I installed a weber cap copper cap module in my 1972 siverface bassman head and it warmed it up nicely. I recomend it to anyone. Very easy to install and reversable if you dont like it. Before i installed it my amp sounded thin.
BADDOG
have you tried the same amp with a new/other rectifier? i dont see how it was due to the rectifier that the amp sounded thin.
having said that, they seem like a great product, just they probably wouldnt change the voicing on amps that are already working correctly.
glad you like it and are happy with your tone.
Did you reset the bias? The reduced B+ with the same bias will run the output tubes colder ie with reduce idle current. As the B+ will be lowered ~20V, the idle current could be increased to maintain the same plate dissipation, compared to how it was before.
High B+ tends to give a 'harder' tonal balance, I could envisage that the copper cap would give a perceived softening of the tone, as well as giving sag type compression at high levels. Peter.
what is the easyest way to check and rebias this amp. Please
keep it simple. I thought about rebuilding the SS rectifier new diodes but am not sure what diodes to use.
thanks
keith
What was the problem with the original rectifier?Unlike tubes,solid state diodes either work or they dont,they dont get weak.To replace the diodes on the board you could have used 1N4007's,much cheaper than the Weber copper cap.To change/set the bias in the SF Bassman you have to change a resistor in the bias supply.I would suggest re-wiring the balance pot to an adjustable bias pot.Fairly easy to do,just a matter of re-wiring what is already there,and much more useful.
I like the balance pot . Could i replace the 15k balance resistor from the balance pot to ground with a 10k resister and a 10k pot which fould give me voltage ajustment both ways for biasing.
keith
Dont have a schem for that particular SF,but assuming it is the same as most other SF's,I would think it should work.I would just replace the 15k from the wiper to ground with about a 30 or 50k pot,using 2X the value of the 15k will put the 15k right in the middle of the pots adjustment range,giving you a wider range of adjustment.
I bought one for my Deluxe Reverb because I felt that the chassis was getting way too hot, and it was getting near time to change that old rectifier tube anyway. With one less tube heating up and a huge copper heat-sink, that did the trick in lowering the temp to something more reasonable. However, I felt it did quite the opposite to my tone. I felt it got thinner, maybe too much of the artificial sag in the B+ voltage compared to the real deal? I rebiased the power tubes when I did this, of course but I forgot to take voltage measurements before and after (D'Oh!)
I think I've gotten used to the sound by now though. I don't really consider it a loss since my amp is now noticeably cooler than it was before, and I didn't spend much more than I would have for a new rectifier tube. Besides, it's real hard to make a Deluxe sound bad!
stratomaster,your case is different,you are subbing a SS rect. for a tube,where baddog is subbing the copper cap for a SS rect.In your case the B+ would rise compared to the tube rect.This usually causes the tone to get harsher or colder,which could be perceived as thinner.Even tho Weber tries to get the "sag" of a tube rect. with the copper cap,it does fall short of the feel of a real tube.So in this case baddogs is getting closer to a tube when compared to his original SS rect.,you are going the other way.
Actually, I've found that replacing a tube rectifier with a CopperCap causes a slight drop in voltage.
...Ted's COPPERCAP™ produces a linear-voltage drop, not the exponential-voltage drop that actually occurs with vacuum rectifiers, ie:
Vd = (Ip/K)^(2/3)
...so, there's basically similar voltage drop at idle and maximum current, but certainly not the same voltage "sag" across the middle of the current range, for sure!
Last edited by Old Tele man; 11-27-2008 at 08:30 PM. Reason: spelling corrections
...and the Devil said: "...yes, but it's a DRY heat!"
And that changes the tone how?Originally Posted by Old Tele man
...the difference between a straight-line between two points and a cantenary-line hung between the same two points...the straight line is a constant voltage, while the cantenary line will ALWAYS be lower (more sag) thru the middle portion, but ramping back to the same voltage at both ends, ie: idle and max, like I mentioned before.
...the linear voltage will sound more 'tight' and crisp, while the exponential/cantenary voltage will exhibit the 'warmth' and 'squish' that we typically associate with vacuum tubes (and, here with vacuum rectifier tubes) and blues playing.
