EH Scott Radio Enthusiasts

The Fine Things are Always Hand Made

Hello,

I assume that the Phantom cross over case should not have 200vdc with respect to the main chassis. Has anyone seen this issue before? Thanks

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John - No...in fact, I believe the Phantom has a ground that continues throughout the speaker system to keep all the parts and speakers at a ground potential. If you've got significant voltage on the crossover frame, I'd look for a wire with bad insulation. Open up the unit and look carefully at the wiring. You should definitely NOT have a significant voltage on the crossover.

Kent

  You could have a bad output transformer, or as Kent said, a wire with bad insulation.   Check resistance from transformer to case.  The case should be grounded via one of the large pins. 

Scott has a great point - output transformer. I had one on a 12 in speaker that only read about 4k ohms from the primary to frame. Resistance checks are on tap!

Carefully review the internal wiring. Riders Vol 14 under Scott, page 12.

NETWORK%20SPEAKER.pdf

This file is a high quality redraw of the network box.  It is for a Philharmonic, but I am pretty sure they are exactly the same for the Phantom.  Only part that is probably different is the output transformer impedance ratio. 

I had a bad output transformer on one of my network bases and I put in a new Hammond unit.  The original transformers have so little iron in them, they are a joke. 

Scott - Can I place this PDF into the Archive?

Kent

Scott Seickel said:

I had a bad output transformer on one of my network bases and I put in a new Hammond unit.  The original transformers have so little iron in them, they are a joke. 

I strongly suspect the Philharmonic and Phantom Deluxe used the same optional high fidelity crossover and set of speakers - 8 ohm main speaker and individual 16 ohm tweeter(s). 15 inch for Philharmonic and either a 12 or 15 for the Phantom Deluxe and Scott Laureate (I have seen both sizes).

 I would think Phantom's 2 6L6's in push-pull 25 watt and Philly's 4 6L6s in parallel push-pull 40 watt would use the same impedance ratio. And the Scott would have sized the output transformer to handle 40  watts regardless of the radio model ordered, keeping inventory simple for the Philly, Phantom Deluxe or Laureate models.

Scott - do you hear an audible and meaningful difference between your two crossovers?

Seen from the output transformer,  quad 6L6's have a lower impedance as their plate resistance is seen in parallel by the transformer.  The impedance ratio of the transformer should be different for a push-pull and a quad parallel push-pull driving the same speaker for that reason.  As for the factory transformer driving 40 watts, power handling is not the issue but rather the frequency response one would get and whether the transformer stays out of saturation.  Maybe someday I will measure response, but my guess is that it is not very good for a "Hi-Fi" unit.  All modern output transformers for quad 6L6's are much larger for good reason.  That said, nobody runs their Philharmonic with the volume at more than a small fraction of what the amp is capable of, so the whole issue becomes moot at lower output.  The network base that I installed the Hammond transformer on was only run for quick testing to confirm proper operation via low fidelity AM radio.   It is a unit that is surplus to my needs at this point, unless I come across a 15" speaker and tweeters for it. 

Great info from all. My output transformer was indeed shorted to case.

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