6L6 rocket

[Markusv]

Hi to all on this wonderful forum, especially the Rocket builders

A while ago I obtained a chassis and tranny's from a company called Judybox

So finally I settled on building a Rocket variant with 6l6's

Tranny specs:
PT
320-260-0-260-320
6.3
5.0
Bias supply

OT
30 watt'ish thing- doesn't look spectacular but hey- it was almost free


The chassis is a solid affair in steel

I run this amp with:
320V taps
5u4 rectifier
500R 20 watt wirewound instead of choke( 2x 1K parrallel because I did not have the right size resistor and I thought 1K may be too much)
Pretty much standard after that except I dropped the last PS dropping resistor value by half

8 and 16 ohm taps although I am not sure of the true reflected impedance for 2x 6L6

The Power tubes are currently cathode biased with a variable 240R resistor/pot combo but I think I can go lower (this is just a ballpark setting and certainly not optimal I`m sure)

Preliminary findings:
Spooky quiet- The first time I switched it on, I freaked because I thought I had no speaker connected.
The amp makes me smile like a fool. The fatness of the big bottles and my lineup of pre's (RCA 12ax7's and a Philips 7025) seem to work really well together. The 6L6's are old chinese tubes I pulled from a twin. I have a hunch I could do better, but I'm not sure I would be able to handle better tone!
There is a shimmer especially at clean settings and I love the interaction especially between the Treble and the Cut
The bass control is a bit weird- unresponsive except at extreme settings, and I'm not sure the tone stack is correctly wired
BTW I wired the first tube as a Normal/Parrallel input and I am glad I did
Parallel is really fat and it seems to boost mids a bit

I have not had a chance to really crank her but I will report back. Currently I am fooling around with the gain on about 10 o'clock and using guitar volume adjustment

I want to thank everyone who replied to my previous Rocket inquiries. Especially RJ who was very helpful

I have no digital camera right now, but I will try and post pics when I do
I plan on installing this chassis in a hardwood combo cabinet with 2x12
Not sure what speakers yet- currently I play her through a 1x 12 semi open cab with Private Jack built from plans on the ax84 site

Best regards,

Markus V

[sst4270]

Very Nice Markus,

I'm sure I speak for the many here when I say
we can't wait to see some nice photos.
And some audio clips as well, please.

Regards,

Steve

[tweedeluxe]

Sounds like a cool amp. I second the request for photos and clips.

[Zippy]

Check out the "66 Rocker" - sounds best with KT66 but works well with other tube sets too.

https://tubeamparchive.com/viewtopic.php?t=7300

[Markusv]

Steve and Tweeddeluxe

Thanks for the replies
I will probably be able to do pictures sometime soon.
Don't expect a neat build- I don`t do neat!

Recordings are a problem as I don`t have the equipment or skills for recording. If there are some ways you could suggest, please do so

Zippy

I read that thread over and over and it is what got me going with the rocket in the first place!- Thanks though
I am very keen to try the KT 66`s. I also have some 5881`s that seems to do the job well. The chinese 6L6GC`s surprize me though. I know RJ rated them as "good" as opposed to "excellent" for other tubes, but they already sound pretty damn good to me!

What can I expect with the KT's and what brand is preferable/ reliable?

Finally, I would like to know if anyone has strong opinions about adding a mid control.

Cheers,

Markus V

[Zippy]

Zippy

I read that thread over and over and it is what got me going with the rocket in the first place!- Thanks though

I am very keen to try the KT 66`s. I also have some 5881`s that seems to do the job well. The chinese 6L6GC`s surprize me though. I know RJ rated them as "good" as opposed to "excellent" for other tubes, but they already sound pretty damn good to me!

What can I expect with the KT's and what brand is preferable/ reliable?

Finally, I would like to know if anyone has strong opinions about adding a mid control.

Cheers,

Markus V

"Strong opinions"? You bet! I do. I pushed RJ to put the mid control in his and I think it's a beautiful thing.

What can you expect with the KT-66s? MORE. More girth, more sparkle, more smiles per gallon. RJ is running a pair of KT-66s that I loaned him - I think it was a "loan". I was recommended to get some Shuguangs - these came boxed as Valley Arts.

