PT Question for el34 build

[tomrasdf]

I'm about to start in on a long awaited HRM build in a funk chassis. I'm reading elsewhere that the alter dumbles all used the a TF130 (fender twin) PT. Before I drop the dough, I want to be sure that a twin OT (4 6l6s) is acceptable for 4 EL34s.

Thanks

[ayan]

I'm about to start in on a long awaited HRM build in a funk chassis. I'm reading elsewhere that the alter dumbles all used the a TF130 (fender twin) PT. Before I drop the dough, I want to be sure that a twin OT (4 6l6s) is acceptable for 4 EL34s.

Thanks

Things will work fine as you describe. However, if you will be building an EL34 amp, you may want to consider getting different iron. I built many non HRM amps of all sorts and the best sounding ones had a Marshall style PT (which yielded about 485VDC on the EL34 plates) and Marshall syle OTs (TF170 in some, or another similar thing from New Sensor... the latter is used in an amp that I still have which, to me, is about as good sounding as any non HRM I have ever heard). So you can drop a lot of coin on "superior" iron but, sometimes the generic stuff works too.

Cheers,

Gil

[martin manning]

I have considered the same question:

4x 6L6 + 3x 12AX7 = 4x0.9 + 3x0.3 = 4.5A

4x EL34 + 3x 12AX7 = 4x1.5 + 3x0.3 = 6.9A

Svetlana's EL34 datasheet says 1.6A for the filament, so that would make 7.3A total.

Hammond's 290FX Fender Twin PT (Claimed equivalent to Fender's 125P34A) windings are listed at 5.5A, so it seems like running 4 EL34's would be a stretch for a typical Twin PT.

MPM

[ayan]

I have considered the same question:

4x 6L6 + 3x 12AX7 = 4x0.9 + 3x0.3 = 4.5A

4x EL34 + 3x 12AX7 = 4x1.5 + 3x0.3 = 6.9A

Svetlana's EL34 datasheet says 1.6A for the filament, so that would make 7.3A total.

Hammond's 290FX Fender Twin PT (Claimed equivalent to Fender's 125P34A) windings are listed at 5.5A, so it seems like running 4 EL34's would be a stretch for a typical Twin PT.

MPM

Careful with your math... How many 12AX7s in a Twin Reverb? Hint: not three.

Gil

[martin manning]

Careful with your math... How many 12AX7s in a Twin Reverb? Hint: not three.

Gil

Not sure I understand your point... A 100W ODS with 6L6's comes in under the rated current of 5.5A, but with 4 EL34's its over by 25-33%. A Twin Reverb should need 4x0.9 + 6x0.3 = 5.4A. What am I missing?

MPM

[tomrasdf]

So Gil (or anyone),
You say a Marshall PT is the way to go? That would have been my default, but I'm not working with much of a shop here and the less new holes I have to drill in the chassis, the better.

Where does a guy go to get a marshall PT that'll drop into a Funk Chassis? The mounts measure 3 3/4 by 3

[martin manning]

Where does a guy go to get a marshall PT that'll drop into a Funk Chassis? The mounts measure 3 3/4 by 3

Metroamp 100W Lay-Down Plexi, 3 3/4 x 3 3/16 mount, re-do the rectifier board and adjust the bias circuit.

MPM

[Funkalicousgroove]

All the EL34 Dumbles I have seen used either Twin (magic parts) PT or Music Man Iron, If you are worried about the filament get a separate small filament trannie to run the preamp tubes, I really don't think it's necessary. The Marshall Iron sounds GREAT I built one a while back like that- Keep in mind that you have to use a much larger dropping resistor after the screens to keep the preamp voltage correct, Like 10-12K should do it.

Heyboer will make you a custom PT for around a hundred bucks if you want a lay down marshall

[dano-rator]

Funk, do you recall if the el34 dumbles with music man power trans used a separate unit to augment the filament current? I think, at most, those MM amps had 4 power tubes and 1 12ax7 PI tube (all solid state circuitry before the inverter). I'm wondering if the iron was over-spec'd in the original design (to be able to handle two additional preamp tubes in the D circuit).

Dan-O

[M Fowler]

martin,

ayan wrote:
Careful with your math... How many 12AX7s in a Twin Reverb? Hint: not three. Gil

If you are going to use tube reverb then you need to add those extra tubes in addition to the three 12ax7's you noted. Maybe 10A supply

But Funkalicousgroove said there wouldn't be a problem a he would know, so 7.5A.

Mark

[talbany]

Most of todays transformers made by reputable companies like Mercury Mag, Heybor, and others named here can handle more current than spec'd out..Generally by a 1/3 is the industry standard these days..Hammond's even more in some cases..In less you plan on running full bore outside in 100 degree heat for a week, a decent Twin style PT should do fine...
I totally agree with Gil on the Marshall style NS Transformers good bang for the buck nice and quiet and very linear w/bridge.. If I were to build an amp that I would want to flip flop output tubes I would go with the Marshall style all the way around (Tone wise speaking) ... If I were to do a straight up 6L no 34's I would of coarse opt for the Twin style

As for the MM 200-130-120 Power handle the extra pre tubes easily..


Good Luck!!



Tony VVT

[dano-rator]

Thanks for the reply, Tony.
I figured w/ the heft of the MM iron, two measly preamp tubes wouldn't bring it down.

Dan

[talbany]

Cool!!
PM me if you need any help!! You will like the MM Dumble!!
Be careful with the 700v..



Tony VVT

[dano-rator]

Thanks, it's still in the planning stages (looking for the $).

And sorry for elbowing this thread a little off track...
Tomsrad - good luck w' your EL34 build!

Dan

[ayan]

Careful with your math... How many 12AX7s in a Twin Reverb? Hint: not three.

Gil

Not sure I understand your point... A 100W ODS with 6L6's comes in under the rated current of 5.5A, but with 4 EL34's its over by 25-33%. A Twin Reverb should need 4x0.9 + 6x0.3 = 5.4A. What am I missing?

MPM

Nothing wrong with your math, entirely my bad.

Cheers,

Gil