Ampeg SB-12 inspired amp

[Banjan73]

Hello!
I`ve just tested my new home grown amp. The quest this time was to build a bass amp for my son. I googled a little bit, and the Ampeg SB-12 stood out as a nice candidate for beeing a base/idea to my build. My approach for new builds is to be inspired by classic amps, get the schematics and draw them all over again the way I want them to be.
So this amp is inspired by the 6L6 version of the SB-12. I have (as always) used SS rectifier for HV and the filament is also rectified. The tonestack (James/Baxandall) is almost identical, with minor modifications. Power transformer is from a Tandberg Huldra 4 radio, and output tranny is a Hammond 1650H.
Well. The first test is performed with a band. I tested it with my Les Paul, and the bass player tested it with a double bass and an electric bass. I must honestly say that I liked the bass sound better than plugging in a guitar to this one. But thats the point with this one, to be a bass amp, hehe.
I need to do some minor mods/measurements to this one, and I need to build a enclosure for it. I didn`t have two ECC83 tubes, so the second one right now is a ECC81. But tubes are ordered. I suspect the sound to be a little different with a ECC83 in the second position.
Anyway, are there any recommendations for a loudspeaker for this one? I am looking for a speaker with high sensitivity. My first chioice right now is a Mojotone greyhound 12" (101db/W), but I don`t know that speaker. Any other suggestions?
Heres some pictures and schematics:

[Banjan73]

Ouch!
I just spotted a minor, but important error on hte schematics. B+ is connected earlier in the filter chain.
Heres updated schematics:

[Banjan73]

No speaker thoughts here? Jensen C12N is supposed to be the original, but 97-98db...
Anything els than mojotone greyhound that I should consider?

[Banjan73]

Hello!
Some huge updates here.
I finished the amp, and it sounded GREAT on guitar! But.... this was supposed to be a bassamp, and it didn`t live up to my expectations. It pulled out about 15W clean power. In my opinion, it was too little punch and too low wattage.
So... Then I went totally bananas.
The new thing now is to use full bridge rectifier for B+ to produce more voltage for the anode. Output now is about 760VDC (!!!) So, thats a little high for those 6L6 tubes. Well... I had stored somewhere a matched quad of JJ EL34 tubes, and it was time to put the gloves on.
As I think that pictures tells more than my blah-blah, heres the new schematics.
P.S. As my output transformer is rated for 40W, I need to restrict this amp a little bit. Therefore I drop the voltage to the screen with that zener diode to obtain, hopefully, around 40-45 watt...
 

[Banjan73]

BTW. The change of v3/v4 from 12AX7 to 12AT7 is due to that the PI gets overdriven. The schematics for 12AT7 is not updated yet (old values from 12AX7).

[Banjan73]

Are there any considerations I should take here? Anything special I haven`t thought about? It`s much more scary working with 700+ volts than 350V, hehe :-)
Please shout out if you guys notice anything.

[jansch]

R17 and R18 seem to be unnecessarily low, which is why the PI gets loaded and over-driven easily and may not produce enough signal to drive the output tubes. My old Philips datasheet shows Rg1 500kohm max for a fixed bias EL34.
The same data lists 425V B+ for anodes and screens, with 1kohm screen resistors, Raa (the impedance of the OT loaded with a speaker) 3.4 kohm. While it is not super critical, we do not know whether your OT has an impedance in this range. 760V B+ is rather for an 80W amp, but with Raa=11kohm and B+2 (for screens) 400V. In your case, 300V seems not enough even for a 40W amp. R23 and R24 of 2.2 kohm make the situation even worse.
Hope this helps a little