Here's a review of KT66s:

http://thetubestore.com/kt66reviews.html

[Markusv]

Zippy

Thanks for the quick reply

Is there a schematic for the Mid Cintrol or could you give me a quick description?
I know it involves the 10K resistor currently on the Bass pot- but how to go about it?

I will most likely order some shuguangs

Markus V

[tweedeluxe]

I just started an octal Rocket build with RJ's transformers.

I am planning to replace the 10k with a 25kB pot and a small (2k2-6k8) resistor in series for the mid control. I'm not sure how others are doing it. I would like to hear suggestions on this too.

Do you find that the cut control is effective with the 6L6s?

What values did you use for Ra and Rk(s) for V1 in parallel?

[Markusv]

Do you find that the cut control is effective with the 6L6s?
What values did you use for Ra and Rk(s) for V1 in parallel?

Very effective with 6L6's!
(edit) I just noticed that up until 11 o'clock the effect is subtle, but useful- after that more pronounced
I find that I can set the treble to about 3'oclock and engage the cut at about the same and get almost a "throaty" vibe. -It has definition, but the spike is goneand it really barks at higher volume. Then you play around with the cut control by backing it down to get different levels of chime


Standard values. With Parrallel, the values are effectively halved. Not sure if it is the best option, but sure sound good!
I stole the idea from a 18 watt lite2b off the 18 watt forum
I believe the matchless spitfire or lightning uses a similar approach. Very clean, and simple
Have a look below

Markus V

[Zippy]

BTW I wired the first tube as a Normal/Parrallel input and I am glad I did Parallel is really fat and it seems to boost mids a bit

Hah! I missed that on my first read, Markus. Very good! That's another mod that is on RJ's list of Things-To-Do. Great to hear that you've already implemented it with good results. RJ, you've been scooped!

Regarding the mid pot: just wire it in as a variable resistor. Since things do tend to go to garbage at values greater than 25k, I would set that as an upper limit.

[Zippy]

Standard values. With Parrallel, the values are effectively halved. Not sure if it is the best option, but sure sound good!

I agree with the 220k on the plates but would go 820 on the tied cathodes (two 1500s in parallel) for a trial. You've already added a bit o' gain with paralleling the two triodes so you may not care for the bit you get back by adjusting the cathodes. You're just tweakin' now (although you may REALLY like the KT-66s in there).

Congrats!

[tweedeluxe]

The Fender 5E8a has single/parallel jacks - also w/o grid stoppers. Here is a schem:

http://www.freeinfosociety.com/electron ... php?id=797

I'm going to try something similar - I don't even know if it will work. Here's a handrawn schem (no graphics programs on my work computer).

[IMG:150:128]http://img113.imageshack.us/img113/7097/img3704.th.jpg[/img]

Zippy - why 220k for Ra? Just curious. I was planning to use 100k to keep it closer to the standard Rocket preamp.

[Zippy]

The Fender 5E8a has single/parallel jacks - also w/o grid stoppers...

As does the 5F4 Super - my fav'.

Recall from the first page of the Dirty Little Monster (DLM) thread, that the DLM had two input jacks. I wonder if this may be what he was thinkin'...

Zippy - why 220k for Ra? Just curious. I was planning to use 100k to keep it closer to the standard Rocket preamp.

If you keep the 100k and double the current, you just doubled the voltage drop. Double the resistance and double the current, quadruple the voltage drop. Yep. If you're paying attention, you'll see that I went the wrong way on that one. "50k" is my final answer.

Voltage matters.

[tweedeluxe]

So then since the standard Rocket uses 220k for Ra, and I'll be doubling the current (I think?) by using a 820 for Rk, or splitting up the cathodes with two 1k5 Rk, won't 100k get me closer to normal rocket preamp voltage?

[Zippy]

Argggggggggggggggggh, Tweedy, you got me.

Mea culpa all 'round. I'm so used to adjusting the dropping string and keeping the 100k plates that I blew it.

Voltage matters.

(I'll shuddup now)