Striving for that old school sound, you purchase a 'vintage' guitar amp. But it doesn't sound quite right. Well, any amp more than 20 years old is gonna need work...
What's the deal with tube amps? Why all the fuss?
Yes, they do have a special sound, one that digital 'modeling' can't quite get right... It's actually the limitations of tubes that impart that special tone--that natural compression and smooth breakup. Sure, they keep improving solid-state amplifiers--but a look at the majority of mid-range to high-quality amps, the current models (mostly all tube, tube/ss hybrids, etc.) should convince you that it's very difficult to capture 'that sound' without tubes.
Does a 'rebuild' ruin the value of my vintage equipment?
No. Maybe. I don't know. Does changing the tubes mean the amp is not longer 'vintage?' Every old amp will need a rebuild at one point or another. If this negates it's 'vintage' status, then there is no such thing as a vintage amp! Functional amps, anyway--o.k. for nutso collectors who don't actually use 'em.... Who cares about them!
This little jem is a 1961 Kay 503A instrument (guitar, harp) amplifier. Output is in the 3-4 watt range. A nice studio, or "living room amp."
Here's a taste, and there's more video on the last step:
#1 -- Mod A (my first attempt--If you only have patience to listen to one clip, play #2):
(recognize the Trash-o-caster?)
#2 -- This is Mod B, IMHO, a much better sound:
(pickups switched from middle to middle/neck phased mix, about half way)
#3 -- Quick one added, with a Gibson Les Paul, just to show the amp has some bluesy distortion..
(pretty 'raggedy' playing on this one, but it's enough to catch the sound...)
All the videos are 'clean'--guitar and amp only, no FX.
Danger! Danger! No, really, DANGER!!!!!
A tube amp, even an unplugged tube amp, stores enough electrical energy in it's capacitors to kill you! YES, KILL YOU. Don't touch it unless you take precautions. See the section on DISCHARGE THOSE CAPS!!!!!
I'm not a tube repair technician, or an expert electrician. I'm just a hobbyist. Don't take my word, do your own research, and please be careful !
What's the deal with tube amps? Why all the fuss?
Yes, they do have a special sound, one that digital 'modeling' can't quite get right... It's actually the limitations of tubes that impart that special tone--that natural compression and smooth breakup. Sure, they keep improving solid-state amplifiers--but a look at the majority of mid-range to high-quality amps, the current models (mostly all tube, tube/ss hybrids, etc.) should convince you that it's very difficult to capture 'that sound' without tubes.
Does a 'rebuild' ruin the value of my vintage equipment?
No. Maybe. I don't know. Does changing the tubes mean the amp is not longer 'vintage?' Every old amp will need a rebuild at one point or another. If this negates it's 'vintage' status, then there is no such thing as a vintage amp! Functional amps, anyway--o.k. for nutso collectors who don't actually use 'em.... Who cares about them!
This little jem is a 1961 Kay 503A instrument (guitar, harp) amplifier. Output is in the 3-4 watt range. A nice studio, or "living room amp."
Here's a taste, and there's more video on the last step:
#1 -- Mod A (my first attempt--If you only have patience to listen to one clip, play #2):
(recognize the Trash-o-caster?)
#2 -- This is Mod B, IMHO, a much better sound:
(pickups switched from middle to middle/neck phased mix, about half way)
#3 -- Quick one added, with a Gibson Les Paul, just to show the amp has some bluesy distortion..
(pretty 'raggedy' playing on this one, but it's enough to catch the sound...)
All the videos are 'clean'--guitar and amp only, no FX.
Danger! Danger! No, really, DANGER!!!!!
A tube amp, even an unplugged tube amp, stores enough electrical energy in it's capacitors to kill you! YES, KILL YOU. Don't touch it unless you take precautions. See the section on DISCHARGE THOSE CAPS!!!!!
I'm not a tube repair technician, or an expert electrician. I'm just a hobbyist. Don't take my word, do your own research, and please be careful !
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Signing UpStep 1: Symptoms: How do I know my amp needs a rebuild?
--Hum: Usually a sign of bad filter caps. Poor routing is often a cause. Adding a three-prong cord will help.
--Weak signal: Bad tubes, failing output transformer.
--No highs/loss of tone: Bad tubes, coupling or bypass caps.
--Unpleasant distortion (not the kind you want): Often, this is bad tubes. Also could be the coupling caps or cathode bypass caps. Or could be filter caps, if the signal is modulated with 60 hz noise.
--Weird noises (squeals, crackles, etc.): Probably bad tubes. Sometimes failing coupling caps.
--In each case, look to the speaker, also. A torn or worn speaker cone could be the culprit. In rare cases the output transformer may be failing.
This amp had the following problems:
--good tone for 5 minutes, then a nasty, harsh clipping distortion on louder notes (yep, bad tubes were the cause.)
--Nasty hum (filter caps and routing problems.)
--Dull, muddy tone (needed new caps and tubes.)
--The original two-prong power cord needed replacing.
--Weak signal: Bad tubes, failing output transformer.
--No highs/loss of tone: Bad tubes, coupling or bypass caps.
--Unpleasant distortion (not the kind you want): Often, this is bad tubes. Also could be the coupling caps or cathode bypass caps. Or could be filter caps, if the signal is modulated with 60 hz noise.
--Weird noises (squeals, crackles, etc.): Probably bad tubes. Sometimes failing coupling caps.
