2xel84 rocket

Express, Liverpool, Rocket, Dirty Little Monster, etc.

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M Fowler
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Re: 2xel84 rocket

Post by M Fowler »

argonaut

Finally got a chance to look at your amp, sweet. Did I say I love PTP already. :)
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daydreamer
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Re: 2xel84 rocket

Post by daydreamer »

Man that is really a work of art!! fantastic.
Why don't you start a new thread with it?, I think no-one but Mark and I noticed it, being hidden down the back of this thread like it is..sorta like an invisible Schrödinger's cat!! :D

Andy
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M Fowler
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Re: 2xel84 rocket

Post by M Fowler »

Yes the amp deserves it's own properly titled thread I agree. That way people always find it by search later.

Mark
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RJ Guitars
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Re: 2xel84 rocket

Post by RJ Guitars »

Point to Point Rocket - that is definitely a unique beast. Will we see the sequel in the Express and Liverpool builds? rj
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argonaut
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Re: 2xel84 rocket

Post by argonaut »

Gee wiz, guys, thanks for nice comments. Like many here, building amps and music is my passion. To hear such kind comments from one's peers is truly appreciated. Thank you.

Good point, Mark, on the search aspect. I don't have the time at the moment to post another thread, but will in the future. Unless, someone else has the time and initiative to do it sooner, feel free. I'll be happy to answer any questions. Should have some clips before long, too.

RJ, I'm elbow deep in builds at the moment and haven't really thought about it. But now that you mention it, I think a Liverpool with a few tweaks (perhaps a Cut function) would be fun.

I have another Rocket-ish build currently on the bench....all octal, pre and power with cathode biased OS Tung Sol 5881s. 8)
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RJ Guitars
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Re: 2xel84 rocket

Post by RJ Guitars »

argonaut wrote:Gee wiz, guys, thanks for nice comments. Like many here, building amps and music is my passion. To hear such kind comments from one's peers is truly appreciated. Thank you.

Good point, Mark, on the search aspect. I don't have the time at the moment to post another thread, but will in the future. Unless, someone else has the time and initiative to do it sooner, feel free. I'll be happy to answer any questions. Should have some clips before long, too.

RJ, I'm elbow deep in builds at the moment and haven't really thought about it. But now that you mention it, I think a Liverpool with a few tweaks (perhaps a Cut function) would be fun.

I have another Rocket-ish build currently on the bench....all octal, pre and power with cathode biased OS Tung Sol 5881s. 8)
Dude!!! I put some old school Tungsol 5881's in my "Rockster" (octal Rocket) and that thing just oozed in smooth sweetness. I don't have your knack for point to point but do admire your work!

rj
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Zippy
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Re: 2xel84 rocket

Post by Zippy »

How 'bout a taste test comparo with the 5881s and some Shuguang KT-66s?
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Deric
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Re: 2xel84 rocket

Post by Deric »

Mark and Argonaut-

Did either of you guys record your voltages? Just finished mine up and am getting some pretty low voltages in the pre-amp.

MPS 270-0-275 PT

2k2 (in place of choke), 22k, 10k, 10k (33uf x2, 33uf, 20uf, 20uf, 20uf)

B+1 = 300
B+2 = 279
B+3 = 197
B+4 = 169
B+5 = 164

Still checking over my layout/wiring but would like a reference to compare to.

Thanks

Argonaut - NICE looking build! 8)
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Re: 2xel84 rocket

Post by RJ Guitars »

Eric,

Maybe you have a typo on the tranny voltage rating but with either value I would expect more volts on the nodes than you are seeing. Do you know if that tranny is rated loaded or unloaded?

rj
Last edited by RJ Guitars on Fri Dec 17, 2010 4:41 pm, edited 1 time in total.
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Re: 2xel84 rocket

Post by Deric »

RJ,

Not sure how it's rated. Here's a link - not much info though.. It's the PT275.2

http://musicalpowersupplies.com/4.html

I was hoping that with the higher voltage the slightly larger values in the dropping string would be helpful. I did some math this morning and it looks like changing to 1k8, 18k, 10k, 10k should get me closer to standard Rocket voltages.

I should probably dig around to see if I have another rectifier to try too. Using a new JJ GZ34 now...

Thanks for the help!
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Re: 2xel84 rocket

Post by RJ Guitars »

Eric,

My guess is that your tranny is rated unloaded. In that case you'll only see the 275 volts with no significant load on it. I see it is also rated for 100mA. With the pull of 2 or more EL-84's you should see that tranny load down and put out something measurably less. It's easy enough to measure next time you power up and have a meter next to you. I don't know if you have a quad of EL-84's but even a pair would work that tranny pretty hard.

I have heard that the Sovtek 5AR4 is the best of the current production rectifier tubes. I have used them with reasonable success but of course nothing beats the old Mullards.

Next time you measure I'd be curious what your plate voltages are. V2 is usually around 100 volts and sometimes slightly lower. Some wonky physics starts happening in a tube when the plates start getting much below 100 volts.

Let us know what that rectifier tube does.

rj
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M Fowler
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Re: 2xel84 rocket

Post by M Fowler »

Eric,

I will re-measure my voltages this weekend and post.

That 275-0-275 should give a nice tone with the lower voltages but yeah as far as the preamp you could change the dropping string to bring them back up.

You don't have to drop down the preamp filter stages in a straight line. A filter cap can be tied to the B+2 or B+3 to lessen the voltage drop to a certain preamp stage rather than going in a step down straight line from cap to cap if you know what I mean. :)
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fishy
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Re: 2xel84 rocket

Post by fishy »

Deric wrote:Mark and Argonaut-

Did either of you guys record your voltages? Just finished mine up and am getting some pretty low voltages in the pre-amp.

MPS 270-0-275 PT

2k2 (in place of choke), 22k, 10k, 10k (33uf x2, 33uf, 20uf, 20uf, 20uf)
B5 looks more out of line to me - All the Rocket info I have seen suggests a value around 120v.. What voltages are you comparing to?

I have used one of those MPS PTs and was pleased overall. It went in an 18W Liverpool and IIRC, all the voltages seemed fine. I don't have the amp anymore though. The guy who sells them is also quite responsive should you have a question.
argonaut
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Re: 2xel84 rocket

Post by argonaut »

Here's my voltages:
B+
1-295v
2-284v
3-207v
4-177v
5-169v

Keep in mind I'm using a 5y3 rectifier and a 270-0-270 120mA PT. Traditional dropping string values, with exception of choke. Also, I'm using both triodes of V1 and V2. The PT gets a bit toasty after a while, but not so much as to be concerned. Hope it helps. Good luck!
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Deric
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Re: 2xel84 rocket

Post by Deric »

Thanks for the input guys!

RJ - Didn't find anything local but another JJ GZ34 so I'll give it a try when I get a chance. It may just be the transformer. This could be a good thing as I was really just worried the voltage would be too high.

Mark - Thanks for the tip on the dropping string.

Fishy - I'm comparing to the voltage chart in the Rocket thread of the files section. It shows B+4 at 187v and B+5 at 183v

Argonaut - Thanks for the info!
Deric®
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