Tube Amps / Music Electronics
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|6/2/2000 2:15 AM|
||Mod Removal Request|
Actually, the request is - if any you guys do a mod, would you please give the owner of the amp's original parts back to him?
Got a customer with a white Bassman who wants all the 'improvements' removed & the amp restored to an attempt of putting back the way it was. Fortunately, the techs who performed the operations did give back the customer his original parts to him. Now he wants me to put 'em all back in. Nearly every single resistor/capacitor was replaced, but the owner doesn't like the tone of it. Even though since there are a lot of folks wanting to go 'retro' and I'm sure it's an influence on him too, I didn't think nearly every component needed to be replaced to simply 'improve tone'. Of course, the amp would be more road-worthy with 'all' new parts, and sure, this is a subjective thing, but I'm putting the old parts back in. It's a big job, removing the added reverb circuit too, but that's what he wants and it's what I think should be done too. Yes, I like Matchless amps, but they sound 'too 'new' even with all the wide range tone controls. THERE IS something to aged less-efficient components inhabiting old amps that newly constructed or recently 'overly repaired' old amps don't have. And all you have to do is play & listen.
Will I argue this any further? No. But I didn't think I would have to mop up this much.
butchering mods as we go along the way of reconstruction
|6/2/2000 5:19 AM|
The way I see it, the de-modding issue is separate from the issue of what resistors and caps to use. Obviously, the circuit needs to be put back to stock in order to satisfy the customer's request. I'm not sure if blindly putting back all of the original parts is either wise or necessary. I would at least measure every single one before putting it back. Carbon comp resistors can drift drastically from the heat of desoldering. Sometimes just age makes them go way out of tolerance, Also, for example, how are you going to know which 100K plate resistor went where?
For future projects of a similar nature, if you are unable to obtain the original carbon comp resistors and blue axial poly film and foil signal caps, here's a solution for obtaining the original tone:
For signal caps, use the SBE orange drop PS series caps (poly film and foil). Their construction is very similar to the originals and they are of high quality. For resistors, use modern carbon films, but use values that are around 10% (or even more, up to 20%) higher than the those called for by the schematic. Not all of them have to be this way, but I would at least do this for all plate and cathode resistors. Most of that "old" tone is due to drifted carbon comp resistors (which almost always drift UP over time) -- but I strongly believe it is the actual resistor value, not its construction, that makes most of the difference (not taking into consideration noise, which is a lot worse with CC resistors).
By the way, I DO always return all the removed parts back to the customer. I look at it as free "malpractice insurance".
|6/2/2000 11:19 PM|
I'm not a modmeister, so I don't hack amps. However, I do return replaced/failed parts. Actually, I have them in a bag when the customer comes to pick up the amp. I show him the bag of dead parts and ask him if he wants them. The usual answer is "no", so based on that, I toss the bag in the trash can in front of the guy.
I've heard a few tech cuss and swear when removing Torres mods.
|6/6/2000 11:52 PM|
I could agree with that
|6/4/2000 3:15 AM|
Well Jim, I read your post last nite & wrote a reply, but hit the "reset form" button by acccident, then decided to go home to get away from the workplace & cyber madness.
Update first: the customer says the change from the 'new modern components" back to the original ones is the difference between night and day. Gee, I didn't think it would be that drastic, but from what I recalled about replacing all the coupling and tone caps in my own SF Vibrolux to orange drops along with silvered-micas and how the amp sounded too frickin' crappy after that, I thought, without measurement other than me ears, it's only logical to preserve or attempt to preserve the original components as well as the rest of the amp unless parts are defective, way out of tolerance, leaky or excessively noisy.
Yes, I had to guess where some original resistors of the same value had to go, but most of them had lead lengths to help me put them back where they were
You had suggested to go ahead and use some "modern" replacement parts instead, but I put the old carb comps & blue Molded caps back in anyway. Are you sure you know the differnce between hi-fi tube stereo amps and guitar amps? Of course, in stereo amps we want eveness from channel to channel as well as a good clean reproduction of the input signal. But on guitar amps, most folks including me want some color, some warmth, sustain & disortion, not sterility, not overly crispiness. From what I've heard by playing after a repair, is if only one or 2 original caps are leakey and replaced by orange drops, the original sound is not too altered to the point of suction like replacing all the caps, and all the resistors too.
If you do not get this, good! More work for me. But again, I never thought I'd have to mop up this much.
If it's smooth, let's roll with it.
|6/5/2000 4:25 AM|
The coloration inherent in guitar amplifiers is mostly due to circuit design, not resistor type, caps, PTP vs. PCB etc. It's the circuitry!
|6/6/2000 1:51 AM|
It's the circuitry!
Well, a nomimal 70uF PS cap reading around 110uF can make an amp sound darker than if you were to replace it with a modern 70uF or 80uF cap. I would agree with you if you were to define "circuitry" as being the actual values measured for an particular amp specimen. Even if the parts are within the rated 20% tolerance that can make a very big difference in the sound...
Jim's suggestion about using the Sprague/SBE PS coupling/tone caps as replacements for an amp from the 60's is right on because I believe that they are very similar to the good caps used back then (like the blue tubular ones).
As for the never-ending debate between types of coupling caps, I recommend the following experiment: for one of the more critical coupling caps wire up a switch so that you can select between different types (ceramic, mica, polyester, polypropylene). The difference can be most noticeable if the signal is very rich with lots of harmonic content. Or not... if there is a lot of compression and high freq roll-off after that point in the circuit you might not hear that much difference. With something like a 470k/470pF RC "couplet" after a distorted stage I could really hear the difference between a ceramic and a mica cap- like night and day.
I suggest that the different brands and styles of caps be used as an artist used colors on his pallet— in some applications you might want the characteristics of one type of cap...
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