--In each case, look to the speaker, also. A torn or worn speaker cone could be the culprit. In rare cases the output transformer may be failing.
This amp had the following problems:
--good tone for 5 minutes, then a nasty, harsh clipping distortion on louder notes (yep, bad tubes were the cause.)
--Nasty hum (filter caps and routing problems.)
--Dull, muddy tone (needed new caps and tubes.)
--The original two-prong power cord needed replacing.
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General rule is that the smaller the cap value, the more it blocks low frequencies.
(jeeze, I see that I have several duplicate component names-- two C3, two C2, etc. Bear with me, I hope this makes sense with the lousy schematic..)
How that works to filter frequencies depends on how it's oriented in the circuit:
-- caps inline with the signal, like the 0.01uF (upper most cap labeled C3), are "high pass" filters. They block low frequencies from passing forward. These are called "coupling caps", and also block any DC voltage offsets from messing with the next stage.
Changing from .05 to .01 blocks more lows from passing.
-- caps that shunt or bleed signal to ground, like the 0.001 that's attached to the tone POT (lower C2) are "low pass" filters. Those caps block low frequencies from passing to the ground--which means the the high frequencies are now escaping away from the signal path.
That's the way a passive guitar tone control works--the cap cuts the high frequencies by letting them pass through to the ground.
So in each case, small caps block more lower frequencies. It's just a matter of how they are used. Here's a simple calculator and illustration of high vs. low pass.
The other caps are cathode bypass and control grid caps for the tubes, and they're a little more tricky to explain...
One thing tubes do is color sound with even-order (mostly second-order) distortion. It's a type of distortion closest to the fundamental sound itself, and is generally found to be pleasing to the ear. Mosfets can do this too, but somewhat differently.
But a good guitar tube amps also have odd-order distortion (third, fifth, etc.), which is the "bite" or "crunch" we love.
Frequency response itself is interesting, since a guitar (or harp) amp doesn't reproduce sound faithfully--as a stereo system they sound like crap. Plus a guitar speaker normally doesn't have a frequency response above 5kHz or so. But you will hear higher frequencies--they come from the speaker cone and the cabinet / baffle board vibrating at higher harmonics.
Just to clarify, when I wrote: small caps block more lower frequencies, that's a little misleading.
Caps block frequencies below the cutoff freq. Smaller caps don't block more lower frequencies--the cutoff frequency moves higher, so more mid-range cut is added to the already blocked frequencies below.
In the chart here of a high-pass filter, the cutoff would move to the right, as the cap value gets smaller.
It could be other things, too, though. Sometime the tubes themselves develop hum and have to be replaced.
You could try pulling the preamp tube and then turning on the amp--unless it's a "radio tube" type amp that has all the filaments wired in series (like the amp in this instructable.) In that case the amp won't work with one tube pulled.
Always nice to have a few backup tubes anyway, so new tubes are good investment...
Good luck finding the caps at RadioShack, though. The store near me doesn't carry electrolytics at the capacitance & voltage needed for a tube amp...(even for the relatively low voltage of "radio tube" amps-- 120V-150V.)
i hadnt realy look at it since then in till last weekend and found out in was a 300w tube amp by eico
im trying to get speakers for it now
(don't run it without speakers...)
its only 14 watts
buts its the famed hf-81
every review i saw was like this
http://www.stereophile.com/integratedamps/606eico/
12-14 watts of tube power is LOUD. Loudness is logarithmic--subjectively, twice as loud as 14 watts is 140 watts.
what dose this mean(i think it the ohms but i dont know...) i do know what g is...
1st is what im talking about 2nd is a bouns
Must be stereo, so two speakers (at least) are required--one per channel.
1st is what im talking about 2nd is a bouns
Sorry, I didn't get that...
You can also wire speakers together. Two (identical) speakers in series doubles the resistance; Two in parallel halves the resistance...
"1st is what im talking about 2nd is a bouns" i was talking about the pics
the 2nd one is the uncoverd bottom of my amp no real need to show but its still fun to look at.
The other possible approach would be to use triode/pentode paired in a single tube. There are quite a few out there. You might even try one of the low-voltage tubes intended for cars and portable radios. This page has some possible combo tubes... These are safer to use than normal high-voltage tubes.
When you said "I'd tear the amp down to the bare chassis and rebuild from there." did you mean rebuild from a kit or design a circuit yourself? Thanks for a great instructable!
By "tear it down and rebuild," I meant that a less "hacked" approach would probably lead to a cleaner, more organized, less cluttered circuit. As-is, it's gonna be more difficult to replace the caps in 30 years. The tangled wiring is more fragile than a well-planned strip-down / rebuild, too.
However, it's extremely quiet and sounds great, so I'm not too disappointed.
I'm not sure what approach is right for you. If you try rebuilding it yourself (and fail), you can always take it in to a profession to get it sorted. Just be REALLY CAREFUL if you do.
If you're not confident you can do this safely, take it to an amp tech...
If it hasn't been touched, then check for a short-circuit from B+ to earth. If this proves false, there may be an internal short in the Transformer:(
But, please do take care as allowing a Transformer to run hot for any reason is dangerous, not only to you but the surrounding electronics.
John Roberts.
Wellington.
New Zealand.
If you're not willing to learn (or unwilling to take the risk), seek out an experienced amplifier technician.
I've been dumb enough to play my old Ampeg in the basement with barefeet....wasn't a painful shock, I could just feel the current flowing from my left hand to the floor. One lesson learned.