Modding a Davis Model 106 P.A. amp

[zozoe]

Good evening all~ I just came into this cute little amp, & after much searching online for possible & necessary alterations to make this a guitar growler, but could come up w/only this schematic,
Having my tech just do his thing & not take it further than simply functioning well, is like bringing a Harley to a lawn mower repair guy. Is it possible for some of you kind folks to chime in with 'must do' value alterations to make this 2xEL84, EZ81, 6EU7 into a little monster.... Would immediately having him wire it for a 12ax7 or the gainy & popular Vox EF86 preamp tube be a good start? Then, what more could be swapped out for different values to make it into a guitar or harp that screams, & something more suitable for RnR than playing my dad's olde '78's through. I realize it might sound like a heap of work for ya'll, but I only know basic electronic & can follow a schematic, but have never done it myself,,, I simply want to hand it over to my tech, as I'm just an end user.
Enclosed is a chassis shot & an original schematic for you generous consideration...
Thnx in advance~

Screenshot_20211103-183613_Gallery.jpg

[sluckey]

Look here for some ideas...

http://sluckeyamps.com/index.htm

[thetragichero]

ez81/6ca4 means you'd have an extra amp of filament current if you decided to go solid state rectification. the el84s might not like that though. definitely has potential

[Phil_S]

There are no indications of PT voltage. It would help to know. My gut reaction is the remove the 6CA4 in favor of a solid state rectifier so you can redirect that filament supply to a second preamp tube. If the PT voltages work for it, you can build a Marshall 18W without the tremolo. I think that qualifies as a growler.

There is no electronic difference between the 6EU7 and 12AX7. They are the same tube with a different pin out. The only notable difference is that you can't run a 6EU7 on a 12.6v filament supply. Since we don't do that anyway, there's no meaningful difference. If you received a good 6EU7 (maybe a Mullard?) then you might want to keep it. It's not a big deal to change it if that's your preference or if you didn't get the 6EU7.

[zozoe]

Thnx, PHIL_S,,, So, with as many specifics you're graciously willing to take time to do, what would 'you' do to this make it into a VOX-like 18w killer, w/o trem of course..? I get that I'm not working with too much in the first place, but neither was Gibson, Valco, Fender, etc., but I'd like to try a few workable tweaks, which could include an EF86 preamp tube, unless the EU7 or an AX7 would offer a tighter, less 'flabby' OD.... But I dig the gain possibilities that I've always gotten from my old low wattage Voxes that've employed the EF.....
Thnx in advance....

[thetragichero]

ef86, or if you're a cheapskate like me a 6au6. i'd probably replace 6eu7 with 12ax7 purely for the availability of replacements. depending on on the transformer specs one could throw in 6l6 power tubes in place of the el84 (also depends on how blank of a slate you wish to start with. i like to strip everything and determine what to build from the transformers)

[trobbins]

I hope you appreciate that the output stage is a 'self-split' format so there is no way that it can be coaxed in to typical output stage overdrive 'tone'. I'd suggest that all you can try and do is overdrive the input and 2nd stages with following vol pots to manage those overdrive levels, but keep the output stage running clean. The first stage could be cathode bypassed for extra gain, as well as splitting the cathode of the 2nd stage to raise its gain and work out what level of feedback (if any) suits your speaker.

[Phil_S]

ef86, or if you're a cheapskate like me a 6au6...

FWIW, in a one time bulk purchase of very cheap used tubes (by what would fit in the box or maybe by the pound, IIRC) I received many 6AU6. I tried the cheapskate route, but I didn't like it. Maybe they were all bad tubes. I dunno.

... i like to strip everything and determine what to build from the transformers)

Me too. Opens up the potential of what's worth saving. My favorite kind of project.

[zozoe]

All good, but is an EF86 a viable & not too complicated option?? Thnx

[sluckey]

yes

[zozoe]

Cool,,, So, with as many specifics you're willing to take the time for, what would 'you' do to this make it like a VOX-like 18w killer, w/o trem of course..? I get that I'm not working with too much in the first place, but neither was Gibson, Valco, Fender, etc., but I'd like to try a few workable tweaks, which could include an EF86 preamp tube, unless the EU7 or an AX7 would offer a tighter, less 'flabby' OD.... But I dig the gain possibilities that I've always gotten from my old low wattage Voxes that've employed the EF.....
Thnx in advance....

[sluckey]

I gave you a link to several amps that could be easily built with this PA. Some Vox and Marshalls in particular. In fact, the Dual Lite combines Marshall and Vox sounds in one small 15 watt amp. Well worth taking a look.

[zozoe]

Thnx all!!