# Roctal - 6V6 mini amp in progress



## Geek (Jun 5, 2007)

Looks like there was a positive response to my DIY curiosity in the other thread, so here's one for you.

This is actually my second amp I'm working on. A little practise amp that's squeezes the most versatility out of its lineup. There's a jack for headphones on the front as well as an external speaker jack on the rear, should the internal 8" just not do it for you.

This project came about as a need I had for a practise amp. I just recently got a guitar after 10 years of being a bass plunker and was pretty pumped.

It was a good way to use up the iron I scavenged from this little "HiFi" monoblock: http://geek.scorpiorising.ca/TTE.html

Tube lineup is a 6CA4/EZ81 rectifier, 6V6GT and a pair of 5751's. Use 12AX7's if you like them (minor component changes needed), or 6SL7's (no component changes needed) if you want to stick to octals in the signal lineup.

The 6V6GT octal + decent overdrive in there is where it got its name - Roctal )

Probably the first thing you'll notice is the unique way the OD section is done. Gain control is drawn over two stages using negative feedback. This gives a much wider sweet spot range.

The tone contouring of the OD section is also in the NFB loop, across another two tubes.

The clean/OD switching is accomplished via a pair of relays to keep stray audio from getting into mischief.

(click thumbs for larger images)



Hand made chassis + some funky lights brings this beast to life!
Faceplate was an el-cheapo print-and-laminate job. The word "Clean" under the Roctal switch shouldn't be there. I originally thought of using a toggle switch and when I came across the big red button switch, I just HAD to use that instead 



Continued...


----------



## Geek (Jun 5, 2007)

Compact innards. The chassis only measured 12" x 6" x 2-3/4".






The cabinet is made from one of my favorite woods to look at (not to work with, ugh!), laminated pine. She's naked now, going to oil it up tomorrow!



Not large or heavy enough for box cuts or dovetails, I decided on quick router-and-drillpress pegged dado joints:



Stay tuned for more pics and a soundclip when I can do more than strum an E and A-chord, lol!


----------



## Gunny (Feb 21, 2006)

Geek: looking at the schematic I don't see what controls the relays (no switching activation for the coils). How does that work?


----------



## Yerffej (Feb 7, 2006)

real clean work, nicely thought out. Waiting excitedly for the clips


----------



## Geek (Jun 5, 2007)

Hi Gunny,



Gunny said:


> Geek: looking at the schematic I don't see what controls the relays (no switching activation for the coils). How does that work?


On the power supply off the rectified filament voltage. The switch labled "Roctal" switches the relay coils.




> real clean work, nicely thought out. Waiting excitedly for the clips


Thanks! :smile:


Cheers!


----------



## Gunny (Feb 21, 2006)

I get it. I was looking for something more complicated..doh!


----------



## Geek (Jun 5, 2007)

I should mention that any future versions of this should/would use a 6K6 output transformer, rather than the 8K (which I had on hand).


----------



## Geek (Jun 5, 2007)

Finished her up tonight :banana:



The Danish oil went well:


Rear view. Yes, that's a discontinued RS 40-1272D speaker. The "D" I swear means "Don't underestimate me for geetah".... incredible mid-bump in those and quite sensitive as 8" goes (sounded as loud as a known 96dB speaker in a side-by-each test) and late breakup:


----------



## Geek (Jun 5, 2007)

I had this amp evaluated by an actual musician yesterday and he was impressed as to how much can be done on it with the available controls. He was having a lot of fun with it!

The suggestion is to use a genuine guitar AlNiCo speaker with it. The existing ceramic RS thing sounds OK, but the added compression of the guitar speaker will give it more .... grumba :banana:

So, I have ordered a Weber Signature 8" AlNiCo: https://taweber.powweb.com/weber/asig8.htm

We plugged it into his 12" cab and for 3.5W (actually, we didn't run it full out), it sounded surprisingly LOUD 

Soundclips as per my REALLY lousy playing can be found here:
http://tonegeeks.sicomm.us/ToneGeeks/index.php?topic=7.msg128#msg128

Cheers!


----------



## Geek (Jun 5, 2007)

Got my Weber last week :banana:



BY GODS it sounds great! 

Also did some tube rolling. Original tube lineup: V1 = 5751 RCA black plate; V2 = 5751 GE-JAN gray plate; V3 = 6V6GTA RCA gray plate, red printing; V4 = EZ81 Rogers (didn't roll this one).

Full mids and darker texture. Awesome Jazz/Blues rig.


V3 to GE 6V6GT wafer base:
Flattens bottom end out a bit, less mids, flatter tone overall. Could be "too flat" tone for many.

V1 to BEL (India) 5751 + V2 as GE-JAN 5751:
Brightens things up an incredible amount. Fastest attack time of all the 5751's I've tested (not just in Roctal). Still keeps the mids and the bass flattens out a bit. Quite a rock sound.

V2 to BEL (India) 5751:
Don't do it. Unstable at best (oscillations) and when you do get it stable, it's really grungy. Might be good for those looking for the "solid state" sound from their tube amp.

V1 + V2 to GE-JAN 5751:
Put on your cowboy boots and hat, 'cause Waylon Jennings has just showed up. YEEEHAWWWW! 

I'm also looking for local (Chilliwack/Abbotsford) musician's to practise/gig/record with this thing and give me their opinion. Volunteers? 

Cheers!


----------



## noobcake (Mar 8, 2006)

Gregg, I would be interested in buying something like this, would you be willing to build any to sell?


----------



## Geek (Jun 5, 2007)

Hi,

Yes, I sure would 

I see you're in Surrey. I'm just an hour east of you. Want to meet and give the proto a whirl for sound?

Cheers!


----------



## noobcake (Mar 8, 2006)

Hmm well that might be a problem as I don't have a car at the momentBut on a side note, could I get some clips of the amp with the Weber installed?


----------



## Geek (Jun 5, 2007)

I'd happily come out there 

I'll get together some clips for you though


----------



## noobcake (Mar 8, 2006)

Alright thanks, and Gregg can you enable PMs, because when I tried to PM you it said that you had it disabled:smile:.


----------



## Geek (Jun 5, 2007)

Hi,



noobcake said:


> Alright thanks, and Gregg can you enable PMs, because when I tried to PM you it said that you had it disabled:smile:.


I re-enabled them this morning. Didn't it work?

You can also reach me at *geek* <at> *scorpiorising* <dot> *ca* if there's a problem.

I'll be back later this afternoon or evening if you get no immediate response.

Cheers!


----------



## noobcake (Mar 8, 2006)

Yep your PMs are enabled, just sent you one:food-smiley-004:


----------



## greco (Jul 15, 2007)

Nice build Geek. Congrats.

I didn't know that you could put a transformer inside the chassis. 

I'm still plugging away on the design of the eyelet board...but I'm finally beginning to have confidence that it is spaced correctly.

Dave


----------



## Geek (Jun 5, 2007)

Hi Dave,



greco said:


> Nice build Geek. Congrats.


Thanks!

I'm quite proud of this one actually :smile:



> I didn't know that you could put a transformer inside the chassis.


That's just the choke.

If you have room, you can mount all the iron under the chassis. Just remember to put adjacent iron at a 90 degree angle to each other. It works well. 



> I'm still plugging away on the design of the eyelet board...but I'm finally beginning to have confidence that it is spaced correctly.


I guess I'm lucky that way. I sell generic tag and turret boards, so they're always handy.

Do you have a Princess Auto or a dollar store nearby? Great source of cheap copper eyelets and crimpers.

Cheers!


----------

