Harmony 415 Power Transformer

[Astronomicum]

I'm guessing that 73mA on the plates is the no-signal bias. This looks like a class AB push-pull stage. I reckon it's going pull a lot more current when driven to full-signal levels.

Like Sluckey said, Idle and Full Output do not vary much with Cathode Biasing.

Two real world examples from my data:

Cathode Biased Amp w/ 6L6GBs and 5U4GB Rectifier: Idle dissipation of 95%, HT Current at Idle 139mA, Full Clean Output 156mA, +17mA, Increase 12% (nearly 8mA of the increase was additional screen current)

Fixed Biased Amp w/ 6973s and 6CA4 Rectifier: Idle dissipation of 60%, HT Current at Idle 63mA, Full Clean Output 110mA, +47mA, Increase 75%

As you can see, the Cathode Biased amp does increase some but just 12%, where the Fixed Bias amp increases by a much greater amount at 75%.

Given this Cathode Biased example applied to the OPs Harmony: 73mA Idle current +12% = 82mA which leaves 18mA for the Preamp which is plenty for one 6AU6 and two 12AX7s.

[didit]

Hello --

That filament spec of 2.35 Amps is short of the 2.42+ Amps this el84 power tubes push, but it's a small delta and trust you'll be OK despite that. The Hammond and Amp Direct have same basic HV spec so a bit puzzled? Old school isn't always the best.

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[foscoe944]

Hello --

That filament spec of 2.35 Amps is short of the 2.42+ Amps this el84 power tubes push, but it's a small delta and trust you'll be OK despite that. The Hammond and Amp Direct have same basic HV spec so a bit puzzled? Old school isn't always the best.

..

For some reason this thread isn't sending me notifications of replies...

I do hear you on the amps, but the Hammond doesn't fit. It would require drilling new holes at the least and very possibly cutting the center hole larger. That would be the absolute last resort. There doesn't seem to be a solution that checks all the boxes. 2.42 amps is only 3% more than 2.35, and I don't even know whether the risk is damaging the transformer or just having a little less current to the filaments.

Yes, old school isn't always best. But sometimes it is best, like trying to make a vintage amplifier sound as close to it's original sound as possible.