As a vehement oponent of fuses i certainly see your point. In all my SS and tube projects i never use fuses and all is fine. Otoh, though the cathode fuses are not that common; Jadis may now something about this design which is not really confidence inspiring. Especially into the taxing load you're gonna have. It may be a good idea to run them with fuses for a while and see at what volume setting the fuses pop. Btw Cerafine are my favourite price/quality caps for tube designs - i've given up collecting mountains of polyprops in the PS.
Looking at the quality of components on the pcb is quite depressing
Hi,
It doesn't have anything to do with the design as such, other then it running in Class A for which you do need reliable tubes.
In the days this amp was designed Jadis had had very bad experience with KT88s misbehaving, hence they'd played it safe and put the fuses in.
You don't think the polyprops with their non-polar construction would be the better cap?
Apogee,
Did I mention upgrading the feedback resistor and cap to better quality as well?
Cheers,
It doesn't have anything to do with the design as such, other then it running in Class A for which you do need reliable tubes.
In the days this amp was designed Jadis had had very bad experience with KT88s misbehaving, hence they'd played it safe and put the fuses in.
You don't think the polyprops with their non-polar construction would be the better cap?
Apogee,
Did I mention upgrading the feedback resistor and cap to better quality as well?
Cheers,
Interesting comments!
I agree the parts on the board are pretty disappointing considering the original cost of the unit... Oh well, it will be fixed soon....
Here's a question for the group elaborating a bit more on the fuse question. Any engineers/physicists out there?
In the SS world, as I posted above, my ears have told me that fuses are bad. But, with them located on the output cathodes might they react differently?
My line of thinking here is they are in a circuit with high voltage and high impedance. In contrast to a fuse being located in a 4 or 8 ohm speaker line that must pass lots of current, might there be less of an impact because of the high voltage and low current?
Or - conversely will the fuses have even a larger effect on the sound?
My mental parallel here is the difference in wire designed to handle low vs high voltage. In addition to high voltage requiring smaller conductors, I also know that the wire insulation is thicker. I'm wondering if because the high voltage has the tendency to jump gaps easier if perhaps the fuses and holders will have less of an effect due to the higher voltage. In effect the electrons having an easier time traversing the gap...
This is just an hunch and I don't know the theory to back it up. Perhaps the voltage isn't high enough to really make a difference.... Any comments on the theory behind this? Am I totally off?
And yes, I can try it both ways... I would just really like to avoid taking this thing completely apart twice to find out...
Thx,
I agree the parts on the board are pretty disappointing considering the original cost of the unit... Oh well, it will be fixed soon....
Here's a question for the group elaborating a bit more on the fuse question. Any engineers/physicists out there?
In the SS world, as I posted above, my ears have told me that fuses are bad. But, with them located on the output cathodes might they react differently?
My line of thinking here is they are in a circuit with high voltage and high impedance. In contrast to a fuse being located in a 4 or 8 ohm speaker line that must pass lots of current, might there be less of an impact because of the high voltage and low current?
Or - conversely will the fuses have even a larger effect on the sound?
My mental parallel here is the difference in wire designed to handle low vs high voltage. In addition to high voltage requiring smaller conductors, I also know that the wire insulation is thicker. I'm wondering if because the high voltage has the tendency to jump gaps easier if perhaps the fuses and holders will have less of an effect due to the higher voltage. In effect the electrons having an easier time traversing the gap...
This is just an hunch and I don't know the theory to back it up. Perhaps the voltage isn't high enough to really make a difference.... Any comments on the theory behind this? Am I totally off?
And yes, I can try it both ways... I would just really like to avoid taking this thing completely apart twice to find out...
Thx,
Hi,
While I follow and agree with your line of thinking, let's not forget that the fuses are in the signal path here.
I feel that with the current KT88s from former USSR we can safely consider leaving the fuses out; anyway you turn it they're never going to improve the sound.
Since this amp will service the tweeter section of your speakers it won't have to work hard at all.
One caveat, the amp is seriously limited in high frequency response by its driver stage, it's starts to roll off gently from ~ 16KHz.
There isn't anything you can do about that...
Cheers,
While I follow and agree with your line of thinking, let's not forget that the fuses are in the signal path here.
I feel that with the current KT88s from former USSR we can safely consider leaving the fuses out; anyway you turn it they're never going to improve the sound.
Since this amp will service the tweeter section of your speakers it won't have to work hard at all.
One caveat, the amp is seriously limited in high frequency response by its driver stage, it's starts to roll off gently from ~ 16KHz.
There isn't anything you can do about that...
Cheers,
12AX7 cathode coupling caps... I'm still wondering about this...
Would it be better to replace the 68uf 63v 12AX7 cathode bypass caps with paralleled 47+22 uf 100v Black Gates
-or-
use a lesser 68uf cap
-or-
switch it to one of BG's standard values (i.e. 100uf)
-or- use a 68uf Solen Fast Cap? (if it will fit)
Will increasing the capacitance in this location to BG's 100uf hurt the sound quality or would should I go the other way and drop it down to 47uf?
Lastly, with the larger can type caps is it bad to locate them a few inches away from the board and connect to them using wire? Does it really make that much of a difference? I am planning on twisting the leads unless discouraged by the forum...
Thx,
Would it be better to replace the 68uf 63v 12AX7 cathode bypass caps with paralleled 47+22 uf 100v Black Gates
-or-
use a lesser 68uf cap
-or-
switch it to one of BG's standard values (i.e. 100uf)
-or- use a 68uf Solen Fast Cap? (if it will fit)
Will increasing the capacitance in this location to BG's 100uf hurt the sound quality or would should I go the other way and drop it down to 47uf?
Lastly, with the larger can type caps is it bad to locate them a few inches away from the board and connect to them using wire? Does it really make that much of a difference? I am planning on twisting the leads unless discouraged by the forum...
Thx,
Hi,
I wouldn't bypass the BG with a smaller value, BG doesn't recommend it they dn't benefit from it, quite to the contrary.
As for the value, I'd stick with 68µF or if you must go with the 100µF one. Certainly not less than the original value.
I recommend the non-polar BG N-series because at these small value thet won't break the bank and from what I heard they're better then the standard BG range.
Cheers,
I wouldn't bypass the BG with a smaller value, BG doesn't recommend it they dn't benefit from it, quite to the contrary.
As for the value, I'd stick with 68µF or if you must go with the 100µF one. Certainly not less than the original value.
I recommend the non-polar BG N-series because at these small value thet won't break the bank and from what I heard they're better then the standard BG range.
Cheers,
Is the roll off caused by the tubes used or just the design in general? What is the cause?
Is there no way to improve on it?
I've been researching Riken resistors. I am planning on converting to them but they are said to have a "warm" sound. Will they compound the roll off problem and make it worse?
Thx!
Frank (et all),
Have you tried the Kiwame resistors? They are about 1/3 the cost of the Rikens...
I'm wondering if there is a less expensive alternative that is nearly as good as using the Rikens through the whole circuit.
I will need about 60 resistors total and at $3.00us each for the Rikens it adds up pretty fast...
Any other lower cost alternatives come to mind?
Thanks!
Have you tried the Kiwame resistors? They are about 1/3 the cost of the Rikens...
I'm wondering if there is a less expensive alternative that is nearly as good as using the Rikens through the whole circuit.
I will need about 60 resistors total and at $3.00us each for the Rikens it adds up pretty fast...
Any other lower cost alternatives come to mind?
Thanks!
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