can replace my el34's with a quad of el84's?

[germanaircooled]

i have another thread where i've asked for help to mod my preamp...I'd like to do something with the PA amp as well.

it's a 78 2204. It's very loud and I can't really clip the PA at a usable volume level.

Thank you...

[martin manning]

See discussion on this subject here: http://ampgarage.com/forum/viewtopic.ph ... highlight=

[statorvane]

You may be better swapping in 6V6s. They'll give some reduction in volume and headroom and the should bias close to EL34s as well. You may want to increase the primary impedance of your OT though.

[roberto]

I suggest you to install four yellow jackets.
If you are not so expert, you can hurt yourself with high voltages.

[germanaircooled]

You may be better swapping in 6V6s. They'll give some reduction in volume and headroom and the should bias close to EL34s as well. You may want to increase the primary impedance of your OT though.

thanks for the comment....

I've been thinkin' about this after coming across a post about it. I would be interested for sure in this swap as, it looks like it's easier since the sockets are the same. i really like that el84 chime, but would welcome the better bass from the 6v6's.

Does anyone know if there are any more than these issues that would be related to changing my EL34's to 6v6's?:
-bias supply change
-screen resistors?
-plate voltage change
*if new xfmr is needed I don't see changing to 6v6's as a reasonable change.
-possible PI interface change as well?

Not sure what else would be needed?

I'm new to this site, but know my way around HV, soldering, etc., but lack in the design side, so I'm not sure of the answers to the above questions, as well as component values to start with, etc., "IF" it turns out to be something that's reasonable to do.

thank you

[martin manning]

Potentially all of those issues you mentioned, plus you need to address impedance matching by e.g. running an 8 ohm load on the 4 ohm tap, and that is where the reduction in power is going to come from.

What plate voltage is this amp running now?

This is a Master Volume model amp, right?

[germanaircooled]

I suggest you to install four yellow jackets.
If you are not so expert, you can hurt yourself with high voltages.

thanks for the comment..

I'm good makin' the mods; i've been around electronics since 84'. Ol' USN trained ET.

I've seen the yellow jackets, and am am interested, and would consider trying a set, but would rather know what the component values need to be...at that point I could build my own...9 pin + components soldered to an 8pin base...etc.....

do you or anyone have any experience with the yellow jackets?

I think the same xfmr questions would come up, so if the yellow jackets are compensating for this, then.....

[matt h]

(deleted)

[germanaircooled]

thanks matt...

roger that on the low power tubes...and for the review of the pre-amp mods

oh...what about components caps/resisters to use?

[martin manning]

I wouldn't dismiss the 6V6 idea so quickly. If this is a lower-voltage 2204, then trying it out would be a matter of swapping the tubes, tweaking the bias, and mismatching the impedance selector one click.

[germanaircooled]

I wouldn't dismiss the 6V6 idea so quickly. If this is a lower-voltage 2204, then trying it out would be a matter of swapping the tubes, tweaking the bias, and mismatching the impedance selector one click.

mm - thanks for the input...i'll collect some voltages and report what I find.

did you have any input on component preference?

[martin manning]

Related to the tube swap or in general?

[matt h]

(deleted)

[statorvane]

I actually went the other way, from JJ 6V6S to EL34s. I had cannibalized a 5F6-A Bassman build into a JMP50ish head using 6V6S power tubes tubes. Plate voltage around 460V. I then went to EL34s since I missed the volume. The only wiring change I made was in the OT wiring to go from 8Kohm impedance with the 6V6Sto to 4Kohm for the EL34s. They did bias differently, but I was able to adjust easily with the available bias trim. Probably no more adjustment than swapping out the EL34s (Chinese) for Mullard RI EL34s. Here's the original w/6V6 tubes:
http://s165.photobucket.com/user/JKCavi ... t=6&page=1

I have never tried any other brand 6V6, just the JJs. Like mentioned above they do sound different than EL34s. You might like them though. For the cost of new tubes and a little rewiring of the OT, I think that would be much easier than trying to fit a quad of EL84s.

Not sure if this is relevant but my head has a MV; pre PI MV type. Post PI MV (PPIMV) didn't sound very good at lower volumes - below say 50%.

[germanaircooled]

Related to the tube swap or in general?

in general..