Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: acheld on May 06, 2018, 10:55:28 am
-
I'm considering building Steve Luckey's AC15 as a combo amp.
It's a big board, and I'm trying to reduce the size of the cabinet. One place to save space would be in the power supply (one less tube). Would there be a big disadvantage in using a solid state bridge rectifier? My BJ conversion has this "feature" and works great.
The voltage is higher, but should be able to use the same 3A/1000V part.
I don't need extreme dirt in the sound.
-
Get your voltages right, add a sag resistor and let her bump.
-
Get your voltages right
that is your homework, hunt up a bunch of schematics that use a fullwave bridge and 2 EL-84's. going from a 5Y3 to FWB might yield as much as +40ish voltage bump.
-
As long as you are only in the "considering" stage, maybe consider using a 250-0-250 PT such as Hammond 370JX to get the voltages just right. Also, Hammond has several suitable chokes that have a much smaller footprint than the one I used.
I also have a short board version that will fit nicely in a 17" long chassis. The caps are all in a doghouse like the Fender amps, or if you use a 17 x 8 chassis, the caps would fit nicely alongside the 11.75" board. One forum member built the short board version.
-
I just love the smell of homework in the morning!
TY, great advice. :happy1:
-
I believe Member Lego4040 Built the chassis filter cap version. Anyway, loads of information on this here, http://el34world.com/Forum/index.php?topic=16874.50
I would use a Rectifier Tube (the proper 9 pin) and the exact cap values. I owned a 63 AC15, bascially the amp Sluckey and Barry wanted to make Marshall Style. I now have built 12 of these, one with verb. Waste of time IMO and I like Reverb.
The 370JX, with a tube rectifier will put the proper voltage to the plates and to me it made a difference. Dropping from 355Vdc to 302Vde reduced the headroom and I was not looking for something like a 18 watt Marshall. I have seen others build the AC15 like the current AC15, with 12Ax7 V1, but the special Voxes IMO were the EF86.
I have never had any problems with Microphonic EF86, but a lot do. I recommend building a head, but if combo is what you prefer or want, you can still seperate the chasssis from the speaker like the Matchless DC30. To me is is just easier to plug into a new cab than change speakers.
The Celestion Blue is a contributing factor, a large one and expensive. The Classictone Transformer is 6K reflected and I have confirmed the original Radiospares were 8K. I used Classictone in 4 of the builds by request to save a little, but I wouldn't use one myself. The AC15 has a characteristic of a extremely long onset of distortion so the sweet spot is large and you may not even notice it until you hit it hard.
I have played the AC15 with the Classictone and Hammond OT like Sluckey used in his and the 18 Watt Heybout OT Doug sells. The Hammond OT is nice. I used Mercury Magnetics in mine. Yes, the price on the website is a joke. Comparing an original to the all, the Mercury Magnetics and Dougs 18 watt Heybout Iron (this is a nice wind) either is great and the Hammond is too, but costs more.
I have also see guys up filteration, increase electrolytics from 8uf to 16 and use different rectifiers and all sound good, but it doesn't sound Voxy.
If you move forward, consider only one input for both the wiggle channel and teh normal channel. This puts the tremolo/Vibrato on the Normal channel too. You can mix the 12Ax7 with the EF86. Mods I consider needed. Multiple cap selections for Brilliance. Sluckey used 3 I think. I used 12 to enable me to allow more bass to pass than the original all the way to cutting all the bass necessary for full on overdrive. Slowing the Tremolo mod is one I think is needed.