100 watt OT in 50 watt amp

[studiodunn]

I have a 50 watt donor amp (Laney LC50) that needs a new OT. Now I have a 100 watt OT on hand and wondered what the implications are sticking it in the amp.

All thing being equal, won't the 100 watt OT do the same job with less effort?

Thanks

[xtian]

It will work fine, assuming its impedances suit your needs. No problem with over spec'd iron.

[studiodunn]

Thank you Sir!

[studiodunn]

It seems this amp could run El34s or 6L6s. It shipped with 6L6s What is the spec/threshold of the PT that would allow this?

Seeing as the primary impedance of both tubes are close 2 x EL34 = 3.4K / 4 x EL34 = 1.7K / 2 x 6L6 = 4K / 4 x 6L6 = 2K . So I understand how the OT can be used.


So a PT designed for 6L6s can be used for El34s, but not the other way around?

[martin manning]

So a PT designed for 6L6s can be used for El34s, but not the other way around?

More likely the opposite. EL34 needs 1.5A for its filament where 6L6 uses only 0.9, an increase of 67%. The HT current at a given voltage is nominally 20% higher for 6L6 due to its 30W Pa max vs. EL34's 25W.

[studiodunn]

So a PT designed for 6L6s can be used for El34s, but not the other way around?

More likely the opposite. EL34 needs 1.5A for its filament where 6L6 uses only 0.9, an increase of 67%. The HT current at a given voltage is nominally 20% higher for 6L6 due to its 30W Pa max vs. EL34's 25W.

Thank You Martin.

Yes, I confused myself there. I'm still trying to learn the basics of all of this. I have no problem painting by numbers, but to understand the design limitations - I still have much to learn.

With the primary impedance of both 4 tube OTs being so close, can one use a Plexi spec'd (1.7K) OT with a Fender Spec'd (attached) PT and still run 6L6s?

[martin manning]

So you want to run two 6L6's into a 3k4 impedance using that 100W PT?

[studiodunn]

Ideally, yes. Since I happen to have a MM O100JM OT and the Laney as a project it would be advantageous to fix the amp with what I had. And if the Laney was made with using both 6L6 and EL34 tubes in mind, it seemed a fit.

I'm hoping to also better learn how the transformers of various styles can and can't work together along the way.

[martin manning]

That's going to be less than ideal for a pair of 6L6's. The high plate voltage and reduced voltage sag from the over spec'ed PT and the low OT impedance are both taking you in the direction of high plate dissipation. I think you would be fine with the PT if you increase the OT impedance to 4k.

[studiodunn]

That's going to be less than ideal for a pair of 6L6's. The high plate voltage and reduced voltage sag from the over spec'ed PT and the low OT impedance are both taking you in the direction of high plate dissipation. I think you would be fine with the PT if you increase the OT impedance to 4k.

Thanks again for all the help Martin.

Sounds like I should really reconsider using the MM for something it was intended for and just but a proper 50 watt OT for the Laney.

[rp]

If you want some reassurance from those that went before, Orange used the same OT for the OR80 and OR120. Myself I'd use something properly spec'd but I guess like Orange you might want to try it and see if you like it.

[studiodunn]

Well, it's a rainy day here so I decided to do the OT swap. It may not be ideal, but I'm learning so I figured I'd give it a shot.

Amp fires up and all the Voltages look good(to my untrained eye), but there are intermittent pops/crackles and almost no volume to be had. The only volume is coming with the drive engaged. I can't get any sound from the clean V1a stage. I used known good tubes. There have been signs of volume after a pop, but I can't get it to happen by physically moving and wire or component.