12AU7 in V2 of Marwatt

[spikeRI]

well as per Sarges advice.....I dropped a 12AU7 in V2 (actually got the tube from the sarge). Fired it up with all setting as usual on hiwatt channel and it sounded pretty thin......not what I was hoping for. Then I plugged into the marshall side and BAM........before that channel had less volume than the hiwatt sound and always sounded good, but the majic of this amp has always been the hiwatt side.
Now the marshall side is bigger a little clearer and definately more musical. The best this amp has ever sounded on either channel........retried the hiwatt side and found if I goosed up the gain to about 3:00 it started sounding better and better, but not as good as the marshall side.
I'm going to go back to a 12AX7 for a few days then drop the AU in for a second time and see if my opinion stays the same....

[zaphod_phil]

Have you tried a 12AT7 in there yet? IMO an AU7 is probably somewhat too severe of a change in terms of the huge gain reduction and the very different bias point.

[spikeRI]

yes tried a mullard AT7 and it sounded like Blues Jr...........thin crappy sound. Did not, however, switch over to the Marshall side and see if it had the same effect on that channel as the AU.
BTW- still liking it...

[DutchMarco]

The AU7 sacrifices a lot of voltage gain to deliver lots of current. Don't overlook the role of current delivery to the power tube grids.

[sgtoverdrive]

i struggled against the au7 myself with the marwatt another huge trick can be acheived .once again thanks to heir unnst my resident rocket tech.i will dig it up and post if for ya spikey my lad.hold tight and hands off the cordite.the sgt will run back to the px and snatch the document..man aint life grand .here we all are tryin to make hiwatts out of grampys heathkit stereo tube! ps at is of no avail nor is 5751 the v2 position must be occupied by au or too much gain there will kill the tone stack and slow the other wise fast response one expects from a hiwatt down to a crawl.thats where i came out.next is the coupling mod.i beleve off hand it is conversion from .o1 to 1.5 or 022 lets see

[sgtoverdrive]

hope this works

[sgtoverdrive]

where the red arrows point is the fat zone on my unit.puttin in a 330 bypass dont hurt either.might suggest a good short plate high gain pre for the v3 final driver.and a set of real tubes dont hurt.hope it helps spike

[sgtoverdrive]

dutch marco is correct for my money the designer required au7 in that slot .there is a reason for that. overall id say my marwatt is a good deal faster then my novmerber knock off both have attributes but dst did a damn good job of impersonation of hiwatts vibe ,.at least in mine .provided you dont go against design parameters .now if i coudl just squeeze 10 more watts out of the little bugger id be sorted.

[spikeRI]

besides the AU I got from you, I put a mullard 12ax7 in v1 and a GE 12ax7 in v3 along with a set of amperex power tubes....
I'm liking it, would like to hear from other Marwatt owners......