ac30 with 6l6s

[rokker]

So I built a hoffman ac30 and I like it but Im one of those guys that cant leave anything alone so I thought about putting a pair of 6l6s in the amp. I realize there would have to be some component changes but Im willing to take the time and work that stuff out.

I think my main concern would be if the transformers I have in the ac30 would work with the 6l6s?

The iron I have:
http://www.classictone.net/40-18049.pdf
http://www.classictone.net/40-18050.pdf

The PT is 280-0-280.

Has anyone built something like this? I guess I just want to see how the thing would sound. Maybe voxish but a bit rounder and more low end with the 6l6s?? Cleaner? Anyone have any thoughts, opinions?

I'm still very much a beginner at building amps so go easy on me.

Thanks

[eleventeen]

First, I would ask "what are you trying to achieve?"

I think you could perform a fair amount of work and not be especially happy with the results...depending of course on what you want to achieve. 6L6's need maybe 60-100 more plate volts to get the "open" characteristic I associate with them...which you could get some of by switching to SS rectifier.  

I'm not the biggest fan of 6BQ5 outputs....but they *do* work and they're cheap. 

[tubenit]

I have NO agenda for you.  Your PT should be fine for a conversion to 6L6's.

However, I will offer this as a consideration.   Geezer's HoSo56 is an amazingly touch sensitive amp.  I built this amp with reverb and also used VVR with it at one point.  So the 6L6's has lower voltages on them and I personally liked that tone.  I am not suggesting using a VVR, just trying to convey that I liked the 6L6's with lower voltages which you would have. 

270-0-270 with GZ34 .................... maybe around 300-325v?

With solid state rectifier maybe closer to 360-380v?

You could rewire V1 for a 5879.

Change the tone stack to be more compatible with a 5881/6L6

Change the power tubes to 5881/6L6.

Maybe leave the rest of it alone remaining Vox?  

Compare the schematics.  

With respect, Tubenit

[rokker]

Guys thanks for the input. I should have been more specific in what Im trying to achieve.

I want a clean to semi clean amp. Not an overdrive machine. I like the vox top boost channel sound ( I have an ac15h1tv, hoff ac30 ) but those small bottle power tubes seem to lack the punch and low end that the larger bottle tubes have. So my thinking was, why not take the top boost channel chime and sparkle, and run it with some larger power tubes to get a thicker more percussive sound? Am I describing a 60s ac50?

[PRR]

Yeah, replace the four 9-pin holes with two 8-pin holes, re-wire, change-up cathode resistor for the larger drop that 6L6 needs (plagiarize other 6L6 amps run at similar voltage).

"Punch and low end" *could* be an under-size OT; fatter tubes may not change that.

[rokker]

Yeah, replace the four 9-pin holes with two 8-pin holes, re-wire, change-up cathode resistor for the larger drop that 6L6 needs (plagiarize other 6L6 amps run at similar voltage).

"Punch and low end" *could* be an under-size OT; fatter tubes may not change that.

Yeah this is what I was kind of thinking of doing just to see how it would sound. If it works ok I could then start to fine tune it.

I coulda have sworn that one of the boutique builders ( top hat, bad cat etc.) did a vox meets fender type of amp ( top boost meets 6l6s )...

[tubenit]

OK, given those parameters ................... here's another idea.

The cathode resistor value for the 6L6's could be anywhere from 250 ohm to 360 ohm.  You can experiment with 47uf to 220uf on the cathode cap.  The larger value will give the amp a somewhat "cleaner" tone with a crispier bass.  

I'd change the tone stack values to be more suited for the 6L6's.  I listed ones that I have used and liked.

The cut control was needed for EL84's ............ I don't think you'll need it with 6L6's, so you can use a dual gang 250k for a PPIMV to control
the volume.

I'd lower the .1 coupling caps to .047 or .033 after the PI and before the power tubes.

I'd change the cathode caps on the first two gain stages. The 6L6 will have sufficient bass to it (IMO) & those larger 22uf caps will just make it sound muddy.  I think the 5uf and 2.2uf will give a more transparent tone.  At least that has been my experience.

I'd probably add the 6L6's, the PPIMV and change the preamp cathode caps to 5uf & 2.2uf and try that.  Then if it needed something else, I'd change the tone stack and post LTPI coupling caps.

With respect, Tubenit

[rokker]

Thanks for all the info and suggestions. I will report back when I have it running. ( crossing fingers )

[rokker]

Quick update, got a new chassis for the build, drilled it out last night. Prob gonna start putting it together tonight.

[Willabe]

Hey now that looks nice.   


             Brad     

[Ed_Chambley]

I cannot know the tone desire you have in your head, but your OT will need to be designed for 6l6.  Look at the Supro with 6l6 for ideas on your power section.  There are other ways to fatten up bottom end.  Easy way is simply a closed back cab.

To be truthful, I have never noticed a ac30 lacking in bass response or playing clean, but a 60's AC50 does not sound like a more powerful AC15 or AC30.  Completely different.  More like a 50 watt marshall.

Look closely at tubenit suggestion of the lowering of the cap values as you will not be pushing the 6l6 hard enough and they will breakup early and be muddy.  I have tried a tone cut on 6l6 and not very effective, but the LARMAR master in its place is a great idea.  It is true you will have volume control, but also can get distortion and with this if it is turned up all the way it puts you back to stock values.

Good luck in your tone seeking and remember there is no cure for tube amp fever.

[rokker]

I cannot know the tone desire you have in your head, but your OT will need to be designed for 6l6.  Look at the Supro with 6l6 for ideas on your power section.  There are other ways to fatten up bottom end.  Easy way is simply a closed back cab.

To be truthful, I have never noticed a ac30 lacking in bass response or playing clean, but a 60's AC50 does not sound like a more powerful AC15 or AC30.  Completely different.  More like a 50 watt marshall.

Look closely at tubenit suggestion of the lowering of the cap values as you will not be pushing the 6l6 hard enough and they will breakup early and be muddy.  I have tried a tone cut on 6l6 and not very effective, but the LARMAR master in its place is a great idea.  It is true you will have volume control, but also can get distortion and with this if it is turned up all the way it puts you back to stock values.

Good luck in your tone seeking and remember there is no cure for tube amp fever.

I came across some 6l6 sized iron that I am going to use in this build. The PT is a 350-0-350 so I should be able to push the 6l6s. I am planning on trying all of tubenits suggestions and kinda fiddle with this build until I feel satisfied with it.

[SILVERGUN]

I am planning on trying all of tubenits suggestions and kinda fiddle with this build until I feel satisfied with it.

And therein lies the fun.....
Enjoy

[rokker]

I am planning on trying all of tubenits suggestions and kinda fiddle with this build until I feel satisfied with it.

And therein lies the fun.....
Enjoy

Yeah I figure it would be a good learning experience since Im a noob with amp building.

Ive done a couple 5e3s, Hoff ac30, few diff mods here and there but this would be my first trial and error type of amp. If for some reason I just cant make it sound good I can just put the ac30 iron back on the chassis and put the el84s in and change it back to a normal Hoff ac30.