K5881 confusion

[davew]

I bought a K5881 amp off Ebay recently and the printed sheet describes it as a MKII which runs in class A. However, the schematic sheet describes the circuit as K5881 push-pull. Isn't that class B?
I'm no expert but the diagram(which matches the amp wiring) looks to be class B with the 2 O/P valve anodes feeding either end of the OPT and what looks like a phase splitter ECC83. Was there also a single ended K5881 - two valves paralled?
Anyway the amp sounds great - what would you suggest as simple component upgrades? Maybe the imput 0.22mF input and 0.47mF coupling caps?
How about the decoupling electrolytics. Would they benefit from an upgrade?
Thanks
dave

[Cobblers]

Push pull topology can be run in class AB or pure class A.
I have a push pull amp which runs purely in class A, so don't worry!

Class A output means that the amplifying device is always on, whether there is a signal or not.

By their nature Single ended amp designs are always class A.

[prince of darkness]

Hi Dave,

The K5881 was pure class A. Comparing the mark II to the mark I, the input stage of the mark II is shunt regulated push pull (SRPP) using a 7025 double-triode, whereas the mark I used a triode connected EF86 pentode. In addition feedback was reduced.
There was also a K5881 parallel single ended.

[davew]

Thanks alot for that - I see that I need to do a good bit of reading up on circuit topologies!
Any ideas on the best simple upgrades to improve sound quality?
Any opinions on which are the best 5881s? Sovteks OK?
thanks
dave

[Cobblers]

Originally Posted by davew

Thanks alot for that - I see that I need to do a good bit of reading up on circuit topologies!
Any ideas on the best simple upgrades to improve sound quality?
Any opinions on which are the best 5881s? Sovteks OK?
thanks
dave

Sovtek 5881's are probably the best power tube for this amp, but you could experiment with the input valve and phase splitters.


I use Sovtek 5881's (which isn't really a genuine 5881, but an equivalent russian tube incidently!), which is a very tough tube and find them clean and articulate sounding.

[NealG]

Dave, there's quite a bit you can upgrade with on the 5881,

You can go down the well trodden path of fitting BlackGate cathode bypass caps and a BG WKz in the PSU. Fast recovery / hyperfast diodes can also be fitted along with some boutique resistors in the signal path. Topology wise the front end can be changed depending if you don't like the MKII SRPP stage.

The phase splitter benefits from a CCS IMHO, I posted about this HERE some time ago and also Iv'e messed around with the feedback cct that to my mind made the bass tighter. Look HERE

It's a great little amp. One I must listen to more!

I also tried triode connected on the o/p stage but didn't like the results, power dropped and distortion went up but YMMV.

Cheers!