Quicksilver KT88 mono 60watt amp schematic

[SY]

The cathode coupling idea is probably inappropriate for this design. Here, you've got a single relatively low amplification factor input stage coupled to a split load. The drive voltage of this arrangement is somewhat marginal as is the gain.

Doubling the drive voltage requirement and halving the gain of the output stage (which is what happens with this sort of O/P stage topology) would be a more reasonable tradeoff for a higher gain, higher swing type of driver.

[dshortt9]

Good Point. I often wondered why more manufacturers did not use this design.

[fdegrove]

Hi,

To be honest I'm looking for mods that can give measureable results.

Granted the example I gave was a bit extreme but....ask yourself are you listening to measurements or to your systems' music?

If you did not hear a change in sound while modding your SS amp then I can only conclude that either the amp uses considerable amounts of NFB or something else wasn't right.
It is easy enough to spend cash on so called better components,it is in fact a daytime job to decide whether these really are better sounding in that application.

To me at least,the Quicksilver amps deliver big time musically and other then the risk of stressing the GZ34 too much due to the high value filter cap I can't find fault with it circuitwise.
If that would have been the case I would have pointed that out before you bought it,Joe.

Enjoy the music,

[GaryB]

Sorry if my post caused any confusion. I only meant to say that C. Bonavolt's site had the 8417 schematic. To save people the trouble of going over there, I posted a compressed version here. I suspect that the KT88 schematic is almost identical.

I'll also second Frank's message - these are nice sounding amps. I never had any trouble with the GZ34 rectifiers. If you want to be safe then you can swap in some GZ37s. I did that and I thought it also was an upgrade in sound. They are just fun to listen to and should give you lots of enjoyment.

---Gary

[fdegrove]

Hi Gary,

You did post the right info IMO.
Ned Carlsson did his homework and if Joe wants to check the actual values of caps and resistors he'd be doing us all a favour.
Mostly himself though.

From experience the GZ34 is pretty sturdy even though,on paper,it is pushed beyond theoritical limits here.

GZ37 are getting harder to come by but I agree they do sound better in this amp and don't suffer from the technical limits of the GZ34 here.

The 8417 and KT88/6550 amps are sharing the same basic circuitry here and Joe's is just an original 8417 one modded to accept the KT88/6550 family of tubes.

I even went as far as to mod this amp to take the American fat bulb 6CA7 and to my ears that was the best ever at the expense of a bit of power.

Cheers,

[Original Burnedfingers]

Frank

My KT88 mono is the next series of amps not a converted 8417 units. This can be verified by the serial numbers. These amps have been upgraded to accept 12BH7 tubes on the front end instead of 12FQ7's. These amps also have the resistor and capacitor mods as you stated. The power supply tubes are 5AR4's also. From looking at the schematics posted there are alot of differences between the 8417 and the KT88 units.

Yes, they do sound great!

Joe

[fdegrove]

Hi Joe,

Yes, they do sound great!

And isn't that all that matters?

Glad to see you're happy with them Joe.

Cheers,

[Original Burnedfingers]

Frank

It has taken me some time to find out that a GZ34 is the same as a 5AR4 tube. Now, is a GZ37 the same as a 5U4 ? If so would it be a direct plug in replacement? In other words if I could substitute a 5U4 for the 5AR4 should I do it?

I'm trying to print out a copy of the 8417 amps schematic so I can make the necessary changes in it to reflect the KT88's circuit.

Joe

[halojoy]

this is a nice thread
fde groovy one has contributed
I am glad

enjoy the cooperation

[fdegrove]

Hi Joe,

Now, is a GZ37 the same as a 5U4 ? If so would it be a direct plug in replacement? In other words if I could substitute a 5U4 for the 5AR4 should I do it?

No,no the GZ37 is not the same as a 5U4G even when some books say it CAN be used as a direct replacement.
The way Quicksilver have designed the PSU even the sturdy 5AR4/GZ34 is taxed way over the design limit.

However,in your particular case you can use a GZ37/CV837 provided you want to hand over the dollars and even so the problem of the potential arc over of the 5AR4/GZ34 would not be solved anyway.
The GZ37 supports 100microF each at the cathodes where you have 330microF installed.
So on paper it would lessen the problem.

In practice though none of the "Quicks" I have seen suffered from that so my advice would be to suck it and see.

Enjoy the music,