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

[RJ Guitars]

thanks guys, I loved the tone that I was getting that day, especially because it just seemed to want to sustain endlessly. When I go back and listen to that clip I keep thinking to myself that the backing track was so crisp and I just couldn't quite seem to hit the timing with my part... I guess that's the ultimate amp builder dilemma. You have built the amp with "the tone", now if you could just get the right guy doing your demos.

[Tone Lover]

RJ just be thankfull your doing your demoes and not me I dont play as well as you do (LOL).Bill

[RJ Guitars]

RJ just be thankfull your doing your demoes and not me I dont play as well as you do (LOL).Bill

My mom thinks I am really an awesome player and my son made me a coffee mug that says I am the worlds greatest guitar player... my wife and my dog on the other hand claim to be more objective and do not rank me in the top 100.

[sliberty]

Great thread (I know, I am a little late to the party - story of my life).

I have a 6V6 Rocket that I am planning on re-purposing for the bigger bottles. I will be replacing both PT and OT to enable this.

What is the concensus on primary imp? 5.2K? I have three transofrmers available currently, and haven't decided if I will use one of them or buy something else. Two are for EL34's, primary around 3.2K, and the other is for an Express with only one tap - 6.6K. Thoughts?

Still need to buy a PT, and may go with one that has two voltages (300, and something lower) so I can try both.

I'd love to hear a bridge pickup sound clip from anyone that has one of these amps running. If anyone has such a clip, please post.

[RJ Guitars]

Great thread (I know, I am a little late to the party - story of my life).

I have a 6V6 Rocket that I am planning on re-purposing for the bigger bottles. I will be replacing both PT and OT to enable this.

What is the concensus on primary imp? 5.2K? I have three transofrmers available currently, and haven't decided if I will use one of them or buy something else. Two are for EL34's, primary around 3.2K, and the other is for an Express with only one tap - 6.6K. Thoughts?

Still need to buy a PT, and may go with one that has two voltages (300, and something lower) so I can try both.

I'd love to hear a bridge pickup sound clip from anyone that has one of these amps running. If anyone has such a clip, please post.

Steve, this party is just beginning...the octals add so many variables to the output options that you can expect a lot of different sounds to come out of this amp with only the output tubes changing. I look for one of the bigger manufacturers to discover our party at any time.

The output tranny of choice seems to vary from 4.3K to 6.6K. Some guys actually stick with the Dynaco style 4.3K and others have used the 6.6K Pacific. I am selling Edcor trannies with all the Rockster and Roadster parts packages but the cool thing is they are exactly the same mounting footprint as Heyboer, Stancor, and Pacific. I typically suggest the 5.2K tap on the 35 watt Edcor trannies.

FWIW - I had Edcor wind me some Dynaco...ish trannies at 5K that I plan to use for my next Rockster build... No data on these yet but I have high hopes.... we'll hear the proof when I get it done. These are rated at 32 watts and I also had them wind me a 45 watt version on a bigger frame for the really big stuff. These are of course rated in the typical ultra conservative Edcor fashion.

My original Rockster used an Edcor 245-0-245 power trans. I think these days I would be inclined to go with 260-0-260 or 280-0-280 for octals in this amp. It's important to note that Edcor uses a "loaded" voltage rating like Pacific does for their power transformers... 280-0-280 Edcor = 300-0-300 Heyboer.

Lowell Hunt had some great clean clips using a Gretsch on his version and I think Ronster also had some great clean clips from his version... I don't recall if either were bridge pickup though.

rj

[dorrisant]

FWIW...

I (and all of the important ears around me) liked the 5.2k taps better than the 6.6ks...

It would be very interesting if someone could clip-lead test a range of output impedances for A to B to C etc. comparison. All I have is the Edcor EM0721 with the above impedances... If I had the extra iron, I would try this out and post clips.

Also... I have one Rockster with about 430v on the plates and one with around 290 on the plates. I'm in love with the one with the higher plate voltage and I have some trusted friends who would probably kill me if I messed with the low voltage one. There is quite a bit of difference between the two. Not my cup of tea... But, to each his own.

Maybe I could post some clips of the two for some comparison... Along with the voltages of course.

Tony

[sliberty]

Is there a significant downside to using a 3.2K trannie and offsetting the impendance selector? One of OT's I have onhand is a nice big Mercury Magnetics (50-60 watts) that was used in a fixed bias EL34 amp. I haven't measureed it yet, but I am guessing it is around 3.2k, like the other trannie I have (also intended for fixed bias EL34's). I am thinking that it would be cool to put it to some user here. If I am not getting this backwards, I could use this trannie on the 4 and 8 ohms settings when using 8 and 16 ohm cabs respecitively, and that would give me an approx reflected imp of 6.4K - "close enough for government work" as they say.

Thoughts?
Suggestions?
Warnings?

[Zippy]

FWIW...

I (and all of the important ears around me) liked the 5.2k taps better than the 6.6ks...

What tubes are you running? Speaker preferences?

