Modded Komet 60

[nek]

There are several Komet 60 modded by KF. I have heard the mods were minimal. Any ideas? Circuit or tubes?

[Allynmey]

There is the Mark Knofler Mods Komet 60. It is 3 resistors and 2 capacitors and substitutes el34's with 5881's. I have one here and like it better than the standard K60's. There was a (4) el34 version made by Ken and then disassembled because he couldn't get it to sound right. I saw that one for sale on ebay a few months back. You could see the magic marker writing all over it. The rest I don't think were mods per se but, tweaking of the bias and tubing.

[j-po]

3 resistors and 2 caps? Care to share what and where?

[wallybob]

I second that - I can't stand the anticipation!

[funkmeblue]

I would suspect one resistor change for the bias, and maybe the other 2 are the screen resistors. The two .022 after the phase inverter would be my guess on the caps. Guessing maybe blackface specs. I've been wrong before

[paulster]

I would suspect one resistor change for the bias, and maybe the other 2 are the screen resistors. The two .022 after the phase inverter would be my guess on the caps. Guessing maybe blackface specs. I've been wrong before

Yep, I'd expect the PI output coupling caps to be changed to .1uF and the screen resistors to 470R. The other resistor could be the bias range resistor, although this amp is designed to have a bias range wide enough for 6L6 tubes anyway so could probably accommodate 5881s straight off, so I think it's likely to be the PI tail resistor from 10K to 27K (22K).

Allyn - what plate voltage do you end up with when running 5881s? I'd have thought the K60 would be a bit hot for them? And are MK's amps running new or NOS?

[funkmeblue]

ya, I forgot the k-60 could already run 6l6's.

[paulster]

I think it's likely to be the PI tail resistor from 10K to 27K (22K).

Scrub that, I've just remembered that the Black/Silver face amps used 12AT7 tubes for the PI, so it's possibly the NFB resistor instead.

[Allynmey]

I though I posted it already somewhere....

Replace the two .02uF PI Caps with .047uF OD's
Replace the two 220K PI>power tube grid/bias resistors to 100K
Change the V2 Plate resistor from 100K to 220K

There you go. Bias it a little hot.

Very dynamic and open

[paulster]

Allyn

Thanks for the info.

What's the plate voltage like on the 5881s in this? It must still be around the 480V mark, which seems a bit brutal.

Cheers
Paul

[castor]

can someone explain these mods?
--> 100k to 220k: I think that this will increase the gain on this stage, am I right?
--> 0.02 to 0.047: what change with this mod? will the sound be more round and with more bass? I thought that the rule of these caps was only a filter..

At the end, the overall gain of the amp will change much?
I love the sound of MK komets..

I read somewhere that the mod was done only in order to make a better sound for single coil guitars.. but have someone tried modded amps with HB ones?

castor

[wallybob]

Allyn

I'm trying to figure out where the 150k bias resistors are. My copy of the schematic has 100k & 82k plate resistors for V3 and 220k resistors supplying the fixed bias to the output tube grids. Am I missing something?

Thanks
wal

[tubedogsmith]

Allyn

Thanks for the info.

What's the plate voltage like on the 5881s in this? It must still be around the 480V mark, which seems a bit brutal.

Cheers
Paul

I would guess he used the old sovtek wafer base 5881's. I've seen them run in old Traynors at 540v with no problems.

[M Fowler]

wallybod,

I will have to second that my schematic and layout shows the same as yours.

Mark

[Roe]

Allyn

I'm trying to figure out where the 150k bias resistors are. My copy of the schematic has 100k & 82k plate resistors for V3 and 220k resistors supplying the fixed bias to the output tube grids. Am I missing something?

Thanks
wal

my guess is replace the two 220k resistors with 100k and up the .022s to .047s inorder to get the same -3db point. this will reduce the pi distortion a little.
changing the 100k plate resistor to a 220k on v2 will lead to more distortion