2xel84 rocket

[M Fowler]

Thanks to Darin I received my lower powered transformers.

Anyone else building one of these two EL84 Rockets?

Mark

[telentubes]

I want to build the 2XEL84 Rocket as well, but will wait till one of you experts gets some of the conversion details ironed out.

Next up for me is a Watts version of the Spitfire. I'm just waiting on some 18 watt iron from Ken.

This is the Rocket Reverb I just finished (actually the tolex and face plate need to be done but I couldn't wait). If the great tone will translate to 2XEL84s, I'm sold. I'll keep my eye on this thread.

[jhaas]

Anyone else building one of these two EL84 Rockets?

I'm thinking about building one as a small head. I've drawn up a layout for it to fit in a 13" x 5.25" x 2.125" chassis, and I'm eying this new Edcor PT for the project:

XPWR156-120/125: http://edcorusa.com/products/758-xpwr156_120-125.aspx
(245-0-245 @150mA) The dual 120V and 125V primaries might offer some HV tweakability.

but I'm getting ahead of myself. I'm currently working on a 4xEL84 Reverb Rocket.

[rhinson]

here is an edcor unit that would be appropriate for a 2-el84 rocket:
CXPP25-MS-7.6K

there's a hammond model that is very similar too that would fit the bill. some hifi guys have used these to replace z-565's (before Triode starting making repros). rh

[dynaman]

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.

http://www.musicalpowersupplies.com/

[TheGimp]

Edcor is making me two sets of transformers for me to experiment with.

One set is specified as 15W 20Hz-20KHz 8K Plate to Plate with 40% UL taps (tie off the UL Taps for guitar amp) with 4-8-16 ohm secondary taps.

This transformer should be fine for 18W in a guitar amp as the roll off will be higher in frequency so core saturation won't be an issue. The price they charged me was $46.29 each (I also had to pay a one time engineering charge of $40 for the design).

I'll test this transformer in a guitar amp when I get them and let you know how it does as it will hopefully be a good transformer for EL84 PP amps.

[M Fowler]

Gimp,

I am sure that Edcor already has engineered transformers you could have ordered.

There are a few pages to look through but usually some one has already been there and done that. Still a good deal for high quality iron.

Mark

[telentubes]

Looks like I'm leaning more towards the 2 X EL84 Rocket than the Spitfire (although I will probably build both).

What would be recommended for PT voltages? Is it best to match the 4 X EL84 PT with 245-0-245, or go with the higher 290-0-290 as seen in other 2 X EL84 amps.

How does the voltage difference affect the circuit and tone? Is there a good book that might explain some of this?

[TheGimp]

According to Phyllis at Edcor they didn't have anything close to what I wanted unless I went with a 25W tranformer.

I'm interested in the 25% taps for audiophle amp with the 6P1P-EV since the geometry of the screen grid spacing (x-ray imaging) indicates it might be better than the traditional 40%. For guitar amp I'll just tape off the screen taps.

I ordered these first two sets f transformers in 8Kp-p as this impedance should deliver more power than 10Kp-p, but at slightly higher distortion. This should be fine for guitar amps.

I plan on ordering another set of 10Kp-p or possibly 11Kp-p transformers once I determine which screen ratio is best for U.L. operation.


WRT operating voltage effecting tone, I know that the higher you run the bias current the cleaner most tubes run. The lower you run the bias current the higher the distortion which is predominatly 2nd order. This can be seen from lookng at the plate curves for the tubes.

When you run higher B+, you have to reduce the bias current to stay within the SOA of the tube.

So I would expect the higher B+ to give slightly more distortion to the amp.

This is based on theory and experience with audiophile amps so I expect it would also apply to guitar amps.

[M Fowler]

Dartanion's smaller 18w PT is 260/290 so I am starting with the 290 since I didn't want to put in a HT switch on this amp.

Here are some photo, might get it done today.

Mark

[telentubes]

Wow Mark... not a lot of time between idea and reality in your world. Seems like you JUST mentioned you might build one, and now here it is. Let us know how it compares tonally to it's big brother (or sister, I guess, if it's a Wreck).

[M Fowler]

To me it sounds the same and is about as loud as the Four EL84's I have built and fun to play. Ran it through pair of Vin 30's and tomorrow will be G12H/Blue cab and then onto Gold/Blue cab for comparisons. All open back cabs two are Dr Z and one cab is Gabkits.

Yeah I admit I need to slow the F--k down some but it's an addiction.

This one is going into Richie's cherry cabinet.

[Reeltarded]

You are fast Mark! You should consider building me a few!

How did they come out?

[M Fowler]

Here is the final shots and the amp sounds good I need to move it to the jam room for play time.

I am going to get a smaller diameter power cord this one is too thick to properly fit the smaller strain relief.

My flash isn't working on my camera time for a new one I have had this Olympus C-470 Ultra zoom for a while. Or get is professional clean and worked on.

[M Fowler]

The two el84 18w Rocket in its Cherry cab, the top one.