...measuring the power-supply voltage (B+) under load (swept sinewave, 100-6KHz) with a real GZ34 and Ted's replacement, will demonstrate the small but noticable difference in B+ (and thus likewise Vp) levels at the plates (yes, my stock '69 Super Reverb OT isn't perfectly balanced).
...and the Devil said: "...yes, but it's a DRY heat!"
I have opened a copper cap module in a Fargen Miniplexi ("EZ81" model for two EL84) and the circuit is:
two diodes in "v" > circular component (Thermistor?) > resistor > output.
The circular component is located over another resistor (no connected) to dissipate heat.
Here, a photo: Does someone know something on this circular component and the effect that produces?
Thanks to all
OK, I'm pretty much up on curves being not equal to straight lines - we all had to memorize 'catenary' in trig.What exactly is it in the amp that responds to the curve instead of the straight line? Does the preamp tube overload? Get more linear? Less? Phase inverter goes into distortion? Screen grids get biased differently? What?
And while we're on that, is it a specific voltage it has to sag to in the middle? A specific percentage? Will any radius of curvature of the characteristic do, or does it need to be limited? If I make an active power supply, huge DC coupled amplifier that provides a real B+ to the amp that is the same B+ as a "master" B+ with sag, will the amp sound the same just because the B+ sags just like it does with a tube, or must the tube actually touch the B+ for the effect to be heard? Does the amp know it's a sagging tube providing B+ or does it only know what voltage it gets and not care what provides the voltage as long as it's the same? If I make a resistor/diode concoction that provides a realistic curve, does the amp sound the same? Or has touching silicon poisoned the electrons in some way?
Then, given that:
What is it that sounds more tight and crisp? Does that mean more treble response? And this "warmth" and "squish" - is that more bass response and less treble? Or is it a form of distortion? Does one tube do this, or do they all? At the same time? Same amount? Or it it phased, one tube starting at one voltage an another at another voltage? Is the linear characteristic the crispness of rice crispies or quartz crystal? Is the warmth a hair dryer warmth? Is the squish the yielding squish of a down pillow or the resilient squish of a cheap foam pillow?...the linear voltage will sound more 'tight' and crisp, while the exponential/cantenary voltage will exhibit the 'warmth' and 'squish' that we typically associate with vacuum tubes (and, here with vacuum rectifier tubes) and blues playing.
That is to say - what the devil are you talking about? In terms that are measurable and repeatable?
Yep, I'm pretty sure that it would. Have you tried two differentG Z-34s? Or the same GZ-34 when new and when nearly worn out? Are they all perfectly identical? Is the effect only that it is curved, not straight, or will any curve do? Is the amount of curvature important? Is the curvature of the linear versus tube more or less than the ripple voltage on the B+?...measuring the power-supply voltage (B+) under load (swept sinewave, 100-6KHz) with a real GZ34 and Ted's replacement, will demonstrate the small but noticable difference in B+ (and thus likewise Vp) levels at the plates (yes, my stock '69 Super Reverb OT isn't perfectly balanced).
What affects what and where are the numbers?
Notice that I don't doubt what you say at all - but, I do remember Lord Kelvin's words:
When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind. It may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science.
...simple, one-word answer: it's the "...voltage..."
...the plate voltages (affecting ALL the tubes) "sag" exponentially with a vacuum tube rectifier (due to Child-Langmuir 3/2's Law equation) while a simple resistor yields a "linear" voltage drop for the same current load.
...one Mullard GZ34 and one Z34 from Ted...so, yes, you might call it a "...test of ones..." if you wish, but a valid test nevertheless--one vs. one.
...to be honest, my 64-year old ears couldn't detect much of a change, but the younger (mid-20s) players claimed the above sonic changes...and, that's why I also did the 'voltage' tests...to quantify the reason for the "changes", and I used a swept sinewave as input signal for consistant & repeatable input and measured the actual DC-voltage "sag" at the 6L6GC plates (on both DMM and oscope)...and, when plotted, the Coppercap™ showed essentially a straight-line "sag" plot, while the GZ34 showed the exponential / cantenary "sag" plot one would expect from the equation: Vp = (Ip/K)^(2/3).
