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Old 21st October 2009, 01:47 PM   #1
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Location: denver area
Default modifying zenith 7d31 amp console

Hey Folks,
I need a bit of help here. I am pretty green to this stuff.
I have a Zenith EL84 PP console amp that I am modifying to a stand alone unit. Model is 7d31. I have attached a schematic, I hope it is readable.
If you notice this has a fairly non-conventional set up with the OPT's. One opt feeds into the other. I would like to replace those with a more suitable, more traditional set up. Probably something from Edcor.

Here is my question, on the schematic the opt's get b+ and then are connected to the plate. The screens are tied together. The opt's from Edcor show the b+, plate, and screen connections. IF I wanted to put in the edcor opt, I assume that all I need to do is change the connection on the schematic. Disconnect the screens from eachother and hook them into the screens on the new OPT;s. Is this correct?

BTW, I measured the impedance on the current OPT's, and assuming an 8 ohm impedance load, the opts measure at 1.2k. I checked, double checked, and rechecked. They are 1.2k. Screwy as heck to me. Mu understanding is that EL84's need about 8k opt's

Finaly, I noticed several other little things that need changed. For example, the resistor/cap in the feedback loop. I am going to copy the values from the HK230 ballad. It looks like a fairly similar ciorcuit. Change the values to 39k and 22pf for each side.

SO, if you have any suggestions or can help, I'll owe you one!

Mark
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File Type: jpg 7d31schematic.jpg (81.4 KB, 68 views)
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Old 21st October 2009, 03:49 PM   #2
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here is a blow up of the opt on hte schemtic - not very clear but ou might be able to get the idea.
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File Type: jpg 7d31schematicA.jpg (61.2 KB, 57 views)
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Old 22nd October 2009, 01:25 AM   #3
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Found my answer. Thanks anyway.
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