AC15 or AC30? (Hammond AC15 OT loudness)

Vox and Hiwatt Discussion

Moderators: pompeiisneaks, Colossal

Post Reply
psychepool
Posts: 260
Joined: Fri Apr 18, 2014 8:29 am

AC15 or AC30? (Hammond AC15 OT loudness)

Post by psychepool »

I want to make Vox AC series someday because of it's bell-like clean tone.

I have already set the Mod-points that I would like to try out on preamps,
The only distress is whether to make it 15 watts or 30 watts.

Perhaps this amp will most likely be played at the bedroom level using an attenuator at home.
But sometimes I work with drums in the practice room.
I do not want the clean headroom to be buried by the drum, but it should not be overly large.

Previously I made two EL84 pair amplifiers using a Hammond output transformer.
One is Marshall 18W LiteⅱB and other is Ceriatone Creme Brulee with Blues Junior output transformer.
Both of them felt lacked a clean headroom.


But the Hammond AC15 transformer is much larger and heavier than other transformers in 15watters.
Therefore, I think that the output is much bigger than other 15watter transformers.

I would like to ask people who have made Hammond AC15 output transformer what output is.

Personally, I think that the Hammond Vibrolux transformer (35W using the 6L6 or 5881 pair) feels the most power output in weight.
Therefore, it would be satisfactory if the output (clean headroom) would come out.

I could just make the AC30 and use it half way, but I do not want to unnecessarily increase size and weight.
So if there's enough headroom with an AC15 transformer, I want to make it.


I'll wait for advice from Hammond AC15 Transformer users.
Roe
Posts: 1643
Joined: Thu May 31, 2007 2:10 pm

Re: AC15 or AC30? (Hammond AC15 OT loudness)

Post by Roe »

I prefer the ac30 with larmar master volume - its perfect
www.myspace.com/20bonesband
www.myspace.com/prostitutes
Express, Comet 60, Jtm45, jtm50, jmp50, 6g6b, vibroverb, champster, alessandro rottweiler
4x12" w/H75s
User avatar
M Fowler
Posts: 14017
Joined: Wed Jan 16, 2008 2:19 am
Location: Walcott ND

Re: AC15 or AC30? (Hammond AC15 OT loudness)

Post by M Fowler »

I agree with Roe the AC30 with LarMar PPIMV works great. Also, the Trainwreck Rocket with LarMar PPIMV but reduce the V1 plate resistors to 100K or 120K so it doesn't break up so fast.

Mark
User avatar
pompeiisneaks
Site Admin
Posts: 4222
Joined: Sat Jan 14, 2017 4:36 pm
Location: Washington State, USA
Contact:

Re: AC15 or AC30? (Hammond AC15 OT loudness)

Post by pompeiisneaks »

I've only had the AC30 myself, but love the tone. One of the biggest confusing points I think is that people think a 15 watt is half the volume of a 30 watt, it's not, its only maybe 3 or 4 dB lower volume, The added complexity to the sound that having a quad of tubes, I think, is totally worth it, and on top of it, as mentioned, adding a PPIMV is one thing I really want to do to mine, so I can get that heavy sound at lower volumes.

I had a big discussion with I think Jelle and some others on a FB thread about how 4 tubes just makes a completely different tone than a simple 2 output tube amp.

~Phil
tUber Nerd!
psychepool
Posts: 260
Joined: Fri Apr 18, 2014 8:29 am

Re: AC15 or AC30? (Hammond AC15 OT loudness)

Post by psychepool »

OK, Thank you. Everyone recommended 30 watts so it was easier to set my mind.

It is good news that Larmar ppimv works well. I have seen a lot of amps that do not suit well.
The original ppimv circuit of Vox was virtually meaningless because the control was too difficult at low levels.


My mind is set, and I have to plan it.
What I would like to add is
-Tube Driven Spring Reverb on Fender Blackface
-Switching the Bright cap(the cap between Preamp Volume 2/3 pin) with 6 to 12 rotary switch
-Larmar PPIMV
-Half Power Switch (EL84 Quad <-> EL84 Pair)
-Pentode/Triode switch


Thanks again for your advice.
sluckey
Posts: 3062
Joined: Sun Jul 22, 2007 7:48 pm
Location: Mobile, AL
Contact:

Re: AC15 or AC30? (Hammond AC15 OT loudness)

Post by sluckey »

You may be interested in this 1960 AC-15. It has several of the mods on your list. Pompeiisneaks has the AC-30.4 which is identical except for four output tubes. If this style appeals to you, Hoffman has the board for the AC-15 and can also supply the board for the AC-30.

http://sluckeyamps.com/VAC15/ac15.htm

PDF documents are at the bottom of the page.
User avatar
M Fowler
Posts: 14017
Joined: Wed Jan 16, 2008 2:19 am
Location: Walcott ND

Re: AC15 or AC30? (Hammond AC15 OT loudness)

Post by M Fowler »

Such sweet instructions/data from BnWitt and Slucky on that AC15 and other projects.

Mark
User avatar
pompeiisneaks
Site Admin
Posts: 4222
Joined: Sat Jan 14, 2017 4:36 pm
Location: Washington State, USA
Contact:

Re: AC15 or AC30? (Hammond AC15 OT loudness)

Post by pompeiisneaks »

I've got the entire AC30/4 build on video if you want to see any part of it :D

~Phil
tUber Nerd!
psychepool
Posts: 260
Joined: Fri Apr 18, 2014 8:29 am

Re: AC15 or AC30? (Hammond AC15 OT loudness)

Post by psychepool »

Many thanks for your support.

My plan is basically a single channel AC30 top boost.
To be more precise, add a Blackface reverb circuit on the Trainwerck Rocket.
I can add a Blackface reverb circuit by adding one 12at7 to the remaining 12ax7 half from the preamp.

The advice to use the Larmar PPIMV was also helpful, and the advice to lower the V1 plate resistor seems to fit well with my plan.
The most anticipated part of the top boost is bell-like clean tone or break-up tone rather than the distortion.

Now I have to start collecting parts. Thanks!
Post Reply