2xel84 rocket

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paisley_tele
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2xel84 rocket

Post by paisley_tele »

any one have the layout for a 2 x el84 rocket ?
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M Fowler
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Re: 2xel84 rocket

Post by M Fowler »

Just drop off the two extra tubes and run the OT at 7k or 8k primary.

Uses the same PT or you can use a 290-0-290 as well with 8k OT.
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Colossal
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Re: 2xel84 rocket

Post by Colossal »

And change your cathode bias resistor to reflect two tubes instead of four
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M Fowler
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Re: 2xel84 rocket

Post by M Fowler »

I knew I was forgetting something important Dave.

120R to 150R should do.
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statorvane
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Re: 2xel84 rocket

Post by statorvane »

I've been thinking about a two banger Rocket too for my son, but with 6V6s. Would the power tube shared cathode resistor need to go to, say 300 ohms? I think the OT could still be 8K. Is that right?

Thanks.
loctal
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Re: 2xel84 rocket

Post by loctal »

My two hole rocket "Bella" uses a 250-0-250 V at 150mA power transformer, a 10K sansui output transformer, and a 100 ohm cathode resistor on the EL-84's.
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FYL
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Re: 2xel84 rocket

Post by FYL »

I've been thinking about a two banger Rocket too for my son, but with 6V6s. Would the power tube shared cathode resistor need to go to, say 300 ohms.
Depends on your B+. With 320V or less, 250R is perfect; 270R to 330R should be used with higher B+.
I think the OT could still be 8K.


Yup.
mcrracer
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Re: 2xel84 rocket

Post by mcrracer »

The 4 hole Rocket uses a 5.2k OT. Shouldn't a 2 banger use a 10k?
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M Fowler
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Re: 2xel84 rocket

Post by M Fowler »

Depends do you want a 8k Marshall tone or the 6k Fender tone or down more to the Spitfire 4k tone.

I have seen many different values used for EL84 or 6V6. :?:
mcrracer
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Re: 2xel84 rocket

Post by mcrracer »

Doesn't the 4 tube Rocket use a 5.2k OT? I am talking about how Ken voiced the Rocket. I just wanted to know if lowering the impedance on a 2 tube EL84 Rocket would change the tone and response?
funkmeblue
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Re: 2xel84 rocket

Post by funkmeblue »

why not use the a470's little brother.....http://store.triodestore.com/z517wadyoutr.html
anything worth doing, is worth doing right
mcrracer
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Re: 2xel84 rocket

Post by mcrracer »

I don't shop at Triode and in my opinion that transformer is over priced for the build in question. I am a more budget minded builder.
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M Fowler
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Re: 2xel84 rocket

Post by M Fowler »

Here is some info on the Marshall 18w transformer

NOTE: ORIGINALLY DESIGNED FOR 3/7/15 OHM LOADS
PRIMARY IMPEDANCE = 8.5K OHMS WITH 3 OHM LOAD
PRIMARY IMPEDANCE = 8.2K OHMS WITH 7 OHM LOAD
PRIMARY IMPEDANCE = 8.0K OHMS WITH 15 OHM LOAD

WITH 4/8/16 OHM LOADS, PRIMARY IMPEDANCE =
PRIMARY IMPEDANCE = 10.8K OHMS WITH 4 OHM LOAD
PRIMARY IMPEDANCE = 9.2K OHMS WITH 8 OHM LOAD
PRIMARY IMPEDANCE = 8.4K OHMS WITH 16 OHM LOAD
loctal
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Re: 2xel84 rocket

Post by loctal »

The dynaco A470 transformer used in the rocket is a hi-fi transformer. I thought about using the little brother transformer but I couldn't find a real one on fleabay. Sansui transformers are high quality and I found one for $20.00 in Peru. It cost $45.00 to ship it to America. When I build a real Rocket clone, I will buy a vintage A470. These rocket amps sound freaking great! If anyone has built one with a Radio-spares type transformer, please share your results with the forum.
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dartanion
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Re: 2xel84 rocket

Post by dartanion »

The Rocket (A470) OT is ~4.3K primary IIRC.

Also, using the PT from a 30W Rocket will cause your voltages to be high across the board as it's not sufficiently loaded. These PTs are over-sized to begin with, so you'd be best served to use a smaller PT.

I have custom transformer sets that would fit the needs of a two hole Rocket if anyone is interested. The PT is a 150mA version of the 5199, and the OT is 8.6K Woden style. For those interested in a set, shoot me a PM.
Eardrums!!! We don't need no stinkin' eardrums!
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