ohm cabinet, set the amp selector to 8 ohms.

If you set it to 16 ohms, the amp will work into a heavier load, and will not sound right.

If you set it to 4 ohms, and push it hard, your will risk tube failure, tubes wearing more quickly, and output transformer failure (pretty expensive).

Regards

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#1351253 - 03/14/02 01:12 AM Re: Feel free to ask Myles
Chip McDonald Offline
MP Hall of Fame Member

Registered: 01/19/00
Posts: 4792
Loc: Augusta, Ga. USA
Quote:
Originally posted by myles111:
So .... I am putting this post up here, so if you have a question or have a comment, just post a comment here and when I see the email notification I will answer back here as quickly as I am able.
(Taking advantage here)

What are the center frequencies and q's of the tone controls on the following amps/FX? Just out of curiousity to see it side by side in one place...

Marshall Super Lead
Fender Deluxe; Twin; Super
Boogie Dual Rect
Vox AC30/Top Boost
Gibson GA-40 (just because I have one and I'm curious if you happen to know by some weird chance (and would be very impressed if you did))
Ampeg SVT
Ibanez TS line
Boss DS-1; OD-1
Fuzz Face

Just curious...
_________________________
www.chipmcdonald.com
(tagline inlieu of having a representational page of downloadable music for the moment...) / "big ass windbag" - Bruce Swedien

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#1351254 - 03/14/02 01:25 AM Re: Feel free to ask Myles
peel_dup1 Offline
Senior Member

Registered: 03/05/02
Posts: 60
Loc: Toronto,,CANADA
Quote:
Originally posted by myles111:
Quote:
Originally posted by peel:
Hi myles
First of all thanks for your time and advice. this forum is amazing. its great to see knowledgable players help others. Polite bunch here too.

I reposted my early thread here to save you time. Here it is:

Im sure the little marshall jubilee posse would love to get your take on this amp - I tracked down the schematic for the 50w version and I wonder if you could take a look at it and advise on:

tube recommendations
getting good tube distortion (preferably high gain saturated)
whether a SS dist pedals or tube based dist pedals are better matched to this amp

..anything that you feel worth passing along.

thx in advance, peel
heres the link to the schematic:
http://home.att.net/~amptech/2550.gif
Peel;

All Marshall's have their own distinctive sound, partly because of their tone stack in the front end, but also partly because they keep a certain amount of crossover notch distortion in the output stage when they are properly adjusted.

The input is of high enough resistance that most pedals work quite well with these amps. I would play some with your bias, set it via the scope and crossover notch method rather than the current draw method on that particular amp, as you need to have the "Marshall notch" in there, but not too much ... not too little. A good Marshall guy can do this pretty easily.

Let he or she know at what settings you expect the play most often so it can be set for that particular area to be optimum, unlike the current draw method that is set at idle. Most amps like the current draw method just fine and dandy, Marshall's prefer a little different treatment to sound their best.

Keep the ECC83's in there if you want the Marshall sound, but try to find a very good one for V1 ... a NOS if you can spring for it. That is your tonal signature right there.

For V3, try to get a balanced (side A and side B of that tube should be less than .15 mA apart at 250 volts with a -2v bias). If you can get one at .1 mA or less, that is even better. Then make sure your output tubes are matched pretty closely.

If you want more clean headroom, I can help you with that, but then your Marshall won't sound as much as a Marshall.

Regards,

Myles
Thx Myles - much appreciated, Ill take this to my amp tech when I get my new tubes. Any particular brand of tubes that might work with this amp better than others?

Peel

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#1351255 - 03/14/02 04:21 AM Re: Feel free to ask Myles
machinex_dup1 Offline
Member

Registered: 03/09/02
Posts: 22
Loc: Delaware, USA
Myles,

What I meant by my question was: I know that the cab and head has to match, but I was wondering why you would set am amp to 4, 8, 16, etc ohms. whats the difference?

Thanks in advance
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#1351256 - 03/14/02 02:34 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by Chip McDonald:
Quote:
Originally posted by myles111:
So .... I am putting this post up here, so if you have a question or have a comment, just post a comment here and when I see the email notification I will answer back here as quickly as I am able.
(Taking advantage here)

What are the center frequencies and q's of the tone controls on the following amps/FX? Just out of curiousity to see it side by side in one place...

Marshall Super Lead
Fender Deluxe; Twin; Super
Boogie Dual Rect
Vox AC30/Top Boost
Gibson GA-40 (just because I have one and I'm curious if you happen to know by some weird chance (and would be very impressed if you did))
Ampeg SVT
Ibanez TS line
Boss DS-1; OD-1
Fuzz Face

Just curious...
Chip,

I don't keep that sort of information for the most part, and don't know of anybody that does actually.

