Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: edthill on February 01, 2018, 10:25:58 pm
-
Hello,
Just curious if anyone on here has converted one of these newish Vox AC30C2's into a handwired number, like The Hoffman AC30, as that is where this amp seems to be heading.
I'm trying to figure out if it is worth keep the original PT, and what is going on with the taps coming off of it. Specifically, please see the schematic, what J42 and J43 are doing? Am I correct in assuming that J42 is the grounded center tap? What is J43's function? would I even need to use that connection in a Hoffman AC30?
http://el34world.com/charts/Schematics/files/Vox/Vox_AC30C2.pdf
Thank you for any tips or suggestions.
Ed
-
Specifically, please see the schematic, what J42 and J43 are doing? Am I correct in assuming that J42 is the grounded center tap? What is J43's function? would I even need to use that connection in a Hoffman AC30?
J42 and J43 supply approx. 25vac to the low voltage +27V and -27v power supplies for all that solid state stuff. Not needed in Hoffman's AC30. I would use the original PT.
-
Yeah I was going to say, so long as you use the right taps, you can use the same exact tube complement and get it going no problem. I.e. pull all the taps doing the low voltage stuff, and just use the heater and main B+ taps and you're golden.
Would definitely be interested in seeing it done! :)
~Phil
-
Thanks for the input, guys,
I ordered the Hoffman AC30 board from Doug in eyelet form, along with all the resistors and caps that I didn't have.
I was doing guitar tech work for a benefit all weekend and the backline company provided a real Vox AC30, from England, with Celestion Blues. I am definitely inspired now. It also means I have to rip out the Chinese Greenbacks in this amp now...There is only forward not backwards with tone.
I will document the progress for you guys.
Thanks again,
Ed
-
Update:
Gutting and drilling has begun,
More parts are on the way.
Another question on the Power transformer taps, Does J37 need to be grounded? It is a white wire that says zero volts on the schematic, oddly enough, it is connected to the bottom pole of the standby switch, not the usual B+ standby switch arrangement I am used to seeing. Also, it looks like the amps does not require a full wave bridge rectifier for the power supply, they use it for DC filaments. What a bizzaro amp this is.
-
If that schematic is right, then yes its the center tap of the high voltage and needs to be on the standby right now switches it on/off it looks like as well.
~Phil
-
I'm just curious; was there something wrong with this amp, or are you just hoping it will sound different/better with the Hoffman board, or what?
-
There was definitely something wrong with it. It had some weird noise, like a kind of hissy scratchiness going on, and the client who gave it to me, won $7500 at the casino 2 weeks ago when he handed it over and said to turn it into a, "real amp."
He tried new tubes which sometimes is almost all you can do with these flimsy PCB amps. Trying to "fix." them, unless it's glaringly obvious is a nightmare.
So why not turn it into a hoffman AC30? Handwire it, put some good iron (OT) and nicer components inside, use some mojo dijons, F&T's, on a hoffman board.
The guy has money and wants a real amp who am I to argue?
-
Thanks Phil,
I am going to ground that sucker.
If that schematic is right, then yes its the center tap of the high voltage and needs to be on the standby right now switches it on/off it looks like as well.
~Phil
-
^^ Nice. If the guy might care about preserving the reverb, Lou Rossi on the ampgarage.com forum has a nice PCB implementation of the Belton digital reverb brick. http://ampgarage.com/forum/viewtopic.php?f=6&t=28294&start=30#p379141
-
Thanks, Drew,
I will check that out.
-
Finally after some months of this sitting around, I decided to finish her off.
Admittedly my confidence was broken after dealing with a garbage customer.
So I was afraid to build.
Alas...She sounds great. Converting these CC2's is not as hard as it looks. The PT is very straight forward, and does not require a fullwave bridge rectifier. I don't even miss the tube rec. If you do convert a CC2 I strongly recommend chucking the Chinese Celestions in a dumpster. Good speakers make all the difference in the world. Thanks again to everyone who helped with deciphering that schematic. I would also like to say, save all the little screws and things that you rip out of the stock CC2, they will come in handy later.
-
Good job, looks like a better amp already.
-
Very cool! I'd love to hear an audio sample.
~Phil
-
Very cool! I'd love to hear an audio sample.
~Phil
Quick thing I recorded for the client using my iphone 8 and very light effects in garageband.
https://soundcloud.com/melatoninsboston/hoffman-vox-ac30-converted-from-ac30cc2
-
Wow sounds outstanding!
~Phil
-
Wow sounds outstanding!
~Phil
Thanks Phil! I wouldn't want to hand any of my friends or clients an amp I wouldn't play out with myself.