...uh, definetly "hair dryer" warmth! (wink,wink)
Last edited by Old Tele man; 11-30-2008 at 09:01 PM.
...and the Devil said: "...yes, but it's a DRY heat!"
When the original chinese GZ34 blew in my '93 AC30, I compared a Weber CopperCap WZ34 and a NOS Amperex GZ34 in it. They were within a couple percentage points of each other as far as the overal effect on the sound. The tube GZ34 made the amp sound just a tad warmer and more touch sensitive and I went with that, but I wouldn't hesitate to use the Copper Cap if needed.
My 2 cents....
Greg
'Does someone know something on this circular component and the effect that produces?'
I thinks it's a NTC inrush current suppressor type thermistor. Cold the resistance is high and so it limits the start up current. As the resistors conduct and heat up, the thermistor's resistance goes down and is chosen to be effectively a short at working currents.
Check out modern fender schematics, most all have one of these in series with the PT primary to limit the switch on surge. Peter.
Also in the interest of honesty, I've done the same test, but quietly, and without the younger players' knowledge. Of the ones that said their amps sounded different, the majority said it was better somehow, in a way they could not put their finger on. But it was not either a big enough sample number to allow good statistical significance testing, to be fair.
Listening test which do not control foreknowledge (and expectations) on the part of the listeners are at best useless, as the result will be whatever the listeners expect if the results are anywhere close. At worst, they're easy to manipulate by the tester - or the testee.
Did you happen to pop those results into something like Excell and fit the curve to see if it really was the 3/2 power equation?and, that's why I also did the 'voltage' tests...to quantify the reason for the "changes", and I used a swept sinewave as input signal for consistant & repeatable input and measured the actual DC-voltage "sag" at the 6L6GC plates (on both DMM and oscope)...and, when plotted, the Coppercap™ showed essentially a straight-line "sag" plot, while the GZ34 showed the exponential / cantenary "sag" plot one would expect from the equation: Vp = (Ip/K)^(2/3).
Also, what was the amount of variation from straight line to curve? We may be on to something big here if we can relate a specific voltage to a specific sound from an amp...
Just offhand, I can't see why sweeping a sine wave would cause any changes in sag. It's current out of the power supply that causes sag anyway, and within the flat(-ish) passband of the amp, the frequency wouldn't matter much, except as that caused issues with speaker impedance curves. At a guess, you'd have to control that by using a resistor instead of a speaker or only testing at one frequency where the speaker was a relatively tame impedance on its curve to get any useful info.
Exactly. Ted sold me a couple to use in replacing the "brimistor" in my '66 AC50.
Then, his only purpose in the cooper cap is to slow down the start-up..?
I observed a "strange" phenomenon in the Fargen Miniplexi with the EZ81 substitute: on having activated the standby It was necessary to wait two or three seconds until the sound was appearing.
Then, with the amp sounding, the only "active" component to emulate the functioning of the rectifier tube is the resistor?
Regards
Resistor and diodes. But the current limiting switch on surge suppressor is a valuable feature, though the warm up is a whole lot quicker than a gz34. Peter.
yes, the "warm-up" is about 3 seconds....
...yes I did, and although the GZ34 value was close to 3/2-power at rated current (slightly above 3/2, ~ 1.58, as I recall), it was way off at idle current (closer to 5/2-power, as I recall)...gotta find my notes for the exact values.
Oh, something else interesting I recall, the Excel-calculated K-constant (representing Perveance) was "different" for the two points and neither was the same as the value calculated when backsolving from GZ34 specs of 17Vp and 225mA, ie: G ~ 0.0032 amp/volt^(2/3).
...more "difference" near low current end of the curve than at the high end current...looked sorta like "tuck under" commonly associated with triode curves.
...I just attribute it all to 'production' variances between different production runs/lots and different companies.We may be on to something big here if we can relate a specific voltage to a specific sound from an amp...
...and the Devil said: "...yes, but it's a DRY heat!"
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