400v plate voltage for 100w amp

[Steveo]

Hello,
I have a laney gh50l that has been converted to 100watts. I measured the plate voltage yesterday and it was at 400vdc. I remembered it used to be 50watts and it still has the same power transformer. Do you think it would be beneficial to get a new power transformer for it? Would something around 470vdc be better. I have to say it does sound pretty good as is. What would the extra 70vdc give me as far as tone goes? I was thinking more bass and a feel a little more stiff?

Thanks

[thetragichero]

so by "converted to 100w" do we mean that the output power was measured/calculated or that two additional power tubes were added and the output transformer was swapped for a 100w model?
I'm not 100% up on the calculations but given W = I x V:
for 50w and 400v that gives us 124 mA which seems reasonable
100w and 400v gives us 250 mA which is a considerable increase in current. can the stock power transformer supply that reliably?

[Steveo]

Yes, two more el34’s were added as well as a 100watt output transformer. The power transformer has remained the stock Gh50l toroidal power transformer.

[SoulFetish]

You're saying that someone converted your amp to use 2 more output tubes and did not change the transformer?
Yes, change the transformer.
Here's why: - you're transformer will probably fail.
For instance, EL34s are by far the biggest demand on the heater supply, and will draw a heater current of 1.5A each. Your transformer was designed to supply 2 of those, and 4 preamp tubes which draw 300mA each (1.2A for all 4 pre's). So, in a transformer designed to supply 4.2A current (and lets round up and say 5A), there is now another 3A demand drawing 7.2A. Not good.
Plus, the reason that you are measuring 400V B+ is because the added load current being taken by those extra 2 output tubes is causing a voltage drop across the secondary (and primary to some extent) winding resistance of probably 60V, give or take.
I've replaced enough Laney stock transformers to tell you this is a bad idea. It's a bad idea in any amp, but toroid transformers have particular characteristics where they are often designed to operated closer to the point of saturation.
Also, change out your output transformer as well.
Laney is only trying to same money by using the same chassis and pcbs for the 100W and 50W version. I can guarantee that they are not going to spend the money on transformers in 50W rated amps that can also reliably used in 100W amps.

[Steveo]

Ok thanks, he did change the output transformer but not the power transformer. I will look for a suitable replacement. Thanks again.