Latest project AC30/2

[randalp3000]

Been messing with this for awhile and this is the latest version using some suggestions from Chief MC for the PI and a new OP transformer. I have been using this amp for about six weeks with an A470 OP but haven't had enough clean volume. When pushed with a screamer the dirty tone was ferocious and I could get a ton of bottom end with the EF86 channel but it lacked sustain.

I've got some pics I'll try to get up soon.

[alvarezh]

If you can, what are the plate voltages on the 84's?

BTW nice work!

Thanks in advance.

[Reeltarded]

Love that!!

[M Fowler]

Nice work Randal.

[randalp3000]

If you can, what are the plate voltages on the 84's?

BTW nice work!

Thanks in advance.

Voltages are on the schematic.

And

Thanks much guys that means alot, I feel like I'm getting better with each build.

[alvarezh]

I should of have given you the reason of asking the question on the first place.

You stated having not enough volume on clean. I have, although not an AC30, an amp with a similar 4XEL84 output section.

I loaned to a friend for a gig and he complained of low volume, or not cutting through well enough in clean.

The plates on mine are running at 325 volts and I asked your plate voltage to compare so I could come up with a clue as to where the issue might be as the tubes test fairly well on my Hickok 752A. I was thinking on going to 350 volts on my next build, with the purpose of increasing power.

BTW my copy (posted) of what I believe to be an original AC30 schematic from Vox has voltages stated only for the PTs primary.

All the best, and have a good weekend.

[jelle]

Wow, clean build! These amps should have some clean headroom with low output singlecoils.... Humbuckers, not so much.

You could leave the cathode bypass cap out that is on the CF. It will reduce gain. Or find stronger powertubes.

[M Fowler]

That is same as Rocket but with lower plate resistors 100k vs. 220k it should be clean?

How about trying NOS Russian 6P14P-EV 7189 (EL84) tubes and screen resistors at 100R.

Mark

[randalp3000]

Tried the CF bypass cap but was way too wimpy. I cranked the plate voltage up to about 250 on V1 and upped the input resistor to 68k.

Mark, I had 100 ohm screen resistors but the screens were glowing red when I started to turn it up. Would these effect the output/volume much? I am also using some 6p14p's that I bought used from the Ukraine. I broke down last summer and bought an Amplitrex(yeah I was on a binge). The tubes in there now are around 36ma, 70% trans and grid emission and I have it biased at around 120% at high voltage.

I use all humbuckers(dimarzio PAF's) and I'm about convinced that 4 EL84's just isn't enough but that's the only sound I like. I need to get my signal generator and scope on it to see where it's breaking up. I also play through a gold so I can't get much more efficient than that.

I do have a 65 AC50 and a JMI AC100, the 50 scares me because of the bias circuit and the 100 needs to be tweaked for guitar but will come in handy for big outdoor gigs.

I think my next project will be the same preamp with El34's with switchable cathode and fixed bias.

Thanks for the suggestions guys
rp

[chief mushroom cloud]

good fuckin god almighty ...change that goddamn 68ohm resistor to 75 or 82 ohms! I GUARANTEE you'll get more clean headroom and it will be noticeably louder.
And the toobs might not start turnin all commie 'n shit on you....

a 2xEL34 cathode biased is your next step.....

[M Fowler]

I would go down to 50R if it were mine And forget about the 18w mode.

[randalp3000]

Yeah the 18w is pretty much useless but I had a hole to fill in the chassis.

good lord I've got 380v on the plates, with 50 ohms I should be able to use the plates to get a tan.

I'll put some bigger resistors on my next CE order.

Mark, just ordered all the mojo dijons to give them a shot.

Time for another jack n coke so I can learn my music for tomorrow and get out of watching breaking dawn pt deux.

thanks gents

[Masco]

I would go down to 50R if it were mine And forget about the 18w mode.

+1. I'd go more toward 50R if extra headroom is desired.

Nice work Randy. I wouldn't go over 40uF+40uF at PI filter. Let her breath a little. 1k's are good at screens. Haven't tried 6p14p's in similar amps, but I've tried Mullard, Sylvania, Westinghouse 7189's -all sound brittle to my ears.

[Roe]

I really prefer ac30s with 310-345v, 50R cathode and 100R screen resistors.

[randalp3000]

Thanks for all the suggestions and comments.

This is the latest version, first filter is now 47uF(thanks Matt), changed all coupling caps with Mojo dijons(thanks Mark) except for the click switch, changed SS recto with 5AR4, Hammond AC30/30H 100mA choke, lowered OP cathodes to split load 2X110R 100uF. Plates are now 350ish, bias around 120%.

Got the chance to use it last Sunday. Both volumes around 9:00 with a AB switch to change channels. Sounded stellar, plenty of cleans and volume, could have been a quieter drummer. Lost a bit of bottom end and not sure if it's the Dijons or the 47uF. Normal channel a tad darker, more mids and bass, great with some dirt. Top boost sounded great clean and more bite, mid scooped with dirt and ferocious at times. This might be the one????

Finally got a chassis from Allen and set of AC30 trannies from Mag. Components to try another one. Also have the parts to do a EL34 version with Hammond power and new Hammond Traynor 50W 4K OP. I'm also tweaking my layout to put the preamp filters on the preamp board for better grounding.