[dorrisant]

Zippy,

I'm using some NOS Sylavanias for the pre and NOS (Radioshack - pretty sure RCA) EL34s for testing A to B. I have also tried the Valve Art KT66s from rj. I always test with the same cab... An old Fender 2x12 sealed back cab loaded with Celestion Greenbacks at 8ohms. I love that cab!

Do you think I would feel differently about the impedance or voltage with a different cab or speakers? This is my standard... I know the tone this cab is capable of... If an amp doesn't sounds good through it, it just doesn't sounds good, in my opinion.

Tony

[M Fowler]

It depends on what type of Rocket your building.

Two of my favorites: One used a laydown Fender type Mag. Comp. 355-0-355 PT and Mag. Comp. 4k2 OT 4,8,16 in a Dumble style cab running EL34's, Rocket tone board but pots wired plexi style with MV. Also has reverb.

The other is more traditional build but does have reverb and uses a Heyboer 300-0-300 PT and Heyboer 5k2 OT. Running 6550 tubes. Foot switchable boost.

But I can't argue with the tone of a traditional Rocket with four EL84's either.

rj's Rockster or other kits are a good value to go with and rj is always willing to help a guy out.

Mark

[sliberty]

Well, it was a long time coming, but I finished the initial build of my KT66 Rockster (mine is called a Rocktal). There are some things I still have to do to it, but here are some basic details:

This amp is a repurposed 6V6 Rocket. I mainly replaced the iron, but also had to relocate the tube sockets as they were too close together for big bottles. So it ended up being a bigger job than just the iron, as it involved removing everything related to the power supply and the power tubes, and then ultimately rebuilding all of that. At least the preamp remained intact.

I used a Heyboer Express OT (6.6K taps only, so that's what I used ) and a Hammond 272JX (600VCT @ 288mA). It already had a Hammond 158L choke. Currently, my cathode resistor is 280 ohms, but I will begin to test with slightly lower values as well heading towards RJ's value of 200 ohms. I also used dioides instead of a GZ34 as that is how the donor amp was setup.

I still have to reconnect my VVR (bypassed for testing) and I might have a bad volume pot (it gets weird during the last 1/8 of it's sweep). And I want to rebuild the little board that my power tube cathode cap and resistor are on so that it will be easier to sub in alternate values. Also might put a trim pot in for mids (I've done this on Bassman amps and it is a useful mod).

The amp sounds really great. On lower settings, it has those chimey beautiful cleans you would expect from a Rocket preamp, but once it gets past 6 on the volume pot, there is a lot more grind that springs up as compared to my EL84 Rocket. It puts the amp in a range that is just where I like it - not over the top, but with lots of rich overdrive. Mine is not very feedback sensative at all, which is different from RJ's apparently. Not sure why. Maybe because I use a lower gain tube for the PI (often a 12AT7 or, in this case, a 5965)?

Tubes: New production Tung Sol 12AX7's in V1 and V2 (my go to X7's). A G.E. made JAN 5965 in V3, and the Shuguang KT66's of course.

I could very well be tweaking for a while, and do want to test with EL34's as well. But I am very pleased so far.

Thanks to RJ and all others who have contributed to this thread.

After I finish a few more things (VVR, etc.) I'll post photos.

Steve

[RJ Guitars]

Steve, we can always count on you to raise the bar a bit... I am anticipating a nice looking build and anxious see one of these with your touch. Can't wait for the photos and some clips! rj

[sliberty]

Thanks RJ. This is a bit of a mongrel since it has been repurposed, but still not too bad looking. Pictures to follow when completed.

I do need some help though. The amp sounds great up to about 8. Then, beyond 8, the entire noise floor disappears, volume drops slightly, and the tone goes to shit with sort of an ugly distortion character. I am thinking maybe blocking distortion is taking hold, and I will probably try larger grid resistors on the power tubes. Currently using standard Rocket values of 1K5 on grids, and 1K on screens.

Did anybody experience anything like this with standard values? How high did you go on grids to eliminate the problem? Did you change your screens too?

Does my description sound like I am on the right track, or do you think something else is at play here?

Note - I tried the obvious (a new vol pot) with no improvement.

Thanks,
Steve

[RJ Guitars]

Steve,

I haven't had that particular issue, but it's entirely believable that you could have everything the same and get a different result in an analog tube circuit. I've started posting the latest version of the schematic and layout on my web site so you can take a look and see if the values match up with what you have... seems like you do. http://www.rjguitars.net/rj_Rockster_Sc ... b_2012.jpg . I am wrestling a problem similar to yours on an Express right now but the Rocket has always been very friendly to me. Maybe take a look at this thread and see if it gives you additional inspiration. https://tubeamparchive.com/viewtopic.php?t=17334

It does seem that one obvious difference is going to be the output transformer behavior.

I'll ponder this a bit and follow along as you sort it out.

rj

[sliberty]

Thanks RJ. The larger grid stoppers (I tried 47K) didn't help at all.

I think I will go back to basics, and do a complete voltage chart before I do anything else.