Most amps use one of a few proven tone stacks, and on my website there are graphs for the Marshall, Fender, and Vox - so you might look there as a start.

Each amp even in the same model has differences as the tolerances were +/- 20% in many cases, so when I have an amp on the bench, I see what its doing at the particular time.

As far as effects, I don't do much with them in the design area as there are more than enough amps to keep me busy enough.

I do look at effects and their impedence though, when doing an amp blueprint. I also look at the aspects and resistance of the pickups in the particular primary guitar.

Regards

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#1351257 - 03/14/02 03:53 PM Re: Feel free to ask Myles
dlb Offline
Member

Registered: 03/07/01
Posts: 10
Loc: Newport,NH,UNITED STATES
Myles, First, thanks for the heap of helping you so kindly give. I have a newer Fender Prosonic that I dig because of it's portability but I want to sweeten the gain channel. Are you familiar with it's schematics and can you offer any assistance?
Thanks again dude.

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#1351258 - 03/15/02 12:51 AM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES

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#1351259 - 03/15/02 01:32 AM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by machinex:
Myles,

What I meant by my question was: I know that the cab and head has to match, but I was wondering why you would set am amp to 4, 8, 16, etc ohms. whats the difference?

Thanks in advance
machinex;

Speakers have a nominal resistance. Nominal means the approxmate lowest value that the speaker will have over its designed frequency range. An 8 ohm speaker may have a lower value of 8 ohms at one area of its frequency range, yet 40 ohms at another frequency. Speakers are an inductive load that is always changing, but here, we are interested in the speakers lowest value.

Tube have a high value .... say 6000-8000 ohms, and we have to make this "Match" the 8 ohm load (or 2, 2.7, 4, 8, 16) load of the speakers. Go too low, and poof .... your output transforer is history. Your transformer in a 50 watt amp is generally designed to be able to deal with 50 watts, and in some amps its even marginal at that point. So .... you have your 50 watt amp, but with a 4 ohm cabinet, and your selector is set to 16 ohms ... or 8 .... now the output section of your amp is looking at a lighter load in comparasion. Things are not matched. Your amp put out more power in the wrong way, and after a very few minutes on a lot of amps .... trouble.

If you have an amp like a Rivera, THD, or Carr, their transformers are very costly and are generally way overbuilt for the amp, so you have a lot more time before disaster when you make the mistake.

In any case, once the transformer overheats and the insulation starts to go, you may already be past the point of having a reliable amp in the future.

Basically, whether you understand it or not, just make the numbers match. .... unless you have a 100 watt amp, but are running it as a 50 watter by pulling two of the output tubes (and WHICH TWO are also very important). Then your output section needs to be matched to 1/2 the resistance of what is the normal resistance of the tubes when all 4 are installed .... so ..... with an 8 ohm cabinet and half the tubes pulled, we then set the selector to 4 ohms.

Regards,

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#1351260 - 03/15/02 01:52 AM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by dlb:
Myles, First, thanks for the heap of helping you so kindly give. I have a newer Fender Prosonic that I dig because of it's portability but I want to sweeten the gain channel. Are you familiar with it's schematics and can you offer any assistance?
Thanks again dude.
dlb;

I am pretty familar with the Prosonic, but need to know if its the head or the combo, as the combo has a slightly different circuit with reverb.

As far as the "gain" channel, you have the options of cascaded gain or not. Which config do you want to change?

If its the cascaded gain, that's a bit harder, as when you use one tube to drive another, that are both high gain tubes, things can get out of control very fast.

Let me know which amp, and what config you want to tone down, and I will give you a few ideas .... the first of which would be to replace the Fender/Sovtek 12AX7WA in V1 and V2, or at least have them looked at to see if they are too stong for the slots they are in. If you have 7025's in those positions, then we have a few other ideas we can go into.

Regards,

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#1351261 - 03/15/02 11:52 AM Re: Feel free to ask Myles
dlb Offline
Member

Registered: 03/07/01
Posts: 10
Loc: Newport,NH,UNITED STATES
Quote:
Originally posted by myles111:
Quote:
Originally posted by dlb:
Myles, First, thanks for the heap of helping you so kindly give. I have a newer Fender Prosonic that I dig because of it's portability but I want to sweeten the gain channel. Are you familiar with it's schematics and can you offer any assistance?
Thanks again dude.
dlb;

I am pretty familar with the Prosonic, but need to know if its the head or the combo, as the combo has a slightly different circuit with reverb.

