Please tell me how to upgrade Music Angel KT88 amplifier?

[kevinkr]

Being no fan of SE I'm going to put my boot in....

Yet more hype and flannel of so many SE circuits claiming of doing better over better of the same thing all giving the same end performance. Not worth the commentare.
Bin it.

richj

OT:
Hi Richj,
Seems like you have a bit of an axe to grind today.. Not the most useful response to a NEW member asking a legitimate question.
Your comments about SE I could with equal vehemence apply to PP, so I guess to each their own..

On topic:
You'll need both 6SL7 and 6SN7. My personal preference lately has been towards 1950's vintage Sylvania in both types. As other posters have indicated this is not the most reliable amplifier out there, so check it out carefully. It does however have the makings of a reasonably good SE particularly at the price.

The best sounding 845 are probably NOS RCA/GE types that are now hopelessly expensive and probably out of reach. I have heard the 845 and 845B in DIY amplifiers, and preferred the NOS frankly. I have heard good things about the 845M, but have not heard a pair.

Edit:
I'm thinking an NTC thermistor in each filament supply for the 845 output tubes might be a wise investment, reducing the cold filament inrush current should improve reliability. The tricky part will be to find a thermistor that has sufficiently low hot resistance not to cause excessive voltage drop in normal operation, but has a cold resistance high enough to limit the inrush current to a couple of amps. You can also do the same thing with a fixed resistor and shorting relay - at the expense of more complexity.

Consider bucking the line voltage with a transformer if your line voltage is much over 230V - otherwise the higher line voltage will provide the voltage margin for mods like the one discussed above.

 

[richwalters]

kevinkr..sorry about that......stripping the emperor of his clothes... my brain was in p-p waiting for the snow..

richj

 

[kevinkr]

kevinkr..sorry about that......stripping the emperor of his clothes... my brain was in p-p waiting for the snow..

richj

Hi Richj,
Now that evokes quite an image...

I hope your snow is nicer than ours, horrible slushy mess, and even worse Mass_*ole drivers...

Let's all share a little thermionic warmth this season, of course your favorite libation will always help. (Mine is Drambuie on a cold winter night.)

 

[eivindjk]

All though there are some disagreements, partly as a consequence of my question, I hope that in the long run this thread stays on-topic

I appreciate all answers - most of them makes me wiser.

I have ordered a XDSE 845 and will be receiving it within the next few days. Don't have too much experience with these kinds of amps, and considered this one a cheap ticket to ride.

I think and hope it'll be fun listening

 

[kevinkr]

All though there are some disagreements, partly as a consequence of my question, I hope that in the long run this thread stays on-topic

I appreciate all answers - most of them makes me wiser.

I have ordered a XDSE 845 and will be receiving it within the next few days. Don't have too much experience with these kinds of amps, and considered this one a cheap ticket to ride.

I think and hope it'll be fun listening

Good luck, and keep us updated!

 

[skorpion]

I would appreciate any comment on the Lampizator mod in the link above.

/Erling

 

[Svein_B]

I would appreciate any comment on the Lampizator mod in the link above.
/Erling

The link above (previous page) is for the modifications of the 845 amp, so it does not belong in this thread.
Lukasz Fikus has also done some mods to the KT88 amp: PROCESS OF KT88 ANGEL TWEAKING

The design is based on the Williamson, but the Grid stoppers (not shown on the factory schematics) seem to be rather high values. That is before Lukasz removed them all.
- 22K from driver to phase-splitter grid.
- From phase splitter to driver, there is first a 120K resistor in series with the signal, then 560K grid-leak, and 10K grid-stopper.
- Grid-stoppers to the KT88 also seem to be 10K.
The resistors mentioned appear to be ear-friendly carbon composite types.

Can anybody understand and explain why the Chinese builders have used all these resistors in the first place ?
I do not see any frequency compensation in the feedback loop. It has also been suggested that the feedback ratio might be a little lower than typical for pentode operation. Could this be a clue?



SveinB