Hi Folks,
Happy New Year , I finished my AA wreck build a few months back, It turned out great, played around with it and have got it where I like it .
I ended up putting the grid resistors directly on the sockets and not on the board ,
I played around with output tubes, tried 6V6's , KT66's and ended up with EL34's ,
Also added the Fischer PPIMV #3 that phase cancels the signal from the grids to of the EL34's , it works OK to a point , from full to about 1/2 is useable , after that it just loses its mojo. I actually keep it on full now .
I squeezed it into a combo cabinet slightly bigger than a 5E3 cab, it's so compact that people don't realise the beast inside 😂 and played around with speakers, I ended up with the Eminence Wizard which is great with the circuit , it's a very efficient (103db) 75w take on the Celestion G12H30 , it can handle the EL34's with ease.
I did have some issues with the biasing , I tried everything from 50 to 70% plate dissipation , there was serious harsh grainy squawks on certain notes when biased too cold ,I discovered the circuit is best suited to 70% plate dissipation , that's the Wreck spot , anything lower just doesn't seem to cut it .
After a few months of testing and playing in gigging situations , I think I'm pretty happy with the results.
I used a combination of Jupiter and Sozo coupling caps, basically what I had in my stash , they're still burning in so it'll only get better with age ....
It's a little compact combo , a wolf in sheeps clothing .... very happy with the results ... next up a Rocket and a Liverpool
here's some pictures
regards
Mark
Hi Folks ,
Haven't been here for a while , an update on the Express build after 9 months, spent a bit of time going through it these last couple of days , been having issues with volume and bias (again) . found two problems that combined made it very frustrating to nut out . the volume was not as loud as you'd expect , I could play it with the volume at noon and it didn't tear your head off, It WAS running a set of Mullard reissue EL34's ,
Checked the bias - cold again - yet it hadn't been played for 4 months , rebiased to 70% and the volume came back nicely , played it for a bit and as the tubes heated up/settled the bias shifted again , from 44mA to over 55mA , reset again and now the volume had dropped back to before .
As I had the screwdriver in the bias pot i watch the bias meter jumping all over the place ... aha ... dodgy bias pot , so I swapped it out for another pcb mounted pot (different brand) worked well for a while, then started doing the same thing .... frustrating , tried another but ended up removing the PCB mounted ones and put the old Fender CTS 10k pot on the chassis and ran some wires (needed to change the value of the 47k bias resistor to compensate for the pot now being 10k )
this seemed to fix it , biased the Mullards again and left the amp on for 4 hours to monitor it ... at 2 hours it was fine - 44mA but at 4 hours it went up to 55mA , then one tube was 55mA and the other was 0mA , then went back to both at 44mA . I wiggled the pot again and it was solid , no more jumping around ... I concluded the Mullards were unstable and would fluctuate up and down the longer they were on , (not good for gigging) , so I put a set of EH6CA7's I had in, reset the bias and the results are great, stable non fluctuating and the volume returned ,
I guess either the reissue Mullards don't like running at 70% for long periods, or they become unstable when running hot for long periods OR I got a bad set of tubes ... I'm liking the 6CA7's a lot, much more glassy , tighter bottom end and less compressed . It's personal choice I know , but so far I'm digging them ...
Anyway I thought I'd share my latest findings , I've read many times on the net that the Mullard reissues are fantastic , They may be but my experience is different and I'm going with that - rock on everyone