As far as the "gain" channel, you have the options of cascaded gain or not. Which config do you want to change?

If its the cascaded gain, that's a bit harder, as when you use one tube to drive another, that are both high gain tubes, things can get out of control very fast.

Let me know which amp, and what config you want to tone down, and I will give you a few ideas .... the first of which would be to replace the Fender/Sovtek 12AX7WA in V1 and V2, or at least have them looked at to see if they are too stong for the slots they are in. If you have 7025's in those positions, then we have a few other ideas we can go into.

Regards,
Thanks for the reply, It is a 2-10 combo in the stock state except for power tubes which I've experimented with. It has the cascading gain. I deally, I would like to achieve more clean head room in channel 1 (past 3 it breaks up quick)and less of the synthetic gain sound on channel 2. I've read of mods to put master volume pots in the reverb slot and moving reverb pot to back of chassis. That interests me. It is a cool amp but hard to harness in a live situation. This little sucker runs hot as well, I have a good PC fan I am going to stick in it.

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#1351262 - 03/15/02 02:46 PM Re: Feel free to ask Myles
machinex_dup1 Offline
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Registered: 03/09/02
Posts: 22
Loc: Delaware, USA
K, that clears it up a little more for me, thanks myles
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#1351263 - 03/15/02 03:30 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
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Registered: 11/28/01
Posts: 5036
Loc: Los Angeles CA, UNITED STATES
Quote:
Thanks for the reply, It is a 2-10 combo in the stock state except for power tubes which I've experimented with. It has the cascading gain. I deally, I would like to achieve more clean head room in channel 1 (past 3 it breaks up quick)and less of the synthetic gain sound on channel 2. I've read of mods to put master volume pots in the reverb slot and moving reverb pot to back of chassis. That interests me. It is a cool amp but hard to harness in a live situation. This little sucker runs hot as well, I have a good PC fan I am going to stick in it.
First off, don't start doing mods to that amp or you will get a lot more noise in the higher gain states. These amps can be noisy enough unless you hand select preamp tubes.

Have your bias checked! If the amp is over or under biased, you will get all sorts of grainy nonsense down in the range you mention.... especially if the amp is overbiased and running too cool. These amps already start to breakup very quickly in the preamp stages, as that is what they were designed to do, so it is even more critical to have a good output stage after the preamp stage. I would bet, after looking at a number of these, that with your volume set to 3-4, that there is a lot of crossover notch distortion if you scope the amp.

To give you more headroom, you need to have somebody look at your first two preamp tubes to see how much above or below 1.2mA they put out with 250 volts on their plates and a -2v bias. If they are the typical Sovtek/Fender tubes, they are probably putting out more than the spec 1.2mA. The 12AX7 has a gain of about 100, so the difference between 1.2 and 1.3 is pretty dramatic.

You need to find a nice 12AX7, perhaps a 12AX7C, that has maybe 1.0mA output. The other thing you can do here is put a JAN 5751 in the V1 position.

Some good places to get either the JAN or a bit lower powered 12AX7 are Watford Valves, Tubeworld, and KCA NOS tubes. All those folks have links on my website. They are the only folks that have the equipment to measure the qualities you need AND have the tubes you'd want if you go the NOS route.

Then, you need to have your output tubes checked. If they are in a midrange, you'd want them to be at a higher range. Something like, if they are a Groove Tubes 4-5 rating, you'd want them to be a rating of 6-7.

Last, your phase inverter, let me know what is currently in there. It is the preamp tube that is closest to the power tubes. Tell me what it says on the tube, what kind it is, and as much as you can tell me about it. This is a critical tube in this amp, especially when you run the amp Class A, as if this is not balanced on the A/B sides, there will be a lot more heat generated than is already done when the amp is in Class A mode.

When you have the bias checked, find somebody uses a scope if they also use a bias probe. Many folks use a bias probe incorrectly. They might use charts or manuals that say what the correct reading for a particular amp should be, and this is often a bit off as different amps have different B+ voltages. Folks that are more technically advanced, try to figure out their real B+ voltage bu pulling one of the output tubes and taking a reading of the plate pin. This is going in the right direction, and is easier than taking the amp apart, but also gives a false reading. When one output tube is removed, the voltage changes a LOT in many amps. In one Marshall I work on, a 50 watter, it goes from about 450v to about 415v when both tubes are in the amp.

To get the proper B+, ESPECIALLY on a Prosonic, you need to pull the chassis and take the reading off the wired side of the socket with all tubes in the amp. Then you can use a bias probe more effectively.

Regards,

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