OT Tranny swap: What to expect?

[Tonegeek]

Amp in question is 50 watt HRM, Skyliner stack (except for 56k slope), bluesmaster PI, AES Marshall OT, JJ EL-34 tubes. If I swap the OT to a MM or Heyboer bassman style and go with 6L6GC tubes, What can I expect in terms of the upper mid and high freq. response? I am trying to make the amp a bit more Fendery. To be more specific, there is a slight upper mid frequency that permeates this amp that I am wanting to tame a bit. The amp has a great Marshall type sound (which I like), but for its current owner it needs to have a bit more round, Fendery sound. I have about decided it is in the output as the usual pre-amp tweaks do not seem to affect the changes it needs. The freq. issue is also independent of whatever speakers we use. We tried many different speakers and cabs with this amp and the owner settled on Celestion Lead 80 speakers in a THD 2X12 open back cab. I have not heard this cab myself but it is very similar to the cab Jason uses on Steelbender.com for his Fuchs clips. Open to suggestions on the brand of tranny to get if this seems like it will help ...

[heisthl]

You may be hammering a nail with a steam shovel. If all you want is more "Scoop" just reduce the value of the treble cap (if its an amp with mid boost change the 390pF to 330pF or even 300pF). If you try that but think you've lost some mids you wanted to keep as an alternate you can change the 500pF/220K pair feeding the grid of V1b (make the cap 350pF or smaller). Personally I would go back to the 150k slope and more importantly, the standard PI too, IMHO the BM PI is a headroom destroyer/ tone disaster in a 50 watt amp and is a major contributer to the hi mid mud you don't like.

[Tonegeek]

You may be hammering a nail with a steam shovel. If all you want is more "Scoop" just reduce the value of the treble cap (if its an amp with mid boost change the 390pF to 330pF or even 300pF). If you try that but think you've lost some mids you wanted to keep as an alternate you can change the 500pF/220K pair feeding the grid of V1b (make the cap 350pF or smaller). Personally I would go back to the 150k slope and more importantly, the standard PI too, IMHO the BM PI is a headroom destroyer/ tone disaster in a 50 watt amp and is a major contributer to the hi mid mud you don't like.

I really think there is more going on here than just eq. which is why I am considering the OT. Funny you should mention the smaller treble cap. Thats exactly what i did on my personal amp (same specs as above). Per a funk suggestion I have a 100k slope too. The treble cap works out to about 235pf. The clean channel is very balanced in this amp. Still my amp has that same slightly middy Marshally sound which becomes a bit more pronounced on the OD channel. I know it is big bucks to swap the tranny, but my curiosity is up now that I have been researching this and reading some of the "testimonials" from people who have done this (not so much on this forum but others). It may be hype, but I need to sort it out somehow. i will meantime mess with the v1b grid network as you suggested (at least on my friends version). I am thinking neg. feedback should be looked at also, although I already have both these amps coming off the 8 ohm tap which is taming the mids more than if I left it on the 4ohm tap which I think is the bluesmaster spec. I did not like NF on the 4ohm tap much. Really over the top on the upper mids that way IMO. I am still on the fence about the BM PI. not motivated enough yet to switch it back....

Thanks

[talbany]

The 34's won't give you the low end the 6L's will. So with that in mind the absence of those frequencies creates the illusion of a more pronounced mids and highs..My take..If you are shooting for the Fender tone especially on the clean channel.. I wouldn't go with the Bluesmaster PI.. For one the 9.1K tail along with the 470 ohm cathode causes the PI to clip sooner you can really hear it on the top end.. Crunch Crunch.. If I were shooting for the Fender vibe I would do the PI and presence like #124 Cleaner w/ a bit less mids and highs due to the added amount of negative feedback and more headroom..You want to use the 4 ohm tap if you can...
It's really pretty simple.. If the player wants the clean channel more like a Mashall.. Go with the 34's and the BM PI and presence.. If he wants the clean channel like a fender Showman Twin go with the 6L's and the stock Dumble presence PI..
If you go with the 6L's you have to change the OPT.. Mashall style transformers w/ 6L's just don't sound right Yuk!! 1st choice is MM Bassman.. 2nd Off the shelf CE Dist. and then Heybor.. then Hammond last..Good Luck