66 Rocker - AKA 66 Rocket ...Eventually the 66 Rockster

[gsb]

Hi !
First thanks to RJ and Tweedeluxe for detailed answers on my questions.
I,m thinking to built a power scalling into amp.I have see on another forum (Hofman amps ) discusion about how to reduce power without
MV .I have see in my builds every MV afect tone of amp.They set volume
with a switch on autobias power amps ,and have tested another version
with pot -and work very good.It does not reduce volume to zero but you
can adjust volume in useful range without afecting tone.I put a link to
discusion about thema.http://www.el34world.com/Forum/index.ph ... 3957;image
gsb

[andrew]

Hi, Has anyone used the 300v taps on this build? Thanks.

[M Fowler]

Andrew you found the thread good job, I would have found it for you but I was right in the middle of some voltage charts, sorry.

Mark

[soma_hero]

Mine runs with a 340V transformer

[Markusv]

Hi, Has anyone used the 300v taps on this build? Thanks.

I have and I run KT 66's, and a 5U4 rectifier. Big resistor instead of choke
Sounds really, really good in my opinion.

Now that I have experimented with these voltages I will probably try the 260 volt secondaries for comparison

Markus V

[andrew]

Did you leave the power resistors the same as the Rocket? What are the preamp tube voltages? Thanks.

[RJ Guitars]

Did you leave the power resistors the same as the Rocket? What are the preamp tube voltages? Thanks.

Andrew, I can't answer for the other guys but for myself I used my own iteration of the Rocket power supply and made no changes in the KT-66 Rockster B+ circuit.

There is a very complete voltage chart a few pages back on this thread that will give you a lot of info on all the tube voltages throughout my build. It includes the use of several varied output tubes.

Thanks,

rj

[Markusv]

Andrew

Sorry for the late reply
I was away from home a lot and could not respond

Yes- the Power resistors are pretty much the same and then I added the 1K/10Watt resistor instead of the choke, pretty much like a liverpool.
I have no access to votages as a buddyu is using the amp in his studio.
Did you find the info you were looking for?

Markus V


(you van also do a search for "markusv" and "6L6 Rocket", where I discuss some of the tweaks I made. RJ and Zippy and others replied with great info of their own too.)

[fishy]

Not sure what I was thinking here but it seemed like a good idea at the time. RJ is responsible for this madness...

I had originally planned on a 2 hole rocket but then RJ's KT build had me thinking.
Its based on a rocket with 2 el84s and 2 octals. As it stands you get one or the other, not both although I might look at that.

Bright switch, Mid pot and variable bias.
Also used a cap can and distributed filtering on the preamp.

Fired up first time and I am still just playing with it at the mo but it sounds ok to my ears which is probably not saying much.

[RJ Guitars]

How could you not love that option... EL84's or KT66's? Is it as easy a flick of a switch? I think I see enough room to add a pair of 7-pin sockets for another output option - maybe you could go for the triple play with a pair of 6AQ5's?

Very nice job Fishy, tell us the sordid details and maybe throw us a clip or two...

Id it loud?

Does it break up early/late?

Interesting stand-up caps on the preamp board... say more about those.

I'm certainly curious about the the behavior differences in the EL84's and KT66's... sonically as well as the technical things like voltages etc..

FWIW - If I am responsible at all... I suppose it is for the dispersion of madness.

rj

[gsb]

Hi !
Are there any sound clips about rocker 66 here or you tube ?
I would like to hear it before i build it .Thanks gsb

[Zippy]

I,m thinking to built a power scalling into amp.I have see on another forum (Hofman amps ) discusion about how to reduce power without MV .I have see in my builds every MV afect tone of amp.They set volumewith a switch on autobias power amps ,and have tested another versionwith pot -and work very good.It does not reduce volume to zero but you can adjust volume in useful range without afecting tone.

These amps are sensitive to the preamp voltages especially. Reducing the voltage globally will give a fizziness to the sound as the preamp tubes quickly fall below the sweetspot voltages.

If you REALLY need to exercise voltage reduction to lower volume, I'd recommend doing it to the output section only. In the range of voltages that you'll have to run to get a real difference in volume, a master volume will work quite well. Better yet, build an Airbrake.

[fishy]

RJ,
Its was quite an interesting project. Initailly I was up for a 2 hole rocket but your experiences with the octals seemed to good an opportunity to miss.

You can switch between the two pretty quickly with just an adjustment on the rheo to get you in the ballpark. I actually liked the octals biased quite hot and then switching the el84s. They have a nice bite when they are biased a bit cooler than the rocket - more like Liverpool but not as gainy.

I'm still waiting on the KTs but I have tried 34s, 6l6s and 6V6s in it. They all sound decent and essentially have more midrange than the el84s. The 84s sound fantastic when you open this up but they are my favorite tube Compared to my rocket, there is not as much meat there but they can definitely make you sit up. That the 2 vs 4 tube thing though.

Clean headroom is limited but there is more on the octals than the 84s. At this point I do not have a bypass cap on the second stage and I think the octals would appreciate that if you want ed to really get down with it.
I think the mid pot is a good addition and I will probably wire in a 10 / 15k between the pot and ground. Presently the pot is referenced directly to ground.

The bright switch works well as it is. 100pF and 300pF. I migh play with it but that will have to wait a while. I don't like to dabble too much early on as things change on you.

The filtering on the board follows the distributed school of thought. I have never tried it before so it seemed like a good idea. They are 400v 20uF caps. The board is a little wider than a usual rocket but no longer. It might not appear so but they are quiet serviceable on the board.

The capcan takes care of the power amp side.

In also tried a different approach with the filament wiring. NO twisted wires but they all the wiring is effectively on top of each other.

I fused the HT which takes the place of the usual fuse on the back of the amp. The main fuse is presently on the front and the lighgt has been omitted.

The volume pot was turned 90 degrees which eliminated most of the bight switch wiring. It also made we wonder aboutusing the smaller pots. Why do we use 24mm pots anyway?

The screen resistors are 100ohm on the 84s and 1k on the octals.

The OT is a 8093 which I took out of my rocket in preference for a Liverpool tap tranny.

I took it over to a friends the other day and they really enjoyed it. They played around with it with 6v6s and the 84s and managed to a far variety of tones depending on the bias and stack settings.

I'll get some clips done at some point and post. From a noise perspective, the amp is extremely quiet.

[Markusv]

RJ,


I will probably wire in a 10 / 15k between the pot and ground. Presently the pot is referenced directly to ground.


Do it- You will be glad you did!
Markus V

The bright switch works well as it is. 100pF and 300pF. I migh play with it but that will have to wait a while. I don't like to dabble too much early on as things change on you.


I have a 200 pF as only option and it seems to work well with the Octals

Markus V

.

With regards to the bypass on the 2nd stage- I really think the Octals appreciate that and it seems to get them into an area where they perform more optimally
You can tweak size to taste
I upped my first coupling cap a bit and added a 22uF bypass on stage 2

Markus V

[andrew]

After a fling with a very grubby paraphase PI I put the standard Rocket PI back in my EL34 Rocket. Should I use the Express values (470r/10k) with the 34s? Thanks!