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Thread: F-40 Tone Cabinet Restoration

  1. #31
    f Forte muckelroy's Avatar
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    IMG_0028.jpg

    The cab is gutted and I am stripping it with Rock Miracle. It's going quite well. Here it is as I was about to tape off the grill.

  2. #32
    f Forte muckelroy's Avatar
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    IMG_0030.jpg

    The walnut veneer is finally showing and broken free of the damaged varnish. I'm actually following the process JoeyB3 did, which worked remarkably well for his Model E restoration.

    I'm doing all of this to the tone cabinet first, so that if I make a mistake, it's less difficult to correct than if the same mistake is made on a complex C type cabinet.

  3. #33
    fff Fortississimo David Anderson's Avatar
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    1 members found this post helpful.
    I think I have the answer to your strange LF oscillation in the amp.

    I just finished repairs on an HR-1A amp and got the same strange LF oscillation when I switched reverb on. I checked my input power/test connector, which uses a line plug plus 3 wires for ground, G+, and G- attached to a 6-pin socket. One of the G wires had come loose. I reconnected it, and the oscillation disappeared. You must have a bad connection somewhere. I can't imagine anything else producing exactly the same condition. It would appear that the combination of capacitors and resistors between the reverb amp and the output driver forms a LF oscillator if one of the G wires lacks a ground reference.

    120Hz background hum at idle with speakers attached is 3.8mV. B+ runs about 20V high. Good luck!

    Edit: To be honest, I've never really liked this aspect of Hammond's design -- having to get the ground reference for a power amp driver stage from the organ preamp's output transformer via a ~40' cable and several connectors.
    Last edited by David Anderson; 02-26-2017 at 06:55 PM.
    I'm David. 'Dave' is someone else's name.

  4. #34
    f Forte muckelroy's Avatar
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    Quote Originally Posted by David Anderson View Post
    I think I have the answer to your strange LF oscillation in the amp.

    I just finished repairs on an HR-1A amp and got the same strange LF oscillation when I switched reverb on. I checked my input power/test connector, which uses a line plug plus 3 wires for ground, G+, and G- attached to a 6-pin socket. One of the G wires had come loose. I reconnected it, and the oscillation disappeared. You must have a bad connection somewhere. I can't imagine anything else producing exactly the same condition. It would appear that the combination of capacitors and resistors between the reverb amp and the output driver forms a LF oscillator if one of the G wires lacks a ground reference.

    120Hz background hum at idle with speakers attached is 3.8mV. B+ runs about 20V high. Good luck!

    Edit: To be honest, I've never really liked this aspect of Hammond's design -- having to get the ground reference for a power amp driver stage from the organ preamp's output transformer via a ~40' cable and several connectors.
    I owe you a beer if I'm ever in the area. Thank you.

    I also am suspect of my D.I. I was using for testing. I wonder if it's pseudo-balanced and not balanced. Will have to see how the transformer is wired.

    The amps are hibernating on the storage shelf while the wood working is going on. I'll get them back on the bench for testing once I'm closer to being done with the woodworking.

    Speaking of wood working... I've almost used an entire can of Rock Miracle (16 oz) on this cabinet alone. Good grief. Either I'm using too much, or I'll have to eat the cost of this stuff.. or find a cheaper alternative.

    I still need one more stripper treatment before I start sanding. A lot of splotchy poly/varnish/lacquer/whatever-this-is still on the veneer.

  5. #35
    fff Fortississimo David Anderson's Avatar
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    Unfortunately, I'm chemically sensitive to many of the products used for wood stripping and refinishing, so I have to hire someone else to do those jobs. I can manage limited use of these chemicals by wearing a mask with organic vapor filter cartridges -- outdoors.

    You will never see me post a picture of a large cabinet I've refinished. I wouldn't survive.

    I used a Leslie 122 kit isolation transformer to drive the HR-1A amp.
    I'm David. 'Dave' is someone else's name.

  6. #36
    f Forte muckelroy's Avatar
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    Quote Originally Posted by David Anderson View Post
    Unfortunately, I'm chemically sensitive to many of the products used for wood stripping and refinishing, so I have to hire someone else to do those jobs. I can manage limited use of these chemicals by wearing a mask with organic vapor filter cartridges -- outdoors.

    You will never see me post a picture of a large cabinet I've refinished. I wouldn't survive.
    That OK! It's toxic stuff. This is being done in my garage, and the door is left open for ventilation while working. A good strong fan in the mix too.

    During the last cleanup, a tiny drop of stripper got on my forearm. It burned like hades. No harm done otherwise after a good rinsing.

  7. #37
    f Forte muckelroy's Avatar
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    It's sanded, and really looking nice. Going to let the wood dry and rest, then fill the gouges and stain.IMG_1751.jpgIMG_1752.jpg
    Attached Images Attached Images

  8. #38
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    First coat of stain. IMG_0904.jpg

  9. #39
    f Forte muckelroy's Avatar
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    Amp #2 rebuild is finished. Replaced almost all of the resistors, and caps. The original oil cap is working nicely as far as I can tell. C4 has around 18 VAC ripple, but C5, and the opposite end of C4 (-55 rail) have 0.18 VAC ripple. I'd need to go back and check the HR-1 amp for its ripple characteristics, but it does not seem to be negatively impacting the amp's performance.

    Sounds great. No reverb to fuss with on this amp, obviously. Pretty straight forward once I got my input transformer and signal input straightened out.

    Next step, layer #2 of stain on cabinet, then poly coating it.

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